Dielectric properties and phase transitions of Bi3Nb1-xTaxO7 fluorite-type dielectrics

A study of Bi3Nb1-xTaxO7 ceramics revealed that these solid solutions undergo ail incommensurate-to-commensurate, Fm3m double left right arrow l $(4) over bar $ m2 transition. An analysis of the microwave dielectric properties showed that an increase of x for the Bi3Nb1-xTaxO7 results in a slight decrease in the permittivity and an increase in the Q x f values for both crystal modifications. However, the order-disorder phase transition at temperatures below 900 degrees C reduces the dielectric losses: the Q x,f values for the commensurate-tetragonal Bi3Nb1-xTaxO7 samples are in the range 300-400 GHz higher than the values of the incommensurate-cubic analogues. In addition, the phase transition induces positive values of the temperature coefficient of resonant frequency (tau(f)) for the cornmensurate-tetragonal Bi3Nb1-xTaxO7 fluorite-type dielectrics. (c) 2007 Elsevier Ltd. All rights reserved.