G.V. Subba Rao

Bio: G.V. Subba Rao is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Superconductivity & Electrical resistivity and conductivity. The author has an hindex of 15, co-authored 66 publications receiving 705 citations.

Semiconductor based photoelectrochemical cells for solar energy conversion—An overview

Abstract: An overview of the semiconductor based photoelectrochemical (pec) cells for solar energy conversion is presented.pec cells are of two types: photoelectrolysis cells and photovoltaic cells. The principles involved, electrode and electrode/electrolyte interface characteristics, experimental methods of investigation and energy conversion efficiency are discussed in detail. Up-to-date data on variouspec cells are also presented and discussed.

Tc suppression and conduction mechanisms in Bi2.1Sr1.93Ca0.97-xRxCu2O8+y (R=Pr, Gd, and Er) systems.

Abstract: Systematic substitutional studies in the Bi 2.1 Sr 1.93 Ca 0.97-x R x Cu 2 O 8+y (R=Pr,Gd,Er; 0≤x≤0.3 in steps of 0.05 and 0.4≤x≤0.97 in steps of 0.1) system were carried out in order to determine the effect of the magnetic moment and ionic radius of the rare-earth ion on the T c suppression rate. X-ray-diffraction studies indicate that the solid solubility of Gd and Er exists up to x=0.97 whereas that of Pr is limited to x=0.6 under the preparative conditions employed. Resistivity and ac susceptibility studies have shown that superconductivity persists up to x=0.4 and a metal-semiconductor transition occurs for x>0.4. The most interesting observation is that the rate of T c suppression for the superconducting phases is found to be identical for all rare earths. We have explained that hole filling rather than Abrikosov-Gor'kov pair breaking is responsible for the decrease in T c . The insulating phases with 0.5≤x≤0.97 exhibit the phenomenon of Mott's variable-range-hopping mechanism (VRH). The physical parameters related to VRH such as localization length (α −1 ), hopping range (R), and activation energy (W) for conduction, have been evaluated and discussed in detail.

Synthesis and electrical properties of shandite-parkerite phases, A2M3Ch2

Abstract: The synthesis, characterization and electrical properties are reported of representative members of the metal-rich ternary system of shandite-parkerite phases, A 2 M 3 Ch 2 and solid solutions at the A site. Typical metallic behaviour is exhibited by all the phases. Analysis of the Seebeck coefficients and resistivity data indicate that the rhodium and palladium containing compounds are broad band metals. Sn 2 Co 3 S 2 exhibits a phase transition below 150 K, possibly magnetic.

Magnetic Pyrochlore Oxides

Abstract: Within the past 20 years or so, there has occurred an explosion of interest in the magnetic behavior of pyrochlore oxides of the type $A_{2}^{3+}$$B_{2}^{4+}$O$_{7}$ where $A$ is a rare-earth ion and $B$ is usually a transition metal. Both the $A$ and $B$ sites form a network of corner-sharing tetrahedra which is the quintessential framework for a geometrically frustrated magnet. In these systems the natural tendency to form long range ordered ground states in accord with the Third Law is frustrated, resulting in some novel short range ordered alternatives such as spin glasses, spin ices and spin liquids and much new physics. This article attempts to review the myriad of properties found in pyrochlore oxides, mainly from a materials perspective, but with an appropriate theoretical context.

Granular electronic systems

Abstract: Granular metals are arrays of metallic particles of a size ranging usually from a few to hundreds of nanometers embedded into an insulating matrix. Metallic granules are often viewed as artificial atoms. Accordingly, granular arrays can be treated as artificial solids with programmable electronic properties. The ease of adjusting electronic properties of granular metals assures them an important role for nanotechnological applications and makes them most suitable for fundamental studies of disordered solids. This review discusses recent theoretical advances in the study of granular metals, emphasizing the interplay of disorder, quantum effects, fluctuations, and effects of confinement. These key elements are quantified by the tunneling conductance between granules $g$, the charging energy of a single granule ${E}_{c}$, the mean level spacing within a granule $\ensuremath{\delta}$, and the mean electronic lifetime within the granule $\ensuremath{\hbar}∕g\ensuremath{\delta}$. By tuning the coupling between granules the system can be made either a good metal for $gg{g}_{c}=(1∕2\ensuremath{\pi}d)\mathrm{ln}({E}_{c}∕\ensuremath{\delta})$ ($d$ is the system dimensionality), or an insulator for $gl{g}_{c}$. The metallic phase in its turn is governed by the characteristic energy $\ensuremath{\Gamma}=g\ensuremath{\delta}$: at high temperatures $Tg\ensuremath{\Gamma}$ the resistivity exhibits universal logarithmic temperature behavior specific to granular materials, while at $Tl\ensuremath{\Gamma}$ the transport properties are those generic for all disordered metals. In the insulator phase the transport exhibits a variety of activation behaviors including the long-puzzling $\ensuremath{\sigma}\ensuremath{\sim}\mathrm{exp}[\ensuremath{-}({T}_{0}∕T{)}^{1∕2}]$ hopping conductivity. Superconductivity adds to the richness of the observed phases via one more energy parameter $\ensuremath{\Delta}$. Using a wide range of recently developed theoretical approaches, it is possible to obtain a detailed understanding of the electronic transport and thermodynamic properties of granular materials, as is required for their applications.

Conversion of carbon dioxide into methanol – a potential liquid fuel: Fundamental challenges and opportunities (a review)

Abstract: As on today, the conversion of carbon dioxide (CO 2 ) into value added chemicals including methanol using exclusively solar energy (i.e., artificial photosynthesis) has been considered as one of the top most research priorities all over the world as this process can indeed deal with (i) the mitigation of CO 2 associated global warming problem, (ii) creation of highly sustainable and renewable energy resources, and (iii) development of one of the best processes to store the energy in a most convenient form of liquid fuels with sufficiently high energy density in comparison to all the existing methods of energy storage. As the CO 2 sequestration process is expensive, there has been a quest for finding other alternative options. The CO 2 can be converted into several value added chemicals including methanol following stoichiometric reactions, thermochemical, electrochemical, photoelectrochemical, photocatalytic, etc., routes. Methanol synthesized from CO 2 can be employed directly in place of fossil fuels without disturbing the present existing energy distribution infrastructure. Further, if H 2 required for CO 2 reduction is produced from water using exclusively solar energy, and methanol is produced with minimum overpotentials with the help of suitable catalytic systems, this process can be employed to address the above-mentioned three major problems. The process for converting CO 2 into methanol can be developed by careful analysis and understanding of the information available on this process reported so far in the literature. Since, none of the existing review articles deals exclusively with this important process of converting CO 2 into methanol, in this review article, all the information including fundamental challenges and opportunities that are associated with the conversion of CO 2 into methanol following various routes has been summarized, discussed and meticulously presented by citing all the up to date relevant references.

A wide-ranging review on Nasicon type materials

Abstract: Nasicons (sodium super ion conductors) are a class of solid electrolytes. Their structure, compositional diversity, evolution, and applications are reviewed. A wide range of materials is considered based on crystalline and glassy Nasicon compositions.