关键词: Ga3PO7晶体/
密度泛函-准谐振近似理论/
热学性质/
声表面波
English Abstract
Theoretical study on thermal and acoustic surface wave properties of Ga3PO7 crystal at high temperature
Hao Juan1,Zhou Guang-Gang1,
Ma Yue1,
Huang Wen-Qi2,
Zhang Peng1,
Lu Gui-Wu1
1.China University of Petroleum, College of Science, Beijing 102249, China;
2.Beijing University of Science and Technology Information, College of Science, Beijing 100081, China
Fund Project:Project supported by the National Nature Science Foundation of China(Grant No: 51372140),and China University of Petroleum (Beijing) Higher Education Young Elite Teacher Project (No: 2462015YQ0603).Received Date:08 December 2015
Accepted Date:15 March 2016
Published Online:05 June 2016
Abstract:The high-temperature piezoelectric crystal Ga3PO7is a versatile functional material widely used in many electromechanical devices. As the Curie temperature of this crystal is as high as 1346 ℃, it can break through the current temperature limitations(1200 ℃) and then be used in extremely high-temperature condition. However, it is very difficult to explore its properties in such a high-temperature environment. Moreover, the relevant theoretical research has not been reported to date. Aiming at this problem, the density function theory combined with quasi harmonic approximation theory is used to investigate the structural, thermal and surface acoustic wave (SAW) properties of Ga3PO7. Firstly, the Gibbs energies of Ga3PO7 crystal with different stains are calculated, and the equilibrium structures of Ga3PO7 crystal at different temperatures (from 0 ℃ to 1200 ℃) are found according to minimal energy principle. Secondly, based on the result above, we optimize Ga3PO7 crystal at different temperatures, and then, the thermal and elastic properties of Ga3PO7 crystal within 0-1200 ℃ are calculated using CASTEP package based on the density functional theory in the generalized gradient approximation. The results show that its lattice constants increase almost linearly as temperature increases while its density decreases. Owing to anisotropy, its lattice constant along the c axis increases much more greatly than along the a axis. The coefficients of thermal expansion along the a and c axis are evaluated to be 1.6710-6 K-1 and 3.5810-6 K-1, respectively, and the volumetric heat capacity is evaluated to be 2.067 J/gK. These values all agree well with the experimental values. Finally, the elastic constants, bulk modulus and SAW properties of Ga3PO7 crystal at different temperatures (from 0 ℃ to 1200 ℃) are calculated. The results show that the bulk modulus can reach 175 GPa, and it changes very little as temperature increases. The fluctuation of elastic constants has slight influences on SAW velocity and the electric-mechanical coupling factor. When the propagation angle is 151, it possesses the stablest SAW properties and the largest electric-mechanical coupling factor which can reach 0.7%. The comprehensive analyses of the thermal, mechanical and SAW properties show that Y-cut Ga3PO7 possesses a greater potential application in high temperature environment.
Keywords: Ga3PO7 crystal/
density functional theory combined with quasi harmonic approximation/
thermal properties/
acoustic surface wave
