LASRCRXNI1-XO4- CRYSTAL-CHEMISTRY, MAGNETISM, AND THE STABILIZATION OF NI-I IN AN OXIDE ENVIRONMENT(DELTA )

Magnetic, structural and reduction data on the K2NiF4 structure Cr-III /Ni-III oxides, LaSrCrxNi1-xO4+delta (0.1 less than or equal to x less than or equal to 0.9, where delta may be negative) are reported; samp les with x > 0.2 adopt the tetragonal I4/mmm space group, while for x less than or equal to 0.2, the samples are multiphasic due to competit ion between a novel vacancy-ordered Immm structure and the undistorted K2NiF4 phase. Magnetic studies in the temperature range 5 less than o r equal to T/K less than or equal to 300 show spin glass behavior for x < 0.9, with freezing temperatures of between 12 and 16 K: at higher temperature the susceptibilities display Curie-Weiss behavior. The mag netism of the x = 0.9 sample resembles that reported for LaSrCrO4, dis playing an antiferromagnetic transition at 150 K and weak ferromagneti sm below 130 K. Reduction of the title compounds in 1 atm of flowing H -2 at similar to 500 degrees C produces stable, oxygen-deficient compo unds, notably La2Sr2CrNiO7, which contains Ni-I with a thermal stabili ty unprecedented in an oxide.