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 incre ases) in the dielectric constant (epsilon') and dielectric loss (epsil on'') are observed for all the glasses between 297 and 320 K. A simila r anomaly showing a change from semiconducting to metallic behavior is also observed in the electrical conductivities around the same temper ature region. The anomalies observed around this temperature are consi dered to be associated with the orientational motion of the BiO3 or Bi O6 structural units present in the glasses. Such motions might give ri se to structural instability and different kinds of phase transitions including a superconducting transition in the crystalline phases.