ANOMALOUS DIELECTRIC-RELAXATION BEHAVIOR OF K-DOPED AMORPHOUS BA1-XKXBIO3-DELTA (X=0-0.75) OXIDES

In this paper we report the dielectric properties of Ba1-xKxBiO3-delta (X = 0, 0.2, 0.4, 0.625, and 0.75) glasses at different temperatures (80-450 K) and frequencies (1-10 kHz). Distinct anomalies (large increases) in the dielectric constant (epsilon') and dielectric loss (epsilon'') are observed for all the glasses between 297 and 320 K. A similar anomaly showing a change from semiconducting to metallic behavior is also observed in the electrical conductivities around the same temperature region. The anomalies observed around this temperature are considered to be associated with the orientational motion of the BiO3 or BiO6 structural units present in the glasses. Such motions might give rise to structural instability and different kinds of phase transitions including a superconducting transition in the crystalline phases.