Efficient electrochromic performance of anatase TiO2 thin films prepared by nebulized spray deposition method

Anatase TiO₂ thin films with high optical modulation, better reversibility, fast switching time, and enhanced coloration efficiency were prepared by nebulized spray pyrolysis technique. X-ray diffraction study confirmed the formation of anatase phase TiO₂ in the present work. This inference was substantiated from the Raman active modes of A_1g, 2 B_1g, and 3 E_g corresponding to O–Ti–O bond in TiO₂. The PL emission peak observed at 400 nm is corresponds to the indirect transition (X_1b?→?Γ₃) from the conduction band to the valence band. The average reflectance of TiO₂ thin films was varied from 31 to 20%. The electrochemical study revealed the excellent performance of TiO₂ films with high optical modulation (ΔT?=?61%), fast switching kinetics (t _b ?=?1.6 s, t _c ?=?2.4 s), good coloration efficiency (100 cm² C^?1), and better reversibility (86%). The efficient electrochromic behavior of films may be due to the smooth microstructure nature, which provides an easy pathway for the diffusion and charge transfer process of Li⁺ ions in TiO₂ film matrix. The fast transfer of Li⁺ ion was realized from the electrochemical impedance spectroscopic measurement.     

A practical synthesis of aryl sulfones via cross-coupling of sulfonyl hydrazides with aryltriazenes using copper/ionic liquid combination

A new and efficient approach adopting copper-catalyzed cross-coupling of sulfonyl hydrazides with aryltriazenes has been developed to synthesize aryl sulfones using Brønsted acidic ionic liquid as promoter under ambient conditions. The process employs stable and easy to handle reacting partners, and is endowed with broad substrate scope.     

Tandem Prins cyclization for the synthesis of 1,8-dioxa-3-azaspiro[4.5]dec-2-ene derivatives

A tandem Prins strategy has been developed for the synthesis of 1,8-dioxa 3-azaspiro[4.5]dec-2-ene derivatives using 5?mol% Cu(OTf)₂ in dichloromethane at 0?°C under mild reaction conditions in short reaction times. This method provides the products in good yields with a diverse substitution pattern.     

Mechanism of the 2H → 6H solid state transformation in SiC

Single crystals of 2H SiC transform directly into the 6H (ABCACB) structure when the transformation nucleates at temperatures above 2000°C. The 2H close-packed structure may be transformed to the 6H structure by displacing every third layer. The theory of X-ray diffraction from one-dimensionally disordered crystals undergoing the 2H to 6H structural transformation by such a layer displacement mechanism has been developed. The fact that all the observed solid state transformations in SiC crystals commence with the random insertion of stacking faults and then proceed further to create a statistically ordered structure, permits such a theory to be developed. Exact expressions for the diffracted intensity from such crystals have been obtained and the different diffraction effects observable on single crystal X-ray photographs predicted. A comparison of the theoretically predicted diffraction effects with those visible on the X-ray photographs of SiC crystals undergoing the 2H to 6H transformation shows that the structural transformations in SiC occur by the layer displacement mechanism.     

The structure,perfection and annealing behaviour of SiC needles grown by a VLS mechanism

Over 50 different single crystals of SiC, grown by a vapour-liquid-solid mechanism, have been examined by optical and X-ray diffraction methods to determine their structure, perfection and annealing behaviour. All the crystals studied had either the hexagonal close-packed 2H (ABAB…) structure or the cubic close-packed 3C (ABCABC…) structure or a combination of both, and invariably contained a random distribution of stacking faults on their basal planes. The thermal stability of the structures was studied by annealing them between 1300–2200 °C in an inert argon atmosphere, and reexamining the structure of the crystals after each annealing run. Structural transformations were found to commence in different crystals at different temperatures between 1400 and 1800 °C. The transformations were found to be irreversible, not martensitic and appear to involve the nucleation of the new phase by the insertion of stacking faults followed by its growth during the annealing. The mechanism of the solid-state transformations, the influence of faults and impurities, and the thermal stability of different SiC structures are discussed.     

A model for the growth of anomalous polytype structures in vapour grown SiC

A number of polytype structures observed in vapour grown SiC crystals have a unit-cell which is an integral multiple of the unit-cell of the basic 6H, 15R or 4H structure. The growth of such anomalous structures cannot be understood in terms of spiral growth round a single screw dislocation in a basic matrix. However many of these polytype crystals display a single growth spiral on their (0001) face indicating that they have resulted from spiral growth round a single screw dislocation. It is shown that this anomaly can be resolved if the basic matrix is assumed to contain stacking faults near the surface at the time of the origin of the screw dislocation ledge. This possibility, overlooked in the earlier deduction of polytype structures, must be taken into consideration since vapour grown SiC crystals frequently contain a high concentration of random stacking faults, producing continuous streaks on their X-ray diffraction photographs. The most probable fault configurations that can occur in 6H, 15R and 4H structures of SiC have been deduced from a calculation of their stacking fault energy. These fault configurations are then considered to lie at different distances from the surface at the time of the origin of a screw dislocation ledge. Such a faulted ledge gives rise to polytype structures during subsequent spiral growth even if the screw dislocation has an integral Burgers vector. The most probable series of polytype structures that can result from such a faulted matrix model are deduced. It is shown that nearly all the polytype structures of SiC hitherto regarded as anomalous (such as 36H, 54H, 66H, 45R, 90R etc.) are among the expected structures and there is no need to postulate a complicated configuration of cooperating dislocations to account for their growth.     

On the deque conjecture for the splay algorithm

Splay is a simple, efficient algorithm for searching binary search trees, devised by Sleator and Tarjan, that reorganizes the tree after each search by means of rotations. An open conjecture of Sleator and Tarjan states that Splay is, in essence, the fastest algorithm for processing any sequence of search operations on a binary search tree, using only rotations to reorganize the tree. Tarjan proved a basic special case of this conjecture, called theScanning Theorem, and conjectured a more general special case, called theDeque Conjecture. The Deque Conjecture states that Splay requires linear time to process sequences of deque operations on a binary tree. We prove the following results:

1. Almost tight lower and upper bounds on the maximum numbers of occurrences of various types of right rotations in a sequence of right rotations performed on a binary tree. In particular, the lower bound for right 2-turns refutes Sleator's Right Turn Conjecture.
2. A linear times inverse Ackerman upper bound for the Deque Conjecture. This bound is derived using the above upper bounds.
3. Two new proofs of the Scanning Theorem, one, a simple potential-based proof that solves Tarjan's problem of finding a potential-based proof for the theorem, the other, an inductive proof that generalizes the theorem.

     

The Hausdorff dimension of random walks and the correlation length critical exponent in Euclidean field theory

We study the random walk representation of the two-point function in statistical mechanics models near the critical point. Using standard scaling arguments, we show that the critical exponentv describing the vanishing of the physical mass at the critical point is equal tov /d_w, whered _w is the Hausdorff dimension of the walk, andv is the exponent describing the vanishing of the energy per unit length of the walk at the critical point. For the case ofO(N) models, we show thatv ₀=, where is the crossover exponent known in the context of field theory. This implies that the Hausdorff dimension of the walk is/v forO(N) models.     

Chemometric investigation of complex equilibria in solution phase II: Sensitivity of chemical models for the interaction of AADH and FAH with Ni(II) in aqueous medium

A detailed study of the species formed in the complex equilibria involving adipic acid dihydrazide (AADH)/2-furoic acid hydrazide (FAH) with Ni(II) using pH titration with glass electrode is performed. The results of modeling studies and effect of errors on the equilibrium constants of AADH/FAH with Ni(II) refined by the non-linear least squares program MINIQUAD75 are reported. Based on the expert system approach developed in our laboratory for the species formed from secondary formation data (n and n (H)), several preliminary chemical models were tested. For the four species identified (MLH, ML, ML(2)H, ML(2)), an exhaustive search of a different combination of models (15) was performed. Then other suspected minor species (ML(2)H(2), ML(3) and ML(3)H) were tested. The final best fit chemical model was found to contain ML(3)H to an extent of 3% along with the other four major species. In order to ascertain the accuracy of the stability constants and consequently distribution of the species, a detailed error analysis is attempted. As the existing least squares procedures cannot suppress the systematic errors, three-dimensional plots of the simultaneous effects of pH and TLO:TMO (1.5:1 to 5:1) on the percentage of species are drawn which are of immense use in arriving at optimum conditions for the preparation of a complex of definite stoichiometry.     

Hydrogen bonding and molecular vibrations of 3,5-diamino-1,2,4-triazole

This work deals with the analysis of hydrogen bonding and the vibrational spectroscopy of 3,5-diamino-1,2,4-triazole by means of quantum chemical calculations. The mid and far FTIR and FT-Raman spectra were measured in the condensed state. The fundamental vibrational frequencies were calculated under different possible symmetries by applying the density functional theory with the B3LYP functional and the 6-31G* basis set. The results of the calculations obtained under C(2) symmetry produces the global minimum on the potential energy surface. The vibrational spectra were interpreted with the aid of normal coordinate analysis based on scaled density functional force field. The infrared and Raman spectra were also predicted from the calculated intensities.