The origin of texture in bulk superconductors fabricated by the melt texture growth process

Abstract

Melt texture growth YBCO bulk superconductors have been fabricated by making use of the nonzero spatial temperature gradients (∇T) at certain locations and with temporal variation (∂T/∂t) inside a common tube furnace. The texture of the YBa 2Cu 3O y (Y123) single crystal layers and Y 2BaCuO 5 (Y211) grains of the specimen are investigated by TEM/EDX, SEM/EDX, XDP, χ-T and R-T measurements. The phase distribution results of Y123 and Y211 using EDX covering an area of single crystal layer and Y211 grain indicate that the crystal layers are not “true layers” but “bulk crystal with gap lines and planes”. The formation of gap lines and planes depends on how the Y123 phase grows from the Y211 grain. If the Y211 grain can act as a nucleus of Y123 phase, “gap plane” can be formed when two Y123 crystal blocks grow to touch each other. However, if the Y211 grain cannot take the role of a nucleus, it can only act as a perturbation and generate a gap line as the crystal growth front passes through the grain. Moreover, since the orientation of the crystal layers relative to the top and bottom surfaces of the bulk specimen depends on ∇T and ∂T/∂t, we can control the crystal layer orientation by varying the above two parameters using a simple tube furnace in order to produce high quality melt texture YBCO material.