Alliovalent Ions in Various Oxide Lattices

Size: px

Start display at page:

Download "Alliovalent Ions in Various Oxide Lattices"

Alexandrina Nicholson
5 years ago
Views:

1 The Intnl Conf 20th Anneversary ETH,Sept.4-6,2008 Valence Stability and Madelung Self-Site Site Potential of Alliovalent Ions in Various Oxide Lattices Masahiro YOSHIMURA (Tokyo Institute of Technology, Japan)

2 The latest 20 years are displayed Results found: 490 Sum of the Times Cited [?] : 8,009 Average Citations i per Item [?] : h-index [?] : 44

3 This was refered By R.Roy in his Orton lecture at Am.Ceram.Soc. 1976,Bull.Am. Ceram.Soc.(1976)

4 CeO 2 +(1/2)V 2 O 5 CeVO 4 +(1/4)O 2 Ce 3+ [V 5+ O 4 ] Cerium was reduced in air. TG-DTA curves for the reaction In air (Po 2 =0.21 atm) (Yoshimura 69) Zircon structure This compd does not decompose (oxidize) even under Po 2 >10 3 atm.

5 Ce 2 O 3 The relationship between the oxygen partial pressure and the composition of Cerium oxide. (a) 1000, 1100, and 1200 C; 8b) 1153, 1200, 1249, 1310, and 1130 C Kitayama, et al. ( 85) J. Solid State Chem.

6 Tem mperature e ( C) VO C 10-5 VO V 2 O 3 VO 2 V 2 P 5 VO V 2 O 5 phase diagram

8 Recent Papers on Valence Stability of Rare Earth Ions 1) Understanding of the Valency of Rare Earths from Firstprinciple Theory, P. Strange, A. Svane, W. M. Temmermann, Z. Szotek, and H Winter, Nature 399 (24 June 1999) ) Valence Stability of Lanthanide Ions in Inorganic Compounds, P. Dorenbos, Chem. Mater. 17 (2005) ) The Eu3+ Charge Transfer Energy and the Relation with the Band Gap of Compounds, P. Dorenbos, J. Lumin, 111 (2005) ) Stability of Rare Earth Oxychloride Phases: Bond Valence Study, J. Hölsä, M. Lahtinen, M. Lastusaari, J. Valkonen, and J. Vijanen, J. Solid State t Chem., 165 (2002) ) Critical Materials a Problems in Fuel Cells: SOFC S, S, H. Yokokawa, Oxford, April 02, 2007

9 Figure 4. E Ff for Eu 2+ in oxide, chloride, and sulfide compounds. The solid triangle symbols pertain to Eu on Ba 2+, Sr 2+, Ca 2+, or Mg 2+ 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 rare earth oxide compounds. The box around date with E VC > 8 ev and E Ff < 0.7 ev contains alkaline carth compounds in which Eu 2+ can be obtained even under oxidizing conditions. P. Dorenbos, Chem. Mater. (2005) 17, 6452

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

11 Enthalpy Diagram a for the reduction of rare earth (A) Manganates; a T. Nakamura a a (1985) AMnO 3 (s) = ½ A 2 O 3 (s) + MnO(s) + ¼ O 2 (g)

12 Energy Diagram for the Reaction: MO 3 (s) + O 2 (g) MO 2 (s) G r U: Lattice energy, D: Dissociation i energy, A: Electron affinity it H f : Standard formation enthalpy, I 4 : 4th Ionization energy 2 1 4

13 MO 3/2 + 1/2O 2 = MO 2 ΔG T=0 T=T MO 3/2 ΔG ΔGº(=ΔHº) MO 2

14 sublattice

15 Madelung Lattice Site Potentials in Europium Containing Oxide Compound structure Lattice site potential φ Eu φ M φ O EuO NaCl Eu 2+ EuTiO 3 Perovskite Eu 3 O 4 Eu 3 O / ~ Eu 2 O 3 B-type ~ ~1.507 EuFeO 3 Perovskite / Eu 3+ EuMnO 3 Perovskite /1.633 EuScO 3 Perovskite / Eu 2 Ti 2 O 7 Pyrochlore /1.640 EuPO 4 Zircon ~1.970

16 Madelung Lattice Site Potentials in Cerium Containing Oxide Ce 3+ Compound structure Lattice site potential φ Ce φ M φ O Ce 2 O 3 A-type /1.405 CeAlO 3 Perovskite /1.582 CeCrO 3 Perovskite CeGaO 3 Perovskite /1.547 CeVO 4 Zircon CeTaO 4 d-sheelite ~1.79 LiCeO 2 NaFeO /1.474 CeTa 3 O 9 Layered Perovskite / ~1.808 Ce 4+ CeO 2 Fluorite BaCeO 3 Perovskite SrCeO 3 Perovskite

17 ΦB ΦB ΦO ΦA ΦA ΦO VA Vo no perovskite -ΦB Site self-potential and Madelung constant For ideal Perovskite lattice, a = Å Φ ΦO ΦA 1.2 Ma=-a qipiφi 2k U=332(Ma/a)

18 U=Ne 2 qp 2k

19 1/2La 2 O 3 +1/2Al 2 O 3 LaAlO 3 ΔU=-35Kcal/mol Loss Site self potential change for the Gain formation of LaMO 3 from La 2 O 3 +M 2 O 3 Φ for Co 2 O 3 and Ni 2 O 3 in High-Spin & Low-Spin states are estimeated from ionic radii. Co 3+,Ni 3+ etc. stabilized by strong Φ M B-ion has a 6-coordination in LaMO 3 as well as in M 2 O 3 (MO 2, MO,..)

20 O SrO, Sr SrO Sr SrMO O SrMO3 O MO φ Sr & φ M /A SrO+MO 2 =SrMO M MO φ O / A Change of Lattice Site Potentials ti of Every Site in the Reacton SrO + MO 2 = SrMO Co Fe M SrMO3 3.2 Ti Mo Sn PbTb Ce a 0 of SrMO 3 /A

21 Lattice energy change in the formation of EuTiO 3 a) EuO + TiO 2 = Eu 2+ Ti 4+ O 3 + Q (-902) + (-3256) = (-4210) + (-52) (-4158) b) (1/2)Eu 2 O 3 +(1/2)Ti 2 O 3 =Eu 3+ Ti 3+ O 3 +Q (1/2)( 3570) + (1/2)( 4031) ( 3806) + ( 6) (1/2)(-3570) + (1/2)(-4031) = (-3806) + (-6) (-3800)

22 Perovskite eo Ce 3+ Fe 3+ O 3 Is not compativle with Ce 2 O 3 nor Fe 2 O 3!! FeO Fe 3 O 4 Fe 2 O 3 ( 85)

23 Summary (1) Valence stability is different in ternary systems from binary systems. X-P O2 T diagram in RO x X-y-P O2 T diagram in RM y O x (2) Valence stability is directly related to electrostatic lattice-site potential (φ), (3) for example: pqφ pq U = Ne 2 Σ Σ φ 2k 2k φ for Eu 2+, φ for Eu 3+ φ for Ce 3+, φ for Ce 4+ [kcal/mol] for φ [Å] (4) In perovskite (ABO 3 3) lattice, High valency state in B-site & difficult defect formation in B-site due to strong φ B potential. (5) CeO 2 may be reduced during the reaction with MO x when M is high valent, small ion and MO x -rich part. Oxysalt : Ce 3+ [MO y ] x

24 Thanking Prof. Sata Prof. Somiya Colleagues

8. Relax and do well.

8. Relax and do well. CHEM 1515.001 Name Exam II John II. Gelder TA's Name March 8, 2001 Lab Section INSTRUCTIONS: 1. This examination consists of a total of 8 different pages. The last three pages include a periodic table,