Phase formation, dielectric and ferroelectric properties of CaxBa1−xNb2O6 ceramics

Lead-free CaxBa1−xNb2O6 (CBN, 0.20≤x≤0.35) ceramics were prepared by the conventional solid state method. Effects of Ca content on the phase formation, microstructure, dielectric and ferroelectric properties for the prepared CBN ceramics were systematically studied. XRD results showed that pure CBN phase with tungsten bronze structure could be obtained from the solid solutions of BaNb2O6 and CaNb2O6 in all ceramics. Higher Ca contents favored the occurrence of grains with anisometric morphology, but no abnormal grain growth could be found in all compositions. With the increase of x, Curie temperature Tc shifted downward, whereas the maximum dielectric constant εm increased initially and then decreased. All the ceramics showed an intermediate relaxor-like behavior between normal and ideal relaxor ferroelectrics according to the modified Curie–Weiss law. Normal ferroelectric hysteresis loops were observed in all compositions. Both remnant polarization Pr and coercive field Ec increased initially and then decreased with the increase of x. The ceramics with homogeneous microstructure, high density and better properties were obtained at x=0.28 with εm=2998, Tc=234 °C, Pr=3.98 μC cm−2 and Ec=14.03 kV cm−1.