THE CRYSTAL-GROWTH ANISOTROPY OF YBA2CU3O7+DELTA FABRICATED BY THE MTG METHOD IN A MICROWAVE CAVITY

The aim of this work is to optimise a microwave melt texture growth pr ocess in a vertical travelling solvent zone technique in a single mode microwave cavity to grow large single-domain Y123 samples. Indeed, th e large observed thermal gradient(> 180 degrees C/cm) in combination w ith the possibility of translating the sample across the microwave cav ity allows this technique to achieve conditions similar to those used in the classical MTG using a vertical furnace. However, the particular heating mechanism, in the microwave case, allows for a novel range of thermal conditions to be accessed, particularly a larger thermal grad ient, to grow large Y123 single-domain in novel thermal conditions. In a first effort to optimise this microwave technique, a composition co rresponding to a Y211-rich Y123 mixture, doped with cerium dioxide, wa s sought in order to improve the Y123 domain size. Secondly, the influ ence of the melt temperature and the bar diameter on the size and orie ntation of the Y123 quasi-crystals was investigated. The influence of each parameter is discussed with respect to the classical Y123 growth mechanism, and an explanation of the angle, which is observed to be ne ar to 45 degrees, between the ab-plane and the pulling direction is pr oposed. The Bean critical current density without applied magnetic fie ld, for a cleaved sample at 77 K reaches 50,000 A/cm(2) showing the hi gh quality of the microwave melt processed material. (C) 1998 Elsevier Science B.V.