Synthesis and Characterisation of Cubic Bi3Zn2Ta3O14 and its Related Divalent-Doped Pyrochlore Materials

Bi3Zn2Ta3O14, P , was crystallised in a cubic unit cell with lattice parameter of a=10.5437 (9) A. The material had permittivity, ε, of around 58 and dielectric loss, tan σ, of 2.3*10-3 at 30oC, 1 MHz; temperature coefficient of capacitance (TCC) of -156 ppm/oC in the range of 30oC to 300oC at 1 MHz. Chemical doping was carried out at either A (Bi1.5Zn0.5-xMx)(Zn0.5Ta1.5)O7, or B site (Bi1.5Zn0.5)(Zn0.5-xMxTa1.5)O7 in search of better performance materials. Various divalent cations such as Cd2+, Ca2+, Mg2+, Ni2+, Pb2+, and Cu2+ were used as dopants. Solid solutions formed were: Bi3Zn2-xCdxTa3O14 (0.x.0.5), Bi3Zn2-xMgxTa3O14(0.x.0.2), Bi3Zn2-xNixTa3O14 (0.x.0.4), Bi3Zn2-xPbxTa3O14 (0.x.0.3), Bi3Zn2-xCaxTa3O14 (0.x.0.3) and Bi3Zn2-xCuxTa3O14 (0.x.0.1). Electrical properties of the materials were investigated using impedance spectroscopy. Conductivities of the solid solutions were higher than that of the parent material Bi3Zn2Ta3O14. These doped materials exhibited similar behaviour as Bi3Zn2Ta3O14, showing a high degree of dispersion of permittivity at low frequencies ( 1 kHz) and at temperatures above 500oC. Between 100 kHz and 1000 kHz, non-frequency dependence was observed in the range of 100 . 300oC. An increase in dielectric loss below 10 kHz was observed. Dielectric loss decreased with frequencies when temperature was above 500oC. Dielectric loss of all divalent cation doped materials was higher than that of the parent material; maximum permittivity value of 68 was recorded at x = 0.3 in Bi3Zn2-xCaxTa3O14. TCC obtained in this study had negative values; no obvious correlation between TCC and composition of the doped materials can be deduced.