Phase Transition in Sr(NiW)0.5O3-Ba(NiW)0.5O3 System

Crystal structures, electrical and magnetic properties of Sr(NiW) 0.5 O 3 -Ba(NiW) 0.5 O 3 system were studied in the temperature range from room temperature to about 400°C. The compound of strontium undergoes a phase transition at about 260°C, where the crystal structure which is perovskite-like changes from tetragonal to cubic. The anomaly was also observed at the transition temperature in the measurements of electrical and magnetic properties. Sr(NiW) 0.5 O 3 shows a rather small value of dielectric constant of about 17 and the magnetic susceptibility of 6.2×10 -6 e.m.u. at room temperature. Ba(NiW) 0.5 O 3 which is cubic in the whole range shows the similar values. Both substances behave as paramagnetic, though a small anomaly is observed in Sr(NiW) 0.5 O 3 at the tetragonal-cubic transition. The effective Bohr magneton numbers of Ni 2+ are estimated as 2.92 in the tetragonal and 3.06 in the cubic for Sr(NiW) 0.5 O 3 and 3.02 for Ba(NiW) 0.5 O 3 . The lattice distortion observed in the compound of strontium is considered to be due to the slight variation of the electronic configuration of the transition metal ions surrounded by oxygen octahedra in the crystal.