Crystal structure, lattice energy and microwave dielectric properties of melilite-type Ba1-xSrxCu2Ge2O7 ceramics

The Ba 1- x Sr x Cu 2 Ge 2 O 7 was successfully obtained through the solid-state reaction method, with single-phase BaCu 2 Ge 2 O 7 formed at 850 °C. Scanning electron microscopy analysis revealed the excellent chemical compatibility of Ba 1- x Sr x Cu 2 Ge 2 O 7 with silver. The properties of Ba 1- x Sr x Cu 2 Ge 2 O 7 ceramics were explained using the P-V-L theory. The ε r-corr decreased with the polarization rate (Σχ u * N b u ) and ion polarization of the unit cell. The Q×f increased with the chemical bond strength and lattice energy (U cal ), particularly the lattice energy of the Ge-O bond (U(Ge-O)). The τ f exhibited an opposite trend to the Q×f value and was influenced by the U(Cu-O) and susceptibility of the Cu-O bond (χ(Cu-O)). Sintering at 875 °C for 3 h yielded optimal microwave dielectric performance for Ba 1- x Sr x Cu 2 Ge 2 O 7 ceramics, with observed values of ε r = 9.26 ± 0.14, Q×f = 85,660 ± 4200 GHz, and τ f = −15.6 ± 1.1 ppm/°C at x  = 0.10. These promising microwave dielectric properties make Ba 1- x Sr x Cu 2 Ge 2 O 7 a potential candidate for LTCC material applications.