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Highlights • SLT crystals with thickness of 3.2 mm were prepared by VTE method. • The chemical composition in SLT crystals is about 49.99 mol%. • The forward and reverse poling fields are 159 V/mm and 145 V/mm, respectively. Abstract A stoichiometric lithium tantalate (SLT) crystal, 3.2 mm in the thickness and approximate 56 mm in the diameter, was prepared employing improved vapor transport equilibration (VTE) method. The chemical composition in SLT crystals is about 49.99 mol%. The compositional depth profile and uniformity along the radial direction were characterized. The composition deviation in the whole wafer is less than 0.02 mol%. The poling fields for ferroelectric domain reversal of SLT crystals were measured by applying ramped voltages using liquid electrodes. The forward and reverse poling fields are 159 V/mm and 145 V/mm, respectively, and their uniformity in the whole SLT crystal is promising. [ABSTRACT FROM AUTHOR]

The twins were observed and investigated in vapor transport equilibration (VTE) treated lithium tantalate crystals by burying congruent lithium tantalate crystals (CLT) in a Li-rich polycrystalline powder. Twins and their etched patterns were observed under an optical polarizing microscope, and the geometry of the twins was discussed. Twin composition planes were the 01 1 ¯ 2 planes. The cause of twinning was analyzed and verified by experiment. The results indicate that the emergence of twins is due to sintering stress, which arises from sintered Li-rich polycrystalline powders at high temperature. 3.2 mm thick stoichiometric lithium tantalate (SLT) crystals without twins were obtained by setting corundum crucibles over the top of the crystals to make crystals free from the sintering stress. In addition, cracks were observed at the intersection of twin bands, and the stress caused by the dislocation pile-up was considered to be the reason for the formation of cracks. [ABSTRACT FROM AUTHOR]