Synthesis of Polar Dielectric Barium Magnesium Niobate at Low Sintering Temperature: Dielectric Relaxation and AC Conductivity Study

Abstract

Ba(Mg1/3Nb2/3)O3 is an important microwave polar dielectric material. However, the large leakage current and losses due to defects incorporated during high temperature processing restricts its use in microwave devices. We have synthesized phase pure perovskite Ba(Mg1/3Nb2/3)O3 by controlling the cooling rates during calcination and sintering, using two stage columbite method at relatively low sintering of 1150°C. X-ray diffraction has been used to determine the structural details. Ceramics stabilizes in hexagonal perovskite structure with lattice constant a=5.7803A˚, c=7.0780A˚. Sintered ceramics with density > 93% exhibit surface morphology having homogeneous grain distribution with average grain size is ≈1.0-2.0 mm. Temperature and frequency dependent dielectric response has been analyzed to understand the dielectric dispersion. Dielectric response is temperature independent up to ≈180°C. Beyond this temperature dielectric dispersion is observed which is more pronounced at lower frequencies and associated with significant electrical conductivity. Impedance spectroscopic formalism has been used to separate out the contributions from gains and grain boundary using equivalent circuit approach, whereas, electrical modulus approach has revealed the role of conductivity relaxation. The frequency/ temperature dependent ac conductivity suggests conduction being thermally activated process. AC conduction activation energies are estimated from Arrhenius plots and conduction mechanism is discussed.