Publications

Positron annihilation in defect KCl crystals

Positron lifetime spectra in pure KCl crystals as well as in crystals with cation vacancies, anion vacancies and color centers clearly show three components. The results show that defects play an important role in the annihilation.

Field-induced polar order at the Néel temperature of chromium in rare-earth orthochromites: Interplay of rare-earth and Cr magnetism

We report field-induced switchable polarization ($P$ \ensuremath{\sim} 0.2--0.8 \ensuremath{\mu}C/cm${}^{2}$) below the N\'eel temperature of chromium (${T}_{N}$${}^{\mathrm{Cr}}$) in weakly ferromagnetic rare-earth orthochromites, $R$CrO${}_{3}$ ($R$ $=$ rare earth) but only when the rare-earth ion is magnetic. Intriguingly, the polarization in ErCrO${}_{3}$ (${T}_{C}$ $=$ 133 K) disappears at a spin-reorientation (Morin) transition (${T}_{SR}\ensuremath{\sim}22$ K) below which the weak ferromagnetism associated with the Cr sublattice also disappears, demonstrating the crucial role of weak ferromagnetism in inducing the polar order. Further, the polarization ($P$) is strongly influenced by an applied magnetic field, indicating a strong magnetoelectric effect. We suggest that the polar order occurs in $R$CrO${}_{3}$, due to the combined effect of the poling field that breaks the symmetry and the exchange field on the R ion from the Cr sublattice that stabilizes the polar state. We propose that a similar mechanism could work in the isostructural rare-earth orthoferrites $R$FeO${}_{3}$ as well.

Relation between high T c superconductivity and structure: A study of La 3--x Ba 3+x Cu 6 O 14--d and YBa 2 Cu 3 O 7--d systems

No abstract is provided for this article.

Evidence for supramolecular organization of alkane and surfactant molecules in the process of forming mesoporous silica

N. Ulagappan and C. N. R. Rao, Chem. Commun., 1996, 2759 DOI: 10.1039/CC9960002759

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

Use of Ionic Liquids in the Synthesis of Nanocrystals and Nanorods of Semiconducting Metal Chalcogenides

We have synthesized nanoparticles of hexagonal CdS in the diameter range 3-13 nm by the reaction of cadmium acetate dihydrate with thioacetamide in imidazolium [BMIM]-based ionic liquids. We have obtained three different particle sizes of CdS by changing the anion of the ionic liquid. Addition of trioctylphosphine oxide (TOPO) to the reaction mixture causes greater monodispersity as well as smaller particle size, while addition of ethylenediamine produces nanorods of 7 nm average diameter. Hexagonal ZnS and cubic PbS nanoparticles with average diameters of 3 and 10 nm, respectively, have been prepared by the reaction of the metal acetates with thioacetamide in [BMIM][BF4]. Hexagonal CdSe nanoparticles with an average diameter 12 nm were obtained by the reaction of cadmium acetate dihydrate with dimethylselenourea in [BMIM][BF4]. In this case also we observe the same effect of the addition of TOPO as in the case of CdS. Addition of ethylenediamine to the reaction mixture gives rise to nanorods. ZnSe nanowires with a cubic structures, possible diameters in the range 70-100 nm by the reaction of zinc acetate dihydrate with dimethylselenourea in [BMIM][MeSO4]. The nanostructures obtained are single crystalline in all the cases. Most of the nanostructures show characteristic UV/Vis absorption and photoluminescence emission spectra. The thermodynamically most stable structures are generally produced in the synthesis carried out in ionic liquids.

Dip-pen nanolithography with magnetic Fe2O3 nanocrystals

Dip-pen nanolithography has been employed to obtain magnetic nanopatterns of γ-Fe2O3 nanocrystals on mica and silicon substrates. The chemical and magnetic nature of the patterns have been characterized employing low-energy electron microscopy, x-ray photoemission electron microscopy, and magnetic force microscopy measurements.

CCDC 145989: 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.

Nanocrystals: Synthesis, Properties and Applications

No abstract is provided for this article.

Graphene Analogues of BN: Novel Synthesis and Properties

Enthused by the fascinating properties of graphene, we have prepared graphene analogues of BN by a chemical method with a control on the number of layers. The method involves the reaction of boric acid with urea, wherein the relative proportions of the two have been varied over a wide range. Synthesis with a high proportion of urea yields a product with a majority of 1−4 layers. The surface area of BN increases progressively with the decreasing number of layers, and the high surface area BN exhibits high CO2 adsorption, but negligible H2 adsorption. Few-layer BN has been solubilized by interaction with Lewis bases. We have used first-principles simulations to determine structure, phonon dispersion, and elastic properties of BN with planar honeycomb lattice-based n-layer forms. We find that the mechanical stability of BN with respect to out-of-plane deformation is quite different from that of graphene, as evident in the dispersion of their flexural modes. BN is softer than graphene and exhibits signatures of long-range ionic interactions in its optical phonons. Finally, structures with different stacking sequences of BN have comparable energies, suggesting relative abundance of slip faults, stacking faults, and structural inhomogeneities in multilayer BN.

A Brillouin scattering study of the quasi-one-dimensional blue bronze, K_0.3MoO₃

Brillouin scattering measurements have been carried out for the first time on K0.3 MoO3 . The spectrum reveals two bulk modes at 18 and 27 GHz and a Rayleigh surface mode at 6 GHz. Both the bulk modes and the surface mode exhibit changes at the Peierls transition (180 K). Interestingly, the 18 GHz mode also shows softening at the incommensurate-commensurate transition around 100 K, suggesting the important role of phasons.

A XANES study of mixed-valence transition-metal oxides and rare-earth alloys

Energies of the 1s → 3d. 1s → 4s and 1s → 4p transitions of Mn, Fe and Co in a series of oxides have been obtained from X-ray absorption near-edge structure (XANES). Bivalent metal oxides do not show separate features in XANES due to the two oxidation states of the metal, but the spectroscopic transition energies. E T: as well as the 3d-4s and 3d-4p energy differences. δE, increase smoothly with the oxidation number of the metal or its effective atomic charge, q. The variation of transition energies as well as δE values with q is best described by the parabolic relation. E T (or δ E) = aq + bq 2. Mixed-valence cerium and ytterbium alloys distinctly show transitions due to the valence states in the XANES.

Effect of deuteration on hydrogen bonds

A study of the 1 : 1 interaction of CH3OD and t-C4H9OD as well as the corresponding hydroxy derivatives with electron donor molecules has shown that the enthalpies of formation of complexes are generally increased by ∼1 to 2 kJ mol–1 on deuteration. Enthalpies of dimerization of t-C4H9OH and t-C4H9OD are comparable. Deuterium bond energies may be lower than hydrogen bond energies only for very short hydrogen bonds. The shift in the O—H stretching frequency Δtext-decoration:overlineνOH is related to Δtext-decoration:overlineνOD by the relation, Δtext-decoration:overlineνOH≈ 1.414 Δtext-decoration:overlineνOD as expected on the basis of mass effect alone.

Exploration of a Simple Universal Route to the Myriad of Open-Framework Metal Phosphates

The reaction of a single amine phosphate, piperazine phosphate, with ZnII ions is shown to yield a variety of open-framework metal phosphate structures. It is noteworthy that the reaction of this amine phosphate with ZnII ions yields a hierarchy of structures, including the linear chain, layer and 3-dimensional systems. Of particular interest is the isolation of the linear chain structure consisting of corner-shared four-membered rings, which has been considered to be the primary building block. By the reaction of piperazine phosphate with CoII ions, we obtained a new strip and a layer structure. Reaction of piperazine phosphate with SnII yields a layer structure. The significant role of the amine phosphates in the formation of open-framework metal phosphate structures is also supported by the isolation of a monomeric four-membered zinc phosphate, which on heating transforms to an open-framework structure.

Insulator–metal transitions induced by electric and magnetic fields, in thin films of charge-ordered Pr1−Ca MnO3

Thin films of charge-ordered manganates, Pr1−x Ca x MnO3 (x=0.3,0.4) are shown to undergo electric current-induced insulator–metal (I–M) transitions, the transition temperature increasing with the current. The occurrence of I–M transitions in these films without prior laser irradiation is noteworthy. The films show interesting memory effects and some non-linearity in the I–V characteristics. The magnetic-field induced I–M transition in the films is independent of the current employed. At low magnetic fields, or at low currents, resistance oscillations occur due to temporal fluctuations between resistive states.

CCDC 600778: 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.

Indo-U.S. conference on chemical education: Design for innovation

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTIndo-U.S. conference on chemical education: Design for innovationG. S. Hammond , V. Ramakrishna , C. N. R. Rao , and M. Tamres Cite this: J. Chem. Educ. 1970, 47, 1, 36Publication Date (Print):January 1, 1970Publication History Received3 August 2009Published online1 January 1970Published inissue 1 January 1970https://doi.org/10.1021/ed047p36RIGHTS & PERMISSIONSArticle Views81Altmetric-Citations-LEARN 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 InReddit PDF (3 MB) Get e-Alertsclose Get e-Alerts

Phenyl lead (IV) azides—preparation, properties and infra-red spectra

Two stable tetravalent lead azides, triphenyl lead azide and diphenyl lead diazide have been prepared and characterized. Physical properties such as crystal morphology, infra-red spectra, X-ray diffraction, solubility and thermal behaviour are reported.