ANOMALY OF DIELECTRIC-CONSTANT OF (BA1-XSRX)(MG1/3TA2/3)O3 SOLID-SOLUTION AND ITS RELATION TO STRUCTURAL-CHANGE

The temperaure dependence of the dielectric constant has been studied in the (Ba1-xSrx)(Mg1/3Ta2/3)O3 solid solution. It is found by transmission electron microscopy and Raman spectroscopy that a new low-temperature phase exists in materials with strontium-rich compositions, and it is transformed into the ordered hexagonal perovskite phase with increasing temperature. The structural change is reversible by cooling and heating treatments. Because the dielectric constant of the low-temperature phase becomes large with increasing temperature, it is explained that materials with strontium-rich compositions have a negative temperature coefficient of resonant frequency. The anomaly of the dielectric constant with increasing temperature is discussed in relation to phase transformation.