Dielectric, pyroelectric, and ferroelectric studies in (1 - x)AgNbO3- x FeNbO4 lead-free ceramics

Abstract

In the present study, the effect of heterovalent Fe³⁺ ions on the dielectric, pyroelectric, and ferroelectric properties of the (1 - x)AgNbO₃-xFeNbO₄ (x = 0.005, 0.01, 0.025, 0.05, and 0.1) system was investigated. The substitution of smaller ionic radius Fe³⁺ in B-sites and the formation of FeNbO₄ as a secondary phase contributed to improved dielectric performance, especially the pyroelectric effect, of (1 - x)AgNbO₃-xFeNbO₄ ceramics by generating electron-rich ceramics. The (1 - x)AgNbO₃-xFeNbO₄ ceramics were prepared by conventional solid-state sintering. Pure AgNbO₃ had a perovskite crystal structure with an orthorhombic crystal system, but the FeNbO₄ in (1 - x)AgNbO₃-xFeNbO₄ ceramics was formed as a secondary phase with a monoclinic structure. In addition, the XRD and Raman spectroscopy data showed that some Fe³⁺ was substituted into B-sites of AgNbO₃. The introduction of FeNbO₄ effectively reduced the average grain size from 1.85 ± 0.09 μm to 1.22 ± 0.03 μm for pure AgNbO₃ and 0.9AgNbO₃-0.1FeNbO₄, respectively. In addition, the relative density of the (1 - x)AgNbO₃-xFeNbO₄ ceramics decreased from 97.96% ± 0.01 for x = 0 to 96.75% ± 0.03 for x = 0.1. The real part of the permittivity ε', at room temperature, increased from 186.6 for x = 0 to a value of 738.7 for x = 0.1. Additionally, the maximum pyroelectric coefficient increased fivefold, reaching values of 2270 nC cm^-2 K^-1 for x = 0.1. Furthermore, a harvested pyroelectric energy density (W) of 1140 μJ cm^-3 for x = 0.025 was achieved, which is appreciably higher than the 840 μJ cm^-3 value for x = 0.