Sheela Devi

Bio: Sheela Devi is an academic researcher from Maharaja Surajmal Institute of Technology. The author has contributed to research in topics: Dielectric & Ferroelectricity. The author has an hindex of 7, co-authored 26 publications receiving 154 citations. Previous affiliations of Sheela Devi include Delhi Technological University.

Dielectric and Pyroelectric Studies of Tungsten—Bronze Structured Ba5SmTi3Nb7O30 Ferroelectric Ceramics

Abstract: In the present work, sample of composition Ba 5 SmTi 3 Nb 7 O 30 was prepared by solid-state reaction method. X-ray diffraction (XRD) analysis reveals the formation of single-phase compound with an orthorhombic structure. The grain morphology of the sample has been investigated by scanning electron microscopy. Dielectric properties of the compound have been studied as a function of temperature and frequency. The variation of dielectric constant (ϵ′r) with temperature at different frequencies shows that the compound has a dielectric anomaly of ferroelectric to paraelectric type at 170°C, and exhibits non-relaxor kind of diffuse phase transition. At different frequencies, the variation of dielectric loss (tan δ) with temperature shows at lower temperatures the loss is almost constant and increases sharply at higher temperatures. The frequency dependence of dielectric constant and loss show a decreasing trend upto 10 kHz and beyond this frequency they remain almost constant. The variation of pyroelectric coe...

Phase transitions and electrical characteristics of tungsten substituted barium titanate

Abstract: In the present work, phase transitions and electrical characteristics of tungsten substituted barium titanate are reported. Structural analysis of the prepared samples was carried out to confirm the formation of the compounds in proper phase. Scanning electron micrographs of the compounds have been used to investigate the grain morphology of the material. The dielectric properties of the samples have been studied as a function of temperature and frequency. The variation of dielectric constant ( e r ) with temperature shows a diffuse kind of ferro–paraelectric phase transition. The diffusitivity of the phase transitions has been calculated. Complex impedance spectroscopy analysis was carried out to investigate the electrical characteristics of the specimen.

A review on tungsten bronze ferroelectric ceramics as electrically tunable devices

Abstract: Ferroelectric ceramics are the most promising material for electrically tunable devices and found its application in microwave devices such as phase shifters, varactors and tunable oscillat...

Effect of W Substitution on Structural, Dielectric and Electrical Properties of BaTiO3 Ferroelectric Ceramics

Abstract: Barium titanate is used as material for many important and widely used ceramic components and devices such as high permittivity ceramic capacitors, piezoelectric ceramic transducers and thermisters with positive temperature coefficient of resistivity (PTCR) [1, 2, 3, 4]. Samples of compositions BaTi 1 − x W x O 3 ; x = 0.0, 0.15 were prepared by solid-state reaction technique using high purity oxides/carbonates. The samples were calcined at 1150°C for 2 hrs and sintered at 1200°C and 1300°C for 2 hrs. XRD diffroctgrams show that a single phase layered perovskite structure is formed in the samples. Lattice parameters and tetragonal strain (c/a) are observed to decrease in the substituted sample. Dielectric constant and dielectric loss have been measured as a function of temperature and frequency. The variations of dielectric constant (ϵ r ) with temperature at various frequencies show that the compounds undergo a diffuse type ferro—paraelectric phase transition. Curie temperature is observed to decrease fr...

Dielectric and complex impedance studies of BaTi 0·85 W 0·15 O 3+δ ferroelectric ceramics

Abstract: 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.