Growth and Dielectric Properties of Ta-Doped La2Ti2O7 Single Crystals

High-quality Ta-doped La2Ti2O7(Ta-LTO) single crystal of about 40 mm in length and 5 mm in diameter was successfully prepared by the optical floating zone method. An X-ray rocking curve reveals that the crystal of LTO has excellent crystalline quality. As-grown crystals were transparent after annealing in air and the transmittance is up to 76% in the visible and near-infrared region. X-ray diffraction showed that this compound possessed a monoclinic structure with P21space group. The dielectric properties were investigated as functions of temperature (0~300 °C) and frequency (102Hz~105Hz). Dielectric spectra indicated an increase in the room-temperature dielectric constant accompanied by a drop in the loss tangent as a result of the Ta doping. One relaxation was observed in the spectra of electric modulus, which was ascribed to be related to the oxygen vacancy. The dielectric relaxation with activation energy of 1.16 eV is found to be the polaron hopping caused by the oxygen vacancies.Keywords:Ta-LTO single crystal;floating zone method;dielectric properties;oxygen vacancy