Dielectric relaxation, lattice dynamics and polarization mechanisms in Bi0.5Na0.5TiO3-based lead-free ceramics

Abstract

In 0.95[0.94Bi0.5Na0.5TiO3-0.06BaTiO3]-0.05CaTiO3 ceramics, the temperature TS (dielectric permittivity shoulder at about 125 °C) represents a transition between two different thermally activated dielectric relaxation processes. Below TS, the approximately linear decrease of the permittivity with the logarithm of frequency was attributed to the presence of a dominant ferroelectric phase. Above TS, the permittivity shows a more complicated dependence of the frequency and Raman modes indicate a sudden increase in the spatial disorder of the material, which is ascribed to the presence of a nonpolar phase and to a loss of interaction between polar regions. From 30 to 150 °C, an increase in the maximum polarization with increasing temperature was related to three possible mechanisms: polarization extension favoured by the simultaneous presence of polar and non-polar phases; the occurrence of electric field-induced transitions from weakly polar relaxor to ferroelectric polar phase; and the enhanced polarizability of the crystal structure induced by the weakening of the Bi-O bond with increasing temperature. The occurrence of different electric field induced polarization processes with increasing temperature is supported by the presence of additional current peaks in the current-electric field loops.

Relaxor-to-Ferroelectric Crossover and Disruption of Polar Order in “Empty” Tetragonal Tungsten Bronzes

“…[77][78][79][80] The presence of an AFE phase was proposed due to pinched/doubled P-E loops, however other explanations have since been offered involving coexisting phases, domains or nano-regions of different symmetries and electric field driven transitions between a weakly or non-polar relaxor phase and that of a polar ferroelectric phase. [77][78][79][80][81][82][83][84] The origin for these properties is still somewhat contested and may differ in each respective solid solution. 83 From SAED we see no evidence of PNRs or subtle compositional segregation in our materials.…”

Enhanced energy storage properties of NaNbO3 modified Bi0.5Na0.5TiO3 based ceramics

“…Therefore, at electrical cycling regime, the polarization effects produced at +E F (or −E F ) can significantly recover during unloading at +E B (or −E B ). 19 With increasing temperature, four current peaks become more obvious, which means the stabilization of weakly polar phase. In addition, E F is determined to be 4.9, 2.8, 2.5, 1.9 kV/mm respectively at 25, 60, 80, 150 • C. The decreasing E F indicates reduced electric field required to induce the transition with increasing temperature.…”

Relaxor-normal ferroelectric phase transition and significantly enhanced electromechanical strain behavior in Bi(Ni1/2Ti1/2)O3–PbTiO3–Pb(Mg1/3Nb2/3)O3 ternary system close to the morphotropic phase boundary

“…This can be more clearly distinguished by looking into their J-E curves in which a single polarization current peak P1 for PMN-rich and BNTrich compositions evolved into double current peaks (P1 and P2) for compositions with 0.15 ≤ x ≤ 0.45. The appearance of two current peaks was usually ascribed to the coexistence of ergodic and nonergodic phases at room temperature [25,40,41]. As discussed above, it seemed more possible to have a coexistence of ergodic and ferroelectric phases for the x = 0.45 sample since it is located at MPB and also its T fr ' value is near room temperature.…”