Characterization of PrBa2Cu3O7-δ single crystals grown by crystal pulling method using MgO crucible

Physica C 235-240 (1994) 361-362 North-Holland

PHYSICA

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Characterization of PrBa2Cu3OT.s single crystals grown by crystal pulling method using MgO crucible M.Tagami, *M. Sumida, Ch. Krauns, Y. Yamada, *T. Umeda and Y.Shiohara SRL-ISTEC, 1-10-13 Shinonome, Koto-ku, Tokyo 135, Japan *Univ. of Tokyo, 7-3-1, Bunkyo-ku, Tokyo, 113, Japan Single crystals of PrBa2Cu3OT.~containing small amounts of Mg were successfully fabricated by the improved crystal pulling method (SRL-CP method) using MgO crucibles. The melt temperature was between 965°C and 970°C. No MgO inclusion was observed by electron probe micro analysis (EPMA). The lattice constants of the grown crystal are a=3.907(1)]k, b---11.768(1)/~, V= 176.6(1)/~,3. The Mg contamination from MgO crucible was relatively small with a composition of Pr1.00Ba2.00Cu2.9406.72 Mg0.06. analyzed by 4-circle single crystal diffractometer. 1. INTRODUCTION PrBa/Cu307_~ (Pr123) is an interesting material because it does not show a superconductivity at low temperatures, but its lattice parameters are almost the same as those of YBa2Cu3OT-s .(Y123) Therefore, large single crystals of Pr123 are expected to be applicable to a subslxate and/or a wafer for quasihomoepitaxial growth of RBa2Cu3074i (R=rare earth) superconductive films. One of the serious problems for growing Pr123 single crystals is the crucible material. In spite of several trials, Pr6Ou crucibles expected to be contamination free could not be successfully utilized for fabrication of Pr123 single crystals. Therefore, we selected MgO as a crucible material due to the lowest wettability of Ba-CuO flux in several materials as we reported earlier [1]. This property of the crucible material makes it possible to hold the Ba-Cu-O melt at crystal growth temperature for a long time. Recently, continuously grown single crystals of Pr123 with small amounts of Mg were successfully obtained using MgO crucibles [2]. In the present study, we investigated the influence of Mg contamination from crucible on the crystal structure and the lattice constants of the grown crystals.

2. EXPERIMENTS MgO was used for the crucible material. The total composition in the crucible selected was the ratio ofPr : Ba: Cu = 4 : 27 : 69.The seed crystal was kept in contact with the surface of the melt and rotated at 120 rpm, while slowly pulled at a rate of 0.1 mm/h. The temperature at the surface ranged from 965°C to 970°C. The existence of MgO inclusions was checked by electron probe micro analyzer (EPMA). Electrical resistivity in direction of a-axis of 02 flow annealed crystal at 500°C for 70h was measured by the dc two probe technique. The measurement of lattice parameter and occupancy of every site of elements was measured by 4-circle single crystal diffractometer. The sample was a sphere crystal having approximate 0.29mm diameter. All measurements were made on a Rigaku AFC5R diffractometer with graphite monochromated Mo Kot radiation. 3. RESULTS AND DISCUSSION Figure 1 shows a photograph of the specimen pulled along the c-axis by this method. It is obvious that the crystal is grown from the bottom of the MgO single crystal seed. Electric resistivity increased

0921-4534/94/S07.00 © 1994 - Elsevier Science B.V. All rights reserved. SSDI 0921-4534(94)00744-6

M. Tctg:ami et al./Physica C 235 240 (1994) 361 362

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Fig.1 Pr123 single crystal pulled along c-axis

large because as-grown crystals were annealed in air atmosphere when slowly pulled up from the furnace. The lattice constants of tetragonal PrBazCu306 with a=3.906(4),~, c=l 1.824(2)/~, V=180.39(5)/~ 3 were reported by C.K.Low-Ma et al [3]. Comparing with our data, the length of the c-axis of our specimens are smaller. This could be due to the different oxygen contents and Mg contamination. Nevertheless, since the effect of the Mg contamination on the lattice constants seems to be small and we could not detect any inclusions, these crystals will be good templates for 123 superconducting films.

with decreasing temperature as shown in fig. 2. No MgO inclusion in the grown crystal was observed by EPMA area analysis. The crystal structure of the asgrown crystal analyzed by 4-circle single crystal diffractometer corresponded to a primitive tetragonal cell with dimensions: a=3.907(1)~, c=11.768(1)]L V=176.6(1)/~ 3. The space group was determined to be P4/mmm(#123). The unweighted factor R was 1.6%. The composition of the grown crystal calculated from occupancy of every elements is

4. CONCLUSIONS We have successfully fabricated Pr123 single crystals with a small amount of Mg contamination from MgO crucible by the crystal pulling method. The lattice constant, composition and electric resistivity of the crystal were investigated. These crystals can be used as the substrate for the superconductive films because of small effect of Mg contamination for lattice constants.

Prl.0oBa2.00Cu2.9406.72Mg0.06. According to our data, Mg substituted the Cu(1) chain sites. Within the error of measurment, the same Mg contents were confirmed by ICP. The oxygen content was relatively

ACKNOWLEDGEMENTS The authors would like to thank Dr. Y. Kino and Dr. S. Sato of Rigaku corporation for X-ray analysis. This work was supported by New Energy and Industrial Technology Development Organization for the R&D of Industrial Science and Technology Frontier Program.

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REFERENCES [1]Ch.Krauns, M.Tagami, Y. Yamada, M.Nakamura, Y. Shiohara, s J. Mat. Res. in print. [2]M. Tagami, M. Sumida, Ch. Krauns, Y. Yamada, T. Umeda, Y. Shiohara, proceedings of ISS'93, in print [3]C.K.Low-Ma, T.A.Vanderah, Physica C 201 (1992)233-248