Preparation and X-ray diffraction, dielectric, and Mössbauer characterization of Co1 − xNixCr2O4 solid solutions

Co1 − xNixCr2O (0 ≤ x ≤ 1) ceramic samples have been characterized by X-ray diffraction and relative dielectric permittivity ɛ(T), loss tangent tan δ(T) (0.1–200 kHz), and thermally stimulated depolarization current (TSDC) measurements in the range 100–350 K. The samples were shown to consist of spinel solid solutions with a cubic (0 < x ≤ 0.98) or tetragonal (0.99 ≤ x < 1) structure. Increasing the Ni content of the samples from 0 to 100 at % increases their tanδ and 1/ρ by three to four orders of magnitude. The ɛ(T), tan δ(T), and TSDC of the samples with 0.2 ≤ x ≤ 0.6 have anomalies at T1 ∼ 220 K and T2 ∼ 240 K, which point to a transition to a polar state below T2. Samples containing 1–4 at % 57Fe as an impurity were characterized by Mössbauer spectroscopy in the range 54–330 K and were shown to be magnetically ordered at 78 K. We conclude that the solid solutions have ferroelectric properties with a Curie temperature T2 and magnetoelectric multiferroic properties.