Muffle and microwave furnaces (VB CERAMIC CONSULTANTS, Chennai, India) were used to sinter the green pellets at 1100 °C for 12 h and 30 min, respectively. The microwave and traditional sintering heating rates were 50 and 5 °C min−1, respectively. Studies employing X-ray diffraction (XRD) were performed using the X-ray diffractometer (Bruker D8 Advance, Karlsruhe, Germany equipped with a 2.2 kW Cu anode and Ni filter over the 2ϴ range of 20–80°, with a step size of 0.05. Field emission-scanning electron microscope (FE-SEM) (Thermo Fisher FEI QUANTA 250 FEG) at 20 keV was used for microstructure investigation and energy dispersive spectroscopy (EDS) analysis of europium-doped CCTO samples. Samples were sputter coated with a thin film of noble metals to offer conductivity before microscopic analysis. Moreover, the samples were thermally etched at 950 °C for 15 min in a standard furnace to easily distinguish the grain and grain boundaries. For the purpose of determining the bonding energies of valence electrons and their function in IBLC, X-ray photoelectron spectroscopy (XPS; ULVAC-PHI, Inc; Model: PHI5000 Version Probe 94 III) was employed in conjunction with an Al monochromatic radiation source at 280 eV. Broadband dielectric spectrometer (BDS) measurements included dielectric constant (ε), tan δ, and relaxation peaks (Concept 80, Novocontrol Technologies, Montabaur, Germany). A silver adhesive paste of sheet resistance 0.25/square at 0.001 mm in thickness (Thermo Fisher Scientific India Pvt Ltd., Mumbai, India) was applied to both ends of the pellets, and then heat treated at 150 °C for 1 h to generate electrodes, which facilitated the dielectric measurement.
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