Growth of Superconducting Oxides

La2 xAExCu04 AE = Alkaline Earth Large crystals of the 30K superconductor, Ba016Laj 86Cu04, having the K2NiF4 structure 

AI2O3 2072 Readily available in high purity and a variety of shapes 

A higher temperature, Tc l 10K, phase in the Bi-Sr-Ca- Cu-O system has also been reported (78-80). This phase contains three infinite two-dimensional Cu-O layers. However, lead appears to play an important role in stabilizing this compound in phase pure form (75)(79)(80). Single crystals grown by eutectic melt growth techniques have been reported (77) but the phase purity of these crystals with respect to intergrowths containing various numbers of Cu-O planes is a concern. 

Crystal growth of these compounds is complicated by the high volatility of thallium oxides and thallium-containing compounds at elevated temperatures and the toxicity of thallium. Also, the similarity in structures leads to problems controlling phase purity and samples which appear to be single crystals based on their morphology can be shown to be complicated intergrowths by X-ray diffraction studies. 

Pb2Sr2M1 xCaxCu3Og. Compounds of formula PbjSrjMj x-CaxCu308, where M = lanthanoid, form a new class of superconductors with Tc s as high as 80K (44)(81). The structure contains double layers of infinite planes of corner-shared CuOB pyramids interleaved 

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The growth of superconductive oxides under vacuum conditions compatible with MBE requires the use of activated oxygen. The atomic oxygen or ozone appear to be such species [150]. The characteristics of a radiofrequency plasma source for molecular beam epitaxial growth of high-Tc superconductor films (200 A) from DyBa2Co30, on SrTiOj are described and discussed in Ref [150]. 

An apparatus for the preparation of pure ozone vapor for use in situ growth of superconducting oxide thin films are designed [151]. Pure condensed ozone is produced from distillation of diluted ozone-oxygen mixture at 77K. The condensed ozone is heated until the pressure of its vapors approaches the necessary for an adequate flow of ozone- gas to the chamber of thin films growth. The thin films from YBa2Cu30, with zero resistance at temperatures of about 85K grow at ozone pressure in the... 

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