The Intnl Conf 20ｔｈ Anneversary、ETH,Sept.4-6,2008

Valence Stability and Madelung Valence Stability and Madelung Self-Site Potential of Self Site Potential of

Alliovalent Ions in Various Oxide Lattices

Masahiro YOSHIMURA(Tokyo Institute of Technology, Japan)

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Thi f dThis was referedBy R.Roy in his Orton lecture at Am Ceram SocAm.Ceram.Soc. 1976,Bull.Am.

Ceram.Soc.(1976)

CeO2+(1/2)V2O5 CeVO4+(1/4)O2Ce3+[V5+O4]

Cerium was reduced in air.

This compd does not decompose

Zircon structure

TG-DTA curves for the reaction

This compd does not decompose (oxidize) even under Po2>103 atm.

In air (Po2=0.21 atm)(Yoshimura ’69)

Ce O

The relationship between the oxygen partial pressure and the composition of Cerium oxide. (a) 1000, 1100, and 1200°C; 8b) 1153, 1200, 1249, 1310,

Ce2O3

and 1130°C Kitayama, et al. (’85)J. Solid State Chem.

e (°

C)

mpe

ratu

re

°C

VO2Te

m 700°C

10-5

VO V2O3 VO2 V2P5

VO – V2O5 phase diagram

Recent Papers on Valence Stability of Rare Earth Ions

1) “Understanding of the Valency of Rare Earths from First-principle Theory,” P. Strange, A. Svane, W. M. Temmermann, Z. Szotek, and H Winter, Nature 399 (24 June 1999) 756-758

2) “Valence Stability of Lanthanide Ions in Inorganic2) Valence Stability of Lanthanide Ions in Inorganic Compounds,” P. Dorenbos, Chem. Mater. 17 (2005) 6452-6456

3) “The Eu3+ Charge Transfer Energy and the Relation with the Band Gap of Compounds,” P. Dorenbos, J. Lumin, 111 (2005) 89-104111 (2005) 89 104

4) “Stability of Rare Earth Oxychloride Phases: Bond Valence Study,” J. Hölsä, M. Lahtinen, M. Lastusaari, J. V lk d J Vij J S lid St t Ch 165 (2002)Valkonen, and J. Vijanen, J. Solid State Chem., 165 (2002) 48-55

5) “Critical Materials Problems in Fuel Cells: SOFC’S,” H. 5) C t ca ate a s ob e s ue Ce s SO C S,Yokokawa, Oxford, April 02, 2007

Figure 4. EFf for Eu2+ in oxide, chloride, and sulfide compounds. The solid triangle symbols pertain to Eu on Ba2+, Sr2+, Ca2+, or Mg2+ sites and in addition to Eu in RbCl and KCl The other data are the same data as in Figure 3 and pertain to Eu in trivalent rareKCl. The other data are the same data as in Figure 3 and pertain to Eu in trivalent rare earth oxide compounds. The box around date with EVC > 8 eV and EFf < 0.7 eV contains alkaline carth compounds in which Eu2+ can be obtained even under oxidizing conditions. P. Dorenbos, Chem. Mater. (2005) 17, 6452

H. Yokokawa (AIST, Japan), Apr. 2007

Enthalpy Diagram for the reduction of rare earth (A) Manganates; T. Nakamura (1985)a py ag a o e educ o o a e ea ( ) a ga a es; a a u a ( 985)AMnO3(s) = ½ A2O3(s) + MnO(s) + ¼ O2(g)

Energy Diagram for the Reaction: MO (s) + O2(g) → MO2(s) 【 ∆G°r 】32

14

U L tti D Di i ti A El t ffi itU: Lattice energy, D: Dissociation energy, A: Electron affinityHf°: Standard formation enthalpy, I4: 4th Ionization energy

MO + 1/2O = MO ··· ΔGMO3/2 + 1/2O2 = MO2 ··· ΔG

T=TT=0

MO3/2

ΔG ΔGº (=ΔHº)

MOMO2

sublattice

Madelung Lattice Site Potentials in Europium Containing Oxide

Lattice site potential

Madelung Lattice Site Potentials in Europium Containing Oxide

Compound structureLattice site potential

φEu φM φO

EuO NaCl -1.359 1.359

Eu2+ EuTiO3 Perovskite -1.380 -3.171 1.653

Eu3O4 Eu3O4 -1.377 -2.076/-2.088 1.423～1.4573 4 3 4Eu2O3 B-type -2.081～-2.107 1.432～1.507

EuFeO3 Perovskite -2.051 -2.500 1.576/1.602

Eu3+

3

EuMnO3 Perovskite -2.055 -2.495 1.574/1.633

EuScO Perovskite -2 038 -2 382 1 543/1 557EuScO3 Perovskite -2.038 -2.382 1.543/1.557

Eu2Ti2O7 Pyrochlore -2.167 -3.100 1.523/1.640

EuPO Zircon 2 116 4 160 1 882～1 970EuPO4 Zircon -2.116 -4.160 1.882～1.970

Madelung Lattice Site Potentials in Cerium Containing Oxide

Compound structureLattice site potential

φCe φM φO

Ce2O3 A-type -2.036 1.400/1.405

CeAlO3 Perovskite -1.965 -2.738 1.578/1.582

Ce3+

CeCrO3 Perovskite -1.908 -2.659 1.535

CeGaO3 Perovskite -1.915 -2.669 1.540/1.547Ce

CeVO4 Zircon -2.103 -3.697 1.803

CeTaO4 d-Sheelite -2.136 -3.595 1.52～1.79

LiCeO2 NaFeO2 -1.962 -1.080 1.438/1.474

CeTa3O9 Layered Perovskite -2.126 -3.646/-3.660 1.679～1.808

Ce4+

CeO2 Fluorite -2.797 1.504

BaCeO3 Perovskite -2.816 -1.226 1.468

SrCeO3 Perovskite -2.893 -1.256 1.503

｜ΦB｜ ｜ΦB｜

｜ΦO｜ ｜ΦA｜

V V kit

｜ΦA｜ ｜ΦO｜

VA Vo no perovskite

-ΦB

Site self-potential and Madelung constant

Φ

For ideal Perovskite lattice, a = 3.881 Å

ΦO

1.20.03

Φ Mqipiφi

-ΦA Ma=-a2k

U=332(Ma/a)

U=Ne2qp2k

1/2La2O3+1/2Al2O3 LaAlO3ΔU=-35Kcal/mol

Loss

GainSite self potential change for the formation of LaMO3 from La2O3+M2O33 2 3 2 3

Φ for Co2O3 and Ni2O3 in High-Spin & Low-Spin states are estimeated from pionic radii.

Co3+, Ni3+ etc. stabilized by strong ΦMCo , Ni etc. stabilized by strong ΦM

B-ion has a 6-coordination in LaMO3 aswell as in M2O3 (MO2, MO, ……..)

-1.2 1.2

-1.6

-1.4 OSrO , Sr SrO

OO SrMO3

Sr SrMO3

1.6

1.4

2 0

-1.8

OMO2

2 0

1.8

-2.2

-2.0

& φ

M/Å

2.2

2.0

φO

/ Å

SrO+MO2=SrMO3

-2.6

-2.4

φSr

&

2.6

2.4

ÅChange of Lattice Site P t ti l f E Sit

-3 0

-2.8

MMO23 0

2.8

Potentials of Every Site in the ReactonSrO + MO2 = SrMO3

3.9 4.0 4.1 4.2 4.3

-3.2

3.0

M SrMO33.2

3.0

CoFe

Ti Mo Sn PbTb Ce3.9 4.0 4.1 4.2 4.3

a0

of SrMO3

/Å

Fe

Lattice energy change in the formation of EuTiO3

a) EuO + TiO2 = Eu2+Ti4+O3 + Q(-902) + (-3256) = (-4210) + (-52)( ) ( ) ( ) ( )

(-4158)

b) (1/2)Eu2O3+(1/2)Ti2O3=Eu3+Ti3+O3+Q(1/2)( 3570) + (1/2)( 4031) ( 3806) + ( 6)(1/2)(-3570) + (1/2)(-4031) = (-3806) + (-6)

(-3800)

Perovskitee o s teCe3+Fe3+O3Is not compativle withCe2O3 nor Fe2O3!!Ce2O3 nor Fe2O3!!

FeO Fe3O4 Fe2O3

(’85)

Summary(1) Valence stability is different in ternary systems from binary

systems.X P T di i ROX-PO2 – T diagram in ROxX-y-PO2 – T diagram in RMyOx

(2) Valence stability is directly related to electrostatic lattice-site (2) Valence stability is directly related to electrostatic lattice site potential (φ),

pqpqNeU 98.3312 φφ Σ⇒Σ=

(3) for example:φ ≈ 1 36 1 38 for Eu2+ φ ≈ 2 04 2 17 for Eu3+

kkNeU

298.331

2Σ⇒Σ

[kcal/mol] for φ [Å]

φ ≈ 1.36-1.38 for Eu2 , φ ≈ 2.04-2.17 for Eu3

φ ≈ 1.8-2.1 for Ce3+, φ ≈ 2.8-2.9 for Ce4+

(4) In perovskite (ABO3) lattice, High valency state in B-site & ( ) p ( 3) , g ydifficult defect formation in B-site due to strong φB potential.

(5) CeO2 may be reduced during the reaction with MOx when M is high valent small ion and MO -rich parthigh valent, small ion and MOx-rich part.

Oxysalt : Ce3+[MOy]x

Thanking Thanking

Prof. Sata Prof. Somiya

Colleagues