Metastability of the K2NiF4type structure of the solid solution LaCa(CrxAl1−x)O4(0⩽x⩽0.10)

✍ Scribed by I. Zvereva; L. Zueva; J. Choisnet

• Publisher: Springer
• Year: 1995
• Tongue: English
• Weight: 480 KB
• Volume: 30
• Category: Article
• ISSN: 0022-2461
• DOI: 10.1007/bf00351871

✦ Synopsis

Metastability of the K2NiF4 type aluminate LaCaAI04 and its chromium diluted solid solution LaCaCrxAIl-x04 (x~< 0.10) was evidenced at 1400~ in air, in terms of demixing into the parent structures of the 1 : 1 intergrowth, i.e. the perovskite and rocksalt type LaAI03 (LaCrxAIl_,,03) and CaO, respectively. This behaviour is discussed comparatively with YCaAI04 and LaSrAI04 whose structures are stable under the same thermodynamic conditions. The results of a structure analysis are used to emphasize the role of the nine-fold co-ordination of the (A 3+ =y3+, La3+; A2+ =Ca2+, Sr2+) cations as "mixing" the twelve-fold co-ordination of A 3+ in A3+AI03 perovskite and the six-fold one of A 2+ in A2+O rocksalt. Calcium-oxygen underbonding in the (La, Ca)-O-AI bridge is assumed to trigger the metastability of the intergrowth structure at high temperature.