S.V. Samoylenkov

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.

Continuous YBCO deposition onto moved tapes in liquid single source MOCVD systems

Abstract In a small scale MOCVD system YBCO films with j c(77 K ) > 1 MA were deposited onto substrates, which were continuously moved through the deposition chamber. Two routes for the buffer layer deposition onto textured Ni tapes were chosen: a) CeO 2 , LaMnO 3 and LaCrO 3 films were deposited in hydrogen atmosphere by MOCVD. On LaAlO 3 and R-Al 2 O 3 crystals epitaxial films were obtained b) textured NiO layers were grown by oxidation of textured Ni tapes. Based on the small scale system an enlarged MOCVD reactor was constructed.

An analysis of charge carriers distribution in RBa2Cu3O7 using the calculation of bond valence sums

Abstract The distribution of charge carriers in the RBa2Cu3O7 structure between Cu(2)O2 planes and Cu(1)O chains was studied using the calculation of bond valence sums with the strain correction taken into account. With a growth of the R3+ ionic radius, hpl decreases and hch increases almost linearly. The optimum value of the hole concentration in Cu(2)O2 planes was found to be about 1 4 . The result implies, that RBa2Cu3O7 phases with R = La, Nd, are underdoped and those with R = Y, SmLu are overdoped. A model of possible real-space charge carrier ordering in Cu(2)O2 planes of RBa2Cu3O7 with the optimum hole concentration was proposed.

Reactive chemical vapour deposition (RCVD) of non-volatile terbium aromatic carboxylate thin films

In this work we report a new RCVD technique which allows the deposition of nonvolatile compounds from the gas phase into thin films. The technique developed is based on the metathesis reaction in the gas phase between the volatile reagents with the following deposition of the nonvolatile product. A novel RCVD reactor has been constructed and consists of two evaporation (T1, T2) zones connected to the reaction zone (T3). This approach has been successfully tested on terbium carboxylates (Tb(Carb)3; HCarb = Hbz (benzoic acid), Hpobz (o-phenoxybenzoic acid)) as nonvolatile but promising complexes for their application as thin film optical materials. We demonstrated that the construction of the reactor plays a crucial role in the controlling of the films composition, morphology and thickness. The optimal parameters have been found and Tb(Carb)3 thin films with roughness ∼2–4 nm and thickness in the range of ∼40–200 nm were obtained.

Metalorganic chemical vapour deposition of high quality LuBa2Cu3O7 −δ thin films Peculiarities of growth and superconducting properties

Abstract Epitaxial LuBa 2 Cu 3 O 7−δ films were prepared by flash evaporation metalorganic chemical vapour deposition (MOCVD) on LaAlO 3 , SrTiO 3 and ZrO 2 (Y 2 O 3 ) substrates. The highest T c and j c (77 K, 100 Oe) values achieved were 89 K, 2.7·10 6 A cm −2 , 88 K, 1.5·10 6 A cm −2 and 87 K, 1.0·10 6 A cm −2 , respectively. An influence of p (O 2 ) (at the deposition temperature T =800 °C) on structural and superconducting characteristics of LuBa 2 Cu 3 O 7−δ films was found to be similar to that in the case of YBa 2 Cu 3 O 7−δ , in spite of the difference in morphology features and j c ( T ) dependencies. Occurrence of secondary phases inclusion in LuBa 2 Cu 3 O 7−δ films was analysed by XRD and TEM. The “fully oxygenated” LuBa 2 Cu 3 O 7 was found to be overdoped: an increase of T c value by 3 K was observed after an annealing of the films at reduced p (O 2 ).

Superconducting properties of oxygen deficient LuBa2Cu3O7−x thin films

An increase of more than 3 K of the Tc value was observed for LuBa2Cu3O7−x epitaxial films, being at first fully oxygenated, after annealing at reduced oxygen partial pressure (0.05-0.3 bar). The effect is related to the optimization of the hole concentration in the Cu(2)O2 planes. The dependence of the normal state electrical conductivity at 300 K on the oxygen partial pressure was found to be linear with the slope coefficient 0.17 in logarithmic coordinates. The oxygen stoichiometry (7−x), estimated from conductivity measurements, and the lattice parameter c of LuBa2Cu3O7−x films correlate satisfactorily with the c(x) variation for YBa2Cu3O7−x. The temperature dependence of the critical current density in LuBa2Cu3O7−x epitaxial films is rather insensitive to the variation of oxygen content in the 0.02 < x < 0.27 interval.

The structure of BaCu3O4 particles occurring on thin HoBa2Cu3O7 films prepared by MOCVD

Abstract The structure of BaCu 3 O 4 phase occurring as particles on the surface of (001) RBa 2 Cu 3 O 7 epitaxial films prepared by metalorganic chemical vapor deposition (MOCVD) has been investigated with quantitative electron diffraction and HREM. The orthorhombic unit cell is a =1.097(9) nm, b =0.554(3) nm, c =0.394(2) nm with space group Cmmm, the values being in agreement with X-ray diffraction (XRD) study. The structure consists of alternating Cu 3 O 4 and Ba layers along the c -axis. The compound is stabilised due to the formation of low-energy coherent boundaries with RBa 2 Cu 3 O 7 and/or perovskite substrate.

Raman investigation of the metastable barium cuprate BaCu3O4 in thin films

Abstract Metastable BaCu3O4 has been synthesised by MOCVD on perovskite substrates. Strain effects lead to an epitaxial island-growth of micrometer-sized crystallites with two orientations relative to the substrate surface. They were used for a polarized single crystal analysis by micro-Raman spectrometry. The results can be used to detect BaCu3O4 as an impurity phase in RBa2Cu3O7 thin films with a mole fraction level of less than 1%, a sensitivity which exceeds that of XRD by at least one order of magnitude.