Š. Buchta

Thin YBCO films prepared by low-temperature spray pyrolysis

Thin YBCO films were prepared from aerosol by a low-temperature deposition process consisting of two steps-the deposition at atmospheric pressure and firing in vacuum degraded by partial pressure of oxygen-both at temperatures not exceeding 600 degrees C. A stoichiometric 1-2-3 aqueous nitrate solution of Y, Ba and Cu constituents was used as a source of aerosol. MgO and Al2O3 substrates were heated to 140 to 160 degrees C during deposition. The obtained films were 1 to 10 mu m thick with Tc>80 K and Jc=103 to 104 A cm-2. However, detailed TG, DTG and DTA studies performed by the authors and others showed that thermal decomposition of the nitrates used only starts at temperatures higher than 200 degrees C. The use of low substrate temperatures during deposition (140 to 160 degrees C in this case) is apparently the reason for rather low Jc values. Optimization of the preparation process is suggested, which could lead to higher Jc values at processing temperatures not exceeding 600 to 700 degrees C. Such temperatures are still interesting for substrates with elevated diffusivity into prepared films.

Experimental study of the intergranular weak link structures YBa2Cu3O7−x with the help of magnetization measurements

AC and DC virgin magnetizations of sintered YBa2Cu3O7−x samples have been measured in dependence of the sintering temperature. The samples were prepared by solid state reaction of stoichiometric decarbonated mixture of Y2O3, BaCO3 and CuO components. Magnetization curves were measured at 77K in the range of magnetic field (10−1−2×104Am−1). The temperature of sintering was being changed in the range 910°C up to 950°C. In the range of weak magnetization fields the magnetization curves are affected by properties of the intergranular medium — the intergranular weak links. The parameters H1w1, H2w1 and H1g characterising the flux penetration into intergrain and intragrain medium were estimated from the magnetization measurements.

Microstructure and superconducting properties of melt textured Y–Ba–Cu–(Ag)–O composites with various Ag content ☆

Abstract The effects of silver doping on microstructure and magnetic properties of YBa 2 Cu 3 O 7− x melt-textured samples prepared by the quench and melt growth technique were studied. Silver was added in the form of Ag 2 O in the range of 0–10 wt%. The increasing silver doping level up to the level of 1.0 wt% Ag 2 O of YBa 2 Cu 3 O 7− x samples results in remarkable improving of their magnetic properties, texturation and porosity. For the given processing conditions, the superconducting properties strongly decrease for the higher doping levels of 5.0 wt% Ag 2 O and more. In our case in reaction systems with higher content of silver doping, which remarkably depresses the formation temperature of the superconductor phase, the texturation process was not completed. The best developed texture as well as the highest magnetisation and first penetration magnetic field showed, under our experimental conditions, the sample containing 1 wt% Ag 2 O.

Substitution and doping of YBa2Cu3O7 by Agn+, Sr2+, Sc3+ and related properties

Abstract We investigated two series of samples of YBa 2 Cu 3− z Sc z O 7− δ prepared at the sintering temperature 967 and 980°C and the two series of YBa 2− y Sr y Cu 3 O 7− δ –Ag 2 O systems differing in silver doping with 2 and 10 wt% Ag 2 O by X-ray diffraction, resistive and detailed magnetization measurements. Doping levels of Sc, Sr and Ag 2 O range from z =0 to 1.0, y =0.0 to 1.0 and Ag 2 O (2 and 10 wt%), respectively. For all doping levels y , z and silver oxide the superconducting phases at 77.3 K were observed. For the higher Sc content z , a deterioration of the critical temperature ( T c ), the density, the volume fraction of superconducting phase, as well as the volume magnetization (magnitude) M , the volume magnetic susceptibility, the first magnetic penetration field ( H p1 ) and the slope of magnetization loops of the samples were observed in relation to sintering temperature. Increasing Sr content results in gradual decreasing of superconducting properties: T c , H p1 , and M , the slope of magnetization loops and magnetization hysteresis, they all decrease with increasing Sr content at higher Sr levels.