Structural, dielectric, electromechanical, piezoelectric, elastic and ferroelectric properties of lanthanum and sodium co-substituted barium titanate ceramics

In this paper, the polycrystalline ceramics Ba(1-x) (La, Na)xTiO30≤x≤0.08 were synthesized by microwave assisted heating of the starting materials. Room temperature X-ray diffraction along with Rietveld refinement analysis confirmed the formation of single-phase polycrystalline compound with the tetragonal crystal structure. A dense microstructure with several grains having different size distribution throughout the sintered pellet has been observed. The incorporation of La3+ and Na+ ions in BaTiO3 enhanced the room temperature relative permittivity. The studies of the temperature dependence of dielectric permittivity indicate ferroelectric-paraelectric phase transition with a clear shift in the Curie temperature (Tc) of BaTiO3 towards lower temperature side on co-substitution. The co-substituted sample with x = 0.08 exhibited superior dielectric constant (ɛ' = 4226) with low dielectric loss (tanδ = 0.0113) which is highly essential for the fabrication of ceramic capacitors. Resonance and antiresonance characteristics of impedance and phase for poled Ba(1-x)(La,Na)xTiO3 samples have been investigated in the frequency range of 300 kHz-1 MHz. Based on IRE standards for piezoelectric ceramics the piezoelectric response has been discussed. The room temperature P-E loop is investigated at an applied electric field of 80 kV/cm at 33 Hz frequency using Precision Premier II.