K J Rao
Articles written in Bulletin of Materials Science
Volume 23 Issue 6 December 2000 pp 461-466 Materials Synthesis
Microwave synthesis of electrode materials for lithium batteries
M Harish Bhat B P Chakravarthy P A Ramakrishnan A Levasseur K J Rao
A novel microwave method is described for the preparation of electrode materials required for lithium batteries. The method is simple, fast and carried out in most cases with the same starting material as in conventional methods. Good crystallinity has been noted and lower temperatures of reaction has been inferred in cases where low temperature products have been identified
Volume 25 Issue 7 December 2002 pp 593-598 Composites
Preparation of Si3N4–SiC composites by microwave route
Si3N4–SiC composites have been microwave sintered using 𝛽-Si3N4 and 𝛽-SiC as starting materials. Si3N4 rich compositions (95 and 90 vol.% Si3N4) have been sintered above 96% of theoretical density without using any sintering additives in 40 min. A monotonic decrease in relative density is observed with increase in SiC proportion in the composite. Decrease in relative density has manifested in the reduction of fracture toughness and microhardness values of the composite with increase in SiC content although the good sintering of matrix Si3N4 limits the decrease of fracture toughness. Highest value of fracture toughness of 6.1 MPa m1/2 is observed in 10 vol.% SiC composite. Crack propagation appears to be transgranular in the Si3N4 matrix and the toughening of the composites is through crack deflection around hard SiC particles in addition to its debonding from the matrix.
Volume 26 Issue 4 June 2003 pp 407-413 Glasses
Conductivity studies in SnO–NaPO3 glasses
M Harish Bhat Munia Ganguli K J Rao
Na+ ion conductivity has been studied in SnO.NaPO3 glasses, which have been prepared over a wide range of compositions using a microwave melting technique. D.c. activation barriers seem to reflect the structural changes in system. A.c. conductivity analysis has revealed that while the power law exponent, 𝑠, seem to bear correlation to the structural changes, the exponent 𝛽 of the stretched exponential function describing the dielectric relaxation is largely insensitive to the structure. Possible importance of the correlation of transport property to the variation of available non-bridging oxygen (NBO) atoms in the structure is discussed.
Volume 27 Issue 2 April 2004 pp 189-198 Glasses
Li+ ion conductivities in boro-tellurite glasses
M Harish Bhat M Kandavel Munia Ganguli K J Rao
Lithium ion conductivity has been investigated in a boro-tellurite glass system, LiCl.LiBO$_{2}\cdot$TeO2.In the absence of LiCl, the conductivity increases with increasing non-bridging oxygen (NBO) concentration. LiCl addition has little influence on total conductivity although the observed barriers are low. Formation of LiCl clusters appears evident. In the a.c. conductivity and dielectric studies, it is observed that the conductivity mechanism remains the same in all compositions and at all temperatures. A suggestion is made that Li+ ion transport may be driven by bridging oxygen $\leftrightarrow$ non-bridging oxygen (BO $\leftrightarrow$ NBO) switching, which is why the two different types of Li+ ions in the clusters and in the neighbourhood of NBOs, do not manifest in the conductivity studies.
Volume 28 Issue 1 February 2005 pp 19-24 Nanomaterials
A strategic approach for preparation of oxide nanomaterials
K J Rao Krishnamurthy Mahesh Sundeep Kumar
A microwave assisted solvothermal method is described for rapid preparation of nano-oxides. This method is based on exploiting differential dielectric constants to induce preferred heating and decomposition of the oxide precursors in the presence of suitable capping agents. This strategic approach has been used to prepare nanopowders of MgO, NiO, ZnO, Al2O3, Fe2O3 and ZrO2.
Volume 29 Issue 5 October 2006 pp 535-546 Electrochemistry
K J Rao B Pecquenard A Gies A Levasseur J Etourneau
Structural and electrochemical aspects of vanadium oxide films recently reported from ICMCB/ENSCPB have been examined using appropriate structural models. It is shown that amorphous films are nonstoichiometric as a result of pre-deposition decomposition of V2O5. It is proposed that the structure of amorphous films corresponds to a nanotextured mosaic of V2O5 and V2O4 regions. Lithium intercalation into these regions is considered to occur sequentially and determined by differences in group electronegativities. Open circuit voltages (OCV) have been calculated for various stoichiometric levels of lithiation using available thermodynamic data with approximate corrections. Sequestration of lithium observed in experiments is shown to be an interfacial phenomenon. X-ray photoelectron spectroscopic observation of the formation of V3+ even when V5+ has not been completely reduced to V4+ is shown to be entirely consistent with the proposed structural model and a consequence of initial oxygen nonstoichiometry. Based on the structural data available on V2O5 and its lithiated products, it is argued that the geometry of VO𝑛 polyhedron changes from square pyramid to trigonal bipyramid to octahedron with increase of lithiation. A molecular orbital based energy band diagram is presented which suggests that lithiated vanadium oxides, Li𝑥 V2O5, become metallic for high values of 𝑥.
Volume 34 Issue 6 October 2011 pp 1163-1171
G M Neelgund S A Shivashankar B K Chethana P P Sahoo K J Rao
Nanopowders of TiO2 has been prepared using a microwave irradiation-assisted route, starting from a metalorganic precursor,
Volume 36 Issue 1 February 2013 pp 71-85
V C Veeranna Gowda C Narayana Reddy K J Rao
Mechanism of ion transport in glasses continues to be incompletely understood. Several of the theoretical models in vogue fail to rationalize conductivity behaviour when d.c. and a.c. measurements are considered together. While they seem to involve the presence of at least two components in d.c. activation energy, experiments fail to reveal that feature. Further, only minor importance is given to the influence of structure of the glass on the ionic conductivity behaviour. In this paper, we have examined several general aspects of ion transport taking the example of ionically conducting glasses in pseudo binary, 𝑦Na2B4O7.(1−𝑦) M$_{a}$O$_{b}$ (with 𝑦 = 0.25–0.79 and M$_{a}$O$_{b}$ = PbO, TeO2 and Bi2O3) system of glasses which have also been recently characterized. Ion transport in them has been studied in detail. We have proposed that non-bridging oxygen (NBO) participation is crucial to the understanding of the observed conductivity behaviour. NBO–BO switching is projected as the first important step in ion transport and alkali ion jump is a subsequent event with a characteristically lower barrier which is, therefore, not observed in any study. All important observations in d.c. and a.c. transport in glasses are found consistent with this model.
Volume 46, 2023
All articles
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Prof. Subi Jacob George — Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bengaluru
Chemical Sciences 2020
Prof. Surajit Dhara — School of Physics, University of Hyderabad, Hyderabad
Physical Sciences 2020
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