Eu-substitution-induced commensurate phase with enhanced ferroelectric property in Ba4(EuxLa1-x)2Fe2Nb8O30 multiferroics

Effects of Eu-substitution on the crystal structure, dielectric, ferroelectric, and magnetic properties have been systematically studied for Ba-4(EuxLa1-x)(2)Fe2Nb8O30 (x=0, 0.3, 0.5, 0.7, 0.9, 0.95, 1) tungsten bronze ceramics. The tetragonal bronze structure is confirmed in all compositions. With the increase of x, Ba-4(EuxLa1-x)(2)Fe2Nb8O30 ceramics transform from paraelectric to ferroelectric. The compositions of x=0.9, 0.95, and 1 show first-order ferroelectric phase transitions above room temperature (391K for x=0.9, 404K for x=0.95, and 425K for x=1). The ferroelectric behavior is associated with a commensurate octahedral tilting, which is caused by large A2-A1 ionic-radius difference. Magnetic hysteresis loops for all compositions at room temperature have been obtained, which could be ascribed to both the secondary phase and tungsten bronze structure per se. It is confirmed that the radius difference between A2 and A1 cations plays a critical role on the structure, dielectric, and ferroelectric characteristics.