Dielectric properties, electrical conductivity, and relaxation phenomena in ferroelectric Bi2WO6

Abstract

Single crystals and polycrystalline Bi2WO6 samples are used to measure the dielectric constant, loss, and electrical conductivity, over a wide range of temperature, oxygen partial pressure in ambient atmosphere, and frequency of the measuring electric field. Maxima of the dielectric constant are observed at phase transitions close to 930 and 960°C. The Curie constant for bismuth tungstate is 1.4 × 105 K, the Curie-Weiss temperature is equal to 926°C. The electrical conductivity of Bi2WO6 in the range 400 to 700°C is practically purely ionic at oxygen partial pressures of 1 to 10−1 atm, and electronic at PO2 = 10−2 to 10−5 atm. The maxima in the dielectric constant and tan δ in the range from 400 to 700°C, as the investigations of their frequency dispersion and the dependence on the composition of the ambient atmosphere revealed, have a relaxation character and are connected with the formation of two types of defect associates in crystals. The possible nature of crystal lattice defects responsible for electrical conductivity and relaxation phenomena is discussed.