Structural and Electromechanical Properties of Sr-Substituted Barium Titanate (BST) as Potential Material for High Performance Electroacoustic Devices

Abstract

First-principles density functional calculations have been performed to study the electromechanical properties, i.e., elastic, dielectric, piezoelectric, and coupling factors, as well as the crystal structure for Ba1―xSrxTiO3 (BST) with 0≤ x ≤1 in the paraelectric and ferroelectric crystallographic phases. The equilibrium ground state structural parameters are calculated using the new Wu–Cohen Generalized Gradient Approximation (GGA―WC) in excellent agreement with the experimental data. The lattice stabilities in Ba1―xSrxTiO3 crystals are analysed from the doped formation energy and phonon dispersions. The mechanical quantities, such as the elastic constants (C11, C12, C44, C13, C33 and C66), mechanical moduli (Young modulus Y, Shear modulus G, Compressibility B), Poisson’s ratio and elastic anisotropy are investigated using the GGA―WC and GGA―PBEsol exchange functionals. The mechanical moduli (B, G and Y) are found to increase by increasing Sr content leads to enhance stiffness and hardness of BST systems. We find that both the para- and ferroelectric phases of all considered Ba1―xSrxTiO3 are elastically stable. The 3D surface anisotropy visualizations show that BST is a pure isotropic material at x∼ 0.5. It was found that Debye temperature (ΘD), milting temperature (TM) and acoustic wave velocities increase as the Sr content increases. The ferroelectric Ba0.75Sr0.25TiO3 (BST) exhibited high piezoelectric coefficients [d15 = 121.4 pC/N, d31= -20.5 pC/N, d33 = 89.3 pC/N], and large dielectric tensors [ε11 = 517.2, ε33 = 31.3], compared to pure BaTiO3 [d15 = 74.2 pC/N, d31= -14.1 pC/N, d33 = 65.0 pC/N; ε11 = 334.7, ε33 = 22.6]. Enhancement in electromechanical coupling factor and bulk acoustic velocity of ferroelectric BST is achieved when the Sr content is added. Ba1―xSrxTiO3 (BST) are extremely interest candidates to be used for the development of high performance electroacoustic devices such as acoustic sensors and resonators.