Investigation of the controlled growth of large undoped and Pt-containing YBCO pseudo-crystals

A thermal processing system incorporating four sets of independently controllable heating elements and a cold finger which generates uniform temperature gradients of up to 25 °C cm−1 has been developed and optimized to fabricate large undoped and Pt-containing YBCO pseudo-crystals by seeded peritectic solidification. Evolution of oxygen gas and loss of liquid during peritectic decomposition have been identified as key variables for the fabrication of large, single grain samples. The processing conditions associated with this system have been investigated for varying precursor body heating rate, undercooling, growth rate and sample thickness. Optimum values of these parameters were determined as heating rate: 10 °C h−1, undercooling: ≈ 15 °C and sample thickness: < 25 mm. A thermal profile for the optimized growth of large YBCO pseudo-crystals is proposed on the basis of these results. Single grain samples fabricated using this profile grow to within 2 mm of the bottom of the YBCO body and exhibit good morphology with 4-fold symmetry.