• Shail Upadhyay

      Articles written in Bulletin of Materials Science

    • Effect of composition on dielectric and electrical properties of the Sr1 −xLaxTi1 −xCoxO3 system

      Shail Upadhyay Devendra Kumar O M Parkash

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      Valence compensated perovskite system Sr1 −xLaxTi1 −xCoxO3 shows dielectric relaxor behaviour with very high value of dielectric constant in the composition range 0·20 <x < 0·40. In this paper the effect of composition on microstructure and the resulting electrical behaviour is reported. The compositions withx = 0·25, 0·30, 0·33, 0·35 and 0·37 have been synthesized by solid state ceramic method and dielectric measurements were made in the temperature range of 300–500 K and frequency range of 100 Hz to 1 MHz. Grain boundaries played an important role in their dielectric behaviour. Complex plane impedance and modulus techniques were used to separate out the contributions of grain and grain-boundaries to the resulting dielectric behaviour. It was observed that the bulk resistivity as well as the grain boundaries resistance decreased with increasingx. Furthermore, impedance analysis demonstrated that extremely high value of dielectric constant observed in these materials was due to barrier layers formation at grain-grain-boundaries interfaces.

    • High temperature impedance spectroscopy of barium stannate, BaSnO3

      Shail Upadhyay

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      Polycrystalline powder of BaSnO3 was prepared at 1300 °C using a high-temperature solid-state reaction technique. X-ray diffraction analysis indicated the formation of a single-phase cubic structure with lattice parameter: 𝑎 = (4.1158 ± 0.0003) Å. The synthesized powder was characterized using X-ray diffraction (XRD) scanning electron micrographs, energy dispersive X-ray analysis, differential thermal analysis, thermogravimetric analysis and Fourier transform infrared techniques. Electrical properties were studied using a.c. impedance spectroscopy technique in the temperature range of 50–650 °C and frequency range of 10 Hz–13 MHz. The complex impedance plots at temperature ≥ 300 °C show that total impedance is due to the contributions of grains, grain boundaries and electrode. Resistance of these contributions has been determined. Variation of these resistances with temperature shows the presence of two different regions with different slopes. The nature of variation for the above three resistances, in both the temperature regions confirms that conducting species (phases) responsible for grain, grain boundaries and electrode are the same. Based on the value of activation energy, it is proposed that conduction via hopping of doubly ionized oxygen vacancies ($V^{\bullet \bullet}_{o}$) is taking place in the temperature region of 300–450 °C, whereas in the temperature region of 450–650 °C, hopping of proton, i.e. OH$^{\bullet}$ ions occurs.

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