CRYSTAL-CHEMISTRY OF THE DILUTED SOLID-SOLUTION YCACRXAL1-XO4 (X-LESS-THAN-OR-EQUAL-TO-0.07) AT 1273K - REVERSED TRENDS IN THE ANISOTROPY OF THE K2NIF4 TYPE-STRUCTURE

Crystal chemistry of the diluted K2NiF4 type solid solution YCa(CrxAl1 -x)O4, (x less-than-equal-to 0.07) at 1273 K, as deduced from an X-ray diffraction powder study shows up a main feature : die overall anisot ropy of the perovskite / rocksalt l/l intergrowth is reversed, as comp ared to the RT data i.e. the (Al, Cr)-Oapical distance no longer incre ases : consequently, the octahedra are more symmetrical. Such a phenom enon is enhanced by Cr3+ cations in agreement with their isotropic ''d 3'' electronic configuration. From that result, one can point out a lo wering of the 2D character of the K2NiF4 structure at high temperature , in so far as pure geometrical effects are concerned.