• A K Jha

      Articles written in Bulletin of Materials Science

    • Dielectric and complex impedance studies of BaTi0.85W0.15O3+𝛿 ferroelectric ceramics

      Sheela Devi A K Jha

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      In the present work, tungsten substituted barium titanate have been synthesized and studied. The structural analysis indicates that the specimen is a single phase material with tetragonal crystal structure. The observed polarization–electric field hysteresis loop confirms the ferroelectric nature of the prepared compound. Variation of dielectric constant with temperature at different frequencies shows that the compound has a dielectric anomaly at 75 °C and exhibits diffuse type phase transition. Variation of dielectric loss with temperature at different frequencies shows a decrease in loss with increasing frequency. The Nyquist plots (Cole–Cole plots) have been measured at temperatures 325 °C, 345 °C and 365 °C. The plot at 365 °C shows a grain boundary effect. Relaxation time has been found to decrease with the rise in temperature and obey the Arrhenius relationship. The variations of d.c. conductivity as a function of temperature have also been studied.

    • Structural, dielectric and electrical properties of CaBa4SmTi3Nb7O30 ferroelectric ceramic

      Prasun Ganguly A K Jha

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      The polycrystalline sample of CaBa4SmTi3Nb7O30, a member of tungsten bronze family, was prepared by solid-state reaction method. X-ray diffraction analysis shows the formation of single-phase compound with an orthorhombic structure at room temperature. Scanning electron micrograph of the material shows uniform distribution of grains. Detailed studies of dielectric properties of the compound as a function of temperature at different frequencies suggest that the compound has a dielectric anomaly of ferroelectric to paraelectric type at 198°C, and exhibits non-relaxor kind of diffuse phase transition. The ferroelectric nature of the compound has been confirmed by recording polarization–electric field hysteresis loop. Piezoelectric and pyroelectric studies of the compound have been discussed in this paper. Electrical properties of the material have been analyzed using complex impedance technique. The Nyquist plots manifest the contribution of grain boundaries (at higher temperature), in addition to granular contribution (at all temperatures) to the overall impedance. The temperature dependence of dc conductivity suggests that the compound has negative temperature coefficient of resistance (NTCR) behaviour. The frequency dependence of ac conductivity is found to obey Jonscher’s universal power law. The observed properties have been compared with calcium free Ba5SmTi3Nb7O30 compound.

    • Electrical characterization of zirconium substituted barium titanate using complex impedance spectroscopy

      Priyanka A K Jha

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      This paper reports complex impedance analysis of polycrystalline complex perovskite structured BaZr0.025Ti0.975O3 prepared by solid state reaction method. XRD analysis reveals the formation of single phase perovskite structure. SEM has been used to investigate grain morphology of the material. Impedance plots have been used as a tool to analyse electrical properties of the sample as a function of frequency and temperature. Bulk resistance is observed to decrease with an increase in temperature showing a typical negative temperature coefficient of resistance (NTCR) type behaviour. Nyquist (Cole–Cole) plots show both inter and intra grain boundary effects. Relaxation time is found to decrease with increasing temperature and it obeys the Arrhenius relationship. The variation of d.c. and a.c. conductivity as a function of temperature is also reported.

    • Structural and mechanical behaviour of 5% Al2O3-reinforced Fe metal matrix composites (MMCs) produced by powder metallurgy (P/M) route

      Pallav Gupta Devendra Kumar Om Parkash A K Jha

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      The aim of this paper is to investigate the effect of sintering temperature and time on the properties of Fe–Al2O3 composite (5 wt% Al2O3; 95 wt% Fe) prepared by powder metallurgy process. X-ray diffraction, microstructure, density, hardness and compressive strength of prepared samples have been investigated. XRD studies show the presence of Fe and Al2O3 along with iron aluminate phase. Iron aluminate is formed as a result of reactive sintering between iron and alumina particles. Microstructural examination of the specimen showed a dense structure with nanosize dispersion of the reinforcement of ceramic phase. Density as well as hardness of specimens depend on the formation of iron aluminate phase, which in turn depends on sintering temperature and time.

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