Nonlinear Temperature Dependence of the Resistivity in Superconducting YBa sub 2 Cu sub 4 O sub x Films.

The ab-plane resistivity of YBa sub 2 Cu sub 4 O sub (8+-delta) (1:2:4) films is measured from 68K to 600K and found to be a nonlinear function of temperature in contrast to that of YBa sub 2 Cu sub 3 O sub (7-delta) (1:2:3) films. The nonlinearity can be understood in terms of a Bloch-Gruneisen type behavior with a transport Debye temperature of theta sub D sup * ~ 500K, as compared to theta sub D sup * ~ 200K for 1:2:3. This difference is attributed to the larger number of charge carriers per unit cell in 1:2:4.