HIGH-PRESSURE SYNTHESIS AND PHYSICAL-PROPERTIES OF THE SOLID-SOLUTION, SRLAAL1-XNIXO4(0-LESS-THAN-X-LESS-THAN-1)

A complete solid solution (SrLaAl1-xNixO4) between insulating SrLaAlO4 and metallic SrLaNi(III)O-4 oxides were prepared under high oxygen pr essure (1.5 kbar, 800 degrees C). They have tetragonal K2NiF4-type str ucture in all the solid solution range. Compared with lattice paramete rs of the same solid solution prepared under normal condition (1 bar, 1200 degrees C), large decrease in the c-parameter was induced by high pressure treatment while no noticeable variation of the a-parameter w as observed Although marked changes of structural parameters, magnetic susceptibilities, and electron paramagnetic resonance spectra were co nsistently occurred before and after x=0.5, overall behaviors were ess entially the same with those of solid solution prepared under normal c ondition. Such a phenomenon is explained by assuming the formation of partially filled narrow sigma(x2y2) band for x>0.5. Lattice contracti on along the c-axis by high pressure treatment seems not to broaden th is band. Particularly, the continuous absorption characteristic of a h igh free carrier concentration for x>0.5 and the absence of Ni-O in-pl ane stretching mode in the infrared absorption spectra supports this p icture. However, the conductivities increasing with temperature for al l solid solution suggest that some localization character, of probably Anderson type, remains for x>0.5.