Dielectric and ferroelectric properties of unfilled tungsten bronze KBa3RNb10O30 ceramics

Unfilled tungsten bronze ceramics with general formula KBa3RNb10O30 (R = La, Pr, Nd, Sm, Eu, Gd) were prepared by the conventional solid state reaction method. XRD patterns show that all ceramics are pure tungsten bronze phase. Dielectric characterization indicates that the ceramics except KBa3GdNb10O30 are relaxors with strong frequency dispersion, while KBa3GdNb10O30 shows diffuse phase transition and belongs to classical ferroelectrics. At room temperature, the KBa3RNb10O30 compounds (R = La, Pr, Nd) are paraelectrics while the KBa3RNb10O30 compounds (R = Sm, Eu, Gd) are ferroelectrics. Among them, KBa3GdNb10O30 has the highest remnant polarization (2P (r) ) of 8.2 mu C/cm(2). Phase transition temperature, remnant polarization (2P (r) ) and tetragonality of the compounds increase with the decrease of ionic radius of the rare earths.