Oleg Yu. Gorbenko

LuBa2Cu3O7–x thin films prepared using MOCVD

LuBa2Cu3O7–x thin films with Tc= 86–88 K were prepared by flash evaporation MOCVD on LaAlO3, SrTiO3, ZrO2(Y2O3) and NdGaO3 single-crystal substrates (deposition temperature 795 °C, partial oxygen pressure 1.35 Torr). Values for the critical current density jc(77 K., H= 100 Oe), of 9 × 105, 1.1 × 106 and 1.2 × 106 A cm–2 were measured for films on ZrO2(Y2O3), SrTiO3 and LaAlO3 respectively. The calculated magnitude of |ΔjcΔT| for LuBa2Cu3O7–x films on coherent substrates was found to be higher than that of YBa2Cu3O7–x films, indicating a more efficient magnetic flux pinning mechanism. The temperature dependence of conductivity fluctuations was considered in terms of a Lawrence–Donniach model and a 3D → 2D dimensional crossover was registered for the films on SrTiO3.

Modification of the ground state in Sm-Sr manganites by oxygen isotope substitution

The effect of O-16-->O-18 isotope substitution on electrical resistivity and magnetic susceptibility of Sm1-xSrxMnO3 manganites is analyzed. It is shown that the oxygen isotope substitution drastically affects the phase diagram at the crossover region between the ferromagnetic metal state and that of antiferromagnetic insulator (0.4

Alkaline-doped manganese perovskite thin films grown by MOCVD

Abstract We report on the preparation and characterization of La 1− x Na x MnO 3 thin films grown by MOCVD on various single-crystalline substrates. Under appropriate conditions epitaxial thin films have been obtained. The Curie temperatures of the films, which are very similar to those of bulk samples of similar composition, reflect the residual strain caused by the substrate. The anisotropic magnetoresistance AMR of the films has been analyzed in some detail, and it has been found that it has a two-fold symmetry at any temperature. Its temperature dependence mimics that of the electrical resistivity and magnetoresistance measured at similar fields, thus suggesting that the real structure of the material contributes to the measured AMR besides the intrinsic component.

Crystal and molecular structure of cyclotetrakis[p-oxo-bis(2,2,6,6-tetramethylheptan-3,5dionate)titanium(IV)] pentane adduct

Abstract The X-ray crystal structure of titanium(IV) oxo-bis-2,2,6,6-tetramethylheptan-3,5-dionate, pentane (1: 1) adduct has been determined. The tetrameric molecule of [TiO(thd)2]4 contains a nearly planar (Ti-O)4 ring with two Ti atoms on a twofold axis. Compared with the dimeric titanium oxo-bis-(acetylacetonate), another type of Ti06 octahedral connection takes place, namely through vertices instead of edges.

MOCVD of perovskites with metallic conductivity

Abstract Single source MOCVD techniques were used to prepare perovskite films with metallic conductivity (CaRuO 3 , LaNiO 3 , La 0.5 Sr 0.5 CoO 3 and (La,Pr) 0.7 (Sr,Ca) 0.3 MnO 3 ). Structural and electric properties of the epitaxial layers on the coherent substrates are close to that of the films grown by PLD and magnetron sputtering. Peculiarities of the growth occur on the worse matched substrates, such as a mixture of two orientations, each aligned in the plane of the interface (LaNiO 3 /MgO) and variant structures in the films on YSZ. XRD of the films points to a pseudocubic lattice for all R 1 − x A x MO 3 films in spite of the distortions in the bulk material.

CVD synthesis and SNMS characterization of thin films of ABO3 perovskite-type materials (PbTiO3, La(Sr)CoO3, La(Sr)MnO3, LaNiO3)

Abstract Powder flash evaporation and aerosol-MOCVD (organometallic chemical vapour deposition) methods were applied for the deposition of thin films and heterostructures of ABO 3 perovskite type-materials. It was shown that the plasma-SNMS (secondary neutral mass spectrometry) can be successfully used for the quantitative analysis of these thin films. High density ceramics were found to be good reference samples for such an analysis. It was shown that the interaction between PbTiO 3 thin films and La(Sr)CoO 3 (electrode material) is negligible under deposition conditions. The interaction between La(Sr)CoO 3 thin films and ZrO 2 (Y 2 O 3 ) substrate takes place only at the temperatures higher than 900 °C. La(Sr)MnO 3 thin films react with the Si substrate during deposition by aerosol-MOCVD with formation of a silicate layer. In the case of La(Sr)CoO 3 this reaction is retarded because of low oxygen partial pressure. This decrease of oxygen content in the gaseous phase near the substrate is caused by the catalytic oxidation of solvent (diglyme) at the surface of a La(Sr)CoO 3 film.

Low-pressure single aerosol source MOCVD of YBCO thin films

Abstract YBCO thin films are obtained by low-pressure aerosol version of MOCVD technique. The effects of different process factors are studied. The conclusion is made that the main disadvantage of the process is the high partial pressure of carbon dioxide in the deposition zone. The ways to improve the situation are considered.

Chemical engineering of CVD of HTc superconductors

Abstract For CVD of HTc superconductors different sources (single or multiple source systems, flash evaporation, aerosol formation) are possible. After a comparison of some of these systems the CVD of Y 1 Ba 2 Cu 3 O x superconductors from aerosol with an ultrasonic nebulizer is described. As precursors thd complexes of Y, Ba, Cu (thd = 2.2.6.6.-tetramethyl-3.5.-heptanedionate) are used and as solvent diglyme. Deposition experiments on flat samples and at the walls of a cylindrical hole show that the process is controlled by transport in the gas phase. The layers are contaminated with C. The maximum transition temperature is 79 K.

High-temperature chemical vapor deposition. An effective tool for the production of coatings

Chemical vapor deposition (CVD) processes have a large throwing power and can operate at atmospheric pressure. Therefore, they are economical for many applications. High-temperature CVD processes give a good control of the crystal structure (e.g., epitaxial layers or other special layer structures) and support diffusion processes. The are used, for example, for the following deposition processes: 1) perovskites, 2) yttrium-stabilized ZrO2 layers as ion conductors or heat barrier coatings, 3) aluminide diffusion coatings in long tubes for corrosion protection, and 4) BN on fibers for fiber-reinforced materials. The special properties of the perovskite CVD are discussed in more detail. These processes are described for small- and large-scale applications. The CVD process is simulated by the computer code Fluent.

Cation disorder influence on magnetic and magnetoelastic properties of (TbNd)0.55Sr0.45MnO3 and (EuNd)0.55Sr0.45MnO3 manganites

Abstract Magnetic, transport, magnetotransport, elastic and magnetoelastic properties of Re 0.55 Sr 0.45 MnO 3 ceramic with fixed carrier concentration and tolerance factor but with different cation disorder parameter σ have been studied. A linear relation between T C and σ 2 was found. Increase of σ leads to suppression of magnetoresistance and enhancement of volume change near T C . At T > T C sharp increase of magnetostriction and magnetization is observed at critical field H C , which increases with temperature rise. H C value, defined at fixed T / T C , decreases with σ .