Effects of A1 site occupation on dielectric and ferroelectric properties of Sr4CaRTi3Nb7O30 (R = Ce, Eu) tungsten bronze ceramics

Abstract

Sr4CaRTi3Nb7O30 (R = Ce, Eu) tungsten bronze ceramics are prepared by a standard solid state reaction method. The effects of A1 site occupation on the dielectric and ferroelectric properties of Sr4CaRTi3Nb7O30 (R = Ce, Eu) tetragonal tungsten bronzes are investigated. The Sr4CaCeTi3Nb7O30 shows a normal transition behavior due to the closer size ion occupation in A1 sites, which could suppress the distortion of B2 octahedra effectively. Sr4CaEuTi3Nb7O30 ceramic exhibits two dielectric anomalies, which might be related to the fact that the large radius difference between Ca2+ and Eu3+ could lead to the uneven distribution of Ca2+ and Eu3+ in A1 sites and form two slightly different kinds of compositions with different transition temperatures in the structure. Our results indicate that the ionic radius difference in A1 sites plays an important role in determining the dielectric and ferroelectric natures of the filled tungsten bronze ceramics. Polarization—electric field (P—E) curves are evaluated at room temperature and both of them show hysteresis loops. Sr4CaCeTi3Nb7O30 shows a fat hysteresis loop, indicating the long-range ferroelectric order in the ceramic. The current density—electric field (J—E) curves are measured at room temperature with a largest leakage current density of ∼ 10−6 A/cm2, indicating that their leakage currents are rather low.