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G.V. Chandrashekhar

Bio: G.V. Chandrashekhar is an academic researcher from Purdue University. The author has contributed to research in topics: Electrical resistivity and conductivity & Atmospheric temperature range. The author has an hindex of 6, co-authored 6 publications receiving 100 citations.

Papers
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Journal ArticleDOI
TL;DR: In this paper, the heat capacity of VO2 was measured both above and below the transition temperature range of 330 − 345 K for 150 µm for the same VO2 model.

38 citations

Journal ArticleDOI
TL;DR: The electrical resistivity of (VxTi1−x)2O3 with 0

34 citations

Journal ArticleDOI
TL;DR: In this article, the resistivity of NbOx (0.99 ⩽ x 1.03) boules containing 3 to 5 grains is reported for the range 77-900°K.

17 citations

Journal ArticleDOI
TL;DR: In this article, the high-temperature X-ray structure of (CrxV1−x)2O3 phases (withx < 0.10) has been studied.

12 citations

Journal ArticleDOI
TL;DR: In this article, the room temperature rhombohedral structure of (Cr 0.01V0.99)2O3 has been determined at different temperatures from the relative X ray intensities.

7 citations


Cited by
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Journal ArticleDOI
TL;DR: In this article, a discussion is given of metal-insulator transitions in VO2, Ti2O3 and also in Ti2-x V x O3, which at low temperatures becomes metallic with increasing x. Although these are band-crossing transitions, there being no magnetic moments on the metallic ions, a large discontinuity is expected in the number of current-carriers, as the degree of pairing of the V atoms is varied.
Abstract: A discussion is given of metal-insulator transitions in VO2, Ti2O3 and also in Ti2-x V x O3, which at low temperatures becomes metallic with increasing x. Although these are band-crossing transitions, there being no magnetic moments on the metallic ions, a large discontinuity is expected in the number of current-carriers in VO2 as the degree of pairing of the V atoms is varied. We relate this to the first-order transition observed as the temperature is raised. In Ti2O3 electrons in the conduction band appear to be much heavier than holes in the valence band and are probably small polarons. The addition of ∼2% of V2O3 appears to push Ti2O3 across the metal-insulator transition, again with a discontinuous change in the number of carriers, the alloy being a semimetal with heavy electrons and light holes. The experiments of Sjostrand and Keesom (1973) are discussed; the reason why the heavy electron polarons form a degenerate gas at helium temperatures, rather than a Wigner crystallization, is that t...

135 citations

Journal ArticleDOI
TL;DR: In this paper, a critical evaluation of phase equilibrium and thermodynamic properties of the VO-VO 2.5 system are presented. But the authors did not consider the V 2 O 3 solid solution.
Abstract: A critical evaluation, and thermodynamic optimization of phase equilibrium and thermodynamic properties of the VO–VO 2.5 system are presented. Optimized model parameters for all the oxide phases were obtained so as to reproduce all available and reliable experimental data within experimental error limits. Liquid oxide phase was modeled using the modified quasichemical model in the pair approximation with components representing various valences of vanadium (VO, VO 1.5 , VO 2 , and VO 2.5 ) in the liquid oxide. Solid VO and V 2 O 3 phases were modeled using simple random mixing models, while all other solid phases were assumed to be stoichiometric compounds. Type of defects in the V 2 O 3 solid solution was shown to be extended cluster type defect, based on the available experimental data. Using the presently optimized model parameters, most experimental data has been well reproduced, therefore, the present work can be further extended for the development of thermodynamic database for V oxide containing system.

63 citations

Journal ArticleDOI
TL;DR: In this article, a qualitative discussion of some of these results is given in terms of the free-energy band-crossing model of Zeiger and co-workers, which is used in this paper.
Abstract: Raman scattering of single crystals of ${({\mathrm{Ti}}_{1\ensuremath{-}x}{\mathrm{V}}_{x})}_{2}{\mathrm{O}}_{3}$ with $0\ensuremath{\le}x\ensuremath{\le}0.3$ has been measured between 80 and 700 \ifmmode^\circ\else\textdegree\fi{}K. All seven Raman-active phonons of the ${D}_{3d}^{6}$ space-group symmetry were found to show appreciable changes in the frequency, linewidth, and relative intensity as a function of temperature and alloy composition composition in the vicinity of the semiconductor-to-metal transition. In particular, a marked anomaly was observed in the temperature behavior of the lowest frequency mode of ${A}_{1g}$ symmetry. For $x\ensuremath{\lesssim}0.04$ it shows an initial softening followed by a partial recovery in going through the transition temperature. Chi and Sladek have observed a similar decrease and partial recovery for the sound velocity in ${\mathrm{Ti}}_{2}$${\mathrm{O}}_{3}$. A qualitative discussion of some of these results is given in terms of the free-energy band-crossing model of Zeiger and co-workers.

48 citations

Journal ArticleDOI
TL;DR: In this article, the elastic constants of metallic (Ti1-xVx)2O3 differ from those of semiconducting (Ti2-O3) Ti1-Vx 2O3 due to vanadium impurity.

45 citations

Journal ArticleDOI
TL;DR: In this article, the authors developed a model to describe the hysteresis of a composites' electrical and thermal conductivities, as well as its specific heat capacity, based on Bruggeman's symmetric effective medium formula and an explicit expression derived for the temperature evolution of the volume fractions of the metallic and isolating domains appearing during heating and cooling of the composites.
Abstract: Based on Bruggeman's symmetric effective-medium formula and an explicit expression derived for the temperature evolution of the volume fractions of the metallic and isolating domains appearing during the heating and cooling of ${\mathrm{VO}}_{2}$, respectively, we develop a model to describe the hysteresis of its electrical and thermal conductivities as well as of its specific heat capacity. The model takes into account the average value and standard deviation of the transition temperatures of the individual domains, as well as their activation energies, which represent the driving force for the existence of the ${\mathrm{VO}}_{2}$ hysteresis. It is shown that the model's predictions driven by these three parameters related to the microstructure of ${\mathrm{VO}}_{2}$ are in good agreement with robust experimental data. Furthermore, as these parameters are intrinsically correlated to the doping, defect, strain, and interface effects of ${\mathrm{VO}}_{2}$, the proposed model enables the seamless integration of these effects, and therefore, its predictions are also expected to be useful for describing the thermal and electrical properties of composites based on ${\mathrm{VO}}_{2}$.

43 citations