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

¹ Centre for Piezoelectric Transducer Materials, Department of Physics, Andhra University, Visakhapatnam, 530 003, India
² Department of Physics, GVP College of Engineering, Visakhapatnam, India
³ Department of Physics, GITAM Institute of Technology, GITAM University, Visakhapatnam, India
⁴ Department of Inorganic Materials Engineering, Kyung Pook National University, Daegu 702701, Republic of Korea

^a e-mail: konapala@sify.com

Received: 20 September 2010
Revised: 7 February 2011
Accepted: 19 April 2011
Published online: 11 August 2011

Abstract

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%, d₃₃ = 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.