Exploration of High-Temperature Conduction Mechanisms in Disordered and Ordered Langasite-Type Piezoelectric Crystals

Langasite-type crystals are widely used in high-temperature piezoelectric sensors owing to their excellent piezoelectric properties and outstanding stability. However, the decrease in resistivity at elevated temperatures can degrade the sensor performance. Understanding the electrical conduction behavior of these crystals is crucial for developing reliable devices under extreme temperature conditions. In this study, the high-temperature conduction mechanisms of ordered Ca₃TaGa₃Si₂O₁₄ and disordered La₃Ga_5.5Ta_0.5O₁₄ langasite-type crystals are systematically investigated, elucidating the influence of intrinsic defects on resistivity and revealing the origin of resistivity differences between ordered and disordered crystals. The results indicate that below 700 °C, La₃Ga_5.5Ta_0.5O₁₄ exhibits predominantly <i>p</i>-type conduction, whereas Ca₃TaGa₃Si₂O₁₄ shows a combination of ionic and <i>p</i>-type conduction; above this temperature, ionic conduction dominates in both crystals, with resistivity significantly reduced due to the influence of oxygen vacancies. This study provides valuable guidance for the design and optimization of langasite-type crystals with enhanced high-temperature resistivity.