Compositional Studies of Lanthanum‐Modified Morphotropic Phase Boundary Pb(Mg1/3Nb2/3)O3—PbTiO3 Ceramics

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Abstract
Investigations have been performed on the La‐modified (1 ‐ x)Pb(Mg1/3Nb2/3)O3—(x)PbTiO3 crystalline solution for compositions close to the morphotropic phase boundary (MPB) using energy‐dispersive X‐ray spectrometry (EDS). Studies were performed on specimens with La contents between 0 and 10 at.% for x= 0.35 which were fabricated by keeping the average Mg/Nb/Ti ratio in the bulk ceramic unchanged. In this series of samples, La3 was compensated for by introducing B‐site vacancies. Quantitative analysis by EDS revealed a change in the B‐site cation concentrations with La substitution. It was observed that the Nb concentration decreases and the Ti concentration increases with increasing La content, indicating that local charge compensation in the perovskite phase is taking place by an adjustment in B‐site cation concentrations. Phase analysis demonstrated the presence of a second phase for La contents above 2 at.%. Scanning electron microscopy then revealed the presence of a secondary pyrochlore phase with an octahedral‐like morphology. The composition of the pyrochlore phase was found to be rich in Nb and poor in Ti. The effects of changes in composition on dielectric properties, polarization, and electrically induced strain were then investigated.