High temperature stable permittivity and large energy storage density in lead-free BiFeO3–BaTiO3 based ceramics

Lead-free piezoelectric ceramics (1–x)(0.65BiFe1.05O3–0.35BaTiO3) modified by x(BiGaO3) and x(0.96Bi0.5(Na0.84K0.16)0.5TiO3 – 0.04SrTiO3) (abbreviated as BFBT–BG (0.000 ≤ x ≤ 0.030), and (BFBT–BNKS (0.000 ≤ x... [ view full abstract ]

Lead-free piezoelectric ceramics (1–x)(0.65BiFe_1.05O₃–0.35BaTiO₃) modified by x(BiGaO₃) and x(0.96Bi_0.5(Na_0.84K_0.16)_0.5TiO₃ – 0.04SrTiO₃) (abbreviated as BFBT–BG (0.000 ≤ x ≤ 0.030), and (BFBT–BNKS (0.000 ≤ x ≤ 0.100), respectively) were synthesized by solid state reaction route. The XRD analysis revealed that the two systems possess a pure perovskite structure, without any secondary phase in the compositional range of BG and BNKS modifier. The addition of BG and BNKS caused slight change in microstructure in the host BFBT ceramics. Around critical composition (BF–BT–0.02BG) the piezoelectric constant (d₃₃) and electromechanical coupling factor (k_p) reached a maximum value of 205 pC/N, and 34.5%, respectively; at room temperature, while significant enhancement in the dielectric properties, ε_r ~ 1005, T_max = 502 ^oC, and ε_rmax =69226 (temperature range; 25–550 ^oC, at 1 kHz), while ε_rmid =2215 ± 12% (temperature range; 200–350 ^oC, at 100 kHz) were obtained for x = 0.025.  Moreover, in BFBT–BNKS system, a large energy storage density (W) up to 0.65 J/cm³ at 6 mol% of BNKS-content was exhibited from the polarization measurement under high applied electric field 100 kV/cm. This significant improvement in dielectric properties and energy storage density of the optimum specimens can be attributed to the BG and BNKS modification; respectively, which makes the system useful for temperature-stable dielectric and energy storage capacitor applications.