RESUMO
Off-stoichiometric Cu-Cr-O delafossite thin films with different thicknesses were grown by metal organic chemical vapor deposition on substrates with different coefficients of thermal expansion. Seebeck thermoelectric coefficient and resistivity measurements were performed on the range of 300-850 K. A qualitative change in the temperature-dependence of the resistivity is observed at the temperature corresponding to the deposition process, where the transition from tensile to compressive strain takes place. Arrhenius plots reveal different slopes in these two thermal ranges. The fact that the shift is more pronounced for the thinner films might indicate the induced strain plays a role in changing electrical behaviour. Furthermore, changes below 0.1% in electrical mobility were measured when the strain is induced by mechanical bending.
RESUMO
Off-stoichiometric copper chromium delafossites demonstrate the highest values of electric conductivity among the p-type transparent conducting oxides. Morphological and structural changes in Cu0.66Cr1.33O2 upon annealing processes are investigated. Chained copper vacancies were previously suggested as source of the high levels of doping in this material. High resolution Helium Ion Microscopy, Secondary Ion Mass Spectrometry and Transmission Electron Microscopy reveal a significant rearrangement of copper and chromium after the thermal treatments. Furthermore, Positron Annihilation Spectroscopy evidences the presence of vacancy defects within the delafossite layers which can be assigned to the Cu vacancy chains whose concentration decreases during the thermal process. These findings further confirm these chained vacancies as source of the p-type doping and suggest that the changes in electrical conductivities within the off-stoichiometric copper based delafossites are triggered by elemental rearrangements.
