Resistivity of La sub (1.825) Sr sub (0.175) CuO sub 4 and YBa sub 2 Cu sub 3 O sub 7 to 1100K: Absence of saturation and its implications.

Resistivity was measured from T sub c to 1100K for La sub (1.825) Sr sub (0.175) CuO sub 4, where it is linear to 1100K, and for YBa sub 2 Cu sub 3 O sub 7, where it is linear to 600K, increases faster than linear at T>600K, owing to loss of oxygen, and changes slope at the 950K structural transition. The observed absence of saturation in the linear parts of the data implies weak electron-phonon coupling in both superconductors, thus excluding the possibility of phonon-mediated superconductivity. Values of the plasma energy are derived in combination with other experimental data.