Publications

Structure-Property Relations in High-Temperature Oxide Superconductors: Nature of Oxygen and Copper

No abstract is provided for this article.

A simple n -state model for water

A simple n-state configurational excitation model which takes into account the presence of weakly connected pentamer units in liquid water is proposed. The model has features of both the “continuum” and “mixture” models. Calculations based on this model satisfactorily account for the important, diagnostic thermodynamic properties of water such as the density maximum, fraction of monomers and so on.

CCDC 203868: 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.

Paramagnetic Meissner effect in YBa2Cu3O7−δ

The low-field dependence of non resonant microwave absorption (MWA) in polycrystalline samples of YBa2Cu3O7−δ with 0.1≤δ≤0.5 has been measured at T < T c along with simultaneous monitoring of paramagnetic impurities in the chain copper (Cu-I) sites by EPR spectroscopy. MWA exhibits a cross-over from the normal zero-field minimum to an anomalous zero-field maximum accompanied by the gradual appearance and growth of the EPR signal as δ is changed from 0.1 to 0.5. It is to be noted that in the δ = 0.3−0.4 composition range, oxygen vacancies are disordered giving rise to magnetic moments due to isolated Cu2+ impurity ions. This correlation of the anomalous MWA with isolated paramagnetic Cu2+ impurities is consistent with the presence of π junctions, earlier implicated in the paramagnetic Meissner effect (PME), which in turn is related to the anomalous MWA.

ChemInform Abstract: A Manganese Sulfite with Extended Metal—Oxygen—Metal Bonds Exhibiting Hydrogen Uptake.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Investigations of a few novel series of thallium cuprate superconductors showing possible change in the sign of charge carriers with composition

Chemistry of materials

No abstract is provided for this article.

CCDC 145228: 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.

Synthesis, anion order and magnetic properties of RVO3−xNx perovskites (R = La, Pr, Nd; 0 ≤ x ≤ 1)

The rare earth vanadium oxynitride perovskites RVO3−xNx (R = La, Pr, Nd; 0 ≤ x ≤ 1) have been prepared by treatment of RVO4 precursors in NH3. The ammonolysis reactions proceed through an initial reduction of RVO4 precursors to RVO3 perovskites that are progressively nitrided and reoxidised to RVO3−xNx materials with varying proportions of V4+/V3+. Variable temperature neutron diffraction studies show that NdVO2N and PrVO2.24N0.76 have orthorhombic Pbnm symmetry between 3.5 and 300 K, but LaVO2.11N0.89 undergoes a broad Pbnm to Rc structural transition over this temperature range. In LaVO3−xNx samples the proportion of the Rc phase at room temperature increases with the nitrogen content. The partial anion order indicative of planes of cis-VN2 chains found in NdVO2N is also present in PrVO2.24N0.76, and is thus robust to the disorder created by non-stoichiometry. Magnetic measurements reveal spin freezing transitions at low temperatures in LaVO2.09N0.91 and PrVO2.24N0.76, but NdVO2N is paramagnetic.

A new precursor route for the growth of NbO₂ thin films by chemical vapor deposition

Niobium dioxide (NbO2) exhibits metal-insulator transition (Mott transition) and shows the potential for application in memristors and neuromorphic devices. Presently growth of NbO2thin films requires high-temperature reduction of Nb2O5films using H2or sophisticated techniques such as molecular beam epitaxy and pulsed laser deposition. The present study demonstrates a simple chemical route of the direct growth of crystalline NbO2films by chemical vapor deposition using a freshly prepared Nb-hexadecylamine (Nb-HDA) complex. X-ray diffraction studies confirm the NbO2phase with a distorted rutile body-centered-tetragonal structure and the film grown with a highly preferred orientation onc-sapphire. X-ray photoelectron spectroscopy confirms the +4 oxidation state. The present method offers facile growth of NbO2films without post-reduction steps which will be assumed to be a cost-effective process for NbO2based devices.

Influence of Cation Size on the Structural Features of Ln_1/2A_1/2MnO₃ Perovskites at Room Temperature

Polycrystalline samples of Ln1/2Sr1/2MnO3 (Ln = La, Pr, La0.33Nd0.67, Nd, Nd0.5Sm0.5, Sm, and Gd) and Ln1/2Ca1/2MnO3 (Ln = La, Pr, La0.5Nd0.5, Nd, Sm, and Y0.5Sm0.5) have been prepared, and structure determinations have been carried out at room temperature using high-resolution synchrotron X-ray powder diffraction data. The octahedral tilting distortion increases as the average ionic radius of the Ln/A cations, 〈rA〉, decreases. The two crystallographically distinct Mn−O−Mn bonds [Mn−O(eq)−Mn and Mn−O(ax)−Mn] are almost identical for Ln0.5Ca0.5MnO3 compounds, with the exception of La0.5Ca0.5MnO3. The La0.5Ca0.5MnO3 compound and the entire Ln0.5Sr0.5MnO3 series adopt structures where the Mn−O(eq)−Mn bond angle is consistently and significantly larger (2−6°) than the Mn−O(ax)−Mn bond angle. All of the Ln0.5Ca0.5MnO3 compounds have Pnma symmetry, whereas across the Ln0.5Sr0.5MnO3 series with increasing 〈rA〉, an evolution from Pnma (tilt system a-b+a-) over Imma (tilt system a-b0a-) to I4/mcm (tilt system a0a0c-) symmetry is observed. It appears that the latter two tilt systems are stabilized with respect to the rhombohedral (R3̄c) a-a-a- tilt system, by short-range layered ordering of A-site cations. Changes in the octahedral tilt system at room temperature are linked to changes in the low-temperature magnetic structure. In particular, the simultaneous onset of charge ordering and CE-type antiferromagnetism in the Ln0.5Sr0.5MnO3 series appears to be closely associated with the Imma structure. The average Mn−O bond distance is relatively constant across the entire series, but individual Mn−O bond distances show the presence of a cooperative Jahn−Teller effect (orbital ordering) at room temperature in Sm0.5Ca0.5MnO3 and Sm0.25Y0.25Ca0.5MnO3.

Hopping conduction in La_1–xSr_xCoO₃and Nd_1–xSr_xCoO₃

Hopping conduction in Ln1 – xSrxCoO3 is discussed in terms of localization due to disorder and in the light of Mössbauer measurements. The hopping times deduced from conductivity and Mössbauer effect differ widely, and an explanation is suggested.

In2O3 nanowires, nanobouquets and nanotrees

In2O3 nanowires have been prepared by carbon-assisted synthesis starting from In2O3 or In metal. The nanowires have been characterized by X-ray diffraction, electron microscopy and photoluminescence spectroscopy. The nanowires are single crystalline growing in the 〈100〉 direction, as established by high resolution electron microscopy. When a mixture of In2O3 and carbon was used as the starting material, nanowires were obtained along with nanotrees and nanobouquets. The observation of these nanostructures indicates that the growth of the nanowires occurs by the vapor–liquid–solid mechanism. Starting with In metal, only the oxide nanowires were obtained.

V. Nanotubes and Nanowires

No abstract is provided for this article.

Generation of Onions and Nanotubes of GaS and GaSe through Laser and Thermally Induced Exfoliation

Although theoretical calculations have predicted that layered GaS and GaSe should form nanotube and related structures, they have not been prepared experimentally to date. We have carried out laser irradiation as well as thermal treatment of GaS and GaSe to cause exfoliation, which yielded onionlike structures and nanotubes by the rolling of the exfoliated sheets.

Dielectric properties of glasses prepared by quenching melts of superconducting Bi-Ca-Sr-Cu-O cuprates

Glasses obtained from quenching melts of superconducting bismuth cuprates of the formula Bi2(Ca,Sr)n+1CunO2n+4 with n=1 and 3 exhibit novel dielectric properties. They possess relatively high dielectric constants as well as high electrical conductivity. The novel dielectric properties of these cuprate glasses are likely to be of electronic origin. They exhibit a weak microwave absorption due to the presence of microcrystallites.

Crystallographic study of the transition in Ti2O3

X-ray crystallographic studies of highly purified Ti2O3 show abrupt changes in the lattice parameters with temperature in the range 390–470°K. The distension of the unit cell in this temperature range is readily correlated with corresponding changes in resistivity.

CCDC 170832: 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.