Publications

CCDC 878040: Experimental Crystal Structure Determination

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.

Electron Microscopy of Ferroelectric Bismuthate Compounds

No abstract is provided for this article.

ChemInform Abstract: X‐RAY SPECTROSCOPIC STUDY OF CHROMIUM, NICKEL, AND MOLYBDENUM COMPOUNDS

Die chemischen Verschiebungen der K‐Absorptionsbanden, AE, einer Reihe der Titelverbindungen, ändern sich gleichsinnig mit den photoelektronenspektroskopisch erhaltenen Rumpfniveau‐Bindungsenergien der Metalle.

In My Element : Oxygen

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 prepared by templating silica spheres

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.

Asymmetric Wacker-Type Cyclization Catalyzed by Pd-SPRIX

Diketones have previously been shown to undergo Wacker-type cyclizations: 5-exo-trig cyclizations lead to furan rings, and pyran rings are formed through 6-endo-trig cyclizations. The first enantioselective 6-endo-trig Wacker-type cyclization is described here, catalyzed by a palladium spiro bis(isoxazoline) (SPRIX) complex.

Surfactant-assisted synthesis of semiconductor nanotubes and nanowires

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.

A simple method of hydrogen insertion in transition metal oxides to obtain bronzes

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.

Low thermal conductivity of 2D borocarbonitride nanosheets

Two-dimensional (2D) borocarbonitrides (BCN) are of interest since their electrical and optical properties can be tuned for renewable energy applications. Although there have been theoretical studies, experimental studies of the thermal transport and thermoelectric properties of BCN nanosheets have not yet been explored. We have synthesized few-layer BCN nanosheets of different compositions, and characterized them by Raman spectroscopy, X-ray photoelectron spectroscopy and transmission electron microscopy (TEM). They exhibit p-type semiconducting thermoelectric transport properties in 300–573 ​K range. More interestingly, the BCN nanosheets exhibit low thermal conductivity (0.58–1.86 ​W/mK) unlike boron nitride (h-BN) and graphene over the temperature range of 300–573 ​K. The low thermal conductivity of BCN nanosheets arises due to significant phonon scattering by the different length scale hierarchical nano/meso architectures such as bonding heterogeneity (e.g. C–B, C–N and B–N), point defects related C/B/N disorder, nanodomains of BN/carbon and grain boundaries.

A New Era for Chemical Superconductors

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.

Properties of nanosheets of 2D-borocarbonitrides related to energy devices, transistors and other areas

We have prepared borocarbonitrides of various compositions with extended sheet morphology, by the reaction of few-layer graphene with boric acid and urea at 900°C and characterized them in detail. Supercapacitor performance of the borocarbonitrides has been studied in detail, the composition containing more pyridinc nitrogen exhibiting a specific capacitance of 306F/g at 0.2A/g. This composition also shows good oxygen reduction reaction (ORR) activity with an electron transfer number close to 4. The extended sheet structures of the B x C y N z samples has enabled us to fabricate field-effect transistors. These materials also show reasonable UV photoresponse.

CCDC 242448: Experimental Crystal Structure Determination

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.

Ultraviolet spectrum of HNCS

No abstract is provided for this article.

An electron paramagnetic resonance study of electron–hole asymmetry in charge ordered Pr_{1 <i>x</i>}Ca_<i>x</i>MnO₃(<i>x</i>= 0.64, 0.36)

We present and compare the results of temperature-dependent electron paramagnetic resonance (EPR) studies on Pr1−xCaxMnO3 for x = 0.64, which is electron-doped, with results of studies on the hole-doped, x = 0.36 composition. The temperature dependence of the various parameters obtained from the powder and single crystal spectra show significant differences between the two manganites. At room temperature the 'g' parameter for the electron-doped system is less than the free electron 'g' value 'ge ', whereas for the hole-doped system it is more than 'ge '. Further, the linewidth obtained from the powder spectra as well as the single crystal spectra show different functional dependences on temperature in the two systems. Quite strikingly, the peak observed at Tco in the temperature dependence of the asymmetry parameter, α, of the single crystal spectra in the hole-doped system, is absent in the electron-doped system. We understand this contrasting behaviour of the EPR parameters in the two systems in terms of the very different nature of microscopic interactions in them.

Uptake of H₂ and CO₂ by Graphene

Graphene samples prepared by the exfoliation of graphitic oxide and conversion of nanodiamond exhibit good hydrogen uptake at 1 atm, 77 K, the uptake going up to 1.7 wt %. The hydrogen uptake varies linearly with the surface area, and the extrapolated value of hydrogen uptake by single-layer graphene works out to be just above 3 wt %. The H2 uptake at 100 atm and 298 K is found to be 3 wt % or more, suggesting thereby the single-layer graphene would exhibit much higher uptakes. Equally interestingly, the graphene samples prepared by us show high uptake of CO2, the value reaching up to 35 wt % at 1 atm and 195 K. The first-principles calculations show that hydrogen molecules sit alternately in parallel and perpendicular orientation on the six-membered rings of the graphene. Up to 7.7 wt % of hydrogen can be accommodated on single-layered graphene. CO2 molecules sit alternatively in a parallel fashion on the rings, giving use to a maximum uptake of 37.93 wt % in single-layer graphene. The presence of more than one layer of graphene in our samples causes a decrease in the H2 uptake.

PHASE TRANSFORMATIONS OF RARE EARTH SESQUIOXIDES La$sub 2$O$sub 3$, Nd$sub 2$O$sub 3$, Pr$sub 2$O$sub 3$, AND Y$sub 2$O .

Relation between the electronic structure and the superconductivity of cuprates as revealed by Cu 2<i>p</i>photoemission and theoretical investigations

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}/${\mathit{t}}_{\mathit{p}\mathit{d}}$.

Effect of size on the Coulomb staircase phenomenon in metal nanocrystals

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.