Metal-insulator transition in thin films of RxR′1-xNiO3 compounds:: DC electrical conductivity and IR spectroscopy measurements

In this work a systematic comparison of DC electrical conductivity and IR optical properties of thin films of (RxR'1-xNiO3), where R' = Nd and R = Sm or Eu, is performed. Independently of the nature of R, it is confirmed that the metal-insulator transition temperature (T-MI) in RxR'1-xNiO3 as well as in RNiO3 is driven by the mean lattice distortion quantified by the tolerance factor of the perovskite. The internal chemical pressure decrease due to substitution of Nd by another rare earth element with smaller cationic radius gives rise to an increasing resistivity in the metallic state together with a decrease of the screening effect in the IR reflectance. We suggest this is due to a modification of the free electron properties at the Fermi level and of the Fermi surface proper-ties consistent with photoemission literature data. On the other hand, similar transmittance spectra for various systems are reported in the insulating state. A systematic temperature independent drop of the transmittance above 0.6 eV is found for each system whatever the value of T-MI.