The large electrical-resistance enhancement of piezoelectric single crystals Sr3Ga2Ge4O14 by compensating for vacancy defects with the doping of high-valence Sm3+ ions

Abstract

Sr₃Ga₂Ge₄O₁₄ (SGG) crystals are widely used in the high-temperature piezoelectric field because of their excellent piezoelectric properties. In this paper, the Sr²⁺ lattice of the SGG crystal is replaced with high-valence Sm³⁺ with a close radius to improve its high-temperature resistivity and to obtain more stable electroelastic properties. The full width at half maximum (FWHM) of the X-ray rocking curves of (Sm_0.01Sr_2.99)₃Ga₂Ge₄O₁₄ (SSGG) and SGG crystals is 29.62′′ and 32.04′′, respectively. In the range of 50 °C to 700 °C, the dielectric constant ε^T₁₁/ε^T₀ of the SSGG crystal increases from 16.51 to 18.49, and the piezoelectric coefficient d₁₁ also increases from 7.32 pC N⁻¹ to 7.97 pC N⁻¹. At 700 °C, the resistivity of the X-cut plates of SSGG and SGG crystals is about 1.52 × 10⁷ Ω cm and 4.6 × 10⁶ Ω cm, respectively. The SSGG crystal contains larger forbidden bandwidths and fewer oxygen vacancies, as measured by UV-vis DRS and X-ray photoelectron spectroscopy analyses, and the reduction of oxygen vacancies can effectively shorten the carrier lifetime, which is a key factor in increasing the resistivity.