TIME DEPENDENT CELL VOLUME (V) CHANGES IN V EXPANDED YBa_2Cu_3O_(605) -A PARADIGM FOR TEMPERATURE AS A VARIABLE SELFDOPANT

摘要

Cell volume expansion effects (175A~3) in isostoichiometric YBa_2Cu_3O_(y~6.5) shot quenched from 670K are almost 2 orders of magnitude larger than when quenched from 570K (compared to conventional room temperature equilibrated materials with 173 A~3). These distinct orthorhombic materials, based on threefold O coordination of Cu(1), transform within hours, presumably in a series of infinitely adaptable ladder structures, to related, more V contracted orthorhombics at lower T and constant y = 6.5. Time dependence data are presented for room temperature. The sequence of distinct cell volume expanded varieties presents a textbook example for temperature gaining the character of a selfdoping agent. This can be explained within an anionic charge order model as a result of lattice pressure. Accordingly, O- is created in stratified steps to ameliorate structural stress (tension selfdoping).