Thermoelectric Power of YBa₂Cu₃O_7-X and YBa₂Cu₄O₈ Under Pressure

Abstract

Thermoelectric power (TEP) of YBa₂Cu₃O_7-X (123) and YBa₂Cu₄O₈ (124) samples are measured as a function of pressure. The TEP of an as-sintered 123 polycrystalline sample shows a broad maximum around 1.25 GPa whereas that of the cold-pressed sample decreases steadily. The ab-plane TEP of 123 single crystal decreases monotonically and the c-axis TEP exhibits a maximum around 1.5 GPa. Disappearance of the broad maximum in the polycrystalline sample upon cold-pressing is interpreted in terms of the crystallite orientation occurring under pressure. TEP of the 124 polycrystalline sample decreases sharply up to 4.5 GPa and at a lower rate with further increase in pressure, a trend similar to that is observed in the variation of T_c as a function of pressure.