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/ adjective1. not bound by or in accordance

with convention

2. being out of the ordinary

3. existing without precedent

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

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

Idealized Subcell for La3Cu2VO9

[La]

[(Cu/V)O2+3/3]

[La]

[A]

[A]

[BO2+3/3]

La3Cu2VO9 Superstructure

P63/ma = 14.448(1) Åc = 10.686(1) Å

CuII

VV

O2-

87% Cu

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%

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)

Idealized Subcell of La4Cu3MoO12

[La]

[(Cu/Mo)O2+3/3]

[La]

[A]

[A]

[BO2+3/3]

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.

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

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

Ln4Cu3MoO12 Powder X-ray Diffraction

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)

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*

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.

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

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?

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

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

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.

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

La4Cu3+xMo1-xO12

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.

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)

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

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.

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.

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