Optical and electrical conductivity of secondary phase of Sr2+/Ca2+ doped La1-xSrx/CaxNbO4 (0≤x≤0.4)

Abstract

In the present study, Sr2+ and Ca2+ ions doped lanthanum niobate (LaNbO4) samples are synthesized using the solid-state reaction method. The effect of sintering temperature on physical, optical and electrical properties are investigated of the pristine and Sr2+/Ca2+ doped LaNbO4 samples using by characterization facilities such as X-ray diffraction, Fourier transform-infrared spectroscopy, thermal gravimetric analysis, scanning electron microscopy & energy-dispersive spectroscopy, UV–Vis spectrophotometer. The observed monoclinic phase is confirmed by XRD. The optical bandgap of LNS samples (3.11 eV–2.08 eV) and LNC samples (2.95 eV–2.86 eV) are calculated. The electrical conductivity of the Sr2+/Ca2+ doped LaNbO4 samples are evaluated by using and Impedance analyzer from ambient temperature to 900 °C, where, the highest conductivity (1.01 × 10−1 Scm−1 at 900 °C) is observed for LNS-4 with 80 % relative density due to presence of higher oxygen vacancies. It is observed that the Sr2+ doping is more effective than Ca2+ doping for enhancing the protonic conductivity of the LaNbO4 system. The doping of Sr2+ and Ca2+ ions is indicated that Sr2+ based polymorphic composites could be more effective electrolytes for solid oxide fuel cell (SOFCs) applications.

Keywords

• Lanthanum niobate
• Solid-state reaction method
• Physical & optical properties
• Electrical conductivity
• SOFCs application