Chemical Heterogeneity in PMN–35PT Ceramics and Effects on Dielectric and Piezoelectric Properties

Pb[(Mg_1/3Nb_2/3)_0.65Ti_0.35]O₃ (PMN–35PT) powder was prepared using the columbite precursor method. Fully dense compacts were formed by hot-pressing the powder at 950°C, and then the compacts were annealed at 1150°C for 5 and 10 h, respectively. Dielectric and piezoelectric properties of the as-hot-pressed and annealed samples were measured and correlated with microstructure. The as-hot-pressed material exhibited relaxor–ferroelectric-like behavior, with a relatively low dielectric constant maximum measured at 1 kHz ( K _m@1kHz) of 8160. Annealing resulted in a transition to weak normal-ferroelectric behavior, a shift in the dielectric maximum temperature from 190°C to 169°C, and a dramatic increase of K _m@1kHz to a maximum value of 41 720 for the longer anneal. The as-hot-pressed microstructure was chemically heterogeneous, characterized by submicrometer-sized regions of varying magnesium, niobium, and titanium content that likely originated from chemical heterogeneities that were present in the as-prepared PMN-PT powder. The as-hot-pressed properties have been explained as being the integrated response of many discrete ferroelectric responses as dictated for each of these regions by the local chemistry. The transition on annealing has been explained in terms of chemical homogenization to a near-morphotropic phase-boundary composition that is intrinsically weak normal-ferroelectric. Differences in polarization-versus-electric-field and strain-versus-electric-field behavior between the hot-pressed and annealed materials have been discussed in terms of differences in domain mobility.