Ferroelectricity in spinel solid solution Co0.8Ni0.2Cr2O4

Temperature dependencies of dielectric permittivity and loss tangent (at frequencies 0.1-200 kHz) together with thermally stimulated depolarization currents, magnetization, and Mossbauer spectra of ceramic solid solutions Co1-xNixCr2O4 (x = 0, 0.2, 0.4, 0.6, 1.0) are studied at temperatures from 80 to 350 K. We find evidence of two reversible phase transitions located at T-1 and T-2 (220 and 245 K, respectively, for x = 0.2), of occurrence of pyroelectric properties below T-2, as well as of a phase transition to magnetically ordered state of ferrimagnetic type (below 86 K for x = 0.2). The obtained results evidence that the compounds possess, additionally to magnetic, ferroelectric properties and are thus new members in the family of multiferroics.