A. M. Makarevich

Chemical synthesis of high quality epitaxial vanadium dioxide films with sharp electrical and optical switch properties

The effective preparation method of epitaxial VO2 films on the r-Al2O3 substrates based on the MOCVD technique and post-deposition annealing is described. The composition, orientation and morphology of the films obtained were investigated by Raman spectroscopy, XRD, EBSD, XPS, SEM and AFM methods. The samples obtained demonstrate high crystal quality and excellent physical properties: sharp metal-insulator (>104 resistance change) and intensive optical reflectivity (IR and THz regions) transitions. The model of VO2 film recrystallization based on the peritectic decomposition of intergrain vanadium oxide phases is proposed.

Customised 2G HTS wire for applications

Reproducibility of superconducting properties and suitability for specific applications by means of customised finish are two important attributes required from commercial 2G HTS wire. This paper reviews the consistent performance of SuperOx production 2G HTS wire and describes two novel customisation options: surround polyimide varnish insulation and composite bulk materials assembled with 2G HTS wires soldered together.

Emission of terahertz pulses from vanadium dioxide films undergoing metal-insulator phase transition

This paper describes research on the optics of functional materials, which can change their dielectric properties according to their function. Vanadium dioxide is a good example of such a material where the insulator-to-metal phase transition offers the possibility to control dielectric properties and to use them as a triggering element for photonic applications in the wide spectral range from optical to terahertz frequencies. We observed emission of terahertz (THz) radiation from VO2 films in insulating and conductive phase states under femtosecond pulse irradiation. We found that the efficiency of THz emission increases up to 30 times after the insulator-to-metal phase transition. This process occurs in thin films while it is fundamentally forbidden in the bulk material, and polarization analysis of the emitted radiation reveals the crucial importance of interface contributions. The properties of the THz radiation emitted by VO2 are determined by displacement photocurrents at the VO2–air and VO2–substrate interfaces induced by the incident laser light. In each phase state the contributions of the two boundaries are different. Properties of the effective dielectric susceptibility χ(2) tensor for the insulating phase were defined. In demonstrating the conversion of optical into THz radiation in VO2 films, we found that fundamental symmetry restrictions are not applicable to problems of nonlinear optics of thin films.

MOCVD Buffer and Superconducting Layers on Non-Magnetic Biaxially Textured Tape for Coated Conductor Fabrication

In this article, we present recent developments in the metal-organic chemical vapor deposition (MOCVD) route to coated conductor fabrication made at SuperOx. Two new buffer layer architectures on nonmagnetic Ni-Cr-W biaxially textured substrates are described. With the use of these architectures we have achieved critical currents in the range of 100-140 A/cm-width for the fully MOCVD produced coated conductors on Ni-Cr-W in the reel-to-reel mode. We have also demonstrated over 10-m-long MOCVD-high temperature superconductor tapes on the ion beam assisted deposition templates with Ic exceeding 300 A/cm-width.

Saturation vapor pressure of the mixed-ligand calcium bis(hexafluoroacetylacetonate) complex with dyglime and water

The vapor composition and thermodynamic characteristics of vaporization of the mixed-ligand complex Ca(hfa)2(diglyme)(H2O) (I) (hfa− is the hexafluoroacetylacetonate anion, diglyme is 1-methoxy-2-(2-methoxyethoxy)ethane) in the temperature range of 298–350 K were studied by the Knudsen effusion method with mass-spectrometric analysis of the gas phase. The mass spectrometry data were juxtaposed with the results of thermal analysis. It was shown that dehydration of I, resulting in a change of the intermolecular bonding system, affects the thermodynamic parameters of sublimation under conditions where dehydration and sublimation occur in parallel.

A novel dimeric complex of barium bis(hexafluoroacetylacetonate) with triglyme: Synthesis, structure, and volatility

181 The interest in mixed ligand complexes of barium bis(hexafluoroacetylacetonate) (Ba(hfa)2) with poly glymes is caused by their high volatility and the possi bility of using them as volatile precursors in the metal organic chemical vapor deposition (MOCVD) method [1]. At present time, this method is widely used in technology of fabrication of second genera tion high temperature superconductive (HTSC) wires based on yttrium barium cuprate RBa2Cu3O7 – x [2].

Formation of heterometallic compounds in mixed solutions of nickel(II)-Schiff base complexes and lanthanide nitrates: Electrospray ionization mass spectrometry data

Atmospheric-pressure electrospray ionization mass spectrometric data are reported for methanolic Ni(SB) + Ln(NO3)3 · nH2O solutions (H2SB = N,N′-ethylene-bis(salicylaldiimine), N,N′-ethylene-bis(3-methoxysalicylaldiimine), N,N′-ethylene-bis(acetylacetonediimine); Ln = La, Eu, Lu). Dinuclear and trinuclear heterometallic complexes of composition [(Ni(SB))xLn(NO3)3] (x = 1, 2) form in these solutions. The dinuclear-totrinuclear ion intensity ratio depends on the natures of the lanthanide and the Schiff base.

Electrospray mass spectra of aqueous solutions of 4f-3d heterometallic chelates

The composition of aqueous solutions of the heterometallic chelates MLnDTPA and Ln2M3(EDTA)3 (H5DTPA = diethylenetriaminepentaacetic acid; H4EDTA = ethylenediaminetetraacetic acid; Ln = Eu, La; M = Ni, Mn) and the monometallic chelates H3Ni(DTPA), HNi2(DTPA), H2La(DTPA), and H2Eu(DTPA) was studied by electrospray mass spectrometry (ESIMS). The mass spectra indicate that there is equilibrium between chelated rare-earth and 3d-metal ions in the aqueous solution of the heterometallic chelates. Both monometallic and bimetallic diethylenetriaminepentaacetates are observed for the 3d elements. The intensity ratio of the chelated rare-earth and 3d-metal ions in the aqueous solutions of the heterometallic complexes is in agreement with the ratio of the stability constants of the respective monometallic chelates.

Mixed-ligand complexes of alkaline-earth metal trifluoroacetates with monoethanolamine

The mixed-ligand complexes of the formula [M(CF3COO)2(MEA)n] (MEA is monoethanolamine; M = Ca (I) and Sr (II), n = 1.5; M = Ba (III), (n = 1) were obtained from appropriate salts M(CF3COO)2 · nH2O and MEA in ethanol. Complexes I–III were characterized by elemental analysis data and IR spectra. Slow crystallization of a solution of complex III in air gave a single crystal of the formula [Ba(CF3COO)2(MEA)(H2O)], which is a coordination polymer with C.N.(Ba) 9 (X-ray diffraction data). Thermal analysis showed that complexes I–III decompose under argon and in air to the corresponding fluorides at T < 400°C.

Volatility and thermal stability of vanadyl β-diketonate complexes

Thermal behavior and thermodynamic characteristics of vanadyl β-diketonates—acetylacetonate VO(acac)2, dipivaloylmethanate VO(thd)2, and tris-hexafluoroacetylacetonate VO(hfa)2 (Hacac, 2,4-pentanedione; Hthd, 2,2,6,6-tetramethyl-3,5-heptanedione; Hhfa, 1,1,1,5,5,5-hexafluoro-2,4-pentanedione)—have been studied by thermal analysis and the Knudsen effusion mass spectrometry study of gas phase composition. The compounds have been shown to undergo congruent sublimation. Saturated vapor over the complexes has been shown to comprise monomeric VOL2 molecules. Absolute values of partial pressures and sublimation enthalpies of these compounds have been determined.