High Tc superconductivity in Y-Ba-Cu-O screen-printed films

High Tc superconductivity in YBaCuO screenprinted films Maurizio Sacchi, Fausto Sirotti, Bruno Morten, and Maria Prudenziati Citation: Appl. Phys. Lett. 53, 1110 (1988); doi: 10.1063/1.100658 View online: http://dx.doi.org/10.1063/1.100658 View Table of Contents: http://apl.aip.org/resource/1/APPLAB/v53/i12 Published by the American Institute of Physics.

Related Articles Absence of boron aggregates in superconducting silicon confirmed by atom probe tomography Appl. Phys. Lett. 101, 182602 (2012) Superconducting epitaxial thin films of CeNixBi2 with a bismuth square net structure Appl. Phys. Lett. 101, 162602 (2012) Normal metal-superconductor decoupling as a source of thermal fluctuation noise in transition-edge sensors J. Appl. Phys. 112, 034515 (2012) Transport critical-current density of superconducting films with hysteretic ferromagnetic dots AIP Advances 2, 022166 (2012) Pressure effects on strained FeSe0.5Te0.5 thin films J. Appl. Phys. 111, 112610 (2012)

Additional information on Appl. Phys. Lett. Journal Homepage: http://apl.aip.org/ Journal Information: http://apl.aip.org/about/about_the_journal Top downloads: http://apl.aip.org/features/most_downloaded Information for Authors: http://apl.aip.org/authors

Downloaded 10 Dec 2012 to 155.185.12.195. Redistribution subject to AIP license or copyright; see http://apl.aip.org/about/rights_and_permissions

High Tc superconductivity in Y"'Ba-Cu~O screen-printed films Maurizio Sacch1, Fausto Sirotti, Bruno Morten, and Maria

Prudenziat~

Dipartimento di Fisica dell'Universita di Modena and Gruppo Nazionale di .S'truttura della Materia, Via Campi 213/a, 41100 Modena, Italy

(Received 25 Ma.y 1988; accepted for publication 25 July 1988) We have prepared screen-printed films of the Y-Ba-Cu-O compound on BeO and A1 2 0.1 ceramic substrates. Transition to full superconductive state was obtained for all the samples. The related parameters (1:""e1' 1~, !J.T) and some structural properties are reported.

The peculia.r superconducting properties of the Y-BaCu-O compounds I have recently attracted a great scientific and technological interest because of their potential applications. Although the greatest efforts have been addressed to improve the preparation of high quality thin films,2-4 promising results have been obtained also using thick-film technology.5,b This is a simple and low cost technique which permits easy patterning and a full integration into hybrid electronic circuits. In this letter we report seJected preliminary results on the preparation of thick-film Y-Sa-Cu-O superconductors. We deliberately avoided specific and expensive substrates (such as Sr Ti01 or Zr0 2 single crystals) and worked on the commonly used alumina and berynia, The starting material YBa 2 Cu 3 0 7 was prepared following the procedure previously described, 7 The original pellets were finely powdered using an agate ball mill. An organic vehicle (a terpineol, ethyl cellulose, and buthil-carbitol acetate) was added (= 30% by weight) to obtain a paste suitable for screen printing. Films 35-40 pm thick were prepared on commercial 96% alumina (Hoechst CeramTec 708) and 99.5% beryHia (Brush & Welldmann, Thermalox 995) substrates and kept for 1 hat 980°C in air. Part ofthese samples was subsequently annealed for 2 h at 440°C in flowing oxygen. Heating and cooling rates were always 1.5 deg/ mm. X-ray diffraction (XRD) patterns (CuK o ' Ni-fil-

tered) relating to beryHia supported films are identical to that of the original powder (Fig. 1), showing the stability of the YBa2Cu.107 orthorhombic phase on this substrate. On the contrary, films printed on alumina undergo clear structural modifications. The new phase is not directly identified either as the standard orthorhombic phase or as the tetragonal one (Fig. 1), Assuming an orthorhombic cell, a fitting procedure on the entire set of peaks for each spectrum gave the parameters reported in Table I. They generally agree with those previously reported for oxygen-deficient orthorhombic phases. R In addition, the formation of relevant amounts of Y 2BaCuOs was observed. The microscopical structure of the films (Fig, 2) was investigated by scanning electron microscopy (SEM). Morphologically, beryllia supported films [Fig. 2(b)] are quite similar to the original pellets [Fig. 2 (a) ], They show a loose pattern of isolated voids and a high proportion of interconnected grains, so that continuous paths are easily found, The same heating and cooling cycles lead to completely different results when alumina substrates are involved [Fig. 2 (c) ]. In this case the final microstructure is much mere compact and connected, thus suggesting the occurrence of a melting process in high-temperature stage. No difference is observed between the as-prepared and the oxygen-annealed samples. From the comparison with the BeO supported films, the responsibility for these microscopical changes is easily assigned to a contamination of aluminum from the substrate. X-ray energy dispersive spectroscopy (XEDS), performed with the electron beam (25 keY) impinging on the sample surface, confirmed the 1:2:3 ratios for Y -Ba-Cu concentrations but gave no positive evidenc~ for the presence of Al on the top of the films. On the other hand, cross-section analysis revealed that the composition of alumina supported films is strongly dependent on the distance from the substrate interface. In the first 10 pm mainly Al and Ba are detected by XEDS, together with a small amount of copper, while yttrium is below the detection limit (=0.5 at. %). XRD on thinned samples clearly shows the BaAl 20 4 spinel phase, TABLE I. Crystal structure parameters obtained by fitting XRD spectra.

FIG. l. XRD patterns relating to the original powder and to four different samples. Peaks marked hy * correspond to the YoBaCuO, "green phase." Intensities of peaks in the range ST-60' are multiplied by 2. 1 i 10

Appl. Phys. Lett. 53 (12), 19 September 1988

ao b" cn

Alumina air

Alumina oxygen

Beryllia air

Beryllia oxygen

Original powder

3.856 3.872 11.073

3.844 3,875 11.645

3,824 3.879 11.653

3.821 3.891 11.684

3.817 3.894 11.680

0003-6951/88/381110-03$01.00

(e)

1988 American [nstitute of Physics

Downloaded 10 Dec 2012 to 155.185.12.195. Redistribution subject to AIP license or copyright; see http://apl.aip.org/about/rights_and_permissions

1110

(Fig. 1). The BaCu0 2 and Y 2CU05 phases reported by Budhani et al. 6 are not detected in our samples. This is probably related to the different thermal cycles, and particularly to the different heating and cooling rates, adopted in their experiments. Finally, some cracking is observable in Figs. 2(b) and 2(e) due to the mismatch between the thermal expansion coefficients of the Y -Ba-Cu-O phases and those of the ceramic substrates. The resistive properties were determined using the fourprobe method in the temperature range 10-300 K ( ± 0.1 K). Electrical contacts were made using silver paste. The geometry was not wen defined (as a consequence absolute values of resisitivity are not reported), but it was almost the same in each measurement to get comparable results. All the samples exhibited a superconducting transitiono Table II lists the onset temperatures 1~1l' the midpoint critical temperatures 1'0 and the transition widths (from 10 to 90%) aT, together with the critical currents Ie measured at 10 Ko The onset of a voltage greater than a II_ V was used as a measure of Ie. An underestimation of the critical current densities can be obtained by dividing Ie values by the maximum sectional area of the films (=- 10- 3 cm 2 ). The best results in terms of Tc and t:.. T are obtained for BeO supported films (see Fig. 3). The steep rise of resisitivity at about 92 K corresponds to the transition usually reported for YBa 2 Cul 0 7 • In addition, a broad tail of resistivity extends to lower temperatures. By considering this curve as composed by two distinct transitions, we have for the oxygen-annealed sample T e• 1 = 81 K, aT\ = 18 K and 1',,2 = 91.5 K, tlT2 = 2 K. Alumina supported films exhibit a single broad transition below 80 K (Fig. 3). Interestingly, oxygen annealing remarkably improves T, and !J. T values for these samples, whereas it is almost ineffective on beryllia supported films. Finally, the critical current measured at 10 K is strongly dependent on the substrate used (see Table II). The much higher values measured on alumina supported films are probably related to their better compaction, as shown by

FIG. 2. SEM micrographs of (a) the original pellet, (b) AlP" and (c) BeO supported films (oxygen annealed). The white bar is 10 pm.

already reported by other authors.