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

Co1 - x Ni (x) Cr2O (0 a parts per thousand currency sign x a parts per thousand currency sign 1) ceramic samples have been characterized by X-ray diffraction and relative dielectric permittivity E >(T), loss tangent tan delta(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 a parts per thousand currency sign 0.98) or tetragonal (0.99 a parts per thousand currency sign x < 1) structure. Increasing the Ni content of the samples from 0 to 100 at % increases their tan delta and 1/rho by three to four orders of magnitude. The E >(T), tan delta(T), and TSDC of the samples with 0.2 a parts per thousand currency sign x a parts per thousand currency sign 0.6 have anomalies at T (1) similar to 220 K and T (2) similar to 240 K, which point to a transition to a polar state below T (2). Samples containing 1-4 at % Fe-57 as an impurity were characterized by Mossbauer 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 T (2) and magnetoelectric multiferroic properties.