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3091411 
Journal Article 
Effect of non-stoichiometry on properties of La1-tMnO3+delta .1. Phase relations 
Sakai, N; Fjellvag, H 
1996 
Yes 
Acta Chemica Scandinavica
ISSN: 0904-213X
EISSN: 1902-3103 
50 
7 
580-586 
WOS:A1996UY44000004 
Phase-relation data for lanthanum manganese oxide, La1-tMnO3+delta, with emphasis on lanthanum and oxygen non-stoichiometry, unit-cell dimensions and structure type are provided. The La deficiency covers the range 0.00 greater than or equal to t greater than or equal to 0.09 +/- 0.02, and is mainly charge compensated by changes in the oxygen content. The maximum formal oxidation state of manganese is reduced rather than increased on increasing the La deficit. Quenching conditions for obtaining one of three structural modifications (RH, ORT1, ORT2), as well as the relationship between slowly cooled samples, quenched samples and samples studied under in-situ, controlled oxygen partial pressure conditions are described. Reoxidation during quenching is not important for air-equilibrated samples and T < 1273 K. However, samples subjected to reducing conditions prior to quenching tend partly to reoxidize. The first-order ORT1 --> ORT2 --> RH-type transitions are rapid, implying that the situation conveyed by quenched samples from specific T,p(O-2) conditions differ from the in-situ equilibrium situation. Thermal expansion and phase-transition data are presented for the three modifications. On heating the Jahn-Teller deformed ORT1-type phase, the cooperative distortion is destroyed around 450-600 K. A pseudocubic phase, possibly of the ORT2-type, and the RH-type modification with regular MnO, octahedra, become stabilized. The transitions are connected with discontinuous volume contractions. (C) Acta Chemica Scandinavica 1996.