Weak ferroelectricity and low-permittivity microwave dielectric properties of Ba2Zn(1+x)Si2O(7+x) ceramics

Ba2Zn(1+x)Si2O(7+x) ceramics were prepared using the conventional solid-state method at 1200 °C for 3 h in air. Apart from the previously reported Ba2Zn(1+x)Si2O(7+x) (x = 0) with a monoclinic structure (C 2/c), the end-member compositions at x = −1 and 1 exhibit single-phase β-BaSiO3 with an orthorhombic structure (P212121) and BaZnSiO4 with a hexagonal structure (P63), and possess a coexistence of weak ferroelectricity and low-permittivity microwave dielectric properties. A reduction in Zn2+ content mainly decreases the intensity of the εr anomaly peak at lower temperature and increases the εr (or frequency) stability against temperature. The Zn2+-rich BaZnSiO4 phase has a τf value of −181 ppm/°C, whereas the τf value of Zn2+-free BaSiO3 phase decreases to −35.4 ppm/°C. The Zn2+ deficiency in Ba2ZnSi2O7 composition could inhibit the presence of BaZnSiO4 phase and improve the τf value, whereas excessive Zn2+ cations prompt the formation of the BaZnSiO4 phase to deteriorate significantly the τf value.