unconventionality in solid state chemistry
DESCRIPTION
Unconventionality in Solid State Chemistry. Douglas A. Vander Griend Department of Chemistry & Biochemistry Calvin College Grand Rapids, Michigan July 7, 2004. Unconventional. ŭn΄kën-věn΄shë-nël/ adjective not bound by or in accordance with convention being out of the ordinary - PowerPoint PPT PresentationTRANSCRIPT
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Unconventionality in Solid State Chemistry
Douglas A. Vander Griend
Department of Chemistry & Biochemistry
Calvin College
Grand Rapids, Michigan
July 7, 2004
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Unconventional
• ŭn΄kën-věn΄shë-nël/ adjective1. not bound by or in accordance
with convention
2. being out of the ordinary
3. existing without precedent
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Conventional Solid State Structures
( ) rA -O A
()r
-OB
L u M n O 3
Y M n O 3 P e ro v sk ite
A - M O2 3
B - M O2 3
C - M O B ix b y ite2 3
Ilm e n ite
A B O S tru c tu ra l P h ase D ia g ram3
D .M . G ia q u in ta , H .-C . zu r L o y e ; C h em . M ate r. 1 9 9 4
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Conventional Compositions
( ) rA -O A
()r
-OB
L u M n O 3
Y M n O 3P e ro v sk ite
A - M O2 3
B - M O2 3
C - M O B ix b y ite2 3
Ilm e n ite
A B O S tru c tu ra l P h ase D ia g ram3
D .M . G ia q u in ta , H .-C . zu r L o y e ; C h em . M ate r. 1 9 9 4
L a L u O 3
L a S c O 3
YA lO 3
E u A lO 3
L u O2 3
L a O2 3
S m O2 3
G d O2 3
Y b O2 3
F eT iO 3
C d S n O 3
A l O2 3
L a F e O 3
N d O2 3
S m In O 3
G d In O 3
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Idealized Subcell for La3Cu2VO9
[La]
[(Cu/V)O2+3/3]
[La]
[A]
[A]
[BO2+3/3]
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La3Cu2VO9 Superstructure
P63/ma = 14.448(1) Åc = 10.686(1) Å
CuII
VV
O2-
87% Cu
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La3Cu2VO9: Frustrated Antiferromagnetism
Inv e
rse
Mo l
a r S
usc e
p ti b
i li t
y (p
e r c
o pp e
r )
Temperature (K)
0 100 200 300 400
0.56 B
1.14 B
1.68 B
54% Paramagnetic
100% Paramagnetic
16%
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LaxLn3-xCu2VO9 Lattice Parameters
10.6
10.65
10.7
10.75
10.8
10.85
10.9
10.95
0 0.5 1 1.5 2 2.5 3
x in La Ln Cu VOx 3-x 2 9
Pr
Nd
Eu
Gd
c-ax
is (
Å)
a-ax
is (
Å)
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Idealized Subcell of La4Cu3MoO12
[La]
[(Cu/Mo)O2+3/3]
[La]
[A]
[A]
[BO2+3/3]
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Electron Diffraction
• La4Cu3MoO12 Ordering of the B-cations leads to a monoclinic supercell ( = 90.03(1)º) which is 4 times larger than the conventional hexagonal subcell.
• La3Cu2VO9*
Ordering of the B-cations leads to a hexagonal supercell which is 13 times larger than the conventional hexagonal subcell.
*K. Jansson, I. Bryntse, Y. Teraoka Mater. Res. Bull., 1996, 31, 827.
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La4Cu3MoO12: B-cation Ordering
b
P 6 /m m c3 P 11 2 /m1
C u I I
M o V I
P 11 2 /m ; = 7 .9 1 3 (1 ) Å , = 6 .8 5 0 (1 ) Å , = 11 .0 11 (1 ) Å , = 9 0 .0 3 (1 )º1 a b c
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La4Cu3MoO12: Frustrated Antiferromagnetism
8 0 07 0 06 0 05 0 04 0 03 0 02 0 01 0 00Temperature (K)
Inve
rse
Mol
ar S
usce
ptib
ilit
y (p
er c
oppe
r)
100% Paramagnetic
35% Paramagnetic
1.02 B
1.73 B
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Ln4Cu3MoO12 Powder X-ray Diffraction
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Ln4Cu3MoO12 Lattice Parameters
6
7
8
9
10
11
12
La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
Lanthanide
Mo
no
clin
ic (
P21
/m)
Un
it C
ell P
aram
eter
b (Å)
a (Å)
c (Å)
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Rare-earth Hexagonal Structure Type Versatility
*Prog. Solid St. Chem. 1993, 22, 197.
"Many new and novel compositions and structures remain to be discovered by more traditional means."
-J.D. Corbett
Ln4Cu3MoO12 Ln = La, Pr, Nd, Sm - Tm
Ln3Cu2VO9
Ln = La, Pr, Nd, Sm - Gd
Ln2CuTiO6
Ln = Tb – Lu*
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Formation of Single Phases
• The primary goal of state synthesis is to form single phases
• Single phases form if and only if their G is less than all possible multiphase mixtures at the reaction temperature.
• The following examples demonstrate the importance of stoichiometric analysis in the search for novel materials.
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An Expected Result8000
6000
4000
2000
80706050403020
La4Cu3MoO12
1200
1000
800
600
400
200
80706050403020
La2Gd2Cu3MoO12
1200
1000
800
600
400
200
8070605040302010Two Theta
Gd4Cu3MoO12
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An Unexpected Result
8000
6000
4000
2000
80706050403020
La4Cu3MoO12
5000
4000
3000
2000
1000
80706050403020
Ho4Cu3MoO12
3000
2500
2000
1500
1000
500
80706050403020
La2Ho2Cu3MoO12? or
La4Cu3MoO12 + Ho4Cu3MoO12?
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Thermodynamic Hierarchy
G(La2MoO6 + Ho2Cu2O5) < G(Ho2MoO6 + La2Cu2O5)
Ln2Cu2O5 is more stable for smaller lanthanides,and/or
Ln2MoO6 is more stable for larger lanthanides.
G
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Ln'2Ln"2Cu3MoO12 Synthesis Results
5 7 5 95 8 6 0 6 1 6 2 6 3 6 4 6 5 6 6 7 0 7 16 7 6 8
L a P rC e N d P m S m E u G d T b D y Y b L uH o E r T m6 9
5 7
5 9
5 8
60
P m6 1
S m6 2
6 3
6 4
6 5
6 6
7 0
71
67
L a
P r
C e
N d
E u
G d
T b
D y
Y b
L u
H o
E r6 8
T m6 9
L n ' L n " C u M o O2 2 3 1 2
L n ' M o O + C u O + L n " C u O2 6 2 2 5
C o m p le x in ter m e d ia te m ix tu re**
* * *
* *
* * *
*
*
* *
*
* *
* * * *
* * * *
*
*
********
*
* A n tic ip a te d resu lts
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Why does La4Cu3MoO12 Form?
• Structure is unconventional.– A-cation coordination is low (6-7).– B-cation coordination is atypical (trigonal bipyramidal).
• But La2+2nCu4+nO7+4n (n = 2) is worse!– “It is remarkable that, given the simple ratio of the
constituent elements, such complex structures form instead of the structurally simpler Ruddleson-Popper series.” - Cava et al. 1991.
• Ln2Cu2O5 is not even known for Ce – Gd.• 75% copper is sufficient to promote single phase.• La4Cu3MoO12 forms so that La2Cu2O5 doesn’t.
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The La2Cu2O5 Umbrella Stoichiometry
E n e rg y S u rfac e
L a C u O2 2 5
L a M o O + C u O2 6
T h e rm o d y n am ic S in k
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La4Cu3+xMo1-xO12
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Why does Ho4Cu3MoO12 Form?
• Ho2Cu2O5 isn’t the problem anymore.
• Ho2MoO6 + CuO is the problem!
• Ln2MoO6 changes structure between Nd and Sm.
• 25% molybdenum is sufficient to promote single phase.
• Ho4Cu3MoO12 forms so that Ho2MoO6 doesn’t.
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Ln2MoO6 Structural Shift
Position [°2Theta]
20 30 40 50 60
Peak List
Nd2 Mo O6
Sm2 Mo O6
Nd2MoO6 (I-42m)a = 4.0010 Å c = 15.7950 Å
Sm2MoO6 (I2/a)a = 15.76 Å b = 11.26 Åc = 5.467 Å
2 (copper K)
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Ln4(Cu/Mo)4O12 Thermodynamic Stability
La138.905557Lanthanum
Pr140.907759Praseodymium
Ce140.1258Cerium
Nd144.2460Neodymium
Pm(145)61Promethium
Sm150.3662Samarium
Eu151.96563Europium
Gd157.2564Gadolinium
Tb158.925365Terbium
Dy162.5066Dysprosium
Yb173.0470Ytterbium
Lu174.96771Lutetium
Ho164.930367Holmium
Er167.2668Erbium
Tm168.934269Thulium
2Ln Cu O2 2 5
"2Ln MoO+ 2CuO"
2 6
G
copper-rich
molybdenum-rich
"Ln MoO+ CuO
+ Ln Cu O "
2 6
2 2 5
multiphase Ln Cu MoO4 3 12
single phase
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More Examples
• La2CuSnO6 vs. La2Cu2O5 + La2Sn2O7– La2Sn2O7, stable pyrochlore, infamous thermodynamic sink– La2CuSnO6, lone example of a layered double perovskite that
forms at ambient pressure.
• La2Ba2Cu2Ti2O11 vs. La2Cu2O5 + 2BaTiO3– La2Ba2Cu2Ti2O11, layered quadruple perovskite– BaTiO3, well known for centuries.
• All known phases exist because at least one of the phases in every multiphase alternative has a sufficiently high G.
• Identifying and applying these Umbrella Stoichiometries is the key to a more rational search for novel matierals.
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Conclusions – searching for unconventionality
• Umbrella stoichiometries promote single phase results by destabilizing multiphase alternatives.
• Umbrella stoichiometries facilitate substitutions that shift compositions towards them.
Example: La4Cu3+xMo1-xO12-2x 0 x 0.12
• Undiscovered phases likely exist near umbrella stoichiometries.
• Phases discovered near umbrella stoichiometries will tend to be unconventional because they can be structurally discontent and still be the thermodynamic product of a solid state reaction.
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AcknowledgementsChemistry Department
Kenneth R. Poeppelmeier
Dr. Kenji Otzschi
Dr. Donggeun Ko
Dr. Sophie Boudin
Dr. Vincent Caignaert
Dr. Sylvie Malo
Dr. Antoine Maignan
Tony Wang
Noura Dabbouseh
Scott Barry
Materials Science Department
Prof. Thomas Mason
Dr. Yanguo Wang
Prof. Vinayak Dravid
Kyoto University
Prof. Mikio Takano
Dr. Masaki Azuma
Hiroki Toganoh
Argonne National Laboratory
Dr. Simine Short
Dr. Zhongbo Hu
Dr. James Jorgensen
Funding
Science and Technology Center for Superconductivity
Japan Society for the Promotion of Science
National Science Foundation Graduate Fellowship