Banarji Behera

Frequency dependent transport properties of Na2Pb2La2W2Ti4Nb4O30 ceramics

The frequency dependent transport properties of tungsten bronze structured ceramic Na2Pb2La2W2Ti4Nb4O30 prepared through solid state reaction route is reported in this paper. Preliminary X-ray diffraction studies confirm the formation of compounds with orthorhombic crystal structure. Complex Impendence spectroscopy (CIS) technique is used to identify the physical processes involved in deciding the transport properties of the compound. In the spectroscopic plot of imaginary part of impedance and modulus a temperature dependent relaxation process of Arrhenius type is observed in the material. The relaxing species were identified from the magnitudes of calculated activation energies. The real and imaginary part of complex impedance and modulus traced depressed semicircle suggesting non Debye type relaxation process in the materials. These semicircles are successfully modeled by introducing constant phase element (CPE) to the equivalent circuit along with resistance(s), capacitance(s).

Study of complex impedance spectroscopic properties of Na{sub 2}Pb{sub 2}Pr{sub 2}W{sub 2}Ti{sub 4}Nb{sub 4}O{sub 30} Ceramic

The polycrystalline sample of Na2Pb2Pr2W2Ti4Nb4O30 was prepared by high temperature solid state reaction technique. The formation of compounds with an orthorhombic structure was confirmed by X-ray diffraction technique. Surface morphology study showed homogenous distribution of plate and rod like grains over the entire surface with less porosity. The study of effect of temperature on impedance parameters in the frequency range 102-106 Hz and temperature range 30-500°C revealed the presence of both bulk and grain boundary effects above 275°C. The bulk resistance of the material decreased with rise in temperature exhibiting a typical negative temperature coefficient of resistance (NTCR) behavior like a semiconductor. Both the complex impedance and modulus studies suggested the presence of non-Debye type of relaxation in the materials. The ac conductivity spectrum obeys Johnsche’s universal power law.

Impedance Characteristics of a New Tungsten Bronze Vanadate: NaPb2V5O15

The new complex Pb based vanadate, NaPb2V5O15 (NPV), of tungsten bronze structure was synthesized by a solid state reaction technique realized at low temperature, (i.e.,550°C). The X‐ray diffraction analysis shows that the sample has orthorhombic structure at room temperature. The SEM micrograph of NPV shows that the grains are homogeneously distributed throughout the sample. The dielectric and impedance properties of NPV, measured in a wide frequency (102–106Hz) and temperature (room temperature‐500°C) range show that the compound exhibits phase transition at 210°C (10 kHz). The ac electrical conductivity (σac) of the material was found to be temperature dependent.

Effect of Ti Doping on Structural and Electrical Properties of Ba(Fe0.5Nb.0.5)O3 Ceramic

Polycrystalline samples of Ba(Fe1−xTi2xNb1−x)0.5O3 (BFTN) with xu2009=u20090, 0.1, 0.2 have been synthesized using a high‐temperature solid‐state reaction technique. The X‐ray diffraction of the sample (xu2009=u20090) at room temperature shows a monoclinic phase. When the doped contents of Ti are over 10 mole% the structure changes from monoclinic to tetragonal. Scanning electron micrographs of the compounds show that grains are uniformly and densely distributed over the entire surface of the sample. The complex impedance plots show that there is only bulk (grain) contribution in the compounds in the said temperature range, and is of non‐Debye type of relaxation. Bulk resistance of the material has been observed to be concentration dependent. Conductivity analysis indicates that ac/dc conductivity of the materials increases with increase in temperature. It shows a typical negative temperature coefficient of resistance (NTCR) behaviour like a semiconductor. The conductivity has been found to decrease on Ti doping.