High temperature electronic conduction mechanisms in YBa₂Cu₄O₈

Equilibrium electrical conductivity and Seebeck coefficient measurements over the temperature range 500-800°C in YBa₂Cu₄O₈ (Y-124) exhibit evidence for two distinct conduction mechanisms, one metallic and one activated. It is speculated that the metallic mechanism is associated with the Cu-O planes, whereas the activated mechanism is associated with the Cu-O chains, just as in YBa₂Cu₃O_6+y (Y-123). Like the other superconducting cuprates, Y-124 electrical properties obey a standard relationship of Seebeck coefficient versus logarithm of conductivity. Analysis of behavior in Y-124 may provide useful insight into the electrical and superconducting behavior of the other cuprates, particularly Y-123.