Atomic and micro-scale structural investigation of Bi/Cu and Bi–Cu-doped BCZT with dielectric properties

In recent years, environment-friendly lead-free dopants-incorporated Ba-based perovskite oxides have found their potential applications in electronic devices due to their improved performances by modifying the crystal structures. In this study, BCZT [Ba0.9Ca0.1Zr0.1Ti0.9O3], Bi-doped BCZT [(Ba0.9Ca0.1)0.925Bi0.05Zr0.1Ti0.9O3], Cu-doped BCZT [Ba0.9Ca0.1(Zr0.1Ti0.9)0.997Cu0.003O3], and Bi–Cu both doped BCZT [(Ba0.9Ca0.1)0.925Bi0.05(Zr0.1Ti0.9)0.997Cu0.003O3] were prepared by conventional solid-state reaction method to study the effect of doping from microscopic and atomic point of view. XRD and Rietveld techniques are used to identify and quantify the phases, respectively. FTIR study confirmed the modification of the cell parameters due to doping, based on its composition. Raman spectroscopy is used to study the nature of symmetry presence in BCZT ceramics before and after doping. It reveals the presence of trace amount of orthorhombic symmetry with Tetragonal in all samples, as well as little cubic symmetry observed in BCZT-Bi and BCZT-BiCu. FESEM is used to study the surface morphology along with different grains in BCZT with doping. Localized structural distortion originated by dopants was investigated by the Atomic Pair Distribution Function (PDF) method. Aside from average structure, PDF gives information about localized structure within short-range zone, which is significantly modified, whereas long-range structure is almost similar. PDF shows the Raman-predicted orthorhombic phase is not exactly orthorhombic but the distorted tetragonal phase. Ultraviolet–visible (UV–vis) spectra show the bandgap energy increased after doping in BCZT. Dielectric measurement of all samples shows a high dielectric constant (>2000), and it is shown that vacancy in the crystal plays an important role in the dielectric behavior with frequency. The average and atomic–scale structure of Bi/Cu and Bi–Cu doped BCZT helped to understand the dielectric behavior for potential application of the barium titanate complex perovskites.