Published online by Cambridge University Press: 21 February 2011
Small structural changes accompany important changes in Tc in some materials. In YBa2Cu3O6+x, Cava et al. have shown that oxidation to YBa2Cu3O7 involves a significant shift of the oxygen bridging CuO-chains and CuO-planes toward the latter. In YBa2Cu4O8, Kaldis et al. have shown that a similar effect is produced with pressure alone. In both cases, Tc increases strongly. In TI2Ba2Cu1O6, Tc varies greatly depending on the precise method of preparation, though the stoechiometry appears unchanged. In this case, Tc may depend on subtle differences in oxygen content, and perhaps Cu-O bond lengths. These effects can be discussed in terms of charge transfer between intercalated layers of CuO-chains or TIO-planes, and conducting CuO-planes.