AN IN-SITU X-RAY-SCATTERING STUDY OF HIGH-TEMPERATURE STRUCTURAL-CHANGES IN BI2SR2CACU2O8+DELTA

The properties of the incommensurate modulation of Bi-2212 have been i nvestigated using X-ray scattering to observe in situ the response of the structure to high temperature (up to 450 degrees C). The results d emonstrate the temperature independent nature of the incommensurabilit y, and several pinning mechanisms which would offer explanations for t his are discussed. The strong influence exerted by oxygen diffusion ov er the structure is also highlighted, and the results clearly indicate the existence of two distinct oxygen diffusion processes. However, it is also found that the wavevector of the modulation is in no way a co ntinuous function of oxygen content; a result contrary to the widespre ad assumptions in the literature. Only after prolonged annealing was e vidence for a structural transition observed, involving the appearance of reflections with an apparently new wavevector of q approximate to 0.14b + c*.