Study of the domain structure evolution in single crystals of relaxor ferroelectric Sr0.61Ba0.39Nb2O6:Ce1

Optical visualization with simultaneous recording of the switching current was used for studying of domain structure evolution in single crystals relaxor ferroelectric strontium barium niobate (Sr_0.61Ba_0.39Nb₂O₆) doped by cerium (0.22 mol %) (SBN61:Ce). It was shown that the maze domain structures can be observed during polarization reversal due to local change of refractive index induced by formation of microscale domains with charged domain walls. It was proposed, that optical inhomogeneities occur in the switching regions, while the optical uniform areas correspond to regions where the switching either has not started yet or has already completed. The original mathematical treatment of the obtained images and switching currents has been used for quantitative characterization of the polarization reversal process.     

Excited-state absorption properties of platinum(II) terpyridyl acetylides

A comprehensive photophysical study is presented which compares the ground- and excited-state properties of four platinum(II) terpyridyl acetylide compounds of the general formula [Pt(tBu3tpy)(CCR)]+, where tBu3tpy is 4,4',4' '-tri-tert-butyl-2,2':6',2' '-terpyridine and R is an alkyl or aryl group. [Ru(tBu3tpy)3]2+ and the pivotal synthetic precursor [Pt(tBu3tpy)Cl]+ were also investigated in the current work. The latter two complexes possess short excited-state lifetimes and were investigated using ultrafast spectrometry while the other four compounds were evaluated using conventional nanosecond transient-absorption spectroscopy. The original intention of this study was to comprehend the nature of the impressive excited-state absorptions that emanate from this class of transition-metal chromophores. Transient-absorbance-difference spectra across the series contain the same salient features, which are modulated only slightly in wavelength and markedly in intensity as a function of the appended acetylide ligand. More intense absorption transients are observed in the arylacetylide structures relative to those bearing an alkylacetylide, consistent with transitions coupled to the pi system of the ancillary ligand. Reductive spectroelectrochemical measurements successfully generated the electronic spectrum of the tBu3tpy radical anion in all six complexes at room temperature. These measurements confirm that electronic absorptions associated with the tBu3tpy radical anion simply do not account for the intense optical transitions observed in the excited state of the Pt(II) chromophores. Transient-trapping experiments using the spectroscopically silent reductive quencher DABCO clearly demonstrate the loss of most transient-absorption features in the acetylide complexes throughout the UV, visible, and near-IR regions following bimolecular excited-state electron transfer, suggesting that these features are strongly tied to the photogenerated hole which is delocalized across the Pt center and the ancillary acetylide ligand.     

Synthesis of 1,5-diaryl-3-tetrazolylformazans

Several 1,5-diphenyl-3-tetrazolylformazans were synthesized by reaction of 1,5-diaryl-3-cyanoformazans with sodium azide.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1679–1681, December, 1977.     

Modeling of the Electric-Field Dynamics in the Atmosphere Using the Test-Structure Method

We propose the test-structure method for modeling of electric-field pulsations in the atmosphere. Numerical calculations necessary for interpretation of the behavior of experimental spectra and structure functions of the electric field are performed. Analysis of experimental data shows that the aeroelectric-field strength, being a nonlocal quantity, is formed by an inhomogeneous distribution of space charges surrounding the observation point. Quantitative assessments of the state of the atmospheric boundary layer, electro-gas-dynamic turbulence and convection parameters are discussed on the basis of spectral and structure functions of the electric field. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 48, No. 8, pp. 648–660, August 2005.     

Ketene reactions with the aminoxyl radical tempo: preparative, kinetic, and theoretical studies

Tetramethylpiperidinyloxy (TEMPO, TO*) reacts with ketenes RR(1)C=C=O generated by either Wolff rearrangement or by dehydrochlorination of acyl chlorides to give products resulting from addition of one TEMPO radical to the carbonyl carbon and a second to the resulting radical. Reactions of phenylvinylketenes 4b and 4f, phenylalkynylketene 4c, and the dienylketene AcOCMe=CHCH=CHCMe=C=O (11) occur with allylic or propargylic rearrangement. Even quite reactive ketenes were generated as rather long-lived species by photochemical Wolff rearrangement in isooctane solution, characterized by IR and UV, and used for kinetic studies. The rate constants of TEMPO addition to eight different ketenes have been measured and give a qualitative correlation of log k(2)(TEMPO) = 1.10 log k(H(2)O) -3.79 with the rate constants for hydration of the same ketenes. Calculations at the B3LYP/6-311G//B3LYP/6-311G level are used to elucidate the ring opening of substituted cyclobutenones leading to vinylketenes and of 2,4-cyclohexadienone (17) forming 1,3,5-hexatrien-1-one (18).     

Mechanisms of coupling of aeroelectric and temperature fields in the lower atmosphere

Based on synchronous observations of the aeroelectric field and the air temperature, performed in August–October 2002 and June–September 2003 at the measuring facility of the mid-latitude geophysical observatory “Borok” (Yaroslavsl’ Region, Russia), we conclude that correlative relations exist between the aeroelectric-field intensity E and the air temperature T in the atmospheric surface layer. We reveal positive correlation between the temperature and electric-field variations under conditions of unstable stratification (late morning-day) and negative correlation under stable stratification (late evening-night). A simultaneous increase in the amplitude of pulsations of the electric field and the temperature occurs most frequently near the local midday. Intense variations in the electric field correspond to variations in the temperature field with a close time period. A positive temporal shift of variations in E with respect to variations in T, which reaches 40 min, is observed during enhanced temperature activity. The structure-temporal analysis of experimental data from remote sensing of the temperature and electric-field variations at five points is performed. We find simultaneous aeroelectric and temperature coherent structures accompanied by short-period pulsations of the field intensity and the air temperature in the atmospheric surface layer. We discuss possible mechanisms of coupling of the aeroelectric-field intensity and the atmospheric air temperature to describe their positive correlation under conditions of unstable stratification (late morning-day) and negative correlation in the late evening and at night. Enhancement of electric activity, which is stipulated by the intensification of turbulent convection and the formation of aeroelectric structures, seems the most significant process. With allowance for nonlocality of the electric field, this process can in particular explain a substantial lead of the aeroelectric-field perturbations compared with the correlated positive temperature perturbations. In this case, the formation of warm “quasi-front,” which is accompanied by the lifting of the near-surface air abundant in moisture and charged particles to the higher atmospheric layers, can play an important role. Other mechanisms of the field-temperature coupling take into account a decrease in the conductivity of near-surface air due to the condensation of water vapor during its cooling, as well as an increase in the mobility of light ions with increasing air temperature. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 49, No. 1, pp. 35–52, January 2006.     

Formation of nanodomain ensembles during polarization reversal in Sr<Subscript>0.61</Subscript>Ba<Subscript>0.39</Subscript>Nb<Subscript>2</Subscript>O<Subscript>6</Subscript>: Ce single crystals

The results of the study of nano- and microdomain structure evolution in single crystals of relaxor ferroelectric strontium barium niobate Sr_0.61Ba_0.39Nb₂O₆ doped by cerium are presented. It was shown that the initial nanodomain structure represents a self-similar three-dimensional maze. The fractal dimension and average period were revealed. It was demonstrated that application of series of alternating electric field pulses makes it possible to produce a single-domain state in the surface layer. The features of the growth and “merging,” as well as the shape of ensembles of isolated nanodomains formed during switching from the single-domain state, were investigated. The formation of the nanodomain ensembles was considered as a result of the self-organized discrete switching controlled by determined nucleation.     

Mechanisms for the Formation of Electric-Field Pulsation Spectra in the Near-Surface Atmosphere

We present the results of detailed measurements of the spectrum of short-term (f 0.001-1 Hz) pulsations of the electric field of the near-surface atmosphere under the fair-weather and fog conditions. It is shown that the electric-field pulsations at frequencies 10^-2-10^-1 Hz have a power-law spectrum under both fair-weather and fog conditions. The spectral index varies in a range of from -1.23 to -3.36 depending on the experimental conditions, but the most probable values of the index fall in a range of from -2.25 to -3.0. The spectra corresponding to long time intervals of about a few hours are more steep. The relation of the spectral characteristics to the formation of aeroelectric structures (AESs) is studied. The distribution obtained for the structured spectra is bimodal, i.e., it exhibits two maxima in the ranges of spectral indices from -2.75 to -3.0 and from -2.25 to -2.5. The nonstructured-spectrum distribution is asymmetric and has a pronounced maximum corresponding to hard spectra with indices from -2.5 to -3.3. The intensity of the electric-field pulsations under fog conditions increases by about an order of magnitude compared to the case of fair-weather conditions. The mechanisms of spectrum formation of electric-field pulsations and their relations to the pulsation spectra of the electric-charge density with allowance for the neutral-gas turbulence and the presence of AESs are analyzed. We point out the key role of the nonlocal relation between the electric-field intensity and the space-charge density under conditions of spatially inhomogeneous turbulence. Model problems of the spectrum of electric-field fluctuations generated by a homogeneous and structured turbulence in the presence of charge-density fluctuations, considered as a passive tracer, are solved.     

Effect of physicochemical properties of water-propane-2-ol mixture and temperature on thermodynamics of Cu complexation with glycine

The stability constants of Cu²⁺ complexes with glycine are determined by potentiometric method in water-propane-2-ol mixture, i.e., [CuL]⁺, CuL₂ (L = Gly^–) (0.070, 0.167, 0.310 mole fraction of alcohol), and [CuHL]²⁺ (0.070 mole fraction of alcohol) at 298.15, 308.15, and 318.15 K. Thermodynamic characteristics of Cu²⁺ complexation with glycine and the Gibbs energy of transfer of complex species [CuL]⁺ and CuL₂ from water to a mixed solvent are calculated. The solvation-thermodynamic analysis of effects of water-propane-2-ol solvents and of separate solvation contributions of reagents to Cu²⁺ coordination with glycine is performed. The increasing stability of the [CuL]⁺ and CuL₂ complexes in water-propane-2-ol as compared to that in pure water is explained by the increasing energy of solvation of complex species [CuL]⁺ and CuL₂ and by the decreasing energy of solvation of Cu²⁺ and Gly^– ions.__________Translated from Koordinatsionnaya Khimiya, Vol. 31, No. 4, 2005, pp. 311–318.Original Russian Text Copyright © 2005 by Tsurko, Bondarev, Shikhova, Khrebto.