Publications

Cation size disorder as the crucial determinant of the unusual magnetic and electronic properties of Gd_0.5Ba_0.5CoO₃

An investigation of three series of cobaltates of the formulae Gd0.5−xLnxBa0.5 CoO3−δ (Ln = Nd or La) and La0.5−xNdxBa0.5CoO3−δ demonstrates the effects of the average radius of the A-site cations, , on the magnetic and electrical properties. Thus, the anomalous magnetic properties of Gd0.5Ba0.5CoO3, such as the transitions in the range 220–290 K, disappear, even with a small substitution of Nd or La in place of Gd, and a gradual evolution of ferromagnetism occurs at low temperatures (130–190 K). Gd0.5Ba0.5−xSrxCoO3, on the other hand, shows increasing ferromagnetic properties with increase in x although the decreases, suggesting the role of size disorder. Studies of cobaltates of the type with fixed values of 1.317 and 1.289 Å (the latter corresponding to Gd0.5Ba0.5CoO3), reveal that on decreasing the size disorder, the materials become ferromagnetic with relative high Tc values. These cobaltates also exhibit size disorder controlled metal–insulator transitions, the compositions with high disorder being insulators. The properties of Dy0.5Ba0.5CoO3 are consistent with the presence of size disorder in this material.

THE INFRARED SPECTRA OF 4-SUBSTITUTED-THIOSEMICARBAZIDES AND DIAZOTIZATION PRODUCTS

The infrared absorption spectra of 4-substituted-thiosemicarbazides, 5-(substituted)amino-1,2,3,4-thiatriazoles, and the corresponding isomeric tetrazolinethiones have been studied and structural assignments of importance to these systems made or suggested. Important conclusions drawn from the spectral data are: there is no suggestion of any thiol–thione tautomerism for the solid 4-substituted-thiosemicarbazides and that the thione structure predominates for these substances; that the so-called 5-thiol-tetrazoles also exist as thiones; and that the diazotization products of the 4-substituted-thiosemicarbazides yield 1,2,3,4,-thiatriazoles rather than the isomeric open chain thiocarbamyl azides. The C==S, —N—C==S, and cyclic —N—N==N— configurational assignments, which are of importance to the classes of compounds studied, are discussed.

Electron states of benzene…HCl and toluene…HCl hydrogen bonded complexes by ultraviolet photoelectron spectroscopy

Electron states of the benzene...HCl complex have been studied by UV photoelectron spectroscopy. Two vertical ionization energies of the complex at 10.84 and 12.10 eV have been assigned to π C6H6 and nCl orbitals, respectively. While the π C6H6 orbital in the complex is shifted by 1.57 eV to higher binding energy, the nCl MO is shifted by 0.63 eV to lower binding energy with reference to the corresponding free benzene and HCl molecules. Ab initio MO calculations confirm these assignments. The toluene...HCl complex has also been studied. The larger shifts in the π(1.90 eV) and nCl(0.88 eV) orbital energies in the toluene ...HCl complex compared to those of the benzene…HCl complex are consistent with stronger π hydrogen bonding in the case of toluene.

Vibrational spectra and normal vibrations of methyl N-methyl-carbamate and N-methylcarbamoyl halides

Infrared spectra of methyl N-methylcarbamate and its N-deuterated derivative have been recorded and the normal vibration analysis carried out employing the Urey-Bradley force field. The vibrational assignments of this secondary amide ester are compared with those of the primary amide ester, secondary amides and the thio analogue. Normal vibration analyses of the N-methylcarbamoyl chloride and bromide have been carried out and the UBF force constants of various secondary amide derivatives compared.

Porous materials: A case study of supramolecular organization in materials design

No abstract is provided for this article.

Separation of metallic and semiconducting single-walled carbon nanotubes through fluorous chemistry

Separation of metallic from semiconducting single-walled carbon nanotubes has been a major challenge for some time and some previous efforts have resulted in partial success. We have accomplished the separation effectively by employing fluorous chemistry wherein the diazonium salt of 4-heptadecafluorooc tylaniline selectively reacts with the metallic nanotubes present in the mixture of nanotubes. The resulting fluoroderivative was extracted in perfluorohexane leaving the semiconducting nanotubes in the aqueous layer. The products have been characterized by both Raman and electronic absorption spectroscopy. The method avoids the cumbersome centrifugation step required by some other procedures.

Phase transformations and electrical properties of bismuth sesquioxide

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTPhase transformations and electrical properties of bismuth sesquioxideC. N. Ramachandra Rao, G. V. Subba Rao, and S. RamdasCite this: J. Phys. Chem. 1969, 73, 3, 672–675Publication Date (Print):March 1, 1969Publication History Published online1 May 2002Published inissue 1 March 1969https://pubs.acs.org/doi/10.1021/j100723a031https://doi.org/10.1021/j100723a031research-articleACS PublicationsRequest reuse permissionsArticle Views393Altmetric-Citations77LEARN 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

Oxygen Excess in Layered Lanthanide Nickelates

Ultra-thin crystalline films of ZnS and PbS formed at the organic–aqueous interface

Ultra-thin films of ZnS have been prepared by the reaction of zinc cupferronate or zinc stearate in a toluene solution with an aqueous solution of Na2S. The films have been examined by electron microscopy and other techniques. The reaction at the interface yields excellent films which are generally single-crystalline. The effects of reaction parameters such as temperature and reactant concentration have been examined. Ultra-thin crystalline films of PbS have been obtained by the reaction of a toluene solution of lead cupferronate with the aqueous solution of Na2S. The organic–aqueous interface provides a simple and elegant method of producing good crystalline films of important semiconducting materials.

The infrared spectra of organic thiocyanates and isothiocyanates

The infrared spectra of several organic thiocyanates and isothiocyanates have been studied. The thiocyanates and the isothiocyanates can be distinguished by their characteristic vibration frequencies around 2140 cm−1 and between 2060–2105 cm−1, respectively. These respective frequencies serve as an analytical tool for distinguishing these isomers both singly and in mixtures.

Kagome network compounds and their novel magnetic properties

Compounds possessing the Kagome network are truly interesting because of their unusual low-energy properties. They exhibit magnetic frustration because of the triangular lattice inherent to the hexagonal bronze structure they possess, as indeed demonstrated by some of the Fe(3+) jarosites, but this is not the general case. Kagome compounds formed by transition metal ions with varying spins exhibit novel magnetic properties, some even showing evidence for magnetic order and absence of frustration. We describe the structure and magnetic properties of this interesting class of materials and attempt to provide an explanation for the variety of properties on the basis of theoretical considerations.

Borocarbonitride, (BN)X(C)1-X, nanosheet-reinforced polymer nanocomposites for high mechanical performance

The enhancement in mechanical and thermal properties of polymer matrices upon reinforcing with nanoparticles strongly depends on the extent of molecular-level interactions and interfacial adhesion between the nanofiller and the matrix material, which are, in turn, governed by the surface functionalities on the nanofiller. Herein, we examine the reinforcing effect of nanosheets of borocarbonitide, (BN)x(C)1-x , which are analogues to graphene (x = 0) and boron nitride sheets (x = 1), whose surface functional groups vary with the composition, on the mechanical and thermal properties of poly(vinyl alcohol), PVA. Results show that substantial improvement in hardness and elastic modulus of PVA is achieved by adding just 0.2 wt% of BCN. A significant enhancement in the thermal stability was also noted. These results are rationalized by recourse to detailed structural characterization, which shows a substantial enhancement in the degree of crystallinity in PVA upon BCN addition, and improved interfacial adhesion between the nanofiller and the polymer matrix via strong intermolecular interactions. Overall, our results show that it is possible to engineer polymer matrix nanocomposites with exceptional mechanical and thermal properties via the addition of a small amount of BCN.

A Nanoporous Borocarbonitride (BC₄N) with Novel Properties Derived from a Boron‐Imidazolate‐Based Metal–Organic Framework

Soak it up: A boron-imidazolate metal–organic framework composed of a mixed ligand system acts as a precursor for the synthesis of a high-surface-area borocarbonitride (BC4N) with remarkable H2 and CO2 storage properties (see figure; ndc=naphthalenedicarboxylate). Furthermore, BC4N has been exploited for the stabilisation of metal (Au and Pd) nanoparticles.

An electron spectroscopic study of the surface oxidation of glassy and crystalline Cu-Zr alloys

Surface oxidation of three metglasses in the Cu-Zr system has been investigated by employing X-ray photoelectron spectroscopy and Auger electron spectroscopy with a view to comparing their oxidation behaviour with that of the corresponding crystalline states of the alloys. Surface oxidation of pure Zr metal has also been examined in detail using these techniques. Sub-oxides of Zr are formed during the initial stages of oxidation of Zr (at oxygen exposures <10L), while at higher exposures, ZrO2 is formed together with the highest possible sub-oxide which the authors designate as 'ZrO'. The relative proportion of 'ZrO' goes through a maximum in the range 25-50 L. Both the glassy and the crystalline states of the Cu-Zr alloys exhibit preferential oxidation of Zr. The glassy alloys exhibit a higher rate of oxidation at intermediate exposures compared with the crystalline states of the alloys; the extent of oxidation at higher oxygen exposures is, however, higher for crystalline alloys. Interatomic Auger transitions have been found in the Zr+O2 system as well as in Cu-Zr alloys.

XPES studies of oxides of second- and third-row transition metals including rare earths

X-ray photoelectron spectroscopy has been employed to investigate oxides of second- and third-row transition metals, including those of rare earths. Systematics in the spin—orbit splittings and binding energies of core levels of the metals are described. In most of the cases studied, the dependence of the spin—orbit splittings on the atomic number Z is given by the relation ΔE = a(Z - Z 0)4, where a is the quantum defect parameter and Z 0 is the effective screening. Core-level binding energies are found to increase with the oxidation state of the metal. Most of the core-level binding energies are related to the atomic number Z by the expression E = x(Z - Z 0)2, giving rise to linear plots of ln E versus ln Z. Specific features of individual oxides, with respect to satellites, multiplet structure, configuration mixing, and other properties are also discussed. The spectra of PrO2, Pr6O11, TbO2 and Tb4O7 are reported for the first time.

Neuromorphic devices realised using self-forming hierarchical Al and Ag nanostructures: towards energy-efficient and wide ranging synaptic plasticity

Closely mimicking the hierarchical structural topology with emerging behavioral functionalities of biological neural networks in neuromorphic devices is considered of prime importance for the realization of energy-efficient intelligent systems. In this article, we report an artificial synaptic network (ASN) comprising of hierarchical structures of isolated Al and Ag micro-nano structures developed

Basic building units, self-assembly and crystallization in the formation of complex inorganic open architectures

No abstract is provided for this article.

Synthesis of complex metal oxides using hydroxide, cyanide, and nitrate solid solution precursors

Precursor solid solutions provide convenient routes for preparing complex metal oxides. Hydroxide solid solutions of the general formula Ln 1−x M x (OH)3 (where Ln = La or Nd and M = Al, Cr, Fe, Co, or Ni) and La1−x−y M′ x M″ y (OH)3 (where M′ = Ni and M″ = Co or Cu) crystallize in the rare earth trihydroxide structure and can be decomposed at relatively low temperatures to yield complex metal oxides. Several oxides of the type LaNiO3, NdNiO3, LaNi1−x Co x O3, and LaNi1−x Cu x O3 have been prepared by the hydroxide precursor route. Thermal decomposition of cyanide precursors of the type Ln[M 1−x M′ x (CN)6] · 5H2O and Ln 1−x Ln′ x [M(CN)6] · 5H2O yields the quaternary oxides which are not readily made by ceramic methods. Nitrate solid solution precursors of the type Ba1−x Pb x (NO3)2, Sr1−x Pb x (NO3)2, and BaSrPb(NO3)6 have been used for preparing several interesting oxides such as BaPbO3, Ba2PbO4, and BaSrPbO4.