High thermal stability and colossal permittivity of novel solid solution LaFeO3/CaTiO3

Abstract

This study presents the novel (LaFeO3)(1-m)(CaTiO3)m (m = 0, 0.1, 0.3 and 0.5 in weight fraction) solid solutions. These materials were obtained by conventional solid-state reaction between LaFeO3 (LFO) and CaTiO3 (CTO) perovskite phases despite the favorable conditions for the composite formation. The X-Ray diffraction (XRD) confirmed the solid solution formation by isomorphic substitution of La3+ and Fe3+ by Ca2+ and Ti4+, respectively. The electric properties were studied by impedance spectroscopy (IS) from 1 Hz to 10 MHz range as a function of temperature and composition. The imaginary part of impedance (Z″), the real part of permittivity (ε′), dielectric loss (tanδ), activation energy (Ea), the real part of conductivity ac-type (σ′ac), capacitance (C) and temperature coefficient of capacitance (TCC), were determined by impedance spectroscopy (IS) analysis. The results demonstrate that the electric properties depend on m, frequency (f), and temperature (T). The colossal values of ε′ at 1 Hz and 30 °C were verified for compositions m = 0, 0.1 and 0.3 (2.59 × 104, 3.90 × 104 and 5.7 × 103, respectively). The sample LFO0.9CTO0.1 had divergent dielectric behavior from the other samples and did not follow the tendency with higher values of ε′, tanδ and lower value of Ea of the series. For this sample, the optimal conditions were determined at 18.5 kHz and 40 °C, respectively. This study indicates that ionic substitution increases the thermal stability of the LFO matrix, resulting in materials with high permittivity and considerable thermal stability, especially in the sample LFO0.9CTO0.1.