Phase transformation analysis throughout an anhydrous fluorine based sol–gel YBCO processing route

This investigation has made use of four complementary chemical analysis techniques (differential thermal analysis, X-ray diffraction, Raman spectroscopy and UV–vis diffuse reflectance spectroscopy) to track the composition of an YBCO-TFA sol throughout the heat treatment cycle. From this, a schematic reaction pathway is proposed: below 400 °C, yttrium acetate transforms to yttrium trifluoroacetate and then to a yttrium intermediate (possibly yttrium(III) oxide, yttrium fluoride or yttrium oxyfluoride), barium acetate transforms to barium trifluoroacetate and then to barium fluoride, and copper acetate transforms to copper trifluoroacetate to copper(II) oxide. Above 400 °C the yttrium intermediate, barium fluoride and copper(II) oxide interact to form YBa2Cu3O7−δ. The gelation reaction up to 170 °C may be monitored by measuring changes in diffuse reflectance at 395 nm, for example, using an LED/photodiode sensor as a component of an inline process control system.