Some niobium containing high temperature relaxors

Abstract

Pervovskites, Ba[B _1/3Nb_2/3]O₃ where B = Mn, Fe and Cu have been synthesised by high temperature solid-state reaction. The X-ray diffraction technique indicates that they are single phase cubic disordered structure (a = 4A°) having ordering in c direction (c=9A° At room temperature these materials give high dielectric constant around 2500 to 5000 at 400 Hz. Their room temperature relaxtion spectra in the frequency from 1Hz to 1Mhz indicates the presence of “interfacial polarization”. However, these spectra are characterised by strong conductivity term and relaxtion time constant < 2γsec obtained from Debye's relaxtion equation. Also, the temperature variation of permittivity at 400Hz has been investigated in the range from 300 to 800°K. These curves show a rather slow, steady rise of permittvity from room temperature till a maximum in the range from 500 to 800°K is obtained. These facts implies the presence “diffused phase”. The properties of these materials have been compared with some well-known relaxors.