Navneet Ahlawat

Effect of microwave-assisted sintering on dielectric properties of CaCu3Ti4O12 ceramic

In this present work, CaCu3Ti4O12 (CCTO) was synthesized by conventional solid-state reaction technique. The synthesis process was carried out in two phases; by conventional process (calcination and sintering at 1080°C for 10 hours) and phase II involves the micro assisted pre sintering of conventionally calcined CCTO for very short soaking time of 30 min at 1080°C in a microwave furnace followed by sintering at 1080°C for 10 hours in conventional furnace. X-ray diffraction (XRD) patterns confirmed the formation of single phase ceramic. Dielectric properties were studied over the frequency range from 50Hz -5MHz at temperatures (273K-343K). It was observed that pre- microwave sintering enhance the dielectric constant values from 10900 to 11893 and respectively reduces the dielectric loss values from 0.49 to 0.34 at room temperature(1 KHz). CCTO ceramics which are found desirable for many technological applications. The effect is more pronounced at low frequencies of applied electric field.

Rietveld Refinement and DC Conductivity of Na0.5K0.5NbO3 Ceramics

Potassium Sodium Niobate, Na0.5K0.5NbO3 is a promising base material for lead free piezoceramics. The polycrystalline sample Na0.5K0.5NbO3 was synthesized using solid state reaction method. The crystal structure and phase purity was studied by XRD and analysed using Rietveld refinement method. Good agreement was observed between the observed and calculated patterns in Rietveld refinement. The refinement inferred orthorhombic crystal structure with Amm2 space group. The impedance spectroscopy of the sample was performed in frequency range 10 Hz to 7 MHz in temperature range 573K to 703K. The activation energy was obtained to be 0.67eV from the reciprocal temperature variation of dc conductivity which follows the Arrhenius law.

Infrared Spectroscopic Study For Structural Investigation Of Lithium Lead Silicate Glasses

Lithium lead silicate glasses with composition 30Li2O⋅(70‐x)PbO⋅xSiO2 (where, x = 10, 20, 30, 40, 50 mol %) (LPS glasses) were prepared by normal melt quench technique at 1373 K for half an hour in air to understand their structure. Compositional dependence of density, molar volume and glass transition temperature of these glasses indicates more compactness of the glass structure with increasing SiO2 content. Fourier transform infrared (FTIR) spectroscopic data obtained for these glasses was used to investigate the changes induced in the local structure of samples as the ratio between PbO and SiO2 content changes from 6.0 to 0.4. The observed absorption band around 450–510 cm−1 in IR spectra of these glasses indicates the presence of network forming PbO4 tetrahedral units in glass structure. The increase in intensity with increasing SiO2 content (upto x = 30 mol %) suggests superposition of Pb‐O and Si‐O bond vibrations in absorption band around 450–510 cm−1. The values of optical basicity in these glasse...

Investigation Of Dispersive Conductivity And Dielectric Losses In Barium Bismuth Silicate Glasses

Barium bismuth silicate glasses (BBS glasses) with composition were prepared by normal melt quench technique. The dispersive conductivity and dielectric losses in these glasses were investigated by impedance spectroscopy. The analyses of ac conductivity spectra show a crossover from ion hopping conductivity to nearly constant loss (NCL) contribution in all the glasses. The variations in dielectric constant e*(ω) = e′(ω)‐ie″(ω) with frequency and temperature indicate an increase in electrode polarization, which reduces the dipolar relaxation effects in these glasses. The increased concentration of BaO in the glass composition reduces the dielectric losses in the present glasses.

Effect of lithium on thermal and structural properties of zinc vanadate tellurite glass

Glasses having composition 60TeO2-15V2O5-(25-x) ZnO-xLi2O where x= 0, 5, 10 mol% were prepared by standard melt quench technique. The glass transition temperature is measured by DSC technique using TA instrument and found to decrease with increase in Li2O signifies that glass formation tendency, thermal stability and compactness of glass structure decreases. The deconvolution of FTIR spectra evidenced the existence of TeO4, TeO3 and TeO6 structural units in glass network and vanadium exists as VO4 and VO5 structural units.

Effect of heating rate on microstructure and electrical properties of microwave sintered CaCu3Ti4O12 ceramics

In the present work, the results of microstructure, dielectric and ferroelectric investigation of microwave sintered CaCu3Ti4O12 (CCTO) ceramic with different heating rate are presented. Scanning electron micrographs revealed that grain size decreases from 1.167 μm to 0.744 μm with increased heating rate from 10oC/min. to 50oC/min which can be explained on the basis of phenomenological kinetic equation for grain growth. Dielectric response also found to influence by heating rate. The CCTO ceramic sintered with 50oC/min. exhibited highest dielectric constant (ɛr~3915) with nominal losses (0.10) at room temperature in broad frequency range from 10Hz-10Hz. Cole-Cole plots revealed the change in grain boundary resistivity mainly caused by the oxygen vacancy activities and affected by varying sintering heating rate. An anomaly observed for 50oC/min heating rate due to trapping of oxygen at grain boundaries. The remnant polarization and coercive field for CCTO ceramic sintered with 50oC/min were 0.1 μC /cm and 1.477 kV /cm respectively. Remnant polarization found to decrease while the coercive field increases with increasing heating rate applying these are micro-structural dependent. Copyright

Structural and Dielectric Properties of Na0.5Bi0.5TiO3 Ferroelectric Ceramics

Na0.5Bi0.5TiO3 (NBT) ceramics were synthesized by conventional solid state reaction method. Structural and dielectric properties of these ceramics were investigated. Crystalline phase of sintered ceramics was investigated by X-ray diffraction (XRD). The Rietveld refinement of powder X-ray diffraction revealed that the prepared ceramics exhibit the rhombohedral space group R3c. Dielectric properties of Na0.5Bi0. analyzer.5TiO3 (NBT) ceramics were studied at different temperatures in a wide frequency range using impedance