Effect of the Crystal Orientation on the Dielectric Properties of SrTiO3 Single Crystals after Annealing in Carbon Powder

Abstract

Strontium titanate (SrTiO₃) is an excellent dielectric material capable of enabling controllable structural and dielectric modifications through defect design; however, the effect of the crystallographic orientation on its structure and dielectric behavior remains underexplored. In this study, SrTiO₃ single crystals were grown by using the Verneuil method, and the dielectric properties were systematically evaluated across distinct crystallographic orientations following carbon powder annealing. The carbon-embedded annealed SrTiO₃ single crystals exhibited remarkable giant dielectric behavior with pronounced anisotropy across orientations. The ranking of dielectric constants in different crystal orientations from largest to smallest is [100] > [110] > [210] > [310] > [311] > [111] > [211]. Dielectric losses increase in high-frequency regions for [311], [310], [111], and [211] crystal orientations, while [110] and [210] crystal orientations exhibit losses exceeding 0.02 at 10³–10⁴ Hz. Notably, the [100] crystal orientations exhibited optimal dielectric properties demonstrating a colossal permittivity of 28,284 and a dielectric loss of 0.0113 at 1 kHz and maintains a colossal permittivity (∼1.7 × 10⁴) with a low dielectric loss (<0.1) throughout a wide temperature (30 °C–300 °C) and frequency (10 Hz–100 kHz) range. The enhancement of the dielectric properties is closely related to the defective dipole clusters Ti³⁺-V_O^••-Ti³⁺ and V_Sr^″-V_O^••. The [100] and [110] crystal orientations displayed higher carrier concentrations and more defective dipole clusters V_Sr^″-V_O^••, where free electrons were effectively localized within these defect structures, thereby enhancing the dielectric performance. This study has elucidated the origin of the excellent dielectric properties of SrTiO₃-based materials by using single crystals as the object of study and has also provided new ideas for the design of SrTiO₃-based giant dielectric materials by combining defect engineering and orientation engineering.