Effect of Sr/Ba ratio on dielectric properties of BSTN ceramics

The phase composition of (1-x)BaO center dot xSrO center dot 0.7TiO(2)center dot 0.3Nb(2)O(5) (BSTN) composite ceramics was analyzed by XRD, and the effect of Sr/Ba ratio on the dielectric properties of BSTN was investigated by impedance analyzer. The results showed that any sample with different x value contained two phases-the perovskite phase and the tungsten bronze phase. The dielectric constants of BSTN basically decreased while the tan delta increased with the increase in x value. Both dielectric constant and tan delta decreased with the applied frequency increased for the same x value. There were two Curie points for BSTN composite ceramics. The first one belonging to the perovskite phase decreased with the increase in x value, but the second one belonging to the tungsten bronze phase kept almost constant at about 300 degrees C.