抄録
Microstructures of Pb(Mg1/3Nb2/3)O3 ceramics were studied by using a x-ray analysis and transmission electron microscope (TEM) with energy dispersive x-ray analysis (EDX). In general, perovskite phase of Pb(Mg1/3Nb2/3)O3 is prepared by four different techniques: Conventional sintering (CS), Presintering (PS), CS with excess MgO (CSE), and PS with excess MgO (PSE). At the low sintering temperature of 850°C in the CS method, pyrochrore phase was located in the triple junctions and surrounded by the amorphous PbO. With increasing the sintering temperature to 900°C, pyrochrore phases were reduced and many MgO particles were observed near the pyrochrore phases. From these experimental results, the synthesis process of single phase of Pb(Mg1/3Nb2/3)O3 was classified into three parts; firstly, PbO among PbO, Nb205 and MgO powders melt and reacted with Nb2O5. The pyrochrore phases were composed at the low sintering temperature. Secondly, the pyrochrore phases gradually transformed into perovskite phases by the diffusion of MgO. The chemical composition of pyrochrore phase in the sample sintered at sintering conditions of 850°C for 2 hrs was Pb2.25(Mg0.27Nb1.79)O3. Thirdly, the single phase of Pb (Mg1/3Nb2/3)O3 perovskite was composed at the more higher sintering temperature by the mutual diffusion of excess Pb and Nb and Mg which are deficient in the pyrochrore phase.
