A chemical approach to an understanding of the fast ion conduction in silver iodide-silver oxysalt glasses

A number of AgI based fast ion conducting glasses, with a general formula AgI---Ag2O---MxOy (MxOy=MoO3, SeO3, WO3, V2O5, P2O5, GeO2, B2O3, As2O3, CrO3) have been studied. A chemical approach is made to investigate the origin of fast ion conduction in these glasses. An index known as Image tructural Image npinning Image umber, SUN (S), has been defined for the purpose, based on the unscreened nuclear charge of silver ions and the equilibrium lectronegativities of the halide-oxyanion matrix in these glasses. The variation of the glass transition temperature, Tg, conductivity, σ, and the energy of activation, Ea, with the concentration of AgI are discussed in the light of the structural unpinning number. Conductivities increase uniformly in any given glass series as a smooth function of S and level off at very high values. The entire range of conductivity appears to vary as ln Image , where ln σ0 corresponds roughly to the conductivity of the hypothetical AgI glass and “a” is a constant which could be obtained as the slope in the graph of ln Ea versus S. It is suggested that the increase in the concentration of AgI beyond 75–80 mole% in the glass is not advantageous from the conductivity point of view.

Electronic phase separation in correlated oxides: The phenomenon, its present status and future prospects

Many transition metal oxide materials of high chemical purity are not necessarily monophasic. Thus, single crystals of chemically pure rare earth manganites and cobaltates of the general formula Ln1-xAxMO3 (Ln=rare earth metal, A=alkaline earth metal, M=Mn, Co) exhibit the phenomenon of electronic phase separation wherein phases of different electronic and magnetic properties coexist. Such phase separation, the length scale of which can vary anywhere between a few nanometers to microns, gives distinct signatures in X-ray and neutron diffraction patterns, electrical and magnetic properties, as well as in NMR and other spectroscopies. While the probe one employs to investigate electronic phase separation depends on the length scale, it is noteworthy that direct imaging of the inhomogeneities has been accomplished. Some understanding of this phenomenon has been possible on the basis of some of the theoretical models, but we are far from unraveling the varied aspects of this new phenomenon. Herein, we present the highlights of experimental techniques and theoretical approaches, and comment on the future outlook for this fascinating phenomenon

Complexes of lanthanide nitrates with N,N-diethylantipyrine-4-carboxamide

New complexes of lanthanide nitrates with N, N-diethylantipyrine-4-carboxamide (DEAP), with the general formulae [Ln2(DEAP)3] [NO3]6 (where Ln = La, Pr, Nd, Sm, Tb, Ho, Er, Yb and Y) have been isolated and characterized by chemical analysis and various physical methods such as electrolytic conductance, IR and13C NMR spectral data. Electrolytic conductance values and infrared spectral studies indicate that the nitrate groups are coordinated. Infrared and13C NMR spectral analysis show that the ligand DEAP is coordinated to the tripositive metal ion through the diethylcarboxamide carbonyl and antipyrine carbonyl oxygens in a bidentate fashion.

Density-wave theory of dislocations in crystals

The density-wave theory of Ramakrishnan and Yussouff is extended to provide a scheme for describing dislocations and other topological defects in crystals. Quantitative calculations are presented for the order-parameter profiles, the atomic configuration, and the free energy of a screw dislocation with Burgers vector b=(a/2, a/2, a/2) in a bcc solid. These calculations are done using a simple parametrization of the direct correlation function and a gradient expansion. It is conventional to express the free energy of the dislocation in a crystal of size R as (λb2/4π)ln(αR/‖b‖), where λ is the shear elastic constant, and α is a measure of the core energy. Our results yield for Na the value α≃1.94a/(‖c1’’‖)1/2 (≃1.85) at the freezing temperature (371 K) and α≃2.48a/(‖c1’’‖)1/2 at 271 K, where c1’’ is the curvature of the first peak of the direct correlation function c(q). Detailed results for the density distribution in the dislocation, particularly the core region, are also presented. These show that the dislocation core has a columnar character. To our knowledge, this study represents the first calculation of dislocation structure, including the core, within the framework of an order-parameter theory and incorporating thermal effects.

2,4-Lutidine-1-oxide complexes of lanthanide perchlorates

2,4-Lutidine-1-oxide (2,4-LutO) complexes of lanthanide perchlorates of the formulae Ln2(2,4-LutO)13(ClO4)6 (Ln = Pr and Nd) and Ln2(2,4-LutO)15 (ClO4)6 (Ln = La, Tb, Dy, Ho and Yb) have been prepared and characterised by chemical analysis, IR, NMR, conductance and electronic spectral data. Proton NMR data along with the IR data show that the ligand coordinates to the metal ion through the oxygen. Conductance data of the complexes in acetone and nitrobenzene indicate that the perchlorate is not coordinated to the metal ion.

Magnetic susceptibility studies on ternary oxides of copper(II)

The magnetic susceptibilities of a large number of ternary oxides of copper having structural features common to the presently identified phases of high-temperature superconductors have been studied in the temperature range 14-300 K. The systems studied are Ln2CuOP( Ln = La, Pr, Nd, etc.), Sr2CuO2CI2,B i2Cu0,, Ca2Cu03,S r2Cu03,S rCu02, MgCu203,B a2Cu3O4CI2Y, 2Cu205,Y2BaCu0,, BaCu02, Li2Cu02, etc. Cu2+ ions take different coordinations, like isolated square planar, square pyramidal or distorted-tetrahedral and octahedral, in these compounds. These compounds also exhibit different varieties of possible magnetic superexchange interactions like 180' or 90' Cu-0-Cu or Cu-0-0-Cu types as well as direct Cu-Cu interactions. Compounds in which there are extended 180' Cu-0-Cu interactions show a low, nearly temperature-independent susceptibility (100 X lod emu/mol). The estimated value of J for the Cu-0-Cu interaction is between 800 and 1500 K in these compounds. Isolated Cu2+ ions in which there are no 180' or close to 180" Cu-0-Cu interactions show Curie-Weiss susceptibility behavior. Compounds with only Cu-0-0-Cu interaction show evidence for the onset of antiferromagnetic coupling between 30 and 50 K. The superexchange rules are useful for explaining the qualitative features of the results. The possibility of disproportionation of Cu2+ ion when there are short Cu-Cu distances as in Bi2Cu04 is discussed. The extended geometry of the copper-oxygen framework seems to be more important than the local geometry around the Cu2+ ion in determining the magnetic properties.

Complexes of lanthanide nitrates with O,O′,N-triisopropyl phosphoramidate

A substituted phosphoramidate has been used as a ligand to lanthanides for the first time. New complexes of lanthanide nitrates with O,O′,N-triisopropyl phosphoramidate (TIP) of the general formula Ln(TIP)3(NO3)3 where Ln=La-Yb and Y have been synthesised and characterised by chemical analysis, infrared and visible electronic spectra and electrical conductance.Infrared spectra indicate the coordination of the ligand to the metal ions through the oxygen of the P=O group. IR and conductance show that the nitrate groups are all coordinated. Electronic spectral shapes have been interpreted in terms of an eight coordinate geometry around the metal ions.

Solid-state chemistry of high-temperature oxide superconductors:The experimental situation

High-temperature superconductivity in oxides of the type(La, Ln)2?xBax(Sr)xCuO4, Y(Ln)Ba2Cu3O7??, La3?xBa3+xCu6O14, and related systems is discussed with emphasis on aspects related to experimental solid-state chemistry. All of these oxides possess perovskite-related structures. Oxygen-excess and La-deficient La2CuO4 also exhibit superconductivity in the 20�40 K just as La2?xBax(Srx)CuO4; these oxides are orthorhombic in the superconductivity phase. The crucial role of oxygen stoichiometry in the superconductivity ofYBa2Cu3O7?? (Tc = 95 ± 5K) is examined; this oxide remains orthorhombic up to ? ? 0.6 and becomes tetragonal and nonsuperconducting beyond this value of ?. Oxygen stoichiometry in this and related oxides has to be understood in terms of structure and disorder. The structure of La3?xBa3+xCu6O14 is related to that of YBa2Cu3O7, the orthorhombic structure manifesting itself when the population of O1 oxygens (along the Cusingle bondOsingle bondCu chains) is preponderant compared to that of O5 oxygens (along thea-axis); nearly equal populations of O1 and O5 sites give rise to the tetragonal structure. A transition from a high-Tc (95 K) superconductivity regime to a low-Tc (not, vert, similar60 K) regime occurs in YBa2Cu3O7?? accompanying a change in ?. There is no evidence for Cu3+ in these nominally mixed valent copper oxides. Instead, holes are present on oxygens giving rise to O? or O2?2 species, the concentration of these species increasing with the lowering of temperature. Certain interesting aspects of the superconducting oxides such as domain or twin boundaries, Raman spectra, microwave absorption, and anomalous high-temperature resistivity drops are presented along with the important material parameters. Preparative aspects of the superconducting oxides are briefly discussed. Phase transitions seem to occur atTc as well as at not, vert, similar240 K in YBa2Cu3O7.

Topological defects in crystals: A density-wave theory

A new approach for describing dislocations and other topological defects in crystals, based on the density wave theory of Ramakrishnan and Yussouff is presented. Quantitative calculations are discussed in brief for the order parameter profiles, the atomic configuration and the free energy of a screw dislocation with Burgers vector b = (a/2, a/2,a/2 ) in a bcc solid. Our results for the free energy of the dislocation in a crystal of sizeR, when expressed as (λb 2/4π) ln (αR/|b|) whereλ is the shear elastic constant, yield, for example, the valueα ⋍ 1·85 for sodium at its freezing temperature (371°K). The density distribution in the presence of the dislocation shows that the dislocation core has a columnar character. To our knowledge, this study represents the first calculation of dislocation structure, including the core, within the framework of an order parameter theory incorporating thermal effects.

Search on a hypercubic lattice using a quantum random walk. II. d = 2

We investigate the spatial search problem on the two-dimensional square lattice, using the Dirac evolution operator discretized according to the staggered lattice fermion formalism. d = 2 is the critical dimension for the spatial search problem, where infrared divergence of the evolution operator leads to logarithmic factors in the scaling behavior. As a result, the construction used in our accompanying article A. Patel and M. A. Rahaman, Phys. Rev. A 82, 032330 (2010)] provides an O(root N ln N) algorithm, which is not optimal. The scaling behavior can be improved to O(root N ln N) by cleverly controlling the massless Dirac evolution operator by an ancilla qubit, as proposed by Tulsi Phys. Rev. A 78, 012310 (2008)]. We reinterpret the ancilla control as introduction of an effective mass at the marked vertex, and optimize the proportionality constants of the scaling behavior of the algorithm by numerically tuning the parameters.

Effect of substrate roughness on growth of diamond by hot filament CVD

Polycrystalline diamond coatings are grown on Si (100) substrate by hot filament CVD technique. We investigate here the effect of substrate roughening on the substrate temperature and methane concentration required to maintain high quality, high growth rate and faceted morphology of the diamond coatings. It has been shown that as we increase the substrate roughness from 0.05 mu m to 0.91 mu m (centre line average or CLA) there is enhancement in deposited film quality (Raman peak intensity ratio of sp (3) to non-sp (3) content increases from 1.65 to 7.13) and the substrate temperature can be brought down to 640A degrees C without any additional substrate heating. The coatings grown at adverse conditions for sp (3) deposition has cauliflower morphology with nanocrystalline grains and coatings grown under favourable sp (3) condition gives clear faceted grains.

Amino acid-lanthanide interactions, Part 2. The X-ray crystal structures of lanthanide and calcium complexes of 1-amino-cyclohexane-1-carboxylic acid (Acc6)

The structures of [Nd-2(Acc(6))(H2O)(6)](ClO4)(6) .(H2O)(6) (1) [Er-2(Acc(6))(4)(H2O)(8)](ClO4)(6) .(H2O)(11) (2) and [Ca-5(Acc(6))(12)(H2O)(6)](ClO4)(10).(H2O)(4) (3) (Acc(6) = 1-aminocyclohexane-1-carboxylic acid) have been determined by X-ray crystallography. The lanthanide complexes 1 and 2 are dimeric in which two lanthanide cations are bridged by four carboxylato groups of Acc(6) molecules. In addition, the neodymium complex (1) features the unidentate coordination of the carboxyl group of an Acc(6) molecule in place of a water molecule in the erbium complex (2). The coordination number in both 1 and 2 is eight. The calcium Acc(6) complex (3) is polymeric; three different calcium environments are observed in the asymmetric unit. Two calcium ions are hexa-coordinated and one is hepta-coordinated. Considerable differences are observed between the solid state structures of Ln(III) and Ca-II complexes of Acc(6

Lanthanide perchlorate complexes of o,o' diisopropyl, n(-4-antipyryl) phosphoramidate

Five new complexes of lanthanide perchlorates with a new ligand O,O' diisopropyl N(-4-antipyryl) phosphoramidate (DIAP) of the general formula Ln(DIAP)4(ClO4)3 where Ln = La, Pr, Nd, Sm and Gd, have been synthesised and characterized by chemical analysis, IR(200–4000cm−1) and electronic spectra and electrical conductance data. Infrared spectral data indicate the coordination of the ligand to the metal ions in a bidentate fashion, through the C=O oxygen of the antipyrine group and the P=O group. IR and conductance values show that the three perchlorate groups are ionic. Electronic spectrum of the Nd3+ complex in the visible region, indicates reasonable covalency in the metal-ligand bond. The available data point to an eight coordinate geometry around the metal ions, with each ligand behaving in a bidentate ‘00’ fashion.

4-Nitro 2-picoline-l-oxide complexes of lanthanide perchlorates

4-Nitro 2-picoline-l-oxide (NPicO) complexes of the formulae La (NPicO)5 (CIO4)3, Ln2 (NPicO)9 (C1O4)6 (Ln = Pr, Nd, and Gd) and Ln (NPicO)4 (CIO4)3 (Ln == Tb, Dy, Ho and Yb) have been synthesised and characterised by analysis, electrolytic conductance, infrared, proton NMR and electronic spectral data. A tentative coordination number of 6 for all the complexes have been assigned

Occurrence of maximum Tc at an optimal carrier concentration in superconducting bismuth and thallium cuprates

The superconducting transition temperatures in Bi2Ca1−xLnxSr2Cu2O8+δ, TlCa1−xLnxSr2Cu2O6+δ, and Tl0.8Ca1−xLnxBa2Cu23O6+δ (Ln=Y or rare earth) vary with composition and show a maximum at a specific value of x or δ. This observation suggests that an optimal carrier concentration is required to attain maximum Tc in such cuprates which seem to be two‐band systems