The Ordered K2NiF4-type Structure of Mixed Crystals La2-xSrxLi1/2Co1/2O4 (x < 0.5) and the Electronic Properties of the Constituting Co^III and Co^IV Ions

Abstract

Solids of the composition La2-xSrxLi1/2Co1/2O4 (x50, x=0.2) crystallize in a superstructure of the K2NiF4 lattice with a doubled unit cell in the (001) plane (space group Ammm; a=b=J2a0), caused by cation ordering between lithium and cobalt on the octahedral sites. The electronic structure of the Co^III O6 and Co^IV O6 polyhedra, which lie isolated in the lattice, were studied by various spectroscopic techniques (XANES, EPR, optical). The groundstates are low-spin in both cases (t^6 2g and t^5 2g , respectively), the ligand 5eld parameters of Co^III being close to those characterizing the high-spin/low-spin crossover.