Microstructure evolution, dielectric response, and conduction mechanism of La1–xYxFeO3, (0 < x < 0.3) annealed perovskites synthesized via a sol–gel combustion technique

Abstract

The structural and dielectric characteristics of nano-crystalline La1−xYxFeO3, (0 < x < 0.3) perovskite samples synthesized through the citrate auto-combustion route were investigated. The findings of X-ray diffraction (XRD) analysis revealed that the synthesized perovskites exhibited a polycrystalline orthorhombic structure with a space group Pnma. Furthermore, the tolerance factor was indicative of the phase stability of the orthoferrite series. Based on the refined XRD data, the size of the crystallites was estimated to be between 11.9 and 18.5 nm using size-strain plots (SSP). To gain more insight into the crystal structure, high-resolution transmission electron microscopy (HRTEM) was employed. The estimated size based on HRTEM calculations agreed with the XRD findings. The influence of annealing temperature on the frequency dependence of the dielectric response was thoroughly investigated for nano-crystalline La1−xYxFeO3 perovskites. The investigation took place at room temperature as well as different annealing temperatures, with a comprehensive frequency range of 50 Hz to ~ 2 MHz. The incorporation of Y3+ ions into LaFeO3 (LFO) has resulted in a significant enhancement of the dielectric constant values. This improvement is attributed to the successful integration of Y3+ ions, which have effectively modified the electrical properties of LFO. Furthermore, the annealing has been shown to enhance both the values of the dielectric constant, ε1(ω) and ε2(ω), which are critical parameters for electronic devices. Based on a power law response, the AC conductivity displays an increase with dopant concentration and frequency. Additionally, it has been noted that the activation energy value for LFOY30 is slightly reduced by 0.01 eV in comparison to pure LFO. The AC conductivity of LFOY30 was observed to increase with thermal annealing over the temperature range of 333 K to 463 K. This result confirms the occurrence of thermally activated conduction in the material. Based on this finding, LFOY30 is deemed appropriate for use in applications that require effective heat dissipation. The frequency exponent, s, decreases with increasing temperature from 0.87 to 0.56 for LFO and from 0.488 to 0.42 for LFOY30, respectively, which is associated with the correlated barrier hopping (CBH) model. The maximum barrier height (WM) was around 0.26 eV. The loss tangent (tanδ) variation was estimated as a function of frequency at different dopant concentrations and temperatures. Doping and annealing have been identified as appropriate measures for enhancing the electrical properties of the La1−xYxFeO3 system, thereby making it a useful material for electronic devices.