Structural and electrical properties of LaNiO3 films by pulsed laser deposition

Abstract

Correlated transition metal oxide has great attention in recent decades due to spin-orbit order, polarity order, high-temperature superconductivity, metal-insulator transition and functional oxide in heterostructure. Among the transition metal oxide, LaNiO3(LNO) is a metallic system and one of the highest active materials having stoichiometry Ni3+ valence state. It is well known that the chemical binding state of between transition metal and oxygen affect the physical properties, e.g., structural defects, non-stoichiometric compositions of transition metal oxide. For this reason, it is essential and important to control the valence state of the transition metal.

In this thesis, LNO films and non-stoichiometry LNO films were grown on SrTiO3(001) substrate by using pulsed laser deposition(PLD). The oxygen partial pressure was systematically changed to control the Ni valence state. By using X-ray scattering, it found that increasing oxygen partial pressure leads to decrease out-of-plane lattice parameters of LNO films and non-stoichiometry LNO films. The increase of oxygen partial pressure caused the Ni3+ oxygen state dominant, which was observed using X-ray photoelectron spectroscopy. To understand the correlation between chemical binding state and electrical properties, low-temperature electrical measurement was performed. Increasing the Ni3+ concentration caused a decrease in resistivity, and lowest resistivity was observed in the sample with the highest Ni3+ concentration. It was confirmed that the Ni oxygen state has sensitive effect on the conductivity, and the Ni valence state was controlled to lower the resistivity of the LNO thin film.