Structural, Optical and dielectric study of Mn doped PrFeO3 ceramics

Khalid Sultan1*, M. Ikram

1 and K.Asokan

2

1Department of physics, National Institute of Technology Hazratbal Srinagar,

J & K-190006, India

2Material Science Division, Inter University Accelerator Centre, Aruna Asaf Ali Marg, New Delhi-

110067, India

Abstract

Polycrystalline bulk samples of PrFe1-xMnxO3 (x=0.0, 0.1, 0.3, 0.5) were synthesized by solid

state reaction method to understand their structural, optical and dielectric properties. X-ray

diffraction (XRD) and Raman spectroscopy were investigated to confirm chemical phase and

the orthorhombic pbnm structure. As the concentration of Mn increases, the lattice parameter

b increases while the lattice parameters a and c/√2 decrease but the change of former is less

than later. PrFe1-xMnxO3 exhibits O-type (a < c/√2 < b) orthorhombic pbnm structure upto

x=0.5. From XRD it is also evident that the peaks shift towards higher 2θ values with

increase in Mn content indicating the development of strain in the crystal structure possibly

due to Jahn-Teller distortion after the incorporation of Mn3+

ions in the parent compound

PrFeO3. From the Raman study, the modes exhibit a blue shift with broadening of spectral

features in the doped samples. The observed shift in wave number with doping clearly

indicates change in the bond lengths of Fe-O / Mn-O as well as their impact on FeO6 / MnO6

octahedra. The dielectric constant (ε') and dielectric loss (tanδ) are also studied as a function

of frequency and temperature. The dielectric constant and ac conductivity increases with Mn

doping. The variation of dielectric properties such as ac conductivity, tanδ and ε' suggests

that small polarons contribute to the conduction mechanism. Activation energy (Eσ) and

optical band gap (Eg) decreases with the concentration of Mn. The observed higher values of

these quantities reveals that there is hopping between Mn3+

to Mn4+

and Fe3+

to Fe2+

at the

octahedral sites of the compound. Possible mechanism contributing to these processes has

been discussed.

Key Words: Solid State Reaction, Mn, PrFeO3, XRD, RAMAN, Orthorhombic, Dielectric

properties.

1. INTRODUCTION

Ferrites are promising eco-friendly material to replace toxic lead-based perovskite

relaxors, sensors, capacitors and optical storage devices [1]. Among ferrites, orthoferrites,

RFeO3 (where R = rare earth metals) belongs to perovskite family and have ABO3 distorted

orthorhombic GdFeO3 type perovskite structure with space group pbnm. In this structure, the

distortion of the Fe octahedron is small and almost independent of „R‟ (rare earth) [2]. But

the distortion of rare earth polyhydra is large and increases with decreasing ionic radius of R.

As distortion increases, the 12 O ions surrounding the „R‟ separate into two types: R with

eight first-nearest O ions and R with four second-nearest O ions. Such structural distortions

influence the magnetic ordering and spin-state transitions [3]. In Orthoferrites, PrFeO3 (PFO)

appears as a potential candidate in microelectronic industry as they enable device

miniaturization due to the high dielectric constant (ε') and low dielectric loss (tanδ). PFO also

shows remarkable electrical and magnetic properties due to mixed valency of perovskites and

also because of anion non-stoichoimetry permitted by 3d ions in B site [4-5]. Like most of the

Orthoferrites, PFO has GdFeO3-type structure, which crystallizes with distorted orthorhombic

perovskite-like lattice symmetry, with four Fe ions and four rare-earth ions per unit cell and

conforms to the space group D2h16 Pbnm at room temperature [6]. The four Fe sites and four

rare earth sites of PrFeO3 are crystallographically equivalent [7-8]. The crystallographic unit

cell of PrFeO3 (Fe being in high spin state) can be visualized as a corner sharing FeO6

octahedron forming a three dimensional distorted perovskite structure [9]. Furthermore PFO

at room temperature is a wide-gap, high-spin Mott insulator placed in the highly correlated

regime (U/t>>1) [10].

The physical properties of PFO can be tailored by substituting the cation Fe by several

elements partly or completely and potentially create new applications [11-13]. The

compound PrFeO3 is Jahn-Teller (JT) inactive as Fe3+

is a JT inactive ion. After replacing Fe

with Mn, the compound PrFe1-xMnxO3 becomes JT-active as Mn3+

is a JT-active ion. It is

reported that the t2g3 eg

1 state of Mn

3+ is subjected to JT effect resulting in the distortion of

MnO6 octahedra with four Mn-O distances of 0.1930 nm and two of 0.2290 nm [14]. The

substitution of Mn ions in PrFeO3 weakens the exchange interaction and reduces the Curie

temperature. It also induces a J-T distortion which results in a large electric field gradient at

the 57

Fe nucleus and modification of crystallographic structure. Present study focuses on the

structural, optical and the dielectric properties of PrFe1-xMnxO3 (x=0, 0.1, 0.3 and 0.5) and

evaluates the parameters like lattice parameters, dielectric constants, a.c. conductivity and

activation energy. Possible mechanism for their conduction is also discussed.

2. EXPERIMENTAL DETAILS

Polycrystalline bulk samples of chemical composition PrFe1-xMnxO3 (x=0.0, 0.1, 0.3,

0.5) (hereafter called as PFMO) were prepared by solid state reaction method using high

purity (> 99.9%) precursors of Pr6O11, Mn2O3 and Fe2O3 taken in the stiochiometry ratio.

Mixed powders were preheated at 10000C for 12 hours and calcinated again at 1200

0C for 12

hours. The homogenous powder was reground and pelletized into pellets of 10 mm in

diameter by the application of 5 kN force. The resultant pellets were sintered at 12500C for

24 hours at a heating rate of 40Cmin

-1 and then cooled to room temperature at a cooling rate

of 30Cmin

-1 in a tubular furnace.

The structure of the sample was analyzed by X-ray diffraction (XRD) using Bruker

D8 Advance diffractometer (Cu-Kα radiation) at room temperature in the 2θ range of 20-

80°. Raman study of the samples PFMO was carried out and the spectra were collected in

back scattering geometry using an Ar excitation source having a wavelength of 488nm

coupled with a Labram-HR800 micro Raman spectrometer equipped with a 50X objective,

appropriate notch filter and a Peltier cooled charge-coupled device detector. No melting or

phase transition was observed in the sample at excitation Laser power of 10 mW. Bulk

Samples of PFMO were dissolved in ethanol and irradiated under ultraviolet-Visible radiation to see

the effect of Mn doping on maximum absorption wavelength and thus on optical band gap of systems.

PFMO pellets with diameter of 10 mm and thickness 2 mm were used for dielectric

measurements. The surface layers of pellets were carefully polished and a silver paste was

applied on the opposite faces which acted as electrodes for the dielectric measurements. The

dielectric properties were measured using Agilent 4285A precision LCR meter and lakeshore

temperature controller as a function of frequency of the applied ac field in the range of 20 Hz

to 1 MHz and at temperature ranging from 80 K to 400 K.

3. Results and discussions

3.1 XRD Analysis

The XRD pattern of PrFe1-xMnxO3 (x=0.0, 0.1, 0.3, 0.5) is shown in Fig.1. PrFeO3

crystallizes into GdFeO3 orthorhombic pbnm structure with Pr at wyckoff position (4c) (x y

1/2), Fe/Mn having position 4b (1/2 0 0) and O2 is at 8d (x y z). The XRD results shows no

variation in the crystal structure and symmetry (orthorhombic) up to x=0.5. The compounds

in single phase having orthorhombic structure and space group pbnm up to the doping range

of (Mn) x=0.5. From the inset of Fig.1, it is also evident that the peaks shift towards higher

2θ values with increase in Mn content indicating the development of strain in the crystal

structure possibly due to JT distortion after the incorporation of Mn3+

ions in the parent

compound PrFeO3. The line width and variation in the intensities of different reflections are

evident with increasing Mn content (for example, the peak (020) in Fig.1) which is not in

accordance with the structure and may have arisen due to structural changes occurred at

higher concentration of Mn ions.

The calculated lattice parameters a, b and c; volume and the interplanar spacing„d‟ are

summarized in table I. The lattice constants a, b and c were determined from the refinement

program and are shown as a function of Mn content. The lattice constants a and c decreases

with increase in Mn content while the lattice constant b increases with Mn content. There is a

small decrease in cell volume and the interplanar distances changed slightly because the

angle of peak (θ) did not vary significantly after Mn doping. Fig. 2 shows variation of lattice

constants a, b and c/√2 against Mn concentration. From the given Fig. it is clear that within

the doping range x=0.5 the lattice parameter c/√2 > a. With increasing Mn, the lattice

parameters a and c/√2 decrease but the change in former is less than later. It was observed

that the compound PrFe1-xMnxO3 exhibits O-type (a < c/√2 < b) orthorhombic pbnm

structure. This behavior is in good agreement with all ABO3 perovskite compounds [15-16].

3.2 Raman study

The Raman spectra at room temperature (300 K) of PrFe1-xMnxO3 (x=0.0, 0.1, 0.3,

0.5) is shown in Fig.3. Inset in this figure shows shifting of B1g mode to higher wave number

region with doping. It is now well known that the rare earth Orthoferrite PrFeO3 crystallizes

with a distorted perovskite structure with space group D2h16 (Pbnm). Following irreducible

representations at the brillouin zone center are presented by the group theory [17-18].

7 Ag + 5 B1g + 7 B2g + 5 B3g + 8 Au +10 B1u + 8 B2u + 10 B3u

The modes corresponding to the PFO (orthorhombic structure) are: Ag+ B1g symmetric;

Ag + 2 B1g + B3g bending modes; 2B2g+2B3g antisymmetric stretching modes; 2 Ag + 2 B2g +

B1g + B3g rotation, tilt modes of the octahedra and 3 Ag + B2g+ 3B1g + B2g modes related

locally to R ion movements [19].

For the PFO (orthorhombic) compound, we have, 24 Raman-active modes (7 Ag + 7

B1g+ 5 B2g+ 5 B3g), 25 infrared-active modes (7 B1u + 9 B2u + 9 B3u), 8 inactive modes (8 Au)

and 3 acoustic translational modes (1 B1u + 1 B2u+ 1 B3u). Out of 5 B3g modes, one

corresponds to the rare-earth atom, one to O(1) and three to O(2) while as out of 7 Ag modes,

two involve mainly in the motion of the R atom, two that of O (1), and three correspond to O

(2). The Fe atom participates only in infrared-active modes (being at centre symmetric).

Table II shows the observed modes with corresponding atomic motion (the concerned

assignments are taken from ref.[18] and are also in good agreement with ref. [20].

In perovskites containing trivalent Fe and Mn, the energy of crystal field splitting is smaller

than the Hund‟s energy between two electrons [21-22]. So the Fe and Mn ions are in the high

spin state. The trivalent Fe and Mn ions with high spin state have electronic configurations as

follows:

t2g (dxy, dyz, dxy) eg (d (x2

-y2

), dz2)

Fe3+

↑ ↑ ↑ ↑ ↑

Mn3+

↑ ↑ ↑ ↑

Mn3+

has a 3d4 configuration and exhibits JT distortion [23-24].

Similar studies were carried out by Mir et al for PrFe1-xNixO3. They observed a new

peak arising at 574 cm-1

with Ni doping. The appearance of this peak was suggested to be a

direct indication of structural phase transition (SPT) or symmetry breaking in PrFe1-xNixO3

(x=0 to 0.5) and other related systems. The possible explanation given in this regard was that

Fe in PrFeO3 is JT-inactive while as Ni3+

is a JT-active ion, therefore replacing Fe (JT-

inactive ion) with Ni (JT-active) ion induces distortion in the system resulting in the

symmetry breaking or structural phase transition in the system. It is apparent from our results

that there is not creation of any new peak in Raman spectra of PrFeO3 after Mn doping (upto

50%) which is also JT-active. One of the possible reasons might be that in present study the

size of Fe3+

and Mn3+

ions was almost similar in contrast to different ionic radii of Ni3+

in the

previous study [25]. Results from Raman study also show consistent with the XRD study and

both studies are supported the stability of orthorhombic structure in compound PFMO upto

50% Mn doping.

Another interesting characteristic of Raman scattering is sensitivity to strain in the

sample [26]. When the material is under strain, its Raman wave will deform/shift from the

original status and in that case this mechanical quantity is possible to be directly measured. It

is now an established fact that compressive stress results in the shift of the position of the

Raman peak towards higher wave number region (commonly called “Blue shift”), while

tensile stress results in a shift towards lower wave no. (“Red shift”) [27]. In this study it is

clear from Fig.4 that the modes exhibit a blue shift (hardening behavior) with broadening of

FWHM‟s in the doped samples which may arise due to the strain developed in the sample

after the inclusion of JT-active Mn3+

ions. The observed shift in wave no. with doping clearly

indicates change in Fe-O / Mn-O bond lengths as well as impact on FeO6 / MnO6 octahedra.

The Raman spectra show that there is a disorder in the vibrational bands with

increasing Mn content, which is primarily obvious because most of the Raman modes below

600 cm-1

are suppressed by the substitution of Mn ions (x = 0.1, 0.3 and 0.5) and the only

mode visible throughout the series is the B1g / J-T mode (near 629 cm-1

in pristine sample).

From the discussion, it is evident that the substitution of Mn ions in PrFeO3 apart from

weakening the exchange interaction also induces a J-T distortion which results in a large

electric field gradient at the 57

Fe nucleus. The crystallographic structure of the compound

(PFO) is modified by the substitution of Mn ions, because the ionic radii of Fe3+

and Mn3+

in

PFMO (x = 0.0, 0.1 and 0.5) are very similar [28]. Hence the double exchange interaction

between Mn3+

and Fe3+

occur in PFMO because Fe3+

and Mn3+

have the same electronic

structure. This double exchange interaction is also in consistent with the similar studies

carried out in Sm based Orthoferrites SmFe1-xMnxO3 [29].

3. 3 Dielectric properties

The dielectric constant is in the complex form in an ac field and is given by

ε = ε' - ϳε"

Where ε' is the real part and ε" is imaginary part designating the stored and dissipated

energy respectively. The frequency dependence of real part of dielectric constant of PFMO in

an ac field ranging from 20 Hz to 1 MHz is illustrated in Fig.4. The decrease of dielectric

constant (ε') and dielectric loss tangent (tan δ) [not shown in Fig.4] with frequency is a

general dielectric behavior of ferrites. The constant behavior in dielectric constant at higher

frequencies indicates the inadequacy of electric dipoles to follow the variation in frequencies

due to alternating applied electric field rather the electronic exchange between the ferrous

and ferric ions i, e Fe2+

↔ Fe3+

can not follow the alternating field. From the Fig. it depicts

that there is a steady decrease in ε' at lower frequencies and a steady behavior at higher

frequencies. The steady behavior of ε' at higher frequencies is associated with heterogeneous

conduction in composites while as the higher values of ε' may be assigned to the changes in

valency of cations and space charge polarization resulting from the creation of electric

dipoles within the system [30-31].

The temperature dependence of dielectric constant (ε') and dielectric loss tangent (tan

δ) at different frequencies for PFMO are shown in Fig.5 and Fig.6 respectively. From Fig.5 it

is obvious that the dielectric constant does not vary at low temperature while at higher

temperature it increases for all ranges of frequencies. Such a behavior at higher temperature

is due to generation of extra thermal energy which enhances the mobility of charge carriers

hence increases rate of hopping. At low temperatures, the thermal energy is not sufficient to

contribute to the mobility of charge carriers. This observed mechanism sets up the higher

polarization at higher temperature which increases the dielectric constant. For higher doping

concentrations, both dielectric constant as well as dielectric loss shows a relaxor type of

behavior which can again be attributed to the chemical pressure induced in PFO with the

doping of Mn ions.

Dielectric constant results from four types of polarizations namely, interfacial, dipolar,

ionic, and electronic [32]. The sharp increase in dielectric constant at lower frequency

exhibits strapping reliance on frequency and temperature and is caused due to dipolar and

interfacial polarization. The electronic and ionic polarization is responsible for dielectric

constant developed at higher frequency and is independent of temperature. This indicates that

temperature dependence dielectric constant at higher frequencies is of little significance

resulting in low dispersion of dielectric constant, hence explains the temperature dependence

of dielectric constant at various frequencies. The dielectric loss (tanδ) is a measure of lag in

the polarization with respect to the applied alternating field. It is evident from Fig.6 that for a

particular concentration of dopant, tanδ decreases with the increasing frequency and is

described using Koop‟s model. The inset of Fig. clearly shows a relaxor behavior of pristine

and higher doped samples which is a typical behavior of ferrites, however the surprisingly the

relaxor behavior got suppressed for intermediate doping. The low frequency domain

consequences the higher resistivity (due to grain boundaries), therefore acquisition of higher

energy forwards the mobility of electrons between ions resulting higher energy loss.

Similarly the higher frequency region corresponds to low resistivity (due to grain) and

smaller energy loss takes place.

The compositional variation of dielectric constant (ε') at various frequencies is shown

in Fig. 5 and the values are also given in table III. It is observed that the dielectric constant

increases with Mn concentrations and attains a typically higher value at x=0.5. The possible

explanation is related to the B site in perovskite ferrites which plays a dominant role in the

phenomena of electrical conductivity due to hopping of electrons in cation Fe3+

+ e ↔ Fe2+

at

B sites. After Mn doping in the compound PrFeO3 chemical pressure created in the

compound because of inclusion of JT-ions (Mn3+

), there is possibility for Mn3+

to get

converted in Mn4+

. To maintain the charge neutrality in the system Fe3+

gets converted in to

Fe2+

. It thus follows that the addition of Mn in place of Fe, converts Fe3+

to Fe2+

resulting in

decrease in the resistance of grain thereby increasing the probability of electrons reaching the

grain boundary. This becomes responsible for increase in polarization and hence the

dielectric constant. Similar results were reported in Mn-substituted Ni-Zn ferrites by

Amarendra et al wherein the dielectric constant was shown to be sensitively controlled by Mn

substitution study of and found that dielectric constant [33].

3.4. AC conductivity

To understand the mechanism of conduction and the type of polarons responsible for

conduction ac conductivity (ζac) was calculated using the following relation:

ζac = 2πfεoε'tanδ

Where εo = 8.854 ×.10-12

.F m-1

and f is the frequency (in Hz) of the applied electric field.

Fig.7 and Fig.8 shows the temperature dependent (at selected frequencies) and frequency

dependent ac conductivity plots respectively. A linear behavior is observed for ac

conductivity with temperature for all frequencies, and shows a sharp increase at higher

frequencies, which may be attributed to the increase in the number of charge carriers and

their drifted mobility which are thermally activated. At higher doping concentrations (x=0.5)

ac conductivity increases by orders of magnitude which can again be attributed to hopping of

Mn3+

to Mn4+

and Fe3+

to Fe2+

. The ac conductivity increases with the increase in frequency

and the obtained results are in good agreement with the literature [34-35]. The ac

conductivity alteration identifies that the conduction mechanism is following the charge

hopping between localized states. The observed results follow small polaron conduction and

is in consistent with the literature [36-37]. The hopping frequency of charge carriers seems to

be the function of the frequency of the applied field results in increase in mobility of charge

carriers, since the conductivity is not increased by charge carriers instead of mobility of these

carriers, therefore at certain higher frequency the hopping of charge carriers ceases to follow

the applied field frequency and deteriorates the conductivity.

The compositional variation of dielectric constant (ε') at (at various frequencies), ac

conductivity (σac), activation energy (Eσ) and optical band gap (Eg) are tabulated in table III.

It is clear from the table the value of dielectric constant increases with Mn doping and

reaches a very high value for higher doping (50%). This increase in dielectric constant with

Mn doping in the compound PrFeO3 was attributed to the fact that substituting Mn in place of

Fe, converts Fe3+

to Fe2+

while as Mn gets converted from Mn3+

to Mn4+

. This results

decrease in the resistance of grains thereby increasing the probability of electrons reaching

the grain boundaries, which becomes responsible for increase in polarization and hence the

dielectric constant. It is also observed from the table there is a steady decrease in ε' at lower

frequencies and a steady behavior at higher frequencies. The steady behavior of ε' at higher

frequencies is associated with heterogeneous conduction in composites while as the higher

values of ε' may be assigned to the changes in valency of cations and space charge

polarization resulting from the creation of electric dipoles within the system. From the

temperature dependent dielectric study it was observed that the Dielectric constant behaves

independently at low temperature while at higher temperature it increases with increasing

temperature for all frequencies, this behavior at higher temperature is due to generation of

extra thermal energy which enhances the mobility of charge carriers hence increases rate of

hopping, while as the thermal energy at low temperature does not contribute to mobility of

charge carriers. This observed mechanism setup the higher polarization at higher temperature

which increases the dielectric constant. Dielectric loss decreases with the increasing

frequency and is described using Koop‟s model. From the temperature dependent ac

conductivity study a linear behavior was observed for ac conductivity with temperature for all

frequencies, and showed a sharp increase at higher frequencies, which may be attributed to

the increase in the number of charge carriers and their drifted mobility which are thermally

activated. The ac conductivity increases with the increase in frequency and also increases

with increase in Mn concentration in the sample PrFeO3 which is also evident from table III.

The ac conductivity alteration identifies that the conduction mechanism is following the

charge hopping between localized states and the observed results follow small polaron

conduction. Activation energy (Eσ) was calculated from the slope of the curve log ζac vs

1000/T (K-1

) using relation ζ = ζ0 e-Eζ/kT

, where ζ0 is the conductivity at infinite temperature

and k is the Boltzmann‟s constant. The values of Eσ for different doping concentrations are

given in table III. It is seen that the value of activation energy decreases with increase in Mn

doping in the compound PrFeO3. The calculated value of Eσ for the pristine compound

PrFeO3 was slightly smaller than calculated by Bandi et al [38] possibly due to different

preparation method of the samples. The optical band gap Eg was calculated from the curve

between (α . hv)1/2

and E (eV) where α is the absorption coefficient and E is energy in

electron volts (figure not shown). The compositional values of Eg are shown in table III. And

it is clear that the optical band gap decreases with increase in Mn doping resulting in increase

in conductivity with Mn doping. Hence the optical results are in consistent with other

dielectric results.

4. Conclusion

Polycrystalline bulk compounds of Mn doped PrFeO3 were synthesized by solid state

reaction technique. The substitution of Mn for Fe ions results significant changes in the

physical properties of compound. The inclusion of Mn clearly brings a distortion in the

sample which is clearly reflected in XRD and Raman study. The results of dielectric study

clearly show there is improvement in electrical properties especially at higher doping and the

dielectric constant can be sensitively controlled by Mn substitution. The higher dielectric

constant and higher ac conductivity led the material suitable for power application as these

may enable device miniaturization. Optical band gap of the compound was also seen to

decrease with Mn doping resulting in increase in conductivity in the compound. The ac

conductivity alteration identifies that the conduction mechanism is following the charge

hopping between localized states and follow the small polaron conduction. The present

investigation clearly indicates that the physical properties Mn doped PrFeO3 depend on the

amount of doping and consequently on the charge state occupied by Fe and Mn ions.

Acknowledgements

We thank Dr. A. Singh, Department of Physics, Guru Nanak Dev University,

Amritsar for the necessary scientific discussions and IUAC-New Delhi for providing the

necessary experimental facilities and funding.

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Table and Figure captions:

Table-I. The lattice parameters, interplanar spacing and the unit-cell volume for different

compositions of PrFe1- xMnxO3 (x = 0.0, 0.1, 0.3, 0.5)

Table-II. The observed Raman modes with corresponding atomic motion for PrFeO3.

Table-III. The dielectric constant ε' (at various frequencies), ac Conductivity σac, activation

energy Eσ and optical band gap Eg for different compositions of PrFe1- xMnxO3 (x = 0.0, 0.1,

0.3, 0.5)

Fig.1. XRD pattern of PrFe1- xMnxO3 samples for (a) x = 0.0, (b) x = 0.1, (c) x = 0.3, (d) x =

0.5 with the inset showing shifting of (112) peak.

Fig.2. Variation of lattice constants a, b and c/√2 against Mn concentration for the

compound PrFe1- xMnxO3 (x = 0.0, 0.1, 0.3, 0.5).

Fig.3. Raman spectra of PrFe1- xMnxO3 samples for (a) x = 0.0, (b) x = 0.1, (c) x = 0.3, (d) x =

0.5. Inset shows shifting of B1g mode to higher wave no. region with increase in doping)

Fig.4. The variation of dielectric constant with frequency of PrFe1- xMnxO3 samples for (a)

x = 0.0, (b) x = 0.1, (c) x = 0.3, (d) x = 0.5 at room temperature.

Fig.5. Variation of dielectric constant with temperature at selected frequencies of PrFe1-

xMnxO3 samples for (a) x = 0.0, (b) x = 0.1, (c) x = 0.3, (d) x = 0.5

Fig.6. Variation of dielectric loss with temperature at selected frequencies of PrFe1-

xMnxO3 samples for (a) x = 0.0, (b) x = 0.1, (c) x = 0.3, (d) x = 0.5with the inset showing

typical relaxor behavior.

Fig.7. Variation of ac conductivity with temperature at selected frequencies of PrFe1-

xMnxO3 samples for (a) x = 0.0, (b) x = 0.1, (c) x = 0.3, (d) x = 0.5

Fig.8. The variation of ac conductivity with frequency of PrFe1- xMnxO3 samples for (a) x

= 0.0, (b) x = 0.1, (c) x = 0.3, (d) x = 0.5 at room temperature.

TABLE-I.

Sample a(Å) b (Å) C (Å) Volume (Å) d (Å)

x = 0 5.486 5.581 7.857 240.56 2.756

x = 0.1 5.482 5.587 7.838 240.06 2.756

x = 0.3 5.476 5.599 7.801 239.18 2.752

x = 0.5 5.465 5.613 7.765 238.19 2.747

TABLE -II.

Symmetry NdFeO3 [26] Observed mode in present Main atomic position

case PrFeO3 (cm-1

)

___________________________________________________________________________

B1g(1) 643 629 Fe-O,stretching, breathing

B1g(2) 464 457 O-Fe-O, rotation, bending

B1g(3) 432 432 FeO6, stretching, rotation

B1g(4) 345 333 FeO6, stretching, bending

B1g(5) 295 288 FeO6, bending, breathing

TABLE -III.

Composition ε' ε' ε' ζac (ohm-1

cm-1)

E ζ (eV) Eg(eV)

(20 Hz) (0.2 MHz) (1 MHz) (300K, 20 Hz)

X=0.0 103

354 332 3.5 x 10-7

0.20 3.39

X=0.1 6.68 x 103

411 401 6.57 x 10-5

0.17 2.91

X=0.3 6.22 x 104

454 398 1.14 x 10-2

0.13 2.76

X=0.5 9.32 x 106

7650 4251 2.92 x 10-1

0.067 2.53

Fig.1.

Fig. 2 :

Fig. 3 :

Fig. 4 :

Fig.5:

Fig.6 :

Fig. 7 :

Fig. 8 :