A kinetic analysis of the formation process of the superconducting phase YBa₂Cu₃O_x

Abstract

The kinetics of the formation process of the superconducting phase YBa,Cu,O,, synthesized by the solid state reaction method with the initial mixture of barium carbonate (BaCO,), yttrium oxide (Y,O,) and copper oxide (CuO) has not been studied in full detail up to now. T o gain an insight into the kinetics of the process one has to know its real reaction mechanism. I n this note we attempt to propose a reaction model which seems to be quite adequate in explaining our own experimental results. For this purpose, X-ray powder diffraction, the differential thermal analysis, and the gravimetric methods have been used. Figure 1 represents the time and temperature dependences of the relative weight changes of the phase being formed. The strong temperature dependences (seen from Fig. 1) predict rather high activation energy. Concerning time dependences, the process occurs rapidly at first, but then it is gradually slowed down. Furthermore, the time dependence always undergoes a maximum, and we might assume that the process of weight changes would consist of two main concurrent processes. In this respect let us conventionally distinguish two different regions, one (I) before the maximum and the other (11) after it. To analyse the mechanism of the process consider the general reaction producing the superconducting phase YBaBCu30, as below: