Segregation during the vertical Bridgman growth of lead magnesium niobate-lead titanate single crystals

摘要

Transparent, high-quality lead magnesium niobate-lead titanate, (1 -x)PbMg_(1/3)Nb_(2/3)O_(3-x)PbTiO_3, or PMNT, crystals were grown using the vertical Bridgman method. Crystals grown from 35% PT (x = 0.35) and 32% PT (x = 0.32) melts were found to vary in composition along the axial direction (from 30% to 72% PT along the growth direction). Crystals grown from 10% PT melts were found to be uniform in composition. Effective segregation coefficients were determined. All crystals examined had uniform radial composition profiles, indicating a flat growth interface. Dielectric measurements were performed on (001) oriented samples cut from a crystal grown from a 35% PT melt. Powder X-ray diffraction analysis revealed the presence of a two-phase region (tetragonal and rhombohedral) between 31% PT and 36% PT. Poling was performed on (001) samples of composition 32% PT. Upon poling, as-grown, cloudy crystals became optically transparent, and observations under crossed polarizers showed the formation of large single domain regions. Analysis of 32% PT samples showed a transition from two phases (rhombohedral and tetragonal) in the as-grown sample to single phase (rhombohedral) after poling. The high-temperature phase diagram for PMNT was estimated using a combination of differential thermal analysis and compositional data from growth experiments.