Dependence of the structure and electronic state of SrFeO/sub x/ (2. 5 less than or equal to x less than or equal to 3) on composition and temperature

Journal Article · Tue Mar 01 00:00:00 EST 1988 · J. Solid State Chem.; (United States)

DOI:https://doi.org/10.1016/0022-4596(88)90063-1· OSTI ID:7203244

Takano, N; Okita, T; Nakayama, N; Bando, Y; Takeda, Y; Yamamoto, O; Goodenough, J B

The system SrFeO/sub x/, 2.5 less than or equal to x less than or equal to 3, forms a continuous solid solution at temperatures T greater than or equal to T/sub t/(x), but a series of discrete ordered-vacancy phases SrFeO/sub 3-(1/n)/ (n = infinity, 8, 4, 2) below temperatures T/sub t/(n =8) = 523 K, T/sub t/(n = 4) = 598 K, and T/sub t/(n = 2) = 1103 K. The most probable vacancy-ordering schemes for Sr/sub 8/Fe/sub 8/O/sub 23/ (n = 8) and Sr/sub 4/Fe/sub 4/O/sub 11/ (n = 4) are proposed. Formation of fivefold-coordinated iron sites on either side of an oxygen vacancy is characteristic of both phases, which contrasts with Sr/sub 2/Fe/sub 2/O/sub 5/ (n = 2) where four-coordinated sites coexist with six-coordinated sites. The high-spin Fe/sup 4 +/(t/sub 2//sup 3/sigma*/sup 1/) configuration of SrFeO/sub 3/ (n = infinity) evolves as follows: (a) for x approx. 3, random vacancies trap Fe/sup 3 +/ ions at five-coordinated sites; (b) for n = 8, Fe/sup 4 +/ ions remain high spin, a localized-electron /sup 5/E/sub g/ configuration giving rise to a cooperative Jahn-Teller distortion with c/a less than or equal to 1 and a (220)/sub n8/ unique axis imposed by structural symmetry; fast Fe/sup 3 +/ + Fe/sup 4 +/ = Fe/sup 4 +/ + Fe/sup 3 +/ electron transfer occurs parallel to this axis at room temperature, but Fe/sup 3 +/ ions are ordered at five-coordinated sites at 4 K; (c) for n = 4, the octahedral-site Fe/sup 4 +/ ions have a low-spin t/sub 2//sup 4/ configuration with four near-neighbor Fe/sup 3 +/ ions in five-coordinated sites not making an Fe/sup 3 +/-O-Fe/sup 4 +/-O-Fe/sup 3 +/ linear chain as in n = 8. Oxygen-vacancy hopping times tau/sub h/ greater than or equal to 10/sup -8/ sec persist for 200 K above T/sub t/ in n = 2, and short-range ordering in this temperature interval is inferred. For n = 8 and n = 4, motional narrowing to single Moessbauer peak occurs within tens of degrees above T/sub t/, and this narrowing is assumed to reflect rapid electron hopping in a mixed-valence state.

• Research Organization: Kyoto Univ. (Japan)
• OSTI ID: 7203244
• Journal Information: J. Solid State Chem.; (United States), Journal Name: J. Solid State Chem.; (United States) Vol. 73:1; ISSN JSSCB
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360202* -- Ceramics
Cermets
& Refractories-- Structure & Phase Studies
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201 -- Chemical & Physicochemical Properties
ALKALINE EARTH METAL COMPOUNDS
CHALCOGENIDES
CRYSTAL STRUCTURE
DATA
DISPERSIONS
ELECTRONIC STRUCTURE
EXPERIMENTAL DATA
HIGH TEMPERATURE
INFORMATION
IRON COMPOUNDS
IRON OXIDES
MIXTURES
MOESSBAUER EFFECT
NUMERICAL DATA
OXIDES
OXYGEN COMPOUNDS
SOLID SOLUTIONS
SOLUTIONS
STRONTIUM COMPOUNDS
STRONTIUM OXIDES
TRANSITION ELEMENT COMPOUNDS
VERY HIGH TEMPERATURE