Prasun Ganguly

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.

Investigations of Structural, Dielectric and Electrical Behaviour of Calcium Substituted Ba5NdTi3Nb7O30 Ferroelectric Ceramics

In the present work, the effect of partial substitution of barium by calcium in Ba5NdTi3Nb7O30 has been investigated. The samples were synthesized by solid state reaction method and studied for their structural, dielectric, conductivity and ferroelectric properties. The X-ray diffractograms confirm the formation of single phase orthorhombic tungsten-bronze structure. Detailed dielectric properties of the compounds as a function of frequency and temperature show that the compounds undergo non-relaxor type ferroelectric-paraelectric phase transition of diffuse nature. An increase in Curie temperature (Tc ) from 100°C to 140°C is observed on the substitution of calcium. The Polarization–Electric field (P-E) studies show that the remanent polarization (2Pr ) increases on the substitution of calcium in Ba5NdTi3Nb7O30. The temperature dependence of dc-conductivity shows that the conductivity increases with increase in temperature revealing the negative temperature coefficient of resistance (NTCR) behaviour of the compounds.

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.

Enhancement of Dielectric Properties by Optimization of Sintering Condition in Ba5SmTi3Nb7O30 Prepared by Mechanical Activation Process

In this work, polycrystalline Ba5SmTi3Nb7O30 tungsten–bronze structured ferroelectric ceramics were synthesized by mechanical activation process using a high-energy planetary ball mill followed by sintering at different sintering temperatures and durations. The X-ray diffractograms reveal the formation of the compounds in orthorhombic crystal system. Scanning electron microscopy (SEM) has been used for the microstructural investigation. Detailed dielectric properties of the compounds have been studied as a function of temperature and frequency. The dielectric constant is found to increase with the increasing sintering temperature and duration. The temperature dependence of ac conductivity of the compound at different sintering conditions has been investigated.

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.

Synthesis and characterization of vanadium doped SrBi2Nb2O9 ferroelectric ceramics

Samples of compositions SrBi2VxNb2¿xO9, x = 0.0, 0.1, 0.3, 0.5 were prepared by solid-state reaction technique using high purity oxides/carbonates. The samples were calcined at 700°C and sintered at 900°C. XRD diffractograms show that a single phase layered perovskite structure is formed in all the samples. Effect of partial substitution of pentavalent niobium ion (0.68A°) by smaller pentavalent vanadium ion ( 0.59A°) at B site on the microstructural, Curie temperature, dielectric constant and dielectric loss have been investigated. Partial substitution of Nb5+ by V5+ is observed to have a profound effect. Dielectric properties of SBVN were investigated from room temperature to 500 °C and frequency of 100 Hz to 1 MHz. Dielectric constant values at their respective Curie points are observed to increase with increasing vanadium concentration. An overall increase in Curie temperature is also observed with increasing vanadium concentration. Strong relaxor like dielectric relaxation at the transition temperature have been observed. With increasing vanadium concentration the dielectric loss is observed to increase significantly. It is also observed that dielectric loss increases with increase in temperature.

Structural, dielectric and electrical studies of Ba5SmTi3Nb7O30 ferroelectric ceramics

Ferroelectric materials have significant scientific and industrial applications. Out of different structural groups of ferroelectric materials, tungsten-bronze structured ferroelectric materials have attracted attention of researchers because of their interesting ferroelectric, pyroelectric, piezoelectric and nonlinear optical properties. In this work, specimen of composition Ba5SmTi3Nb7O30, a tungsten bronze structured material, was prepared and investigated. The preparation conditions for this compound have been optimized. X-ray diffraction (XRD) analysis reveals the formation of single-phase compound with orthorhombic structure. Scanning electron microscopy was used to investigate grain morphology of the material. The average grain size of the compound is found out to be in the range of 4 ¿m. Dielectric properties of the compound have been studied as a function of frequency and temperature. The variation of dielectric constant (¿¿r) with temperature at various frequencies show that the compound undergoes a diffuse type ferro - paraelectric phase transition. At different frequencies, the variation of dielectric loss (tan ¿) with temperature shows that the loss is almost constant initially but at higher temperatures it increases sharply. The frequency dependence of dielectric constant and loss show a decreasing trend upto 10 kHz and beyond this frequency it remains almost constant. The temperature dependence of ac and dc conductivity of the compound have been investigated. The activation energy has also been calculated from the Arrhenius plot.