Electron microscopic observations of Bi and Tl bearing cuprate high temperature superconductors

The second generation of high temperature superconductors typified by Bi2Sr2Casub(n-1)CunOsub(2n+4) and Tl2Ba2Casub(n-1)CunOsub(2n+4) exhibits curious structural properties which have direct relevance to the superconducting behaviour particularly transition temperature (Tc). The present paper reports on investigations of structural properties at microlevel in Bi-bearing HTCS. Curious structural characteristics which manifest in the form of transformation from ap x ap x c to (2)sup(1/2)ap x (2)sup(1/2)ap x c through the loss of calcium atoms and the formation of five-fold modulated phase along b through the loss of Ca and Sr atoms have been found. The evidence of high periodicities (n=4) Bi2Sr2Ca3Cu4O12 have also been found. The microstructural characteristics of HTCS showing the higher Tc(R=O)∼120K exhibit unusual characteristics. (author). 8 refs., 8 figs