Strain-mediated effects of oxygen deficiency and variation in non-Fermi liquid behavior of epitaxial PrNiO3-δ thin films.

To understand the effects of oxygen variation in combination with different strains in perovskite nickelates, three sets of PrNiO3-δ thin films S 1, S 2 and S 3 were deposited on (0 0 1) oriented single-crystal wafers of SrTiO3, LSAT [(LaAlO3)0.3(Sr2TaAlO6)0.7] and LaAlO3, respectively. Two sets of films, S 1 and S 2, have tensile strain whereas the films of S 3 show compressive strain. For each set, two thin films of fixed thickness (5 nm) were deposited; one film was annealed in situ in oxygen partial pressure just after deposition, the other film was not annealed. The difference in oxygen stoichiometry caused a different state of epitaxial strain in the films. So, the strain was induced in the films due to lattice mismatch with substrate, which modified due to oxygen deficiency. These films show non-Fermi liquid (NFL) behavior in the metallic state. The fitting parameters to power-law equation show a systematic tuning of NFL fitting parameters because of variations in strain. Our results show that not only lattice mismatch induced strain, but also oxygen stoichiometry are crucial parameters in changing the state of strain and hence the NFL behavior and electronic properties of perovskite nickelates.