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Indore, India

Choudhary K.K.,Shri Vaishnav Institute of Technology and Science | Choudhary K.K.,Devi Ahilya University | Prasad D.,Shri Vaishnav Institute of Technology and Science | Prasad D.,Devi Ahilya University | And 2 more authors.
Journal of Physics and Chemistry of Solids | Year: 2010

We develop a theoretical model for quantitative analysis of temperature-dependent thermoelectric power (S) of Zn nanowires. In doing so, we first use the Mott expression to compute the electron diffusive thermoelectric power (Sc diff.) using Fermi energy as electron-free parameter, Sc diff. shows linear temperature dependence. Further, the Sc diff. contribution is subtracted from the experimental data and the difference (Sexperimental-Sc dif) is characterized as phonon drag thermoelectric power (Sph drag) which is obtained within the relaxation time approximation where the thermoelectric power is limited by the scattering of phonons with impurities, grain boundaries, charge careers and phonons in the nanowires. The Sph drag shows anomalous temperature-dependent behaviour, which is an artifact of various operating scattering mechanisms. The observed anomalies are well accounted in terms of interaction among the phonons-impurity, phonon-grain boundaries, phonon-electron and the umklapp scattering. It is also shown that for phonons the scattering and transport cross-sections are proportional to ω4 in the Rayleigh regime where ω is the frequency of the phonons. Numerical analysis of thermoelectric power from the present model shows similar results as those revealed from experiments. © 2009 Elsevier Ltd. All rights reserved. Source

Sisodia N.,Holkar Science College
AIP Conference Proceedings | Year: 2014

Present paper deals with a critical and comprehensive analysis of the dependence of photo emission (PE) electronic band gap and optical absorption (OA) excitonic band gap on the size of CdSe QD, via connecting it with excitonic absorbance wavelength. Excitonic absorbance wavelength is determined through an empirical fit of established experimental evidences. Effective excitonic charge and Bohr radius is determined as a function of size. Increase in size of the CdSe QD results in greater Bohr radius and smaller effective excitonic charge. Excitonic binding energy as a degree of size of QD is also calculated which further relates with the difference in PE electronic and OA optical band gaps. It is also shown that with increase in size of CdSe QD, the excitonic binding energy decreases which consequently increases differences in two band gaps. Our results are very well comparable with the established results. Explanation for the origin of the unusual optical properties of CdSe QD has been also discussed. © 2014 AIP Publishing LLC. Source

Choudhary K.K.,Department of National Defence | Gupta N.,Department of National Defence | Kaurav N.,Holkar Science College | Katiyal S.,Devi Ahilya University | Ghosh S.K.,Vikram University
Bulletin of Materials Science | Year: 2014

The anomalous temperature-dependent electrical resistivity ρ(T) of La0.875Sr0.125MnO3 manganite nanoparticles (particle size 18 nm) is theoretically analysed. ρ(T) exhibits semiconducting phase in lowtemperature regime (20 K < T < 53 K), shows a minima near 53 K and increases with T at high temperatures (53 K < T < 170 K). The resistivity in metallic phase (T > 53 K) is theoretically analysed by considering the strong spin-fluctuation effect, which is modelled using Drude-Lorentz type function. In addition to the spin fluctuation-induced contribution, the electron-phonon and electron-electron ρe-e(T) = BT2 contributions are also incorporated for complete understanding of experimental data. The contributions to the resistivity by inherent acoustic phonons (ρac) as well as high-frequency optical phonons (ρop) were estimated using Bloch-Gruneisen (BG) model of resistivity. It is observed that the resistivity contribution due to electron-electron interaction shows typical quadratic temperature dependence. Spin fluctuation-induced resistivity is dominant over electron-electron and electron-phonon contributions in overall temperature range in the manganite nanoparticles. Resistivity in the semiconducting phase is discussed with small polaron conduction (SPC) model. SPC model consistently retraces the low-temperature resistivity behaviour (T < 53 K). Finally, the theoretically calculated resistivity compared with experimental data is found to be consistent in wide range of temperature. © 2014 Indian Academy of Sciences. Source

Choudhary K.K.,Department of National Defence | Kaurav N.,Holkar Science College | Ghosh S.K.,Vikram University
International Journal of Modern Physics B | Year: 2014

The thermoelectric properties of LaCo1-xCuxO 3-δ ceramics are theoretically analyzed, it is observed that thermoelectric figure of merit ZT ( = S2σT/κ) is maximized by Cu substitution in LaCo1-xCux O 3-δ at x = 0.15. The lattice thermal conductivity (κph) and phonon drag thermoelectric power $(S-{\rm ph}^{\rm drag})$ were estimated by the scattering of phonons with defects, grain boundaries, electrons and phonon umklapp scattering to evaluate the thermoelectric figure of merit ZT. The Mott expression is used to estimate the electron diffusive thermoelectric power $(S-{e}^{\rm diff})$ using Fermi energy as electron free parameter, $S-{e}^{\rm diff}$ shows linear temperature dependence. The electron contribution to thermal conductivity (κe) is estimated using temperature-dependent electron relaxation time. We found that Cu substitution increases the phonon scattering with grain boundaries and defects which significantly decrease the thermal conductivity and subsequently increase the thermoelectric power. The present numerical analysis of thermoelectric properties will help in designing more efficient thermoelectric materials for thermoelectric applications. © World Scientific Publishing Company. Source

Khanuja P.,Shri Neelkantheaahwar Government Postgraduate College | Chourey V.R.,Holkar Science College
Asian Journal of Chemistry | Year: 2013

Density and viscosity measurements were performed for amino acids in 0.05-0.25 M aqueous maltose at 293.15, 303.15 and 313.15 K. The measured values of density and viscosity were used to estimate some important parameters, such as the partial molal volume, the partial molal volume of transfer, the second derivative of the infinite dilution of the standard partial molal volume with temperature, the viscosity B-coefficients, variation of B with temperature, dB/dT, the free energy of activation per mole of solvent amino acid in a ternary system. These parameters were interpreted in terms of solute-solute and solute-solvent interactions and structure making/breaking ability of solutes in the given solution. Source

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