The resulting materials were examined with a Siemens
D5000 X-ray diffractometer to study the development
of the crystalline phases at different temperatures. In
NixTi13xNb2xO2 and Ni0.1A0.7B0.2O2 (A=Ti, Sn;
B=Sb, Nb) fired samples, a structure profile refinement
was carried out by the RIETVELD method17 with the
data obtained in the [20–100] o2 Bragg angle interval.