Enhanced dielectric and piezoelectric properties of BNT-KNNG piezoelectric ceramics

Highlights: • XRD analysis revealed a rhombohedral phase confirmed by SAED and HRTEM analysis for first time. • The existence of relaxor behaviour was analyzed by Vogel-Fulcher law and Uchino-Nomura laws. • AC−conductivity of all samples obeys Mott's variable-range-hopping mechanism. • Leakage current density was analyzed by space charge limited conduction is related to deep acceptor traps. • The enhanced piezoelectric properties suitable for high power electromechanical applications. The structural, morphological and electric properties of (1-x) Bi_0.5Na_0.5TiO₃ – x K_0.5Na_0.5NbO₃ + 1 wt. % Gd₂O₃ (BNT-KNNG; x = 0–0.02) ceramics were investigated in detail. XRD studies revealed the rhombohedral phase, which is also confirmed by HRTEM. The diffuse phase transition of BNT-KNNG samples exhibited a relaxor behaviour supported by modified Curie Weiss law and Vogel–Fulcher law. The AC-Conductivity of BNT-KNNG ceramics in terms of hopping length, hopping energy and density of states across the Fermi level was analyzed by Mott's variable range hopping mechanism. The addition of KNNG effectively reduced grain size, transition temperature, leakage current and improved dielectric (ε′ = 1074 and tanδ = 0.059 @ 1 kHz) and piezoelectric properties; electromechanical coupling factors (k₃₃, k₃₁, k_t ∼ 48% and k_p = 53%), and piezoelectric constants (d₃₃ = 108 pC/N and g₃₃ = 1.14 × 10⁻² Vm/N) are observed for x = 0.01 sample, which is a potential candidate for high power electromechanical applications.