Comparative Study of the Electronic Transport in YBaCo4O7+δ Thin Films Grown on Different Substrates

YBaCo4O7+δ thin films with thicknesses of 180 nm were grown by means of magnetron sputtering technique onto (100)-SrTiO3,(100)-LaAlO3,(100)-MgO, and (0001)-Al2O3 substrates. The structural characterization performed by X-ray diffraction shows that films deposited on MgO, SrTiO3, and c-Al2O3 substrates grow with preferential orientation in the (203) direction. For LaAlO3 substrates, the preferred growth direction is the (212). The coupling between the lattice parameter of the compound and those of the substrates seems to determine the preferred orientation for the growth onto the different substrates. We carry out measurements of the resistivity as a function of the temperature in the standard four-terminal configuration, and analyze the results in the framework of some transport models such as simple thermal activation, small polaron hopping, and Mott’s variable range hopping (VRH). A better agreement with the experimental data is observed by applying the latter model. The fitting of this model to the experimental data allows for determining important physical parameters related to the electrical conduction in these materials such as the density of states at the Fermi level.