Chain contribution to the Seebeck coefficient in YBa2Cu3O7-

Measurements of the Seebeck coefficient (T) and the resistivity R(T) of polycrystalline YBa2Cu3O7- quenched from different temperatures Tq and of polycrystalline (Y1-xCax)(Ba2-xLax)Cu3O6.960.01 were made to distinguish the contributions to (T) from the Cu(1)O chains and the CuO2 sheets. The CuO2 sheets give a positive contribution to (T) that is composed of a weakly temperature-dependent part 0 that decreases sensitively with increasing oxidation and an enhancement part that gives a broad maximum to (T) at a Tmax140°C. These two features together have been shown to distinguish the superconductive compositions from the parent and overdoped compositions in other copper-oxide supeconductors. In fully oxidized YBa2Cu3O6.96, the contribution to (T) from the CuO2 sheets is obscured by a dominant, competitive negative contribution to (T) from the chains that has a similar, but negative, enhancement.