Structural, dielectric and ferroelectric properties of four-layer Aurivillius phase Na0.5La0.5Bi4Ti4O15

Monophasic Na0.5La0.5Bi4Ti4O15 powders were synthesized via the conventional solid-state reaction route. The X-ray powder diffraction (XRD), selected area electron diffraction (SAED) and high resolution transmission electron microscopy (HRTEM) studies carried out on the as synthesized powdered samples confirmed the phase to be a four-layer Aurivillius that crystallizes in an orthorhombic A21am space group. The microstructure and the chemical composition of the sintered sample were examined by scanning electron microscope (SEM) equipped with an energy dispersive X-ray analyzer (EDX). The dielectric properties of the ceramics have been studied in the 27–700 °C temperature range at various frequencies (100 Hz to 1 MHz). A sharp dielectric anomaly was observed at 580 °C for all the frequencies corresponding to the ferroelectric to paraelectric phase transition. Saturated ferroelectric hysteresis loops were observed at 200 °C and the associated remnant polarization (Pr) and coercive field (Ec) were found to be 7.4 μC/cm2 and 34.8 kV/cm, respectively. AC conductivity analysis confirmed the existence of two different conduction mechanisms in the ferroelectric region. Activation energies calculated from the Arrhenius plots were ∼0.24 eV and ∼0.84 eV in the 300–450 °C and 450–580 °C temperature ranges, respectively.