Publications

Formation of B, Al, Ga, and Si nitrides from their oxides: a reactive laser ablation study

Nitrides such as Si3N4 and GaN are made by the reaction of the respective oxide with N2 or NH3. In order to understand the mechanism of formation of nitrides, reactive laser ablation of B2O3, Al2O3, Ga2O3, and SiO2 in pure form, as well as in mixture with carbon, has been carried out in an atmosphere of nitrogen or ammonia in a pulsed supersonic jet. The reaction of N2 with SiO2 gives nitridic species such as Si2N y (y≤5) in the vapor phase. On reaction with N2 in the presence of carbon, B2O3 and Ga2O3 yield species of the type B x N y and GaN y , respectively. Nitridic species are preponderant in the reaction with ammonia only in the case of SiO2. Al2O3 predominantly gives oxynitridic species under the reaction conditions examined.

Simulation of supported metal catalysts: adsorption of CO on Ni/Al2O3 prepared in situ in the electron spectrometer

Simulated catalysts wherein controlled amounts of Ni are deposited on Al2O3 layers grown in situ on an Al surface have been investigated; dissociative adsorption of CO is favoured on these catalyst surfaces.

Growth Kinetics of Gold Nanocrystals: A Combined Small-Angle X-Ray Scattering and Calorimetric Study

The growth of gold nanocrystals prepared by the reduction of tetrachloroauric acid by tetrakis(hydroxymethyl)phosphonium chloride, which allows slow reduction, is investigated by small-angle X-ray scattering and isothermal titration calorimetry in combination with transmission electron microscopy. The growth of the nanocrystals does not follow the diffusion-limited Ostwald ripening but instead follows a sigmoidal rate curve. The activation energy obtained from the temperature-dependent growth study is very small. The heat change associated with the growth is determined for the first time as approximately 10 kcal mol(-1) per 1 nm increase in the nanocrystals' diameter.

Interatomic Auger transitions in transition-metal oxides

Interatomic ${L}_{3}(M){M}_{23}(M)V(O)$ and ${L}_{3}(M)V(O)V(O)$ Auger transitions of some transition-metal oxides are reported for the first time. The interatomic mode of decay becomes progressively more dominant (relative to the intra-atomic mode) as the metal $d$ level gets depleted or as the oxidation state of the metal increases. The usefulness of interatomic Auger transitions in studying oxidation of metals has been examined.

A combined EELS-XPS study of molecularly chemisorbed oxygen on silver surfaces: Evidence for superoxo and peroxo species

Both superoxo and peroxo species are formed when oxygen is adsorbed on a polycrystalline Ag surface as evidenced by the characteristic O-O stretching frequencies in the EEL spectra. Based on temperature-variation studies of the vibration bands in the EELS and of the O(1s) core level peaks in the XPS, characteristic O(1s) binding energies are assigned to the two molecular species; the superoxo species is associated with a significantly higher binding energy as expected. The superoxo species appears to be relatively less thermally stable than the peroxo species, being associated with a ∼1300 cm−1 stretching vibration, the highest O-O stretching frequency observed so far due to a chemisorbed species.

Chapter 8 NANOSCALE CATALYSIS BY GOLD

Recent work related to gold catalysis has been discussed addressing the important issue ofhow the nobleness of gold breaks down at nanometric sizes when in contact with oxidic supports. The high reactivity of gold catalysts in comparison to other metal catalysts is illustrated by reactions such as oxidation of CO and reduction ofNO under ambient conditions, as weil as epoxidation and hydrochlorination of unsaturated hydrocarbons. Investigations carried out on gold catalysts using a variety of spectroscopy and microscopy techniques are discussed along with the general mechanism of the catalytic process. The observation ofmaximum reactivity at a cluster size of2-3 nm, coincident with the size-induced metal to non-metal transition in gold forms the central theme of the article.

The Metal-Nonmetal Transition: A Global Perspective

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTThe Metal-Nonmetal Transition: A Global PerspectiveP. P. Edwards, T. V. Ramakrishnan, and C. N. R. RaoCite this: J. Phys. Chem. 1995, 99, 15, 5228–5239Publication Date (Print):April 1, 1995Publication History Published online1 May 2002Published inissue 1 April 1995https://pubs.acs.org/doi/10.1021/j100015a002https://doi.org/10.1021/j100015a002research-articleACS PublicationsRequest reuse permissionsArticle Views696Altmetric-Citations92LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access options Get e-Alerts

CARBONYL STRETCHING VIBRATIONS AND ELECTRONIC TRANSITIONS DUE TO NONBONDING ELECTRONS IN SATURATED RING KETONES

No abstract is provided for this article.

Dipole ordering in dilute solutions of ferroelectrics in antiferroelectric materials

Structure, magnetism and giant dielectric constant of BiCr_0.5Mn_0.5O₃synthesized at high pressures

BiCr0.5Mn0.5O3, synthesized at high pressure and high temperature, has a monoclinic structure (space group C2/c) at room temperature with a = 9.4590(3) Å, b = 5.5531(2) Å, c = 9.6465(3) Å and β = 108.149(2)°. It undergoes a structural transition from the monoclinic to an orthorhombic (Pnma) symmetry around 650 K. Magnetic measurements show three distinct anomalies at 25, 50 and 97 K. AC susceptibility measurements confirm the occurrence of the magnetic anomalies, but suggest no spin frustration. Interestingly, this oxide shows a giant dielectric constant at room temperature. Two clear relaxation processes commencing around 200 K and 300 K are exhibited by this material. The first relaxation process is due to Maxwell-Wagner polarization at the grain boundary whereas the second relaxation may arise from hopping of electrons in the B-site.

Hydrothermal Synthesis and Structure of a Mixed Valent Heteropoly-oxometallate Keggin Salt: [PMo4.27W7.73O6−40] [H3N(CH2)6NH2+3]3

The polyoxometallate Keggin (αtype) [PMo4.27W7.73O6− 40] [H3N(CH2)6NH2+ 3]3, involving molybdenum and tungsten present in both V and VI oxidation states, has been synthesized under hydrothermal conditions and its structure determined by single crystal X-ray analysis. Black platelet crystals are formed in the monoclinic system, space groupC2/m(No. 12),a=10.336(9),b=20.097(5),c=13.276(6) Å,β=106.41(7)°,V cell=2645(3) Å3,Z=8,d calc=3.555 Mg m−3(CuKαradiation, 2θ max=144°,R(F)=6.56 for 1729 reflections). Due to its location at the origin (2/msite), the anion is found to be disordered, its four independent metal sites occupied with molybdenum and tungsten atoms; a significant preferred localization of the molybdenum on two sites is also reported. The structure has a lamellar organization formed from alternating organic–inorganic planes with their normal parallel toc. A study by ESR has proven the presence of paramagnetic Mo/W(V) in the compound with the observation of a strong signal (g=1.983).

An introduction to nanotechnology policy: Opportunities and constraints for emerging and established economies

Nanotechnology has captured wide attention all over the world and excited the imagination of young and old alike. Interest in the subject has increased remarkably during the last few years because of potential technological applications, and commercial interest has skyrocketed. The promise of nanotechnology as an economic engine that can redefine the wellbeing of regions and nations is pervasive; yet the imprecise language, and overuse of the term nanotechnology, has made that term fuzzier, broader, and trendier than many imagined possible. This is especially evident in nanotechnology market projections, which rose dramatically over the past five years as more traditional “product families” were engulfed by the expanding use of the term. Government policy regarding nanotechnology has often resembled an embrace of imagination rather than a systematic use of what Sun Tzu and others have taught about strategic decision making. Further, if nanotechnology is truly the next wave of technology product paradigms, how will we provide an educated workforce to support it? Moreover, in company with these societal benefits come increased societal risks. This paper is intended to provide policy makers and strategists with observations that might limit actions such as those that led to the “over-hype” of nanotechnology and to the fear (or discounting) of societal risks. In the latter case we might learn from the experiences of policy makers connected with other emerging enabling-technology bases, such as nuclear energy and, to a lesser extent, the “dot-com” boom.

A study of the electronic structures of nv addition compounds of BH3 by a combined use of ups and eels

Orbital energies and electronic transition energies of BH3·H2S and BH3·CO obtained from ultraviolet (HeI) photoelectron spectroscopy and electron energy loss spectroscopy are discussed in the light of quantum mechanical calculations. BH3·H2O has been characterized, for the first time, by means of the HeI spectrum and the ionization energies assigned to the various orbitals based on calculations.

Synthesis and properties of novel nanocomposites made of single-walled carbon nanotubes and low molecular mass organogels and their thermo-responsive behavior triggered by near IR radiation

For the preparation of novel organogel–carbon nanotube nanocomposites, pristine single-walled carbon nanotubes (SWNT) were incorporated into physical gels formed by an L-alanine based low molecular mass organogelator (LMOG). The gelation process and the properties of the resulting nanocomposites were found to depend on the kind of SWNTs incorporated in the gels. With pristine SWNTs, only a limited amount could be dispersed in the organogels. Attempted incorporation of higher amounts of pristine SWNTs led to precipitation from the gel. To improve their solubility in the gel matrix, a variety of SWNTs functionalized with different aliphatic and aromatic chains were synthesized. Scanning electron microscope images of the nanocomposites showed that the texture and organization of the gel aggregates were altered upon the incorporation of SWNTs. The microstructures of the nanocomposites were found to depend on the kind of SWNTs used. Incorporation of functionalized SWNTs into the organogels depressed the sol to gel transition temperature, with the n-hexadecyl chain functionalized SWNTs being more effective than the n-dodecyl chain functionalized counterpart. Rheological investigations of pristine SWNT containing gels indicated that the flow of nanocomposites became resistant to applied stress at a very low wt% of SWNT incorporation. Again more effective control of flow behavior was achieved with functionalized SWNTs possessing longer hydrocarbon chains. This happens presumably via effective interdigitation of the pendant chains with the fatty acid amides of L-alanine in the gel assembly. Remarkably, using near IR laser irradiation at 1064 nm for a short duration (1 min) at room temperature, it was possible to selectively induce a gel-to-sol phase transition of the nanocomposites, while prolonged irradiation (30 min) of the organogel under identical conditions did not cause gel melting.

Macroporous oxide materials with three-dimensionally interconnected pores

Ordered mesoscale hollow spheres (1000 nm diameter) of binary oxides such as TiO2 and ZrO2 as well as of ternary oxides such as ferroelectric PbTiO3 and Pb(ZrTi)O3 have been prepared by templating against colloidal crystals of polystyrene, by adopting different procedures.

CCDC 276978: 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.

Superconductivity in Ba(Pb,Bi,Sb)O3, Ba(Pb,Bi,Te)O3 and (Ba,La) (Pb,Bi,Tl)O3 systems

It is possible to substitute Bi in the superconducting BaPb0.75Bi0.25O3 by Sb or Te without destroying the superconductivity. With Sb, a continuous series of solid solutions BaPb0.75Bi0.25−ySbyO3 (0 ⩽ y ⩽ 0.25) exists, while with Te, perovskite BaPb0.75Bi0.25−yTeyO3 exists only upto y = 0.15. With increasing substitution by Sb or Te, Tc decreases continously in both the systems. Superconductivity with a maximum Tc of 8K is found in Ba0.9La0.1Pb0.9−yBiyTl0.1O3 for y = 0.25.

Synthesis of cuprate superconductors

A variety of synthetic strategies has been employed to prepare pure monophasic cuprates of different families with good superconducting properties. Besides the traditional ceramic method, other methods such as coprecipitation and precursor methods, the sol-gel method, the alkali flux method and the combustion method have been employed for the synthesis of cuprates. Depending on the requirements, varying conditions such as high oxygen or hydrostatic pressure and low oxygen fugacity are employed in the synthesis. In this review, the authors discuss the synthesis of the various types of cuprate superconductors and point out the advantages and disadvantages of the different methods.