Dielectric and Impedance Studies on 0.5Li(2)O-0.5K(2)O-2B(2)O(3) Glasses

Transparent glasses in the system 0.5Li(2)O-0.5K(2)O-2B(2)O(3) (LKBO) were fabricated via the conventional melt quenching technique. Amorphous and glassy nature of the samples was confirmed by X-ray diffraction and differential scanning calorimetry (DSC) respectively. Complex dielectric and impedance studies were conducted on the samples at different temperatures in the 100 Hz-10 MHz frequency range. ac conductivity was calculated from the dielectric data and the conductivity relaxation was found to obey the Jonscher's law. The Nyquist's plots (Z `'(omega) vs. Z'(omega)) showed single suppressed semicircles at all the temperatures under study indicating the non ideal Debye type relaxation process to be active. Activation energies for conduction and relaxation process were calculated using the Arrhenius relation. The UV-visible optical transmission spectra was shown a wide transmission window and calculated optical band gap was found to be 5.67 eV.

1, 2-Bis (diphenylphosphino) etane bridged dinuclear copper (I) complexes: Investigations of solid state and solution structures by CP/MAS31P NMR spectroscopy, X-ray crystallography, IR spectroscopy and solution 31P NMR and 63Cu NMR spectroscopy

Three different complexes of copper (I) with bridging 1, 2-bis(diphenylphosphino)ethane (dppe), namely [Cu2 (mu-dppe) (CH3CN)6] (ClO4)2 (1), [Cu2 (mu-dppe)2 (CH3 CN)2] (ClO4)2 (2), and [Cu2 (mu-dppe) (dppe)2 (CH3CN)2] (ClO4)2 (3) have been prepared. The structure of [Cu2 (mu-dppe) (dPPe)2 (CH3CH)2] (ClO4)2 has been determined by X-ray crystallography. It crystallizes in the space group PT with a=12.984(6) angstrom, b=13.180(6) angstrom, c=14.001(3) angstrom, alpha=105.23(3), beta=105.60(2), gamma=112.53 (4), V=1944 (3) angstrom3, and Z=1. The structure was refined by least-squares method with R=0.0365; R(w)=0.0451 for 6321 reflections with F0 greater-than-or-equal-to 3 sigma (F0). The CP/MAS P-31 and IR spectra of the complexes have been analysed in the light of available crystallographic data. IR spectroscopy is particularly helpful in identifying the presence of chelating dppe. P-31 chemical shifts observed in solid state are very different from those observed in solution, and change significantly with slight changes in structure. In solution, complex 1 remains undissociated but complexes 2 and 3 undergo extensive dissociation. With a combination of room temperature H-1, Cu-63, and variable temperature P-31 NMR spectra, it is possible to understand the various processes occurring in solution.

Electrical Relaxation and Transport in 0.5Cs(2)O-0.5Li(2)O-3B(2)O(3) Glasses

The frequency and temperature dependence of the dielectric constant and the electrical conductivity of the transparent glasses in the composition 0.5Cs(2)O-0.5Li(2)O-3B(2)O(3) (CLBO) were investigated in the 100 Hz - 10 MHz frequency range. The dielectric constant for the as-quenched glass increased with increasing temperature, exhibiting anomalies in the vicinity of the glass transition and crystallization temperatures. The temperature coefficient of dielectric constant was estimated (35 +/- 2 ppm. K-1) using Havinga's formula. The dielectric loss at 313 K is 0.005 +/- 0.0005 at all the frequencies understudy. The activation energy associated with the electrical relaxation determined from the electric modulus spectra was found to be 1.73 +/- 0.05 eV, close to that of the activation energy obtained for DC conductivity (1.6 +/- 0.06 eV). The frequency dependent electrical conductivity was analyzed using Jonscher's power law. The combination of these dielectric characteristics suggests that these are good candidates for electrical energy storage device applications.

Synthesis, structure and ionic conductivity in scheelite type Li(0.5)Ce(0.5-x)Ln(x)MoO(4) (x=0 and 0.25, Ln = Pr, Sm)

Scheelite type solid electrolytes, Li(0.5)Ce(0.5-x)Ln(x)MoO(4) (x = 0 and 0.25, Ln = Pr, Sm) have been synthesized using a solid state method. Their structure and ionic conductivity (a) were obtained by single crystal X-ray diffraction and ac-impedance spectroscopy, respectively. X-ray diffraction studies reveal a space group of I4(1)/a for Li(0.5)Ce(0.5-x)Ln(x)MoO(4) (x = 0 and 0.25, Ln = Pr, Sm) scheelite compounds. The unsubstituted Li0.5Ce0.5MoO4 showed lithium ion conductivity similar to 10(-5)-10(-3) Omega(-1)cm(-1) in the temperature range of 300-700 degrees C (sigma = 2.5 x 10(-3) Omega(-1) cm(-1) at 700 degrees C). The substituted compounds show lower conductivity compared to the unsubstituted compound, with the magnitude of ionic conductivity being two (in the high temperature regime) to one order (in the low temperature regime) lower than the unsubstituted compound. Since these scheelite type structures show significant conductivity, the series of compounds could serve in high temperature lithium battery operations.

Effective action and adiabatic expansions for the 1-D and 2-D hubbard models at half-filling

We analyze here the occurrence of antiferromagnetic (AFM) correlations in the half-filled Hubbard model in one and two space dimensions using a natural fermionic representation of the model and a newly proposed way of implementing the half-filling constraint. We find that our way of implementing the constraint is capable of enforcing it exactly already at the lowest levels of approximation. We discuss how to develop a systematic adiabatic expansion for the model and how Berry's phase contributions arise quite naturally from the adiabatic expansion. At low temperatures and in the continuum limit the model gets mapped onto an O(3) nonlinear sigma model (NLsigma). A topological, Wess-Zumino term is present in the effective action of the ID NLsigma as expected, while no topological terms are present in 2D. Some specific difficulties that arise in connection with the implementation of an adiabatic expansion scheme within a thermodynamic context are also discussed, and we hint at possible solutions.

Factors contributing to phantom bonds in inorganic molecules: Interpretations and predictions

The validity of various qualitative proposals for interpreting and predicting the existence of short contacts between formally non-bonded atoms, as in cyclodisiloxane and related inorganic ring systems, is critically evaluated. The models range from simple considerations of geometric constraints, lone pair repulsions and pi-complex formation to proposals such as the unsupported pi-bond model and the sigma-bridged-pi bond concept. It is pointed out that a unified description based on a combination of closed and open 3-centre 2-electron bonds is possible. The role of hybridisation is emphasized in the short phantom bond computed in an earlier model system. These insights are used to predict structures with exceptionally short Si..Si and B..B phantom bonds. The proposals are confirmed by ab initio calculations.

Processing of an α-2 aluminide alloy, Ti---24Al---11Nb

Compressive stress-strain curves have been generated over a range of temperatures (900-1100-degrees-C and strain rates (0.001-100 s-1) for two starting structures consisting of lath alpha2 and equiaxed alpha2 in a Ti-24Al-11Nb alloy. The data from these tests have been analysed in terms of a dynamic model for processing. The results define domains of strain rate and temperature in which dynamic recrystallization of alpha2 occurs for both starting structures. The rate controlling process for dynamic recrystallization is suggested to be cross-slip in the alpha2 phase. A region of processing instability has also been defined within which shear bands form in the lath structure. Recrystallization of the beta phase is shown to occur for different combinations of strain rate and temperature from those in which the alpha2 phase recrystallizes dynamically

Electrical transport properties of 0.5Li(2)O-0.5M(2)O-2B(2)O(3) (M = Li, Na and K) glasses

Transparent glasses in the system 0.5Li(2)O-0.5M(2)O-2B(2)O(3) (M = Li, Na and K) were fabricated via the conventional melt quenching technique. The amorphous and glassy nature of the samples was confirmed via the X-ray powder diffraction and the differential scanning calorimetry, respectively. The frequency and temperature dependent characteristics of the dielectric relaxation and the electrical conductivity were investigated in the 100 Hz-10 MHz frequency range. The imaginary part of the electric modulus spectra was modeled using an approximate solution of Kohrausch-Williams-Watts relation. The stretching exponent, (3, was found to be temperature independent for 0.5Li(2)O-0.5Na(2)O-2B(2)O(3) (LNBO) glasses. The activation energy associated with DC conduction was found to be higher (1.25 eV) for 0.5Li(2)O-0.5K(2)O-2B(2)O(3) (LKBO) glasses than that of the other glass systems under study. This is attributed to the mixed cation effect. (C) 2011 Elsevier By. All rights reserved.

Reactions of the hexachlorocyclodiphosphazane [MeNPCl3]2 with primary aromatic amines: formation of highly basic bisphosphinimines

Reactions of hexachlorocyclodiphosphazane [MeNPCl3]2 with primary aromatic amines afforded the bisphosphinimine hydrochlorides [(RNH)2(RN)PN(Me)P(NHMe)(NHR)2]+Cl- (R = Ph 1, C6H4Me-4 2 or C6H4OMe-4 3). Dehydrochlorination of 2 and 3 by methanolic KOH yielded highly basic bisphosphinimines [(RNH)2(RN)PN(Me)P(NMe)(NHR)2] (R = C6H4Me-4 4 or C6H4OMe-4 5). Compounds 1-5 have been characterised by elemental analysis and IR and NMR (H-1, C-13, P-31) spectroscopy. The structure of 2 has been confirmed by single-crystal X-ray diffraction. The short P-N bond lengths and the conformations of the PN, units can be explained on the basis of cumulative negative hyperconjugative interactions between nitrogen lone pairs and adjacent P-N sigma* orbitals. Ab initio calculations on the model phosphinimine (H2N)3P=NH and its protonated form suggest that (amino)phosphinimines would be stronger bases compared to many organic bases such as guanidine.

Dynamic recrystallisation during hot working of Zr-2 center dot 5Nb: Characterisation using processing maps

The characteristics of the hot deformation of Zr-2.5Nb (wt-%) in the temperature range 650-950 degrees C and in the strain rate range 0.001-100 s(-1) have been studied using hot compression testing. Two different preform microstructures: equiaxed (alpha + beta) and beta transformed have been investigated. For this study, the approach of processing maps has been adopted and their interpretation carried out using the dynamic materials model. The efficiency of power dissipation given by [2m/(m + 1)], where m is the strain rate sensitivity, is plotted as a function of temperature and strain rate to obtain a processing map. A domain of dynamic recrystallisation has been identified in the maps of equiaxed (alpha + beta) and beta transformed preforms. In the case of equiaxed (alpha + beta), the stress-strain curves are steady state and the dynamic recrystallisation domain in the map occurs with a peak efficiency of 45% at 850 degrees C and 0.001 s(-1). On the other hand the beta transformed preform exhibits stress-strain curves with continuous flow softening. The corresponding processing map shows a domain of dynamic recrystallisation occurring by the shearing of alpha platelets followed by globularisation with a peak efficiency of 54% at 750 degrees C and 0.001 s(-1). The characteristics of dynamic recrystallisation are analysed on the basis of a simple model which considers the rates of nucleation and growth of recrystallised gains. Calculations show that these two rates are nearly equal and that the nucleation of dynamic recrystallisation is essentially controlled by mechanical recovery involving the cross-slip of screw dislocations. Analysis of flow instabilities using a continuum criterion revealed that Zi-2.5Nb exhibits flow localisation at temperatures lower than 700 degrees C and strain rates higher than 1 s(-1).

Characterization of hot deformation behaviour of Zr---2.5Nb---0.5Cu using processing maps

The characteristics of hot deformation of beta-quenched Zr-2.5Nb-0.5Cu in the temperature range 650-1050 degrees C and in the strain rate range 0.001-100 s(-1) have been studied using hot compression testing. For this study, the approach of processing maps has been adopted and their interpretation done using the Dynamic Materials Model. The efficiency of power dissipation given by [2m/(m + 1)], where m is strain rate sensitivity, is plotted as a function of temperature and strain rate to obtain a processing map. The processing map for Zr-2.5Nb-0.5Cu within (alpha + beta) phase field showed a domain of dynamic recrystallization, occurring by shearing of alpha-platelets followed by spheroidization, with a peak efficiency of 48% at 750 degrees C and 0.001 s(-1). The stress-strain curves in this domain had features of continuous flow softening and all these are similar to that in Zr-2.5Nb alloy. In the beta-phase field, a second domain with a peak efficiency of 47% occurred at 1050 degrees C and 0.001 s(-1) and this domain is correlated with the superplasticity of beta-phase. The beta-deformation characteristics of this alloy are similar to that observed in pure beta-zirconium with large grain size. Analysis of flow instabilities using a continuum criterion revealed that the Zr-2.5Nb-0.5Cu exhibits flow localization at temperatures higher than 800 degrees C and strain rates higher than about 30 s(-1) and that the addition of copper to Zr-2.5Nb reduces its susceptibility to flow instability, particularly in the (alpha + beta) phase field.

Perturbative growth of cosmological clustering .2. The two-point correlation

We use the BBGKY hierarchy equations to calculate, perturbatively, the lowest order nonlinear correction to the two-point correlation and the pair velocity for Gaussian initial conditions in a critical density matter-dominated cosmological model. We compare our results with the results obtained using the hydrodynamic equations that neglect pressure and find that the two match, indicating that there are no effects of multistreaming at this order of perturbation. We analytically study the effect of small scales on the large scales by calculating the nonlinear correction for a Dirac delta function initial two-point correlation. We find that the induced two-point correlation has a x(-6) behavior at large separations. We have considered a class of initial conditions where the initial power spectrum at small k has the form k(n) with 0 < n less than or equal to 3 and have numerically calculated the nonlinear correction to the two-point correlation, its average over a sphere and the pair velocity over a large dynamical range. We find that at small separations the effect of the nonlinear term is to enhance the clustering, whereas at intermediate scales it can act to either increase or decrease the clustering. At large scales we find a simple formula that gives a very good fit for the nonlinear correction in terms of the initial function. This formula explicitly exhibits the influence of small scales on large scales and because of this coupling the perturbative treatment breaks down at large scales much before one would expect it to if the nonlinearity were local in real space. We physically interpret this formula in terms of a simple diffusion process. We have also investigated the case n = 0, and we find that it differs from the other cases in certain respects. We investigate a recently proposed scaling property of gravitational clustering, and we find that the lowest order nonlinear terms cause deviations from the scaling relations that are strictly valid in the linear regime. The approximate validity of these relations in the nonlinear regime in l(T)-body simulations cannot be understood at this order of evolution.

Reactivity Of Pph3 Toward Ru2cl(O2cme)4 - Synthesis And X-Ray Crystal-Structure Of [Ru(O2cme)(Mecn)2(Pph3)2](Clo4)

A new ruthenium(II) complex of the type [Ru(O2CMe)(MeCN)2(PPh3)2](CiO4) (1) has been isolated from a reaction between Ru2Cl(O2CMe), and PPh3 in MeCN followed by the addition of NaClO4. The structure of 1 is determined by single crystal X-ray studies. The crystal belongs to the monoclinic space group C2/m with the following unit cell dimensions for the C42H39N2O6P2ClRu(M = 866.15): a = 23.295(1)angstrom, b = 23.080(1)angstrom, c = 9.159(1)angstrom, beta = 107.32(1)-degrees, V = 4701(1)angstrom3, Z = 4, D(c) = 1.224 gcm-3, lambda(Mo - K-alpha) = 0.7107 angstrom, mu(Mo - K-alpha) = 4.09 cm-1, T = 293K, R = 0.081 (R(w) = 0.094) for 2860 reflections with I greater-than-or-equal-to 3-sigma(I) and g = 0.015853. In the complex cation, the symmetry about the metal centre is essentially octahedral showing the presence of a chelating acetato, two cis-oriented MeCN and two trans-disposed PPh3 ligands. The mechanistic aspects of the core cleavage reaction are discussed.

Structure of N-nitroso-r-2,c-7-diphenylhexahydro-1,4-diazepin-5-one

C17H17N3O2, M(r) = 295.34, orthorhombic, P2(1)2(1)2(1), a = 7.659 (1), b = 12.741 (1), c = 15.095 (1) angstrom, V = 1473.19 (2) angstrom 3, Z = 4, D(m) = 1.33, D(x) = 1.32 Mg m-3, lambda(Cu K-alpha) = 1.5418 angstrom, mu = 0.68 mm-1, F(000) = 624, T = 295 K, R = 0.031 for 1549 unique observed reflections with I > 2.5-sigma(I). The seven-membered heterocyclic ring adopts a boat conformation flattened at the nitroso end of the ring. The substituent phenyl rings occupy pseudo-axial positions and the nitroso group is coplanar with the C(2), N(1), C(7) plane of the central ring. The crystal structure is stabilized by intermolecular N-H...O and weak C-H...O hydrogen bonds.

Organometallic Chemistry of Diphosphazanes. 11. Reactions of fac-[Mo(CO)3(MeCN){.eta.2-Ph2PN(Pri)PPh(DMP)}] (DMP = 3,5-Dimethyl-1-Pyrazolyl) with Diphosphazanes and Diphosphinoalkanes and Oxidative Addition with Iodine

The use of fac-[Mo(CO)(3)(MeCN)(eta(2)-L(1))] (1a) {L(1) = Ph(2)PN(Pr-i)PPh(DMP)}(2) as a precursor to metalloligands and bimetallic, heterotrimetallic, and heptacoordinated complexes is reported. The reaction of 1a with diphosphazane, dppa, or a diphosphinoalkane such as dppm or dppe yields the fac-eta(1)-diphosphine substituted metalloligands, fac-[Mo(CO)(3)(eta(2)-L(1))(eta(1)-PXP)] {PXP = dppa (2), dppm (3), and dppe (4)}. These undergo isomerization to yield the corresponding mer-diphosphine complexes (5-7). Oxidation of the uncoordinated phosphorus atom of the mer-eta(1)-dppm-substituted complex eventually provides mer-[Mo(CO)(3)-(eta(2)-L(1)){eta(1)-Ph(2)PCH(2)P(O)Ph(2)}](8). The structure of the latter complex has been confirmed by single crystal X-ray diffraction {triclinic system, P ($) over bar 1; a = 11.994(3), b = 14.807(2), c = 15.855(3) Angstrom; alpha = 114.24(1), beta = 91.35(2), and gamma = 98.95(1)degrees; Z = 2, 4014 data (F-0 > 5 sigma(F-0)), R = 0.066, R(W) = 0.069}. Treatment of the dppe metalloligand 7 with [PtCl2(COD)] yields the heterotrimetallic complex cis-[PtCl2{mer-[Mo(CO)(3)(eta(2)-L(1))(eta(1)-dppe]}(2)] (9). Attempts to prepare a related trimetallic complex with the dppm-containing metalloligand were unsuccessful; only the tetracarbonyl complex cis-[Mo(CO)(4)(eta(2)-L(1))] (1b) and cis-[PtCl2(eta(2)-dppm)] were obtained. Reaction of la with dppe in the ratio 2:1 yields the mer-mer dinuclear complex [{mer-[Mo(CO)(3)(eta(2)-L(1))]}(2)(mu-dppe)] (10) bridged by dppe. Oxidation of 1a with iodine yields the Mo(II) heptacoordinated complex [MoI2(CO)(2)(eta(3)-L(1))] (11) with tridentate PPN coordination. The same Mo(II) complex 11 is also obtained by the direct oxidation of the tetracarbonyl complex cis-[Mo(CO)(4)(eta(2)-L(1))] (1b) with iodine. The structure of 11 has been confirmed by X-ray diffraction studies {monoclinic system, Cc; a = 10.471(2), b = 19.305(3), c = 17.325(3) Angstrom; beta = 95.47(2)degrees; Z = 4, 3153 data (F-0 > 5 sigma(F-0)), R = 0.049, R(W) = 0.051}. This complex exhibits an unusual capped-trigonal prismatic geometry around the metal. A similar heptacoordinated complex 12 with a chiral diphosphazane ligand {L(3) = (S,R)-P(h)2PN-(*CHMePh)*PPh(DMP)} has also been synthesized.