The solid combustion synthesis of small REBa2Cu3Ox samples (RE≡Y, Er)

We critically assess the solid combustion synthesis (SCS) of small (about 23 g) REBa2Cu3Ox samples (RE≡Y, Er) from mixtures of Cu, RE2O3 and BaO2 in an oxygen atmosphere. We examined the dynamics of the SCS process by means of temperature profile analysis and, for the first time on such a complex system, employed time-resolved X-ray diffraction using synchrotron radiation. We determined the phase composition, structure and magnetic properties of the resulting combustion product, which is a multiphase composite containing only about 30 wt.% of superconducting material. The superconducting phase exhibits transition temperatures of 80-90 K and oxygen transport and diffusion into the material appear to be sufficient. In contrast to results reported for large combustion samples, the absence of a sufficiently developed reaction zone seems to preclude complete formation of the superconducting phase in small combustion bodies. While combustion synthesis may have its advantages in technical-scale production of ceramic superconductors, it does not appear to be suitable for laboratory synthesis of small amounts of high-quality material. ((orig.))