Structural evolution, dielectric, electric, and energy storage properties of BaTi1‐xLixO3‐3xF3x oxyfluorides

Abstract

AbstractSintering behavior, structural evolution, dielectric, electric, and energy storage properties of BaTi1‐xLixO3‐3xF3x (x = 0–0.10) oxy fluorides have been investigated by X‐ray diffraction, Raman spectroscopy, scanning electron microscopy (SEM), impedance, and ferroelectric analyzer in this paper. The oxy‐fluoride ceramic (x = .06) could be densified at ∼1000°C/2 h in an N2 atmosphere without reduction of Ti4+. The solid solutions experienced a transformation from a tetragonal phase into a pseudo‐cubic phase at room temperature with increasing doping levels, exhibiting typical relaxor features. Pseudo‐cubic phase with a small amount of residual tetragonal phase could be observed in x = .02, while a trace amount of BaF2 secondary phase appeared, resulting in the formation of oxygen vacancies in the x ≥ 0.08 compositions. Temperature‐dependent Raman analysis of the doped compositions seems to imply the presence of local polar clusters even above the Burns temperature. Insulation of the grain could be improved by appropriate doping of BaLiF3 due to an increase in the band gap, whereas high‐level doping (x > 0.06) leads to a decrease in insulation due to the formation of oxygen vacancies (BaTi0.94‐xLi0.06+xO2.82‐2xF0.18+x). Optimized energy storage properties with recoverable energy density Wrec = 2.92J/cm3, efficiency η = 85%, and breakdown strength (BDS) = 315 kV/cm can be achieved at x = .06 composition. Sintering of BaTi1‐xLixO3‐3xF3x in the ambient atmosphere leads to the deterioration of the dielectric, electric, and energy storage properties compared with the counterpart sintered in N2 due to the formation of F− vacancies (BaTi0.94Li0.06O2.82+xF0.18‐2x).