Effect of strontium concentration on electrical conduction properties of Sr-modified BaSnO3

Strontium-substituted barium stannate having a general formula Ba1-xSrxSnO3 (0 <= x <= 0.15) has been prepared by a high-temperature solid-state reaction method. The formation of the materials has been confirmed by X-ray diffraction study. A preliminary analysis of XRD data indicates a cubic unit cell as the best fit for both pure and Sr-substituted BaSnO3. The strontium substitution has resulted into modification of sample microstructure evidenced by textural changes and enhancement in the sample porosity evaluated using XRD data. The surface morphology investigated by scanning electron microscopy reveals a polycrystalline texture and a porous microstructure that has been found to increase with increase in strontium concentration. The effect of microstructural changes on doping has resulted in a modification of the electrical properties. Electrical properties investigated using impedance analysis technique indicate (i) presence of negative temperature coefficient of resistance (NTCR) behaviour that is also retained on doping (ii) evidences of single electrical relaxation attributed to the presence of bulk contribution to the electrical properties, (iii) presence of temperature dependent electrical relaxation phenomenon and (iv) an enhancement in the barrier to the mobility of charge carrier on Sr-substitution. Electrical conductivity has been found to increase substantially at higher temperature (>300 degrees C) and it may be attributed possibly to the oxygen vacancies. Conductivity spectrum analysis suggests the hopping of charge carrier among localized site as the possible mechanism for electrical conduction. The effects of Sr concentration on changes in the electrical conductivity as a function of temperature and frequency are described based on impedance spectrum analysis. (C) 2005 Elsevier Ltd and Techna Group S.r.l. All rights reserved.