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Chapter-5

Photoelectrochemical studies on Iron (Fe)-and Ruthenium (Ru)-doped BaTiO3

Abstract: In this chapter we use a combination of experiments and first-principles density functional theory based calculations in a study of the photoelectrochemical properties of Fe & Ru-doped BaTiO3 nanopowder. BaTiO3 with Fe and Ru doping is synthesized via polymeric precursor route and characterized with X-Ray Diffractometer (XRD), Scanning Electron Microscopy (SEM), High Resolution Transmission Electron Microscopy (HR-TEM), UV-Vis spectroscopy, Mossbauer Spectroscopy. A reasonable agreement between the changes in measured spectra and those in calculated electronic structure augurs well for a judicious use of first-principles calculations in screening of dopants in design of doped oxide materials with enhanced photoelectrochemical activity, such as that of Fe & Ru-doped BaTiO3 demonstrated here.

Sumant Upadhyay et.al., “Enhanced Photoelectrochemical Response of BaTiO3 with Fe Doping: Experiments and First-Principles Analysis”, J. Phys. Chem. C, 115, 24373–24380, 2011.

Photoelectrochemical studies on Iron & Ruthenium-doped BaTiO3 Chapter 5

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The Photoelectrochemical response of Iron (Fe)-doped BaTiO3

5.1 Introduction

Hydrogen is a recyclable and clean fuel, as it generates water after its use in combustion,

and the water can be split to generate hydrogen back. The latter is a crucial step and can

be facilitated through use of a photocatalyst in splitting of water into hydrogen gas by

accessing solar energy, another important source of energy for the planet. Indeed, it is

important to discover and develop a photo-catalytic material for this process. An optimal

material should have a band gap that allows absorption of light in the visible range and

should remain stable when in contact with water. In addition, it should be non-toxic,

abundant and easily processable into a desired shape. In 1972, Fujishima and Honda first

reported the photo-assisted splitting of water into H2 and O2 on TiO2, providing a

possibility to convert solar energy into chemical energy in a renewable and cheap way [1-

6]. Since then, considerable efforts have been devoted to related areas of research, such

as photocatalysis, dye-sensitized solar cells, and so on [7-16]. Hydrogen, generated by

splitting water using solar energy, is even called “solar-hydrogen”. It is a kind of clean

and low-cost fuel [17]. Thus, the development of stable and efficient photosensitive

materials becomes a key to the future of “solar-hydrogen”. In search for a suitable

photoelectrode and photocatalyst, perovskite based metal oxides (ABO3) have been the

subject of extensive studies during the past two decades, because they offer a wide range

of possibilities for tailoring their structure through cationic substitutions at either A or B

sites, and tuning their optical and electrical properties [18].

BaTiO3 exhibits a mixed ionic-covalent chemical bonding between Ba and O, and a

strong hybridization between d-states of Ti and p-states of O leading to sensitivity of its

structure to external conditions such as pressure, and it is one of the most commonly used

titanates in splitting of water [19]. Advantages of BaTiO3 as a photoelectrode in hydrogen

production by photoelectrochemical water splitting include its: i) high resistance to

corrosion and photocorrosion in aqueous media, ii) easy availability at low cost, iii)

environment friendliness, iv) well-matched energy band-edges with the redox level of

water, and v) electronic properties that can be varied by changing the lattice defect


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chemistry or the oxygen stoichiometry [20]. However BaTiO3, with energy band gap of

about 3.2eV, mostly absorbs in the ultraviolet portion of the solar spectrum and only a

small amount of visible light [21]. For efficient photoelectrochemical activity it is

necessary to modify BaTiO3 and extend its photo response to visible part of the spectrum

[22]. While many methods have been proposed to address this issue, doping with ions is

one of the most promising strategies for sensitizing BaTiO3 to visible light [23]. A few

reports suggest the possibility of using Fe-doped BaTiO3 for photoelectrochemical

generation of hydrogen [24, 25]. As a thorough experimental analysis of BaTiO3 with

each type of dopant is quite demanding, it can be quite effective to use first-principles

based density functional theory calculations in short-listing dopants that have the promise

for enhanced photo-catalytic activity of BaTiO3. Such Calculations are quite useful

method in semi-quantitative determination of the trends in band gaps upon doping a

given material [26-28].

5.2. Experimental Methods 5.2.1 Materials Preparation Fe-doped BaTiO3 nanopowder was synthesized by polymeric precursor route [29, 30].

The titanium solution was prepared by dissolving titanium tetraisopropoxide (Aldrich

97%) to a solution of citric acid (Aldrich, 99.9%) and ethylene glycol (Aldrich, 99.9%)

mixed in a molar ratio of 1:4. The appropriate amount of required stoichiometry of

BaCO3 (Aldrich, 99%) and 0.5-2.0 at.% of Fe2O3 (Aldrich, 97%) were dissolved in the

above titanium solution. This solution was heated at 90°C with constant stirring till it

became a clear transparent yellow solution. This solution was heated at 200°C for 5 hours

in an oven to promote polymerization and remove solvents with continued heating at

200°C, the solution become more viscous accompanied by color change from pale yellow

to brown. There was no precipitation or turbidity observed and finally the viscous mass

solidified into dark brown, glassy resin. Charring the resin at 400°C for 2 hours in an

electric furnace resulted in a black solid mass that was lightly ground into a powder using

agate mortar and pestle. The precursor obtained was sintered at 500°C, 700°C, and 900°C

in air for 5 hours, in Al2O3 boat with intermittent grindings. The phase synthesis was

monitored after every sintering using XRD.


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5.2.2 Materials Characterization

Powder X-ray diffraction (XRD) patterns were obtained on a D8 Advance X-ray

diffractometer (Bruker, Germany), using Cu-Kα radiation at a scan rate of 0.02° 2θ s-1.

Scanning electron microscopy (SEM) and Energy-dispersive X-ray spectroscopy were

performed by an MV 2300T/40 field emission SEM Model Tescan Vega using an

accelerating voltage of 25 KV at the working distance of ~10mm. High resolution

transmission electron microscopy (HR-TEM) analysis were conducted with the use of

JEOL 1230, Japan. UV-Vis spectra were obtained using a spectrophotometer JASCO

model V-530, Japan.

Fe valence state, occupational site and site ratio in the perovskite lattice were recorded

using a Mössbauer spectrometer for a representative sample [Mössbauer spectrometer

System (Type: MC1002), Nucleonix Systems Pvt. Ltd., Hyderabad, India] operated in

constant acceleration mode (triangular wave) in transmission geometry. The source

employed is Co-57 in Rh matrix of strength 50 mCi. The calibration of the velocity scale

is done by using a-Fe metal foil. The outer line width of calibration spectra is 0.29 mm/s.

Mössbauer spectra were fitted by a least square fit (MOSFIT) programme assuming

Lorentzian line shapes. The result of isomer shift is relative to α-Fe metal foil.

5.2.3 Photoelectrochemical Performance

Powered samples of Fe-doped and undoped BaTiO3 were compacted into pellets using a

pelletization unit (Technosearch Instruments, Mumbai, India) at 5 tonn pressure followed

by sintering at 500°C for 2 hours. The electrical contacts on all pellet samples for PEC

measurements were made through a fine copper wire loop attached to the back side of the

pellet sample with conducting silver paint. The back side of each pellet including the

copper wire loop were covered and sealed by an epoxy resin (Hysol, Singapore) which

was non-conducting and opaque. The entire structure was heated in an oven at 70º - 80ºC

to ensure complete drying.


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A three electrode potentiostat system was used to measure the photoelectron current,

which allowed the measurement of the electron and hole pair formation as a function of

the externally applied potential necessary for water splitting. The photoelectrodes were

placed in the electrolyte (0.1M, NaOH), while potentiostatic control was maintained with

a PAR versastat II, U.S.A. at a scan rate of 25 mV/s. A large area platinum wire mesh

was used as the counter electrode and Ag/AgCl as the reference electrode. The

illumination source employed was a 150W-Oriel 6690 Xe arc UV-Vis lamp directed at

the quartz photoelectrochemical cell with an intensity of 0.18W/cm2. A water filter was

used to remove the IR energy and avoid overheating. The photocurrent densities were

calculated using the difference between the light off (dark current) and light-on currents

acquired consecutively. Resistivity and Open circuit photovoltage (Voc) was calculated

for all samples from the current-voltage characteristics recorded under dark conditions.

To obtain the Mott-Schottky curves, capacitance (C) at semiconductor/electrolyte

junction with AC signal frequency of 1 KHz was measured using LCR meter (Agilent

Technolgy, Model: 4263 B, Singapore) at varying electrode potentials in the same three

electrode configuration. These curves are used to calculate the flatband potentials and

donor density for all the samples.

5.3 Computational Details

All calculations were performed using Quantum Espresso implementation of density

functional theory (DFT) [31] within the generalized gradient approximation (GGA). The

interaction between the valence electrons and nucleus core electrons was modeled with

ultrasoft pseudopotentials [32]. We simulated effects of Fe-doping using 2 x 2 x 2 (40-

atom) BaTiO3 supercell and replacing one Ti atom by an Fe atom, amounting to 12.5%

doping amount. Calculated crystal parameters of the unit bulk tetragonal BaTiO3 are a=

3.9904Å and c= 4.0689Å, in good agreement with experimental data [33]. Monkhorst-

pack [34] mesh of 4 × 4 × 4 k-points was used in sampling the integrals over the

Brillouin zone and a much finer mesh was used in accurate determination of the density

of the electronic states. Kohn-Sham wave functions were represented in a plane-wave

basis with an energy cutoff energy of 30Ryd and charge density was represented with a

plane-wave basis with a cutoff of 180 Ry. Structural optimization was carried out using


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Hellman-Feynman forces to minimize the total energy. To check the convergence of our

results, we carried out test calculations with higher energy cutoffs on the plane-wave

basis and finer meshes of k-points, and making sure that there are negligible changes in

energy (the difference between the total energies is less than 0.02%) and the structure and

electronic structure are essentially unchanged. Electronic structures reported here have

been calculated at the optimized structures.

5.4. Results & Discussion

5.4.1 XRD Studies

The phase structure and purity of the as-fabricated samples were studied by powder X-

ray diffraction (XRD). Fig.1, 2 shows the XRD patterns of BaTi1-xFexO3 (0.0≤x≤0.02) as

a function of sintering temperature and doping concentration. All the diffraction peaks

can be well-indexed to BaTiO3 (JCPDS card no. 031-0174), suggesting successful

preparation of BaTiO3 crystals. It is revealed that as the sintering temperature increased

to 900°C the intensity of the unreacted phases like barium carbonate was reduced, and the

counts due to tetragonal BaTiO3 phase increased due to increase in crystallinity of the

sample. Formation of impurity phases such as hexagonal BaTiO3 along with marginal

cubic phase were observed in sample sintered at 500°C as shown in curve c of Fig. 1. The

tetragonal phase of BaTiO3 is predominantly present when sample was sintered above

600°C. The complete transformation of precursor into tetragonal BaTiO3 along with

small peaks of hexagonal and cubic phase at 900º C for 5 hours was confirmed by the

XRD pattern of sample which matches with that of tetragonal BaTiO3 also marked by the

presence of distinct 002 and 200 peaks in curve c in Fig.1. Maximum crystallinity was

obtained in 2.0 at. % Fe-doped samples sintered at 900°C, similar results have been

obtained by other researchers also [35]. XRD patterns of BaTi1-xFexO3 as a function of

doping concentrations is shown in Fig.2 where all Fe substituted samples are single

phasic and have crystallized in perovskite BaTiO3 tetragonal lattice.

Photoelectrochemical

Fig. 1: X-Ray diffraction patterns of B=700

Fig. 2: X-Ray diffraction pattern of Fe

2.0 at.%, E= 3.0 at.%, F= 4.0 at.% sintered at 900

Photoelectrochemical studies on Iron & Ruthenium-doped BaTiO

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Ray diffraction patterns of the powder samples of undoped BaTiOB=700°C, C=900°C) prepared at different sintering temperatures.

Ray diffraction pattern of Fe-doped BaTiO3 (A= undoped, B=0.5 at.%, C=1.0 at.%, D=

2.0 at.%, E= 3.0 at.%, F= 4.0 at.% sintered at 900

doped BaTiO3 Chapter 5

the powder samples of undoped BaTiO3 (A=500°C, C) prepared at different sintering temperatures.

(A= undoped, B=0.5 at.%, C=1.0 at.%, D=

2.0 at.%, E= 3.0 at.%, F= 4.0 at.% sintered at 900°C.


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As calculated by the Debye Scherrer equation, crystallite diameters for tetragonal phase

of 110 peak as a function of Fe substitution and sintering temperatures are listed in Table

1.The crystallite diameter of doped BaTiO3 gradually decreases with increasing

concentration of Fe. Thus it appears that Fe3+ with given concentration is soluble in

BaTiO3 lattice and the dopant influences the growth of a secondary phase in a peculiar

way. As seen from Table 1, the sample with Fe substitution has crystallite size lower than

undoped BaTiO3. We suppose that Fe3+ ions inhibit further grain growth leading to

decreasing the crystallite diameter. This is attributed to the aliovalent substitution of Ti

by Fe at B sites, such that micro-structural defects and nonstoichiometry are generated as

a result of substitution [36].

TABLE 1. Crystallite size of BaFexTi (1-x) O3 samples as calculated from XRD line width using Scherrer equation as a function of Fe content (x) and sintering temperatures.

Crystallite size as a function of sintering temperature was also calculated by the Debye

Scherrer equation using XRD line width for all Fe-doped and undoped BaTiO3. The

growth in crystallite size with increase in sintering temperature as evident from Table 1 is

attributed to the sintering effects. Taguchi et al [37] have demonstrated that the crystallite

size decreases in the perovskite-type (La1-xCax) FeO3 samples and such samples with

smaller crystallite size exhibited a higher catalytic activity. These results suggest that the

substitution-induced micro-structural defects and non-stoichiometry created on lattice

reorganization during synthesis also play a role in deciding the morphology of the

sample.

Samples BaTiO3

sintered at 500oC

BaTiO3 sintered at 700oC

BaTiO3 sintered at 900oC

Undoped BaTiO3 20 nm 32 nm 43 nm

0.5 at.% Fe 26 nm 30 nm 42 nm 1.0 at.% Fe 24 nm 27 nm 41 nm

2.0 at.% Fe 18 nm 23 nm 36 nm 3.0 at.% Fe 16 nm 20 nm 34 nm 4.0 at.% Fe 14 nm 24 nm 32 nm


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5.4.2 Morphology and Growth Mechanism

Stoichiometry of prepared powder is confirmed by the EDX (Fig. 3a). The observed

average atom% values from the data collected at three different locations are well in

agreement with expected values for BaTiO3 within the experimental error.

SEM (Fig. 3b-c) analysis reveals that, both Fe doped/undoped BaTiO3 particles are

approximately spherical in shape. SEM analysis reveals formation of particles with

different shapes and sizes for the undoped BaTiO3 (Fig. 3b).

Fig. 3: SEM micrographs a= EDX of Undoped BaTiO3, b= SEM of undoped BaTiO3 and c =

SEM of 2.0 at.% Fe doped BaTiO3.


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It seems appropriate to consider that the particles which appear in SEM images are, in

fact, aggregates of grains agglomerated in undoped samples, whereas Fe incorporation

has inhibited the grain growth and prevented agglomeration of sample prepared under

identical conditions (Fig.3c). Our results are in agreement with the work reported by

Gupta et al [38], where Fe doping resulted in smaller unagglomerated grains of ZnO

samples with well defined spherical shaped particles arranged in regular fashion. The

random distribution of grains, in projection and size, only suggests a random nucleation

mechanism, and random orientation of grains show that the grain growth is isotropic in

doped samples showing complete solubility of dopant ion in BaTiO3 lattice.

HR-TEM (Fig. 4) analysis also exhibits better crystallinity, well defined shape and

homogenous nature of the powders. Fig. 4a shows electron diffraction pattern of 2.0 at.%

substituted sample where it was indexed and found to be in tetragonal BaTiO3.

Homogeneous formation of 10-26 nm nanosized crystallites by polymeric precursor

synthesis observed from the HR-TEM (Fig. 4b) are in agreement with the XRD results.

HR-TEM in Fig. 4c shows that atoms are arranged periodically in well defined planes

inside nano sized particles of Fe doped BaTiO3.

Fig. 4: HR-TEM images of 2.0 at.% Fe-doped BaTiO3 sintered at 900ºC.


5.4.3 Band gap measurements

The diffuse and total

wavelength from 200 to 800 nm using the diffuse reflectance attachment of Perkin

Elmer spectrophotometer.

plots (Fig. 5), and the best fit was

direct band gap with values of 3.11 eV for the undoped and 2.81 eV for 2 at. % Fe doped

BaTiO3. This observation is in agreement with that of F.M. Pontes et.al [39].

Fig. 5: UV-Vis spectra of (a) undoped and (b) 2.0 at.% Fe


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Band gap measurements

The diffuse and total reflectance (Fig. 5) of the samples was measured as

wavelength from 200 to 800 nm using the diffuse reflectance attachment of Perkin

Elmer spectrophotometer. The optical band gap of samples was calculated from tauc

plots (Fig. 5), and the best fit was found for the indirect band gap transition rather than


. This observation is in agreement with that of F.M. Pontes et.al [39].

(a)

(b)

Vis spectra of (a) undoped and (b) 2.0 at.% Fe-doped BaTiO


(Fig. 5) of the samples was measured as a function of

wavelength from 200 to 800 nm using the diffuse reflectance attachment of Perkin-

The optical band gap of samples was calculated from tauc-

found for the indirect band gap transition rather than


. This observation is in agreement with that of F.M. Pontes et.al [39].

doped BaTiO3 sintered at 900°C.


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With the increase in doped amount of Fe3+ in BaTiO3 the UV-vis spectra show red-shift

and the band-gap lowering upto 2.81eV. The variation of band gap energy with the

doping concentration is given in Table 2. The charge transfer transition between Fe 3d

electrons and conduction band (CB) may explain the appearance of the red-shift. The

absorption patterns of BaTi1-xFexO3 (0.0≤x≤0.02) are highly dependent on the dopant

concentration as shown in Fig. 5.

The result has been further confirmed by first-principles theoretical calculations. This

red-shift in doped BaTiO3 increases the number of photogenerated electrons and holes to

participate in the photocatalytic reaction, which support the enhanced the photocatalytic

activity of Fe-doped BaTiO3.

5.4.4 Mössbauer Spectroscopy

The room temperature Mössbauer spectrum for 2.0 at.% Fe doped BaTiO3 sintered at

900°C is shown in Fig. 6. The observed spectrum can be fitted with one magnetic sextet

and a paramagnetic doublet. The Value of Mössbauer parameters for sextet such as

Hyperfine field (Hhf), Quadrupole splitting (∆EQ), Isomer shift (δ), Outer line width (Γ)

and Area (%) derived from Mössbauer spectrum are 515.3 kG (Hhf), 0.0851 mm/s (∆EQ),

0.476 mm/s (δ), 0.346 mm/s (Γ) and 67.2 (%), respectively. Mössbauer parameters for

doublet such as Quadrupole splitting (∆EQ), Isomer shift (δ), Outer line width (Γ) and

Area (%) derived from Mössbauer spectrum are 0.004 mm/s (∆EQ), 0.241 mm/s (δ),

1.728 mm/s (Γ) and 32.8 (%), respectively.

Isomer shift (δ) values for sextet and paramagnetic doublet are 0.476 mm/s and 0.241

mm/s, respectively with respect to α-Fe (δ = 0.00 mm/s). It indicates that Fe is in Fe3+

ionic state [40-43]. Isomer shift is related to s-electron density. Higher isomer shift means

that s-electron density at the Fe-nucleus will be lower. The isomer shift of tetrahedral site

is lower than that of octahedral site. It suggests that Fe3+ ion in tetrahedral site has more

s-electron density than that in octahedral site. It results in shorter Fe-O distance in

tetrahedral site than that in octahedral site. Chemical isomer shift increase in the sequence

δ (tetrahedral Fe3+) < δ(octahedral Fe3+) < δ(tetrahedral Fe2+) < δ(tetrahedral Fe2+). These

results suggest that sextet belongs to octahedral site.


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The presence of Fe2+ was ruled out based on the absence of absorption at higher velocity

(a center shift of at least 1.0 mm/s relative to α -Fe would be expected, e.g.[44]). The

presence of Fe-metal is also ruled out based on the absence of absorption line between -

7.96 to – 4.33 mm/s velocity and no other sextet observed in the Mössbauer spectrum. In

the Fe- metal foil spectrum (single sextet) the first line absorption position at -5.312

mm/s velocity. Quadrupole splitting (∆) values for doublet is almost 0.00 mm/s with

respect to α-Fe suggesting that Fe3+ ions show cubic symmetry of polyhedron.

Quadrupole splitting for both Fe2+ and Fe3+ in sites of accurately cubic symmetry is zero

and for non cubic sites (∆ (Fe3+) << ∆ (Fe2+). The value of isomer shift and quadrupole

splitting of doublet suggest that Fe is in Fe3+ ionic state.

Fig. 6: Room temperature Mossbauer spectrum of 2.0 at.% Fe doped BaTiO3 sintered at 900°C; Component spectra are represented by dotted lines.

-10 -5 0 5 1099.4

99.5

99.6

99.7

99.8

99.9

100.0

100.1

85

90

95

100

BaTi0.98

Fe0.02

O3

Rel

ativ

e Tra

nsm

ission

(%

)

Velocity (mm/s)

α -Fe foil

1 2 3 4 5 6


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There is superposition of sextet and doublet patterns in the Mössbauer spectrum. Doublet

pattern arises from the presence of superparamagnetic fraction whereas sextet pattern

comes from the presence of ferromagnetic fraction. However, the relative percentage of

sextet to doublet patterns was found to be 67:33 indicating that the superparamagnetic

fraction is small.

5.4.5 Band Structure and Photoabsorption properties

Electronic structure of the oxide semiconductor plays a crucial role in determining its

photocatalytic activity. In the present study, the electronic structures of BaTiO3 and

BaTiO3 doped with 12.5% iron were determined with DFT calculations. Band structures

of undoped and doped systems for 40-atom supercell are shown in Fig.7 (a-b) for

undoped BaTiO3 and Fe-doped BaTiO3. Calculated band-gaps are listed in Table 2.

(a)


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(b)

Fig. 7: Showing electronic band structure for (a) undoped BaTiO3 and (b) Fe-doped BaTiO3. Fermi energy is set at zero.

Typically, band gaps estimated with DFT are smaller than the experimental values [45],

not surprisingly because DFT solves the electronic ground state problem. Accurate

estimation of absolute values of band gaps requires one to go beyond the density

functional theory by including self-interaction corrections or using hybrid functional.

While conduction band properties are not accurately captured, those associated with

valence bands and corresponding off-sets are described reasonably well within DFT. In

the present work, we are more interested in how band gaps change with doping rather

than their absolute values and find the changes in band gap with Fe-doping are:

∆∆∆∆Eg = 0.31eV (theoretical)

∆∆∆∆Eg = 3.2 – 2.81 = 0.39eV (experimental)

Our results for band-structures obtained with DFT calculations show that the top of

valence band and bottom of conduction band of undoped BaTiO3 are at M point and Г

point of brillouin zone respectively [Fig. 7 (a-b)] suggesting that pure BaTiO3 is an


106

indirect band gap material. However, the band gap is significantly reduced in the Fe-

doped BTO because of the appearance of defect band at the Fermi energy which is closer

to the valence band. The band-gap changes to the Г-X point of brillouin zone, keeping it

still an indirect gap material.

TABLE 2 Change in Band-gap for Undoped and Fe-doped BaTiO3 at different high symmetry points in Brillouin zone.

Undoped BaTiO3

High symmetry points Band-gap in Brillouin zone Г –M 1.80 eV

Г – Г 1.85 eV

Fe-doped BaTiO3 High symmetry points Band-gap in Brillouin zone

Г – X 1.23 eV

Г - Г 1.54 eV

Consequently, the gap is reduced to 1.23 eV. The total density of states (DOS) in Fig. 8

(a-b) demonstrates that there appears a sharp peak near fermi-energy, corresponding to

the defect band associated with 3d states of Fe. It is clear from the partial DOSs Fig. 9(a-

d) that this sharp peak in the total DOS essentially comes from Fe impurity. These first-

principles calculations are consistent with the large red-shift in UV-Vis spectra.

(a)


Fig. 8: Total density of states plots of (a) undoped and (b) Fe

Fig. 9: Showing partial density of states (PDOS) of (a) Fe, (b) O, (c) Ti and (d) Ba ions.


107

(b)

Fig. 8: Total density of states plots of (a) undoped and (b) Fe-doped BaTiOset at zero.

Showing partial density of states (PDOS) of (a) Fe, (b) O, (c) Ti and (d) Ba ions.

Fermi energy is set at zero.


doped BaTiO3. Fermi energy is

Showing partial density of states (PDOS) of (a) Fe, (b) O, (c) Ti and (d) Ba ions.


108

5.4.6 Photocurrent Investigation

On studying the PEC response of various samples prepared at different sintering

temperatures and varying doping concentrations of Fe, it was found that sample doped

with 2.0 at.% Fe sintered at 900°C exhibited the highest photocurrent density. The

Photocurrent density obtained with undoped BaTiO3 sample sintered at 900°C was 0.07

mAcm-2 at 0.5 V/SCE. Whereas maximum photocurrent density recorded in the sample

doped with 2.0 at. % Fe was 2.55 mAcm-2 at 0.5 V/SCE (Fig. 10) (Table 3).

TABLE 3. Measured parameters of optical and photoelectrochemical properties for undoped and Fe-doped BaTiO3 samples sintered at 900ºC.

Compared to other researchers [46-48] we have recorded a good photocurrent density in

the present experimentation. Doping of iron into the BaTiO3 structure caused a decrease

in resistivity, resulting in decrease in the numbers of recombination centres. It is

supposed that decrease in the number of recombination centres results into an increase in

the photocarriers lifetime, leading to the increase in photoconductivity [49]. Moreover,

the red shift caused due to Fe doping resulted into more absorption in the visible region

causing an increase in photocurrent. Thus, it was observed that 2.0 at.% is the optimal

doping level above and below which (i.e. 0.5, 1.0, 3.0 and 4.0 at.% Fe doping)

photocurrent density decreased. Maximum value of open circuit photovoltage obtained

for this sample also supports the significant rise in the photocurrent density as compared

to the undoped BaTiO3 sample (Table 3).

Samples Band gap Energy (eV)

Open circuit Photovoltage Voc, (V/SCE)

Photocurrent Density at 0.5 V/SCE (mA/cm2)

Undoped BaTiO3

3.11 0.10 0.07

0.5 at.% Fe 3.06 0.16 0.12 1.0 at.% Fe 2.94 0.23 0.14

2.0 at.% Fe 2.81 0.36 2.55 3.0 at.% Fe 2.84 0.26 1.70 4.0 at.% Fe 2.89 0.19 0.62


Sharp decrease in resistivity values for 2.0 at.% Fe

for the better performance of the sample upon Fe doping. On the other hand, higher

concentration of doping would provide more defect

inhibiting the increased separation efficiency [50].

TABLE 4. Electrical and photoelectrochemical properties of all undoped and FeBaTiO3 samples deduced from Mott

Fig 10: Photoelectrochemical characteristics of Undoped and 0.5, 1.0, 2.0 at.% Fe

Samples

Un-doped BaTiO0.5 at.% Fe1.0 at.% Fe

2.0 at.% Fe3.0 at.% Fe4.0 at.% Fe


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Sharp decrease in resistivity values for 2.0 at.% Fe-doped sample (Table 4), also accounts


concentration of doping would provide more defect-scattering/recombination propert

inhibiting the increased separation efficiency [50].

TABLE 4. Electrical and photoelectrochemical properties of all undoped and Fesamples deduced from Mott-Schottky and Current

Fig 10: Photoelectrochemical characteristics of Undoped and 0.5, 1.0, 2.0 at.% FeBaTiO3 sintered at 900oC

Samples Donor Density,Nd (cm-3)

Flatband Potential, Vfb

(V/SCE)

Resistivity(

doped BaTiO3

8.23 × 1018 -0.46 19.0

0.5 at.% Fe 8.34 × 1018 -0.51 17.2 1.0 at.% Fe 3.59 × 1019 -0.55 16.9

2.0 at.% Fe 1.24 × 1021 -0.88 13.9 3.0 at.% Fe 4.53 × 1020 -0.68 16.5 4.0 at.% Fe 1.09 × 1019 -0.63 18.5


doped sample (Table 4), also accounts


scattering/recombination properties

TABLE 4. Electrical and photoelectrochemical properties of all undoped and Fe-doped Schottky and Current-Voltage curves.

Fig 10: Photoelectrochemical characteristics of Undoped and 0.5, 1.0, 2.0 at.% Fe-doped

Resistivity (Ω cm)

19.0 × 105

17.2 × 105 16.9 × 105

13.9 × 104 16.5 × 104 18.5 × 105


110

The good photoresponse of this sample has also been supported by maximum value of

flatband potential and donor density obtained (Table 4) (Fig.11). All the above factors

address to the better performance of Fe-doped BaTiO3 in the PEC cell.

Fig. 11: Mott-Schottky plots for (a) undoped and (b) 2.0 at.% Fe-doped BaTiO3.


111

Photoelectrochemical studies on Ruthenium (Ru)-doped BaTiO3

5.5 Background

Hydrogen is widely considered to be the fuel of the future and as energy carrier is

anticipated to join photovoltaic electricity as the foundation of sustainable energy system.

The general enthusiasm for the use of hydrogen as an environmentally friendly fuel has

been encouraged by the fact that the combustion of hydrogen results in the generation of

water, which neither results in air pollution or leads to the emission of green house gases.

This consideration is correct – assuming that hydrogen is generated using a source of

renewable energy, such as solar, wind, hydroelectric, or hydrothermal energy. Generation

of hydrogen by direct water splitting using photo electrochemical (PEC) systems is the

“Holy Grail” of the hydrogen economy: as both solar light and water are abundantly

available. Semiconductor electrodes in PEC cell absorbs solar energy and generates the

electrical charges that drive the electrolysis reaction, splitting the water into hydrogen at

cathode and oxygen at anode. Although simple in concept, the challenge is to find a

material that can drive this one step process. Preparation of photoelectrode with desired

characteristics has been, central to nearly all the researches carried out to achive efficient

PEC splitting of water and several new dimensions have been added, in recent years, for

material modifications. Nanostructured materials, in contrast to their bulk counterparts,

exhibit significant alteration in their properties viz. band gap, porosity and surface area,

which are crucial for PEC applications [51, 52]. Besides, alteration in above properties is

particle size dependent to the extent that even a small change in particle/grain size may

generate a material with drastically different characteristics [53] Oxide nanomaterials

have unique optical and electrical properties due to very small size of the particles and

the quantum confinement phenomenon. Oxide nanomaterials are good catalysts due to

their high surface to volume ratio and may lead to favourable material for PEC spliiting

of water. In search for a better semiconductor various metal oxide semiconductors such

as Cr2O3, Fe2O3, CuO, PbO, ZnO, and TiO2 that have been used in PEC splitting of

water, but it was difficult to get large quantities of hydrogen from these oxides due to less

negative conduction band edge than the reduction potential of water. Another problem

plaguing most semiconductors when illuminated in an aqueous environment is their


112

corrosion. On account of these limitations in the oxide semiconductors alternative

materials with newer methods of preparation are being looked upon by the scientific

community at large. One such group of material under development is mixed oxides

offering many exciting properties with respect to their use in PEC splitting of water. The

application of mixed metal oxides as photoelectric, ferroelectric, piezoelectric and

dielectric materials is an area of tremendous promise in research currently. Perovskite

family includes many titanates used in various applications; for example, electronic,

electro-optical, and electromechanical applications. The possibility of using BaTiO3

(BTO) in solar induced photoelectrochemical splitting of water has also been explored.

BaTiO3 has a unique set of properties that make it a promising candidate as

photoelectrode in the PEC cell having wide band gap and has long term chemical stability

in many solvents over a wide pH range. An effective way to enhance the photorefractive

performance is by generating suitable defects in a crystal’s structure. The performance of

photorefractive crystals depends strongly on impurities, which can act as donors and

acceptors for charge carriers. The defects can be modified either by appropriate doping or

by nonstoichiometric crystal growth. Moreover BTO crystals can be easily doped and this

is a suitable way for the crystal properties to be tailored in a desired direction. The

important dopant factors are their concentration, valence state, distribution coefficient,

occupied sites symmetry, etc. The properties of BTO crystals with different doping

elements have already been studied [54-55]. However, up to now the influence of Ru on

BTO charge-transport properties is still under investigation. It was found that low Ru

concentration could enhance the optical and photoelectrochemical properties of BTO

crystals at He–Ne laser wavelengths [56]. Furthermore, it was reported that Ru addition

shows perspective feature in Sr0.61Ba0.39Nb2O6 crystals [57]. However, ruthenium (Ru)

doping in BTO remains practically unexplored, despite few studies indicating that it may

lead to significant changes in material properties. The aim of our investigation is to

determine the influence of Ru doping on the photoelectrochemical properties of BTO

powders in an attempt to improve the photoelectrochemical properties in the near visible

region. While the computational simulation on Ru-doped BaTiO3 was done in the present

chapter, the experimental part was done on Ru-doped BaTiO3 earlier by Ms. Jaya

Shrivastava in her Ph.D. thesis in the year 2011. However, the experiments were re-


113

conducted again and the results were confirmed in the present work in order to compare

them with computational results.

This section of study deals with Ru doping in BaTiO3. BaTiO3 exhibits mixed ionic –

covalent chemical bonding with the Ba-O bonds being almost entirely ionic, and the Ti-O

substructure has a substantial covalent contribution leading to a unique structure, which

makes it one of the most commonly used titanates. Doped BaTiO3 has a unique set of

properties that makes it a promising candidate as photoelectrode and photocatalyst. Use

of transition metal (TM) doped nanostructured BaTiO3 for PEC splitting of water has

interested some researchers in recent years. Further, Fe(3d5 4s1), (Ru)3d5 4s1 and Ni (3d8

4s2) are important dopant as these may shift EF upward and downward, respectively, with

respect to undoped BaTiO3. There are various reports on Ru doped BaTiO3 (BT) for many

applications, but so for no report is available on the photoelctrochemical and

photocatalytic studies. Samples of BaTiO3 were prepared by polymeric precursor method,

described earlier in previous section, at different added concentrations (0.5-2.0 at.% of

Ruthenium and three different sintering temperatures (500, 700 and 900ºC). Table 5

presents a description of the samples prepared under this part of investigation.

Table 5 Description of undoped and Ru doped BaTiO3 (BT) prepared at different sintering temperatures

Sintering Temperature

(°C)

Precursor solution concentration of Ru

(% at.)

Sample Identity

BT undoped

500

--

0.5

BT500,700,900

Ru0.5 BT500

700 0.5 Ru0.5 BT700

900 0.5 Ru 0.5BT900

500 1.0 Ru1.0 BT500

700 1.0 Ru 1.0BT700

900 1.0 Ru1.0BT900

500 2.0 Ru2.0 BT500

700 2.0 Ru2.0BT700

900 2.0 Ru2.0BT900


114

5.6 RESULTS & DISCUSSION

5.6.1 Phase determination: XRD analysis

The effect of sintering temperature on the crystal growth of the tetragonal BaTiO3 phase

was monitored by XRD. Fig. 12 shows the XRD patterns of BaTi1-xRuxO3 as a function of

x, where, as the concentration of dopant increases the crystallinity and peak intensity of

barium carbonate decreases. Peak corresponds to 2θ values at 31.5, 34.5, 38.9, 42.0, 46.8

and 56.2 confirms the formation of BaTiO3 with cubic, hexagonal and tetragonal phases

with very less intense peak of BaCO3 as unreacted species.

30 35 40 45

[200

,002

]

[111

][110

]

[a]=Ru0.5

BT500

[b]=Ru0.5

BT700

[c]=Ru0.5

BT900

[b]

[c]

[a]

Inte

nsit

y (a

.u)

2θθθθ (degree)

A


115

Fig. 12: X-ray diffraction pattern of 0.5 (A), 1.0 (B) & 2.0 (C) at.% Ru doped BT

30 40 50 60

[111

]

[201

]

[211

]

[200

,002

]

[110

]

[a]= Ru1.0

BT500

[b]= Ru1.0

BT700

[c]= Ru1.0

BT900

[c]

[b]

[a]

Inte

nsi

ty (

a.u

)

2θθθθ (degree)

35 40 45 50 55 60

[211

]

[200

,002

]

[201

]

[111

][110

] [a]=Ru2.0

BT500

[b]=Ru2.0

BT700

[c]=Ru2.0

BT900

[c]

[b]

[a]

Inte

nsi

ty (

a.u

)

2θθθθ (degree)

B

C


116

As the concentration of dopant increases the intensity of [110] peak which was attributed

to tetragonal phase also increases leading to increase in crystallite diameter. Maximum

crystallinity was obtained in 2% at Ru doped samples sintered at 900°C (curve c in Fig.1

C. Intensity of BaCO3 also decreases by increasing the dopant amount and sintering

temperature. Furthermore, no peaks due to the other impurity appear in XRD patterns,

indicating that doping of Ru has no obvious negative effect on the formation of

perovskite structure.

5.6.2: Surface morphology: FE-SEM & HR-TEM analysis

Surface morphology of the powders was obtained by recording SEM images of few

representative samples. Observed images are presented in Fig. 13 A-D. SEM (Fig: 13 A-

D) analysis reveals the porous structure agglomerated with very small particles and

particle sizes increased with the sintering temperatures. HR-TEM was done for a

representative sample. HR-TEM (Fig. 14 A-B) analysis also exhibits better crystallinity,

well defined shape and ordered arrangement of atoms in the powders. HR-TEM in Fig.14

A-B shows that atoms are arranged periodically in well defined planes inside nano sized

particles of Ru doped BaTiO3.


Fig. 13: FE-SEM images of Ru doped BT, A = Ru

D = Ru2.0BT700

A


117

SEM images of Ru doped BT, A = Ru0.5BT500, B = Ru0.5

Fig. 14: HR-TEM of Ru doped BT (Ru0.5BT700

A

C

B


0.5BT700, C = Ru2.0BT500 &

700)

D

B


118

5.6.3: Grain / crystallite size

Scherrer’s calculations were attempted, by employing the observed X-ray diffraction

data, to estimate average crystallite/grain size in the powders. The results are presented in

Table 6, which indicate crystallite size varying from 20–47 nm. Gradual increase in

crystallite size with rise in sintering temperature and Ru doping is also evident. As

calculated by the Debye Scherrer equation crystallite diameters as a function of Ru

doping and sintering temperature are listed in Table 6.

5.6.4: Absorbance and band gap analysis

As stated earlier, the band gap energy of the semiconductor samples is an important

property for their application in photoelectrochemical cells. Doping of the semiconductor

by an impurity may result in the creation of defect states which may lead to a significant

change in the band gap energy of the material.

The diffuse and total reflectances (Fig: 15-17) of the samples were measured as functions

of wavelength from 200 to 800 nm using the diffuse reflectance attachment of a Jasco

spectrophotometer. The reflectances were measured relative to a BaSO4 standard. The

diffuse reflectance curve shows a strong decrease in the reflectance from (3.35 eV) at

wavelengths below 400 nm, indicating an absorption edge at around 2.90 eV.

Table 6 Average size of grains / crystallites in undoped and Ru doped BT

Dopant

concentration

(at. %)

Sintering

Temperature

(ºC)

Phase Crystallite size

(nm)

Undoped

BaTiO3

500 Hexagonal,

Cubic

20

700 Tetragonal 28


119

900

Tetragonal 40

0.5 at. % 500 Hexagonal 25

700 Tetragonal 26

900 Tetragonal 27

1.0 at. %

500 Hexagonal 25

700 Tetragonal 29

900 Tetragonal 47

2.0 at%

500 Hexagonal 23

700 Tetragonal 28

900 Tetragonal 45

Table 7 Observed bandgap energies of undoped and Ru doped BT

Dopant

concentration

(at. %)

Sample

Identity

Sintering

Temperature

(ºC)

Bandgap energy

(eV)

BT undoped BT500,700,900 500 3.20

700 3.18

900 3.10


120

0.5 at. %

Ru0.5 BT500 500 3.35

Ru0.5 BT700 700 3.10

Ru 0.5BT900 900 3.17

1.0 at. %

Ru1.0 BT500 500 3.09

Ru 1.0BT700 700 3.02

Ru1.0BT900 900 3.03

2.0 at%

Ru2.0 BT500 500 3.0

Ru 2.0BT700 700 2.90

Ru2.0BT900 900 2.90


121

Fig. 15: Observed Absorbance spectra for 0.5 at.% Ru doped BT

200 300 400 500 600 700

0

20

40

60

80

100Ru

0.5BT 700

Eg=3.1 eV

Ab

sorb

ance

(a.

u)

Wavelength (nm)

200 300 400 500 600 700

0

20

40

60

80

100

Eg=3.17eV

Ru0.5

BT900

Ab

sorb

ance

(a.u

)

Wavelength (nm)


122


200 300 400 500 600 700

0

20

40

60

80

100Ru

1.0BT 500

Eg=3.09 eV

Ab

sorb

ance

(a.

u)

Wavelength (nm)

200 300 400 500 600 700

0

20

40

60

80

100Ru

1.0 BT 700

Eg=3.02 eV

Ab

sorb

ance

(a.u

)

Wavelength (nm)

300 400 500 600 700

0

20

40

60

80

100Ru

1.0 BT 900

Eg=3.03 eV

Ab

sorb

ance

(a.u

)

Wavelength (nm)


123


200 300 400 500 600 700

0

20

40

60

80

100Ru

2.0 BT 500

Eg=3.0 eV

Ab

sorb

ance

(a.u

)

Wavelength (nm)

200 300 400 500 600 700

0

20

40

60

80

100Ru

2.0 BT700

Eg= 2.90 eV

Ab

sorb

ance

(a.u

)

Wavelength(nm)

200 300 400 500 600 700

0

20

40

60

80

100Ru

2.0 BT900

Eg= 2.90 eV

Ab

sorb

ance

(a.u

)

Wavelength(nm)


124

With the increase in doped amount of Ru3+ in BaTiO3 the UV-Vis spectra show red shift

and the band-gap lowering up to 2.90 eV. With the increase in doped amount of Ru in

BaTiO3 the UV-Vis spectra show red shift and the band-gap lowering as determined from

the absorption edge from the equation, E(eV)= 1240/λ(nm). This shows that the band

gaps of the specimens become narrow. It is evident from the Table 7 that bandgap energy

for the sample doped with 0.5 at.% was 3.35 eV was recorded which is highest value and

after increasing the dopant amount a continuous decreasing trend was observed from this

value to 2.90 eV. It is clear from the table a marginal decrease in the values was observed

for middle concentration of dopant i.e., 1.0 at.% Ru doped BT. It is noteworthy that the

curve for this sample shifted to higher wavelengths, indicating a decrease in the optical

gap with enhanced absorption towards visible range.

5.6.5 Band Structure and Photoabsorption properties

In the present study, the electronic structures of BaTiO3 and BaTiO3 doped with 12.5%

ruthenium were determined with DFT calculations. Band structures of undoped and

doped systems for 40-atom supercell are shown in Fig.18 (a-b) for undoped BaTiO3 and

Fe-doped BaTiO3. Calculated band-gaps are listed in Table 3.

TABLE 8 Change in Band-gap for Undoped and Ru-doped BaTiO3 at different high symmetry points in Brillouin zone.

Undoped BaTiO3

High symmetry points Band-gap in Brillouin zone Г –M 1.80 eV

Г – Г 1.85 eV

Ru-doped BaTiO3 High symmetry points Band-gap in Brillouin zone

Г – X 1.30 eV

Г - Г 1.58 eV


Fig. 18: Showing electronic band structure for (a) undoped BaTiO


125

(a)

(b)

howing electronic band structure for (a) undoped BaTiOBaTiO3. Fermi energy is set at zero.


howing electronic band structure for (a) undoped BaTiO 3 and (b) Ru-doped


126

Our results for band-structures obtained with DFT calculations show that the top of

valence band and bottom of conduction band of undoped BaTiO3 are at M point and Г

point of brillouin zone respectively [Fig. 18 (a-b)] suggesting that pure BaTiO3 is an

indirect band gap material. However, the band gap is significantly reduced in the Ru-

doped BTO because of the appearance of defect band at the Fermi energy which is closer

to the valence band. The band-gap changes to the Г-X point of brillouin zone, keeping it

still an indirect gap material.

Fig. 19: Showing partial density of states (PDOS) of Ru, O, Ti and Ba ions. Fermi energy is

set at zero.

Our results of Ru-doped BaTiO3 are found quite similar with the Fe-doped BaTiO3 but as

we stated previously that we are more interested in the how band gap changes with the

dopants rather than their absolute values. The band at the top of the valence band of Ru-

doped BT is made of 4d-orbitals of Ru. Also, the defect state formed due to Ru 4d is

found to be more delocalized as compared with the Fe-doped BT [Fig. 19].


127

5.6.6: Photoelectrochemical Performance

Calculated values of photocurrent densities (Iillumination-Idarkness) are summarized in the

Table 4. In the undoped sample which was sintered at 900ºC, the photocurrent density

was recorded to be 0.43 mA/cm2 at 0.5 V/SCE (ig.21) (Table 9). On doping these samples

with different concentration of Ru, a remarkable increase in the photocurrent density was

observed for the samples sintered at 700ºC. Maximum photocurrent density was recorded

in the sample doped with 0.5 at. % Ru, i.e. 0.7 mAcm-2 at 0.5 V/SCE (Fig. 20 a-c). It is

evident from the table that highest photocurrent density is obtained at lower concentration

i.e. 0.5 at. % Ru doped sample sintered at 700ºC. At this concentration and sintering

temperature the crystallite diameter was also lowest; hence it can be easily said that

decrease in crystallite diameter lead higher surface area for better light absorption leading

to increase in photocurrent. As we are moving for higher concentrations (dopant) the

photocurrent densities decrease gradually. This can be attributed to the reason that doping

of Ru into the barium titanate structure caused a decrease in resistivity, hence increase in

conductivity, resulting into the decrease in the numbers of recombination centres. It is

supposed that decrease in the number of recombination centres results into an increase in

the photocarriers lifetime, leading to the increase in photoconductivity. Moreover, the

red shift caused by Ru3+ doping resulted into more absorption in the visible region, hence

causing an increase in photocurrent. Therefore the tetragonal phase of Ru+3 doped

BaTiO3 prepared by polymeric precursor route gives significant photocurrent at low

temperature.

5.7: Conclusion

Doping of BaTiO3 with 2.0 at.% Fe is shown experimentally to result in remarkable

increase in the photocurrent density (2.55 mAcm-2) as compared to Ru-doped BaTiO3

(0.70 mAcm-2 at 0.5 V/SCE). The observed change in band gap values with Fe & Ru-

doped BaTiO3 as compared to undoped BaTiO3 using both theory and experiments

complemented each other. Observed change in the electronic band-gap and that estimated

with first-principles calculations compare well, thus (a) helping understand the origin of

change in the band gap in impurity band in the gap and (b) suggesting that such

calculations have the potential to be used in screening various dopants. This should


128

effectively reduce the number of possibilities promising to yield favorable properties to

be tested experimentally. This approach would not only speed up the research efforts but

also save lots of chemicals and expenses thereof.

Fig. 20 a: I-V Characteristics of 0.5 at.% Ru doped BT

0.0 0.3 0.6 0.9-0.3

-0.2

-0.1

0.0

dark

light

Ru0.5

BT500

Cur

rent

den

sity

(mA

cm-2)

V/SCE(V)

0.0 0.3 0.6 0.9

-2.0

-1.5

-1.0

-0.5

0.0

dark

light

Ru0.5

BT700

Cu

rren

t d

ensi

ty (

mA

cm-2)

V/SCE(V)

0.0 0.2 0.4 0.6 0.8 1.0-0.8

-0.6

-0.4

-0.2

0.0

dark

light

Ru0.5

BT900

Cur

ren

t den

sity

(mA

cm-2)

V/SCE(V)


129

Fig. 20 b: I-V Characteristics of 1.0 at.% Ru doped BT

0.0 0.2 0.4 0.6 0.8 1.0-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

dark

light

Ru1.0

BT500

Cu

rren

t de

nsit

y(m

Acm

-2)

V/SCE(V)

0.0 0.2 0.4 0.6 0.8 1.0-0.5

-0.4

-0.3

-0.2

-0.1

0.0

dark

light

Ru1.0

BT700

Cur

rent

dns

ity(m

Acm

-2)

V/SCE(V)

0.0 0.3 0.6 0.9-0.25

-0.20

-0.15

-0.10

-0.05

0.00

dark

light

Ru1.0

BT900

Cu

rren

t de

nsi

ty (

mA

cm-2)

V/SCE(V)


130

Fig. 20 c: I-V Characteristics of 2.0 at.% Ru doped BT

0.0 0.2 0.4 0.6 0.8 1.0-2.0

-1.5

-1.0

-0.5

0.0

dark

light

Ru2.0

BT700

Cu

rren

t d

ensi

ty (

mA

cm-2)

V/SCE(V)

0.0 0.2 0.4 0.6 0.8 1.0-0.4

-0.3

-0.2

-0.1

0.0

dark

light

Ru2.0

BT500

Cur

ren

t den

sity

(mA

cm-2)

V/SCE(V)

0.0 0.3 0.6 0.9

-0.15

-0.10

-0.05

0.00

darklight

Ru2.0

BT900

Cu

rren

t d

ensi

ty (m

Acm

-2)

V/SCE(V)


131

Fig. 21: Comparison of I-V Characteristics of 0.5, 1.0 and 2.0 at.% Ru doped BT

0.0 0.2 0.4 0.6

-0.6

-0.3

0.0

[A]=Ru0.5

BT500

[A]=Ru0.5

BT700

[A]=Ru0.5

BT900 [B]

[A]

[C]

Ph

otoc

urr

entd

ensi

ty (

mA

cm-2)

V/SCE(V)

0.0 0.2 0.4 0.6

-0.2

-0.1

0.0

[A]=Ru1.0BT500

[B]=Ru1.0BT700

[C]=Ru1.0BT900

[c]

[B]

[A]

Ph

oto

curr

entd

ensi

ty (

mA

cm-2)

V/SCE(V)

0.0 0.2 0.4 0.6

-0.8

-0.6

-0.4

-0.2

0.0

[A]= Ru2.0

BT500

[B]= Ru2.0

BT700

[C]= Ru2.0

BT900

[C]

[B]

[A]

Pho

tocu

rren

tden

sity

(m

Acm

-2)

V/SCE(V)


132

Table 9 Observed photocurrent densities showed by undoped and Ru doped BT

Dopant

concentration

(at. %)

Sample

Identity

Sintering

Temperature

(ºC)

Photocurrent

density(mAcm-2)

at 0.5 V/SCE

BT undoped BT500,700,900 500 0.05

700 0.02

900 0.43

0.5 at. %

Ru0.5 BT500 500 0.03

Ru0.5 BT700 700 0.70

Ru 0.5BT900 900 0.11

1.0 at. %

Ru1.0 BT500 500 0.04

Ru 1.0BT700 700 0.14

Ru1.0BT900 900 0.01

2.0 at%

Ru2.0 BT500 500 0.01

Ru 2.0BT700 700 0.23

Ru2.0BT900 900 0.03


133

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