X-RAY-DIFFRACTION STUDY OF THE DECOMPOSITION PROCESS OCCURRING IN SINGLE-CRYSTALS OF THE K2NIF4-TYPE ALUMINATE LACAALO4

The results of an X-ray diffraction study of the decomposition process occurring in the K2NiF4-type aluminate LaCaAlO4 are reported, The exp erimental data concern two small single crystals heated for 1 and 10 h at 1200 degrees C, respectively. As a final result, the presence of L aAlO3 perovskite and CaO is unambiguously observed, After 1 h of heati ng, several intermediate phases can be identified as small-size LaAlO3 -like microprecipitates. Well-defined orientation phenomena with respe ct to the matrix LaCaAlO4 are evidenced for these phases and for CaO a s well. On the basis of the variation of the perovskite cell volume of the intermediate phases, the decomposition process is tentatively mod eled, In this respect, a tetragonal phase is considered as the precurs or of LaAlO3 perovskite. (C) 1997 Academic Press.