Large resistance decrease around 90 160 K in sputtered Xe-doped Y-Ba-Cu-O thin films on Si substrates

A resistance decrease of about five orders of magnitude around 90 160 K has been observed in Xe-doped YBa1.5Cu6.3Ox, Xe-doped YBa1.5Cu3.7Ox, and Xe-doped YBa1.5Cu2.2Ox thin films. These films were deposited on unheated (100)Si substrates by Xe ion-beam sputtering and annealed in an oxygen flow at 100 500 degree C for 24 h. The resistance decrease was measured reproducibly for all samples except 500 degree C-annealed films even after exposure to atmosphere for two years. The x-ray diffraction pattern study revealed that the films mainly contain YBa2Cu3O6.8 lattices having compressed a-b lattice planes and an expanded c-axis bond length and YBa2Cu3O6 lattices. The presence of xenon-oxygen bonds in the films was determined by x-ray photoelectron spectroscopy. The resistivities first increased with decreasing temperature, exhibited a maximum value at 200 260 K, then exponentially decreased and reached very low resistivities at 95 130 K. copyright 1997 The American Physical Society