Dielectric behavior and Raman spectra of lanthanum-doped lead magnesium niobate ceramics

Abstract

Lanthanum-doped lead magnesium niobate (PLMN) ceramics were fabricated by columbite route. The effects of La-addition on dielectric behavior and Raman spectra were investigated. The trivalent La3+-doping showed inhibiting effects on grain growth process. The average grain size decreased and pyrochlore phase was detected along with the perovskite phase above 2 mol% La-addition. Temperature dependence of permittivity measured at 1 kHz was investigated. Due to La3+-doping, the maximum of dielectric constant decreased and the temperature of the maximum permittivity moved to lower temperature. An oval-form hysteresis loop was observed on La-doped (3 mol%) lead magnesium niobate (PMN) sample, which revealed that La-doped PMN owned partially normal ferroelectric feature. Raman spectra showed a shift of the peak around 270 cm−1, which identified a distortion of the center symmetric ordered structure and enforced B-site compositional fluctuation. The shift of A1g mode (around 780 cm−1) indicated that degree of chemical order at B-site increased and PLMN contained 1:1 B-site ordered nanoregion (clusters) with Fm-3m symmetry.