2,089 publications from this institution
Pairwise defect interactions between divalent cation impurities, cation vacancies and anion vacancies have been studied in the extrinsic and intrinsic temperature ranges for the KClSr2+ system. Pair correlation functions have been derived for the various defect interactions distinguished by their site symmetries and these show the existence of associated divalent cation—cation vacancy and cation—anion vacancy pairs even at high temperatures. Pair formation gives way to dissociation at low impurity concentrations and high temperatures.
Hydrocarbon (LPG) sensors based on the nanostructures of V2O5 do not exhibit satisfactory characteristics, while sensors based on WO2.72 nanowires show high sensitivity (∼1800) for 2000 ppm of LPG at 200 °C as well as relatively short recovery and response times. Impregnation of WO2.72 nanowires with Pt in the 0.1–1.0 at% range, significantly improves the sensor characteristics, the sensitivity increasing with Pt concentration and reaching a value of ∼106 for 2000 ppm of LPG in the 100–200 °C range with 1 at% Pt. The sensitivity remains high even for 50 ppm of LPG, and is not affected significantly by repeated cycles or humidity. The mechanism of sensing of hydrocarbons by WO2.72 nanowires is explained on the basis of adsorbed oxygen species.
No abstract is provided for this article.
The In My Element series celebrates the personal accounts from Chemistry – A European Journal Editorial Board members for the 2019 International Year of the Periodic Table. In this contribution, C. N. R. Rao gives his story on oxygen. My love for oxygen can be traced to the very beginning of my research career. This is not because oxygen was discovered by the Father of Chemistry, Lavoisier, and it is essential for life as O2 and as H2O, but because it forms a variety of metal oxides with interesting structures and a wide range of properties1 (Table 1). Oxygen can exist as O21−, O22− and O2− in solids and as O1− on certain surfaces. Oxygen stoichiometry is an important aspect of oxides, oxygen deficiency often giving rise to new types of ordered structures (TinO2n−1 Magneli phases, Pr2O2n−2). Metallic: ReO3, NbO, LaNiO3 Dielectric: BaTiO3 Antiferromagnetic: NiO, LaCrO3 Ferromagnetic: CrO2, La0.5Sr0.5CoO3, SrRuO3 Ferroelectric: BaTiO3, KNbO3 Ferroelastic: Gd2(MoO4)3 Superconducting: BaPb0.75Bi0.25O3, YBa2Cu3O7 Insulator-Metal Transition: V2O3, VO2, La1−xSrxCoO3 Colossal Magnetoresistance (CMR): La0.7Ca0.3MnO3 Multiferroic: BiFeO3, YMnO3, TbMnO3 I have worked on metal oxides for a long time,2 and my very first research paper in materials chemistry in the late 1950′s was on the transformation of the anatase form of TiO2 to the rutile form. I also studied the so-called nonstoichiometric oxides of rare earths of the type Pr6O11, Pr7O12 and Tb4O7. Soon I realized how perovskite oxides (ABO3) exhibit a variety of phenomena and properties such as ferroelectricity and magnetism, and how the pervoskite motif is present in several families of oxides. I have been working on perovskite oxides including two-dimensional oxides for many years. I worked on La2CuO4, as early as 1971, mother of cuprate superconductors. My group was one of the first to characterize YBa2Cu3O7, the first liquid nitrogen superconductor, which also has the perovskite motif. The number of cuprate families exhibiting high temperature superconductivity is impressive.3 The discovery of colossal magnetoresistance in rare earth manganites of the type La1−xCaxMnO3 which show both orbital and charge-ordering led to a variety of investigations and to the observation of the phenomenon of electronic phase separation.4 We observed major effects of phase separation in Nd0.5Sr0.5MnO3, which is ferromagnetic at ordinary temperatures, and occurs in three phases (FM+2AFMs) at liquid helium temperatures. I started working on multiferroics in the 1990’s, the well-known examples being BiFeO3 and YMnO3. Cation substitution in oxides is commonly carried out to cause changes in structures and properties. An impressive example is that of Sr substituted LaCoO3 where a paramagnetic insulator becomes a ferromagnetic metal on substitution of Sr in place of La. Cation substitution generally affects the unoccupied states and anion substitution, specially aliovalent anions on the other hand, cause drastic changes in the valence bands. In recent months, I have been working on oxide analogues wherein oxygen is substituted by nitrogen and fluorine, resulting is novel electronic and catalytic properties.5 For example, Zn2NF and TiNF are isoelectronic with ZnO and TiO2 respectively, but exhibit entirely different electronic structures and properties. Position Linus Pauling Research Professor E-mail [email protected] Homepage http://www.jncasr.ac.in/cnrrao Education B.Sc (Mysore, 1951), M.Sc (Banaras, 1953) Ph.D (1957, Prof R.L. Livingston, Purdue, “Molecular structure investigations by gas phase electron diffraction)” D.Sc (1960) Mysore “Studies of Structural Chemistry and Nitrogen Chemistry” Post-doctoral fellowship (1958-1959; Berkeley, Prof K.S. Pitzer) Awards Dan David Prize for Science in the Future Dimension (2005) Ernesto Illy Trieste Science Prize (2011) for materials research The Royal Medal (The Queens Medal) of the Royal Society, London, U.K (2009) The August-Wilhelm-von-Hoffmann Medal for outstanding contributions to chemistry by the German Chemical Society (2010) Von Hippel Award for materials research by Materials Research Society, US (2017) Chevalier de la Légion D′Honneur by the President of the French Republic (2005) Order of the Rising Sun, Gold and Silver Star by the Emperor of Japan (2015) Bharat Ratna (Jewel of India), Highest Civilian Award of India (2014) Research interests Chemistry of Materials, in particular, oxide materials, 2D materials, solar water-splitting Hobbies and interests Listening to classical music and cooking
Macroporous carbons of different pore sizes, containing three-dimensionally connected voids, have been prepared by an elegant method. The method involves the coating of ordered silica spheres with sucrose, followed by carbonization using sulfuric acid, and the removal of silica with aqueous hydrofluoric acid. The carbon samples show the expected optical properties. The surface area of the macroporous carbon samples varies between 120 to 550 m2g−1, depending on whether nonporous or mesoporous silica spheres were used as templates.
Nanotubes and nanowires of CdSe and CdS have been obtained from solutions containing a surfactant such as Triton 100-X. They have been characterized by x-ray diffraction, electron microscopy, and optical spectroscopy.
Reaction of WO3, MoO3 and V2O5 with alcohols or glycols is shown to yield hydrogen bronzes of the oxides. Cubic and tetragonal HXWO3, H0.47MoO3 as well as H0.4V2O5 have been prepared by this method.
A review of the development of ceramic superconductors and the steady increase in the superconducting transition temperature which currently stands at 135 K or about 164 K under pressure.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
Cu 2p core-level photoemission studies of ${\mathrm{La}}_{2\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{CuO}}_{4}$, ${\mathrm{BiPbSr}}_{2}$${\mathrm{Y}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ca}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Cu}}_{2}$${\mathrm{O}}_{8}$, and other cuprates show that the relative intensity of the satellite varies with the composition in a direction opposite to that of the hole concentration, ${\mathit{n}}_{\mathit{h}}$. The ${\mathit{I}}_{\mathit{S}}$/${\mathit{I}}_{\mathit{M}}$-${\mathit{n}}_{\mathit{h}}$ relations in the different cuprate series can be understood in terms of the \ensuremath{\Delta}/${\mathit{t}}_{\mathit{p}\mathit{d}}$ ratio, where \ensuremath{\Delta} is the charge-transfer excitation energy and ${\mathit{t}}_{\mathit{p}\mathit{d}}$ is the hybridization strength between the Cu 3d and O 2p orbitals. Interestingly, the ${\mathit{I}}_{\mathit{S}}$/${\mathit{I}}_{\mathit{M}}$ ratio increases with the \ensuremath{\Delta}/${\mathit{t}}_{\mathit{p}\mathit{d}}$ ratio in the cuprates. At a given value of ${\mathit{n}}_{\mathit{h}}$, e.g., around the value corresponding to maximum ${\mathit{T}}_{\mathit{c}}$, ${\mathit{I}}_{\mathit{S}}$/${\mathit{I}}_{\mathit{M}}$ increases in the same direction as ${\mathit{T}}_{\mathit{c}}$ among the different series of cuprates, suggesting thereby that ${\mathit{T}}_{\mathit{c}}$ itself may be determined by \ensuremath{\Delta}/${\mathit{t}}_{\mathit{p}\mathit{d}}$.
The Coulomb staircase in polymer-covered Pd and Au nanocrystals of varying diameters in the 1.7–6.4 nm has been investigated by employing tunneling conductance measurements. Charging up to several electrons is observed at room temperature in the I–V data. Small nanocrystals show charging steps exceeding 200 mV while the larger ones exhibit smaller steps. Significantly, the charging energies follow a scaling law of the form, U=A+B/d, where d is the diameter of the nanocrystal. Furthermore, the line widths in the derivative spectra also vary inversely with the diameter.
