High-Temperature Properties of Langasite

A Review on High Temperature Piezoelectric Crystal La3Ga5SiO14 for Sensor Applications

In this review article, we have investigated the credibility and suitability of the lanthanum gallium silicate (La₃Ga₅SiO₁₄, LGS) crystals in the application of high-temperature sensing. All the basic properties of the langasite family piezoelectric crystals, such as elastic properties, are taken into consideration and discussed. The crosstalk effects between different vibration modes of LGS crystal are investigated to optimize the crystal cuts. Thereafter, dependences of properties, such as electroelastic properties, resistivity, and electromechanical coupling coefficients of langasite family crystals on higher temperatures, are discussed. Finally, thermal-related properties of langasite family crystals, such as specific heat as well as thermal expansion coefficients, are studied for higher temperature ranges and a comparison with other piezoelectric crystals has also been presented.

Diffusion-related implications for langasite resonator operation

Oxygen and gallium diffusivities in langasite were experimentally determined by analysis of diffusion profiles of 18O and 71Ga tracers by SIMS analysis as functions of temperature and doping. Strontium-enhanced diffusivities and activation energies of approximately 1.2+/-0.2 eV confirm the predominant role of oxygen vacancies in controlling the electrical conductivity of langasite at elevated temperature and oxygen partial pressure. The potential impact of high levels of porosity and the use of an oxygen primary ion beam on the accuracy of some of the data is discussed. The gallium diffusivity, with activation energy of 3.13 eV, was found to be more than two orders of magnitude lower than that of oxygen. Surface exchange measurements enabled estimation of gallium loss at elevated temperatures and oxygen partial pressure; the level is not believed to be of major concern for resonator performance.