Zirconium and lanthanide effects on the structural, dielectric and optical properties of Na0.8Ba0.2Nb0.8Ti0.2O3 ferroelectric ceramic

Lead-free ferroelectric Na-0.8(Ba(1-y)Ln(2y/3))(0.2)Nb-0.8(Ti1-xZrx)(0.2)O-3 perovskites are prepared by solid solution reaction method. The effects of zirconium and lanthanide (Er, Pr) incorporation on their structural, dielectric and photoluminescence properties are investigated. The room temperature XRD analysis revealed that all the ceramics are crystallized in single-phase perovskite structure, presenting a tetragonal structure with P4mm space group. Large crystal-lattice and BO6-octahedron distortions are induced in doped ceramics. Unexpected crystallite growth and large microstrain with Zr content increasing are evidenced through microstructural analysis. These structural features significantly influenced the dielectric and optical properties of the materials. The results show that the transition temperature T-m and the degree of diffusion of the phase transition are found to be very sensitive to both the level and the ionic size of doped elements. The incorporation of Zr and lanthanide elements led to the obtaining ferroelectric ceramics with a strong relaxer-behavior in the vicinity of ambient temperature. The Ln-doped ceramics showed intense absorption in near blue-red regions and possessed narrowed optical band gap energy. The Effective reduction of the band gap with rising Zr content and Ln-doping in relationship with the width of defect bands is discussed. Upon light excitation at 450 nm, the Er-doped ceramic exhibited strong green PL emissions at 532 nm and 559 nm, while a bright red emission at 609 nm is observed for the Pr-doped ceramic. The simultaneous existence at room temperature of relaxor-ferroelectric and luminescence properties in the Ln-doped materials could be promising for multifunctional applications such as electro-optical devices.