Hydrogenation of thin Y-Ba-Cu-O films: Electrical transport and structure properties of YBa2Cu3O7 and YBa2Cu4O8.

Abstract

c-axis-oriented ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ (1:2:3) and ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{4}$${\mathrm{O}}_{8}$ (1:2:4) thin films were charged with hydrogen at 463 K and a ${\mathrm{H}}_{2}$ pressure of 100 mbar. The hydrogen concentrations and depth profiles were measured with the $^{15}\mathrm{N}$ nuclear reaction method. In contrast to earlier studies on bulk samples where a constant ${\mathit{T}}_{\mathit{c},\mathrm{o}\mathrm{n}\mathrm{s}\mathrm{e}\mathrm{t}}$ is reported, we find in our 1:2:3 films that the superconducting transition temperature decreases continuously with increasing hydrogen concentration and that the transitions remain relatively sharp, e.g., ${\mathit{T}}_{\mathit{c},\mathrm{o}\mathrm{n}\mathrm{s}\mathrm{e}\mathrm{t}}$=38 K and \ensuremath{\Delta}${\mathit{T}}_{\mathit{c}}$=6.2 K for [H]/cell\ensuremath{\simeq}0.6. The electrical resistivity and Hall-effect measurements in the normal state indicate that the main effect of hydrogen doping is a reduction of the charge carrier concentration, whereas the carrier mobility is not changed significantly. At an average hydrogen concentration of [H]/cell\ensuremath{\simeq}2 in both systems, a new hydride phase is observed, which for 1:2:3 is characterized by a c-axis expansion of 16% and for 1:2:4 by a c-axis expansion of 1.5%.