X-ray, Mössbauer, and dielectric studies of the Co1 − x Ni x Cr2O4 ceramic system

Abstract

The temperature dependences of the dielectric constant, ɛ(T), dielectric loss tangent, tanδ(T), and thermostimulated depolarization currents of (Co1 − xNix)Cr2O4:y57Fe2O3 samples with 0.2 ≤ x ≤ 0.6 and 0.01 ≤ y ≤ 0.04 exhibit anomalies at temperatures of T1 ≈ 220 K and T2 ≈ 240 K that indicate a transition to an ordered ferroelectric state at temperatures below T2. Also observed at the same temperatures are abrupt changes in the isomer shift and quadrupole splitting for two Mossbauer spectral doublets of a sample with x = 0.2.