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

Solids of the composition La2-xSrxLi1/2Co1/2O4 (x = 0, x congruent to 0.2) crystallize in a superstructure of the K2NIF4 lattice with a doubled unit cell in the (001) plane (space group Ammm; a = b = root 2a(0)), caused by cation ordering between lithium and cobalt on the octahedral sites. The electronic structure of the (CoO6)-O-III and (CoO6)-O-IV 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(2g)(6) and t(2g)(5), respectively), the ligand field parameters of Com being close to those characterizing the high-spin/low-spin crossover. (C) 1999 Academic Press.