Effects of Off-Stoichiometry in the Epitaxial NdNiO₃ Film on the Suppression of Its Metal-Insulator-Transition Properties

Abstract

Neodymium nickelate (NdNiO 3 : NNO), which is a typical strongly correlated metal oxide, has attracted considerable attention because of its large resistance changes due to its metal-insulator transition (MIT). Since MIT in NNO is quite sensitive to the stoichiometry, we precisely fabricated four NNO thin films with different Nd:Ni ratios and comprehensively studied stoichiometry-dependent MIT properties using a temperature-dependent resistance measurement, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and a first-principles density functional calculation. We found that the resistance change in MIT is strongly enhanced when the Ni 2+ /(Ni 2+ + Ni 3+ ) component and estimated oxygen deficiency are sufficiently reduced by optimizing Ni/Nd. The relative change in resistance was sensitive to the Nd:Ni ratio of the NNO thin films, varying from 1 (no transition) to 42 of the resistance change ratio. XPS studies revealed that the cationic deficiency from stoichiometry in NNO films led to the deviation of the Ni valence from 3+. DFT calculations supported that a lack of Ni causes metallicity due to a reduction in the Ni valence from 3+ to 2+ and the collapse of the band gap, followed by oxygen defect introduction, which causes the degradation or absence of MIT properties.

Catalytic Hydrogen Doping of NdNiO3 Thin Films under Electric Fields

“…The transition temperature can be seen clearly at 200–210 K in the plot of dρ/d T % versus T in the inset of Figure b, which is indicated by the change in the sign of the temperature coefficient of resistivity from dρ/d T < 0 (insulating state) to dρ/d T > 0 (metallic state) or vice versa. Similar MIT characteristics have been observed in other reports of bulk NNO , as well as of NNO films deposited on STO substrates. , The XRD and ρ– T results prove the high quality of the as-deposited NNO film. The NNO film was then formed into a two-terminal resistor with Pt–Au/Ti heteroelectrodes, as shown in Figure a.…”

Controllable Strongly Electron-Correlated Properties of NdNiO3 Induced by Large-Area Protonation with Metal–Acid Treatment

“…NNO films of 70 nm thickness were deposited on SrTiO 3 (STO) substrates (typically 10 × 10 mm 2 ) by pulsed laser deposition (ArF excimer laser, λ = 193 nm, 3 Hz, 90 mJ) at a growth temperature of 923 K with an oxygen pressure of 30 Pa. An NNO target with a Nd:Ni atomic ratio of 1.5 was employed . To gain a deeper understanding of the effect of interfacial bonding on the hydrogenation-induced phase transition in perovskite nickelates, NNO films (around 70 nm) were grown on (001)- and (111)-oriented STO substrates. , …”

“…15 To gain a deeper understanding of the effect of interfacial bonding on the hydrogenation-induced phase transition in perovskite nickelates, NNO films (around 70 nm) were grown on (001)-and (111)oriented STO substrates. 6,15 2.2. NNO Hydrogenation.…”

Hydrogen Atom Doping—A Versatile Method for Modulated Interface Resistive Switching

“…[ 16a,c ] Thus, hydrogenated nickelate films, which are classified as iontronic devices, require excellent crystal quality for H + ions movement within the solid lattice to perform resistive switching. [ 16a,c,17 ] It is to be noted that studies related to H + doped perovskite nickelate resistive switching are restricted to film thicknesses of about a few hundred nanometers [ 16a,b,18 ] because of material quality [ 19 ] and synthesis process. [ 16a,c ] However, hydrogenated thicker nickelates films have been employed for different applications, such as electric field sensors, bioelectronics, and fuel cells.…”