Sheela Devi

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

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 coefficient with temperature is reported in the present work. Pyroelectric figure of merit have been calculated from the pyroelectric coefficients.

Structural, Dielectric and Ferroelectric Studies of Molybdenum Substituted Sr2Bi2Nb2O9 Ferroelectric Ceramics

In the present work, samples of compositions SrBi 2 Nb 2 O 9 and SrBi 2 Nb 1.9 Mo 0.1 O 9 were prepared by solid state reaction method. X ray diffraction analysis reveals the formation of single phase perovskite structure. Although the perovskite structure of SBN is retained but slight change in the lattice parameters is observed. Dielectric constant and dielectric loss have been measured as a function of temperature (300 K–800 K) and frequency (1 kHz, 10 kHz and 100 kHz). Peak Dielectric constant is observed to increase from 465.05 for pure SBN to 613.17 for molybdenum substituted SBN while Curie temperature is observed to decrease from 420°C for pure SBN to 365°C for molybdenum substituted SBN. Dielectric loss is observed to increase from 0.066 for pure SBN to 0.123 for the doped sample at their respective Curie temperature. P-E loops have been recorded and retentivity and coercevity have been determined. The coercive field and remanant polarization values are observed to decrease from 10.647 μzv/c.m. and 0.437 μc/c.m. 2 for pure SBN to 8.989 μv/c.m. and 0.338 μc/c.m. 2 for molybdenum substituted SBN.

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

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 from 120°C to 85°C in the tungsten substituted sample. The temperature dependence of dc conductivity of the compound have also been investigated.

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 oscillators and detectors. It has been reported that various non-ferroelectric compound such as carbon nanotubes (CNT), ferrites and microwave dielectrics are used for electrically tunable dielectric materials. This review paper gives overall summary of tungsten bronze ferroelectric ceramics on developing electrically tunable ferroelectric material and improving performance of dielectric material for various applications in microwave devices.

Synthesis and characterization of polycrystalline Ba5CaTi2-xMxNb8O30 (M=Cu) tungsten bronze electro ceramics

ABSTRACT The polycrystalline electro ceramic of composition Ba5CaTi2-xCuxNb8O30 (x = 0.0, 0.02) is synthesized using high-temperature solid state reaction technique. The synthesized ceramics studied for their structural and ferroelectric properties. X-ray diffraction (XRD) analysis reveals the formation of single-phase compound structure at room temperature with tetragonal tungsten bronze structure. Scanning electron microscope (SEM) depicts that the compound has well defined grains. The average grain size of the compound is observed in range (∼5 to 8 μm). The ferroelectric nature has been confirmed by recording polarization–electric field hysteresis loop. Raman Spectra at room temperature used to study the internal lattice properties of the ceramics.

Structural, Dielectric and Ferroelectric Studies of Tungsten Substituted Barium Strontium Titanate

In the present work, effects of tungsten substitution on the microstructure, dielectric constant, dielectric loss and polarization in barium strontium titanate ferroelectric ceramics have been investigated. Samples of compositions Ba0.8Sr0.2Ti1-x WxO3 (x = 0.0, 0.05) were prepared by solid state reaction method. The dielectric measurements were carried out from −60°C to100°C at 1 kHz, 10 kHz and 100 kHz. X-ray diffraction analysis reveals the formation of single-phase perovskite tetragonal structure. The present work concludes that tungsten substitution in BST at titanium site changes lattice parameters and tetragonal strain. This results in the change of curie temperature, dielectric constant and dielectric loss. P-E hysteresis loops were recorded and the remanent polarization and coercevity have been determined.

Ferroelectric, pyroelectric and piezoelectric studies in Ba 5 SmTi 3 Nb 7 O 30 ceramic

In the present work, the polycrystalline sample of Ba<inf>5</inf>SmTi<inf>3</inf>Nb<inf>7</inf>O<inf>30</inf>, a member of tungsten bronze family, was prepared by solid-state reaction method and studied for their ferroelectric, pyroelectric and piezoelectric properties. 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. The average grain size of the compound is observed to be in the range of 2 µm. The temperature variations of polarization—electric field (P-E) loops of the compound have been reported. The remanent polarization (2P<inf>r</inf>) value of the compound is found to be ∼ 2.3 µC/cm² at room temperature. The variation of pyroelectric coefficient with temperature is reported. Pyroelectric figure of merit have been calculated from the pyroelectric coefficients. Piezoelectric coefficients (d<inf>33</inf> and g<inf>33</inf>) of the compound have also been measured.

Effect of sintering temperature on dielectric properties of tungsten doped barium titanate

In the present work, samples of compositions BaTi1¿xWxO3; x= 0.00 and 0.15 were synthesized by solid-state reaction technique at various sintering temperatures of 1200°C, 1250°C and 1300°C and durations 2hr and 5hr. The X- ray diffractograms analyses reveal the formation of the samples having single phase crystalline structure. Tetragonal strain of the samples has been calculated and its variations with sintering temperature and duration have been studied. Particle size of the studied samples has been found to change with sintering temperature and duration. Dielectric properties of the samples have been studied as a function of temperature and frequency. The variation of dielectric constant (¿r) with temperature shows that the samples undergo a diffuse type ferro - paraelectric phase transition. The dielectric constant is found to increase with increasing temperature and duration. Variation of dielectric loss (tan¿) with temperature have also been measured. Further, diffusivity of the samples have been calculated and is reported in this paper.

Interdependence between electrical and magnetic properties of polycrystalline cobalt-substituted tungsten bronze multiferroic ceramics

Polycrystalline cobalt-substituted tungsten bronze ferroelectric ceramics with chemical composition Ba5CaTi2−xCoXNb8O30 (x=0.00, 0.02, 0.04 and 0.08) were synthesized by solid state reaction technique. X-ray diffraction (XRD) technique was used to confirm the phase formation and it revealed the formation of single phase tetragonal structure with space group P4bm. The surface morphology of the samples was studied by using the scanning electron microscopy (SEM) technique. The dielectric properties such as dielectric constant and dielectric loss have been investigated as a function of temperature and frequency. The P–E and M–H studies confirmed the coexistent of ferroelectricity and magnetism at room temperature. The P–E loop study indicated an increase in the coercive field while the M–H study depicted a decrease in the magnetization with the incorporation of cobalt ions.

Microstructural and Electrical Characterization of W Substituted Barium Strontium Titanate Ferroelectric Ceramics

In the present work, the effect of partial substitution of titanium by tungsten has been investigated. X-ray diffractograms confirm the formation of single phase pervoskite structure. SEM micrograph shows randomly distributed grains in the sample. Variations of dielectric constant with temperature at different frequencies show that compounds undergo a ferroelectric to paraelectric phase transition at 296 K. A well defined hysteresis loop is formed at room temperature. Variation of dielectric loss with temperature at different frequencies shows a decrease in loss with increasing frequency. The Nyquist plots (Cole–Cole plots) were plotted at temperatures 285°C, 310°C and 335°C. The variation of dc conductivity as a function of temperature has also been studied.