LOCAL DISTORTION AND CHEMICAL SURROUNDINGS OF NIO6 OCTAHEDRA FOR NI(III) OXIDES WITH K2NIF4-TYPE STRUCTURE

Ni(III) oxides with the K2NiF4-type structure, (A, A')(2)M'0.5Ni0.5O4 (A' = alkaline earth, A = rare earth, and M' = Mg, Zn, Ti, Al, Ga) hav e been prepared under high oxygen pressure (similar to 150 MPa). The e volution of the local distortion of NiO6 octahedra in such lattices wa s studied using X-ray diffraction analysis (XRD), electron paramagneti c resonance (EPR) and infrared (IR) spectroscopies. The observed disto rtions are discussed on the basis of covalency and relative strength o f the axial [(A',A)-O] and equatorial(M'-O) competing bonds surroundin g the NiO6 octahedron in the lattice. These results are related to the structural tolerance factor proposed by Poix.