Understanding the Role of Defective Phases on the Conductivity Behavior of Strained Epitaxial LaNiO₃ Thin Films

Abstract

Rare earth nickelates (RNiO 3 , where R is rare earth) possess detailed phase diagrams and exhibit a wide variety of physical phenomena such as antiferromagnetism, metal-toinsulator transitions, as well as rich strain-dependent physics. Among them, LaNiO 3 is unique as it retains its metallic character down to ultralow temperatures, as well as offering the promise of various topological effects and exotic phenomena. Practically speaking, however, the fabrication of LaNiO 3 in thin-film form is challenging since its various oxygen-deficient phases are close in formation energy. Here, we study a series of epitaxial LaNiO 3 films fabricated on (001) LaAlO 3 substrates by pulsed laser deposition under various growth and postannealing conditions. A complex correlation between structure, processing, and conduction properties is found, which is explored using a host of complementary characterization tools including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transport measurements, and scanning transmission electron microscopy. The conclusions of this study are as follows: (i) the XRD patterns of LaNiO 3 films cannot be used to predict whether films will be conductive or insulating, (ii) the surface XPS of defective and "nondefective" LaNiO 3−x films can appear identical, despite the bulk having a complex defective structure, and finally, (iii) LaNiO 3−x films with up to 50% defective phase can exhibit metallic-like transport behavior down to 40 K.

Reset-First and Multibit-Level Resistive-Switching Behavior of Lanthanum Nickel Oxide (LaNiO3−x) Thin Films

“…Among RNiO 3 , LaNiO 3 (LNO) is a highly conductive oxide with a perovskite-type structure, exhibiting an electrical resistivity of only a few hundred μΩ⋅cm to mΩ⋅cm at room temperature [ 6 , 7 , 8 , 9 , 10 ]. Therefore, LNO, owing to its crystallinity and high conductivity, has been primarily used as the bottom electrode (BE) in multilayer film devices, along with other ferroelectric, ferromagnetic, or multiferroic functional oxides [ 11 , 12 , 13 ].…”