Crystal structure, lattice energy and microwave dielectric properties of melilite-type Ba1-xSrxCu2Si2O7 solid solutions

Abstract Ba1-xSrxCu2Si2O7 solid solutions with melilite-type structure were synthesized by solid-state reaction method. The Rietveld refinement, P-V-L theory and impedance spectroscopy were carried out for Ba1-xSrxCu2Si2O7 to investigate the correlations between the crystal structure and microwave dielectric properties. Single BaCu2Si2O7 phase with orthorhombic structure (Pnma) was obtained in the range of 0–0.35. The corrected dielectric constant (er-corr) showed a monotonously decreasing trend with the x value, which was caused by decreasing of total bond susceptibility (Σχμ) and ionic polarizability of primitive unit cell ( α D T /Vm). The variation of Q×f value was closely correlated to the total lattice energy (Ucal) and activation energy (Ea) of Ba1-xSrxCu2Si2O7. The Q×f value increased linearly until reaching the maximum value (51515 GHz) at x = 0.20 and then decreased. The temperature coefficient of resonant frequency (τf) presented an opposite trend with the Q×f value and it was dominated by the lattice energy (ΣU(Cu-O)) and the susceptibility of Cu-O bond (χ(Cu-O)). Moreover, excellent microwave dielectric properties were achieved at x = 0.20 with er = 8.43, Q×f = 51515 GHz and τf = −29.70 ppm/°C.