The aim of this study was to investigate the effects of the rare earth element neodymium on the phase formation and microstructural development of relaxor ferroelectric lead magnesium niobate, Pb(Mg 1/3 Nb 2/3 )O 3 (PMN) system. Perovskite phase PMN powders were prepared using the sol-gel method and the effect of neodymium doping was investigated at different doping levels ranging from 0.1 mol% to 30 mol%. The precursors employed in the sol-gel process were lead (II) acetate, magnesium ethoxide, and niobium (V) ethoxide. All the experiments were performed at room temperature while the calcination temperatures ranged between 800°C and 1,100°C. Results showed that it was possible to obtain the pure perovskite phase at 950°C using the sol-gel method. Nd +3 addition influenced the phase formation and microstructure of the multicomponent system. Pyrochlore was detected along with the perovskite phase above 10 mol% Nd. Results also demonstrated that grain size of the synthesized powders depended on the Nd +3 concentration.
IntroductionLead magnesium niobate (PMN) is a relaxor ferroelectric material that is characterized by a diffuse phase transition over a broad temperature range and a frequency dependent maximum in its relative dielectric permittivity. It demonstrates very high dielectric constant around -10 to -5°C [1]. It has many potential applications such as multilayer ceramic capacitors, actuators and electro-optic devices [2].In the processing of PMN ceramics, synthesis of pure perovskite phase is crucial, the most important problem being the formation of pyrochlore phase which degrades the electrical properties. Previously, several attempts have been made to eliminate the pyrochlore in the PMN structure. The Columbite method introduced by Swartz and Shrout, addition of excess MgO to promote the perovskite formation, and excess PbO addition to compensate lead oxide evaporation during calcination are the commonly used techniques to prevent pyrochlore formation [3][4][5].Among others, the sol-gel method offers several advantages for the preparation of ceramic oxides. This method provides high degree of homogeneity and stoichiometry especially for multicomponent systems in addition to allowing doping on a molecular scale. Hence, there is considerable interest in the preparation of PMN ceramics using sol-gel method [6][7][8][9][10][11].The phase formation and electrical properties of piezoelectric ceramics can be modified by use of dopants. Effects of rare earth elements (RE) doping on the phase formation and electrical properties of piezoelectric ceramics such as barium titanate and lead zirconate titanate are well studied [12][13][14][15]. The effect of RE addition on the PMN system has also been studied in the literature to a degree. Zhong et al. [16] studied the effects of adding a fixed amount of rare earth additives on the microstructure and dielectric properties of PMN-PT ceramics. Their results showed that doping of neodymium (Nd +3 ) resulted in a slight decrease in the grain size and a lowering...
