R. S. Kundu

Temperature and frequency dependent conductivity of bismuth zinc vanadate semiconducting glassy system

The ac conductivity of bismuth zinc vanadate glasses with compositions 50V2O5. xBi2O3. (50-x) ZnO has been studied in the frequency range 10−1 Hz to 2 MHz and in temperature range 333.16 K to 533.16 K. The temperature and frequency dependent conductivity is found to obey Jonschers universal power law for all the compositions of bismuth zinc vanadate glass system. The dc conductivity (σdc), crossover frequency (ωH), and frequency exponent (s) have been estimated from the fitting of experimental data of ac conductivity with Jonschers universal power law. Enthalpy to dissociate the cation from its original site next to a charge compensating center (Hf) and enthalpy of migration (Hm) have also been estimated. It has been observed that mobility of charge carriers and ac conductivity in case of zinc vanadate glass system increases with increase in Bi2O3 content. In order to determine the conduction mechanism, the ac conductivity and its frequency exponent have been analyzed in the frame work of various theore...

Hopping conduction in bismuth modified zinc vanadate glasses: An applicability of Mott's model

The dc conductivity measured in a wide range of temperatures (room temperature to 533.16 K) for glass samples of compositions 50V2O5·xBi2O3·(50-x) ZnO; x = 0, 5, 10, 15, and 20, is discussed in this paper. The temperature dependent dc conductivity has been analyzed in the framework of various theoretical models, which describe the hopping conduction in disordered semiconducting systems. It has been observed that Motts model of polaron hopping in transition metals is in good agreement with the experimental data in high as well as intermediate temperature regions. The various polaron hopping parameters have also been deduced. It has been ascertained by these estimated quantities and different approaches that the electrical conduction in present glass system is due to non-adiabatic variable range hopping of small polarons. Moreover, it has been found that Motts and Greaves’ variable range hopping models are in good agreement with the experimental data in the whole studied temperature range in the present i...

Structural, optical, electrical, and magnetic properties of Zn0.7MnxNi0.3−xO nanoparticles synthesized by sol–gel technique

Abstract The structural, morphology, optical, electrical, and magnetic properties of Zn0.7MnxNi0.3−xO (x = 0.05, 0.1, 0.15, 0.2) nanoparticles synthesized by sol–gel technique have been systematically investigated by using X-ray diffractometer (XRD), scanning electron microscope (SEM), UV–vis-NIR spectrophotometer, impedance analyzer, and vibration sample magnetometer (VSM). XRD patterns reveal that all samples have hexagonal wurtzite structure along with secondary phases such as NiO and ZnMnO3. The average crystalline size increases with the increase in the Mn concentration in the host matrix. Diffuse reflectance studies (DRS) show an increment in optical band gap with increasing Mn content. AC conductivity of present samples has been studied as a function of frequency (100 Hz–10 MHz) of the applied AC signal in the temperature range of 323–463 K. The results showed that AC conductivity increases with an increase in frequency and temperature. The frequency exponent shows that small polaron conduction mechanism is the most favorable for all samples. The value of AC conductivity is observed to decrease with an increase in the Mn dopant concentration in the Zn0.7MnxNi0.3−xO system. At room temperature, magnetic characterization of the samples indicates the presence of both paramagnetic and ferromagnetic behavior. Magnetic saturation decreases with the increase in the Mn concentration in the host lattice.

Structural and dielectric properties of Ca0.95 Nd0.05Cu3Ti3.95Zr0.05O12 ceramic

ABSTRACT The unique dielectric properties of CaCu3Ti4O12 (CCTO) are a promising feature for capacitor applications. Polycrystalline Ca0.95Nd0.05Cu3Ti3.95Zr0.05O12 ceramic was synthesized via conventional solid state method. XRD and Rietveld studies confirmed that crystal structure is cubic with space group Im3. Microstructural study by scanning electron microscopy (SEM) suggests that the compound has some abnormal grains embedded with small grains depict inhomogeneous microstructure. The dielectric properties were analyzed in frequency range from 100 Hz to 5 MHz at different temperatures. A giant dielectric constant (∼19,426) with minimal loss tangent (∼0.067 at 1 KHz) at room temperature is achieved in studied composition.

Modified Physical, Structural and Optical Properties of Bismuth Silicate Glasses

Iron-containing bismuth silicate glasses with compositions 60SiO2·() have been prepared by conventional melt-quenching technique. The amorphous nature of the glass samples has been ascertained by the X-ray diffraction. The density (d) has been measured using Archimedes principle, molar volume () has also been estimated, and both are observed to decrease with the increase in iron content. The glass transition temperature () of these iron bismuth silicate glasses has been determined using differential scanning calorimetry (DSC) technique, and it increases with the increase in content. The IR spectra of these glasses consist mainly of [BiO6], [BiO3], and [SiO4] structural units. The optical properties are measured using UV-VIS spectroscopy. The optical bandgap energy () is observed to decrease with the increase in content, whereas reverse trend is observed for refractive index.

ZnCl2 Modified Physical and Optical Properties of Barium Tellurite Glasses

The optical properties of tellurite based glass systems are composition dependent. For this purpose glass samples of the composition 70TeO2-(30–x)BaO-xZnCl2 with x = 5, 10, 15, 20 and 25 have been synthesized by rapid melt quenching technique. Glassy nature has been confirmed by X-ray diffraction pattern. The physical properties like density, molar volume and crystalline volume have been estimated and found that density decreases while the molar volume increases with increase in ZnCl2 content. The glass transition temperature decreases with increase in halide content due to increase in the non-bridging oxygen contribution. Direct allowed optical transitions are favourable in these glasses and the optical band gap energy (Eopt) has been observed to increase with increase in ZnCl2 content. The value of Urbach energy of these glasses shows increasing behaviour with ZnCl2 concentration indicating the breaking of weak bonds into defects. Metallization criterion for these materials shows that these glasses may be potential candidates for non linear applications.

Structural characterization of ZnCl2 modified tellurite based glasses

Glass composition 70 TeO2-(30-x) BaO – x ZnCl2; x = 5, 10, 15, 20 and 25 have been prepared by rapid melt quenching technique under controlled atmospheric conditions. Amorphous nature of the samples was confirmed by x-ray diffractogram. The glass transition temperature (Tg) has been determined using differential scanning calorimetry (DSC) and its value is observed to decrease with increase in ZnCl2 content. The peaks in the Raman and FTIR spectra have been estimated by deconvolutation of the spectra and each of deconvoluted spectra exhibits several peaks. IR and Raman spectra of the present glass system indicate that TeO2 exists as TeO3 trigonal pyramidal (tp), TeO4 trigonal bipyramidal (tbp) and TeO6 polyhedra structural units. With increase in zinc halide content, transformation of some of TeO4 structural units into TeO3 structural units is observed Increase in TeO3 structural units shows that non-bridging oxygen contribution increases which confirms the decrease in glass transition temperature.

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.

Optical Characterization of Zinc Modified Bismuth Silicate Glasses

The optical characterization of glass samples in the system 40SiO2 · ZnO · ()Bi2O3 with , 5, 10, 15, 20, 25, 30, 35, and 40 prepared by conventional melt-quench technique has been carried out in the light of Hydrogenic Excitonic Model (HEM). The absorption coefficient spectra show good agreement with theoretical HEM for the present glass system and the values of different parameters like , , , , and have been estimated from fitting of this model. The values of energy band gap estimated from fitting of HEM with experimental data are in good agreement with those obtained from Tauc’s plot for direct transitions. The band gap energy is found to increase with increase of ZnO content. The decrease in values of Urbach energy with increase in ZnO content indicates a decrease in defect concentration in the glass matrix on addition of ZnO content. Optical constants and obey - consistency and the dielectric response of the studied glass system is similar to that obtained for Classical Electron Theory of Dielectric Materials. The calculated values of the metallization criterion () show that the synthesized glasses may be good candidates for new nonlinear optical materials.

Effect of ZnO on the physical and optical properties of tellurite base glasses

Glass samples in the system 60 TeO2–10B2O3−(30−x)Bi2O3−xZnO with mole fraction x = 10, 15, 20, 25 and 30 were synthesized by conventional melt quenching technique under controlled atmospheric conditions. The glassy nature of the synthesized glass samples have been confirmed by X-ray diffractogram. It is observed that density (d) and molar volume (Vm) decreases with ZnO concentration and the same trend is also followed by theoretical calculations of crystalline density (dc) and crystalline volume (Vc). The theoretical optical basicity and electronic polarizability both decreases with increase ZnO content. The fundamental absorption edge or cut off wavelength shifts to the lower wavelength side and increase of Eop to higher energies with increase in zinc content is related to the increase in the concentration of the bridging oxygen (BO) atoms.