Electrical and electromechanical studies in ferroelectric Gd³⁺ modified lead potassium niobate ceramics

The change in dielectric constant relaxation time over temperature (35-590 °C) and frequency (45 Hz-5 MHz) in ceramics of Pb_0.77K _0.115Gd_0.115Nb₂O₆ (PKGN, T _c = 340 °c) has been studied. Powder X-ray diffraction revealed the single-phase formation with orthorhombic crystal structure. The P-E hysteresis loop parameters are P_s = 21.77 μC/cm², P_r = 17.09 μC/cm², E_c = 11.86 kV/cm; the piezoelectric constants, K_p = 31.7%, K_t = 47%, d ₃₃ = 115 × 10^-12 C/N, d₃₁ = -41 × 10^-12 C/N, are determined in the material and some transducer applications are discussed. Cole-Cole (Z^ll vs. Z^l) plots showed a non-Debye type relaxation. Conductivity obeyed Jonscher's universal power law, σ = σ₀ + Aωⁿ. The theoretical values of ε^l and σ are computed using the parameters 'A(T)' and 'n(T)' (0 < n < 1) and are well fitted with the experimental data. The hopping ion frequency (ω_p) and charge carrier concentration (K^l) have been analyzed using Almond-West formalism. The dielectric relaxation processes are associated with localized oxygen vacancies conduction at high frequency region. A long-range conductivity by Gd³⁺ ions is found to be predominant at low frequency region. The activation energies from impedance and modulus formalisms revealed the ionic type conduction in PKGN.