Novel monoclinic zirconolite in Bi2O3–CuO–Ta2O5 ternary system: Phase equilibria, structural and electrical properties

Abstract

Synthesis of novel monoclinic zirconolite, Bi1.92Cu0.08(Cu0.3Ta0.7)2O7.06 (β-BCT) using solid state reaction had been finalised at the firing temperature of 900°C over 24h. The X–ray diffraction pattern of β-BCT was fully indexed on a monoclinic symmetry, space group, C2/c with lattice constants, a=13.1052 (8), b=7.6749 (5), c=12.162 (6), α=γ=90° and β=101.32° (1), respectively. The reaction mechanism study indicated phase formation was greatly influenced by the reaction between intermediate bismuth tantalate binary phases and CuO at elevated temperatures. β-BCT was thermally stable up to a temperature of 900°C and contained spherulite grains with sizes ranging from 1 to 14μm. Electrical properties of this material were characterised over a broad temperature range covering temperatures from 10K to 874K. At the temperature of 304K, two semicircles were discernible in complex Cole–Cole plot showing an insulating grain boundary with Cgb=6.63 ×10−9 F cm−1 and a bulk response capacitance, Cb=6.74 × 10−12 F cm−1. The Power law frequency-dependent ac conductivity of β-BCT was apparent in three frequency regimes; a low–frequency plateau regime, a high-frequency plateau regime and a dispersive regime taking place in the temperature range of 220–576K. The frequency-dependent ac conductivity of β-BCT with increasing temperature was attributed to the thermal activated electrical conduction mechanism within the structure.