Metallic LaNiO3 Research Articles

Wide-range thermal conductivity modulation based on protonated nickelate perovskite oxides

The perovskite oxides ReNiO3 (Re = rare-earth elements) are promising functional materials due to their strongly correlated electrons. Except for the well-known intrinsic metal-insulating transition in these materials, recent progresses have proved that protonation of ReNiO3 can bring about interesting Mott transition in this series. To date, in these protonated species (H-ReNiO3), huge resistance switching, fast ionic diffusion, and their applications as an iontronic transistor, memristor, and fuel cell are reported. In this work, the thermal conductivities of H-ReNiO3 (Re = La, Nd, Sm, and Eu) epitaxial thin films are investigated. The protonation-induced Mott transition can effectively modulate the electronic thermal conductivity while the lattice thermal conductance is less affected. Hence, at room temperature, the metallic LaNiO3 and NdNiO3 exhibit reversible wide thermal conductivity modulation, in ranges of 2.6–12.0 and 1.6–8.0 W m−1 K−1, respectively. These values are much larger than other thermal regulation materials based on transition metal oxides. Thus, our work reveals the great potential of ReNiO3 being applied as a thermal-regulating material. The fast ionic diffusion in H-ReNiO3 also guarantees that a fast response and wide-range thermal transistor can be realized by H-LaNiO3 and H-NdNiO3 in the future.

Preparation of Epitaxial Metallic LaNiO3 Thin Film by Polymer Assisted Deposition

Preparation of Epitaxial Metallic LaNiO₃ Thin Film by Polymer Assisted Deposition

Narrow-Bandgap LaMO3 (M = Ni, Co) nanomaterials for efficient interfacial solar steam generation

Photothermal water evaporation provides a pathway towards a promising solution to global freshwater scarcity. Synergistic integration of functions in a material in diverse directions is a key strategy for designing multifunctional materials. Lanthanum-based perovskite complex oxides LaMO3 (M = Ni and Co) have narrow band gaps with a high absorption coefficient. These functionalities have not been appropriately explored for photothermal energy conversion. Here, we synthesized nanostructured metallic LaNiO3 and semiconducting LaCoO3 and used them to design interfacial solar steam generators. Effective light absorption capability over the entire solar spectrum of these materials leads to a photothermal efficiency of the order of 83% for both materials. Using a cone-shaped 3D interfacial steam generator with a LaNiO3 absorber, we achieved an evaporation rate of 2.3 kg m−2 h−1, corresponding to solar vapor generation efficiency of over 95%. To the best of our knowledge, this evaporation rate is higher than any oxide-based interfacial solar steam generator reported so far. Furthermore, we have also shown an effective way of using such evaporators for long-term seawater desalination.

Template Engineering of Metal-to-Insulator Transitions in Epitaxial Bilayer Nickelate Thin Films.

Understanding metal-to-insulator phase transitions in solids has been a keystone not only for discovering novel physical phenomena in condensed matter physics but also for achieving scientific breakthroughs in materials science. In this work, we demonstrate that the transport properties (i.e., resistivity and transition temperature) in the metal-to-insulator transitions of perovskite nickelates are tunable via the epitaxial heterojunctions of LaNiO3 and NdNiO3 thin films. A mismatch in the oxygen coordination environment and interfacial octahedral coupling at the oxide heterointerface allows us to realize an exotic phase that is unattainable in the parent compound. With oxygen vacancy formation for strain accommodation, the topmost LaNiO3 layer in LaNiO3/NdNiO3 bilayer thin films is structurally engineered and it electrically undergoes a metal-to-insulator transition that does not appear in metallic LaNiO3. Modification of the NdNiO3 template layer thickness provides an additional knob for tailoring the tilting angles of corner-connected NiO6 octahedra and the linked transport characteristics further. Our approaches can be harnessed to tune physical properties in complex oxides and to realize exotic physical phenomena through oxide thin-film heterostructuring.

(Invited) Beyond LaNiO3 - Direct Epitaxy of More Exotic Rare Earth Nickelates By ALD

The report of direct low temperature ALD epitaxy of metallic LaNiO3 in 2020 spurred a lot of interest in the ALD- and electronics communities [1]. Thin films deposited at temperatures as low as 225 °C by thermal ALD exhibit MBE/PLD-like quality, and may be a door-opener for direct integration of functional oxides in a range of applications. Not only are the films metallic with low resistivity (≈100 μΩ cm), they also serve as templates for integration of other compounds adopting the perovskite structure. In other words, they are perovskite-templating conductors that can be used as electrodes in oxide-electronics.LaNiO3 is, however, considered the most boring of the rare-earth nickelates. Being metallic at all temperatures and exhibiting close to ohmic behavior, it offers few surprises even if it is versatile in terms of applicability. Other rare-earth nickelates are more interesting from a fundamental perspective, exhibiting current driven resistivy variation and metal-insulator transitions (MITs) at temperatures determined by the size of the rare earth cation (indirectly the Ni-O-Ni bond angle).ALD is proving to be a brilliant tool to study the rare earth nickelates. Low temperature epitaxy gives ample opportunity to study temperature dependent behavior of pristine films. The intrinsic thickness control provides the possibility to study thicknes dependency on both resistivity variation and MIT.In this talk, I will highlight how we have used the learnings from direct epitaxy of LaNiO3 to deposit NdNiO3, SmNiO3 and EuNiO3. I will note similarities and differences in the processes, underpinning why careful process and precursor control is of the essence for these ternary oxides. I will go on to show how these materials may be interesting in electronics applications, discussing their functional electronic properties. Composition, thickness, thermal history and strain all prove to be important parameters when tuning in on wanted parameters. These compounds exhibit a remarkable versatility in electronic properties such as MIT and resistivity modulation.I will furthermore talk about some of the more challenging rare-earth nickelates, such as PrNiO3 and TbNiO3. Why are these challenging, and can we overcome these challenges? Their electronic properties may be of wide interest, and so processes for preparing the by ALD would carry significant impact.I will also spend some time on the underlying mechanisms allowing direct epitaxy of the rare-earth nickelates. Are other materials than nickelates attainable? Why are the processes for rare-earth nickelates so special, and how can we use the learnings from these processes to open for other B-site cations?This is a very good example of why novel process development by ALD is very important, showing how small changes in processing carry large implications for deposited films.[1] H. H. Sønsteby et al., Nat. Commun. 11, 2872 (2020)

Elucidating intrinsic contribution of d-orbital states to oxygen evolution electrocatalysis in oxides

Although numerous studies on oxide catalysts for an efficient oxygen evolution reaction have been carried out to compare their catalytic performance and suggest new compositions, two significant constraints have been overlooked. One is the difference in electronic conduction behavior between catalysts (metallic versus insulating) and the other is the strong crystallographic surface orientation dependence of the catalysis in a crystal. Consequently, unless a comprehensive comparison of the oxygen-evolution catalytic activity between samples is made on a crystallographically identical surface with sufficient electron conduction, misleading interpretations on the catalytic performance and mechanism may be unavoidable. To overcome these limitations, we utilize both metallic (001) LaNiO3 epitaxial thin films together with metal dopants and semiconducting (001) LaCoO3 epitaxial thin films supported with a conductive interlayer. We identify that Fe, Cr, and Al are beneficial to enhance the catalysis in LaNiO3 although their perovskite counterparts, LaFeO3, LaCrO3, and LaAlO3, with a large bandgap are inactive. Furthermore, semiconducting LaCoO3 is found to have more than one order higher activity than metallic LaNiO3, in contrast to previous reports. Showing the importance of facilitating electron conduction, our work highlights the impact of the near-Fermi-level d-orbital states on the oxygen-evolution catalysis performance in perovskite oxides.

High-Temperature Thermoelectricity in LaNiO3-La2CuO4 Heterostructures.

Transition metal oxides exhibit a high potential for application in the field of electronic devices, energy storage, and energy conversion. The ability of building these types of materials by atomic layer-by-layer techniques provides a possibility to design novel systems with favored functionalities. In this study, by means of the atomic layer-by-layer oxide molecular beam epitaxy technique, we designed oxide heterostructures consisting of tetragonal K2NiF4-type insulating La2CuO4 (LCO) and perovskite-type conductive metallic LaNiO3 (LNO) layers with different thicknesses to assess the heterostructure-thermoelectric property-relationship at high temperatures. We observed that the transport properties depend on the constituent layer thickness, interface intermixing, and oxygen-exchange dynamics in the LCO layers, which occurs at high temperatures. As the thickness of the individual layers was reduced, the electrical conductivity decreased and the sign of the Seebeck coefficient changed, revealing the contribution of the individual layers where possible interfacial contributions cannot be ruled out. High-resolution scanning transmission electron microscopy investigations showed that a substitutional solid solution of La2(CuNi)O4 was formed when the thickness of the constituent layers was decreased.

Atomic Heterointerfaces and Electrical Transportation Properties in Self‐Assembled LaNiO3–NiO Heteroepitaxy

AbstractVertical nanostructure heteroepitaxy opens new opportunities for designing next‐generation electronic devices due to the enthralling multifunction combinations and the abundant heterointerfaces manipulated effects. In this study, self‐assembled heteroepitaxial thin films, vertically aligned metallic LaNiO3 (LNO) and semiconducting NiO with diverse heterointerfaces, are created and systematically investigated by advanced transmission electron microscopy. With the increase of LaNiO3 content, the LaNiO3 phases present as isolated islands encircled by the connected NiO nanoplates and eventually become the continuous matrix with embedded NiO nanopillars. The atomic heterointerface between NiO and LaNiO3 phases is determined to be [NiO2–LaO]LaNiO3–LaO–[NiO]NiO, in which an extra La–O layer is enriched at the heterointerface. Besides, the formation mechanism of the heterointerface and antiphase boundaries observed in LaNiO3 phase is discussed. The electrical transport properties at room temperature can be tuned gradually by changing the volume ratio of constituents. The correlation among the insulator‐to‐metal transition, the carrier types associated with transport behaviors, and the heterostructure evolutions are explored. This study offers a desirable platform to design new multifunctional electronic devices based on the oxide heterojunctions.

High-Pressure Floating-Zone Growth of Perovskite Nickelate LaNiO3 Single Crystals

We report the first single crystal growth of the correlated metal LaNiO3 using a high-pressure optical-image floating zone furnace. The crystals were studied using single crystal/powder x-ray diffraction, resistivity, specific heat, and magnetic susceptibility. The availability of bulk LaNiO3 crystals will (i) promote deep understanding in this correlated material, including the mechanism of enhanced paramagnetic susceptibility, and (ii) provide rich opportunities as a substrate for thin film growth such as important ferroelectric and/or multiferroic materials. This study demonstrates the power of high pO2 single crystal growth of nickelate perovskites and correlated electron oxides more generally.

Comparative study of LaNiO3/LaAlO3 heterostructures grown by pulsed laser deposition and oxide molecular beam epitaxy

Variations in growth conditions associated with different deposition techniques can greatly affect the phase stability and defect structure of complex oxide heterostructures. We synthesized superlattices of the paramagnetic metal LaNiO3 and the large band gap insulator LaAlO3 by atomic layer-by-layer molecular beam epitaxy (MBE) and pulsed laser deposition (PLD) and compared their crystallinity and microstructure as revealed by high-resolution transmission electron microscopy images and resistivity. The MBE samples show a higher density of stacking faults but smoother interfaces and generally higher electrical conductivity. Our study identifies the opportunities and challenges of MBE and PLD growth and serves as a general guide for the choice of the deposition technique for perovskite oxides.

Oscillatory Noncollinear Magnetism Induced by Interfacial Charge Transfer in Superlattices Composed of Metallic Oxides

Interfaces between correlated complex oxides are promising avenues to realize new forms of magnetism that arise as a result of charge transfer, proximity effects and locally broken symmetries. We report upon the discovery of a non-collinear magnetic structure in superlattices of the ferromagnetic metallic oxide La2/3Sr1/3MnO3 (LSMO) and the correlated metal LaNiO3 (LNO). The exchange interaction between LSMO layers is mediated by the intervening LNO, such that the angle between the magnetization of neighboring LSMO layers varies in an oscillatory manner with the thickness of the LNO layer. The magnetic field, temperature, and spacer thickness dependence of the non-collinear structure are inconsistent with the bilinear and biquadratic interactions that are used to model the magnetic structure in conventional metallic multilayers. A model that couples the LSMO layers to a helical spin state within the LNO fits the observed behavior. We propose that the spin-helix results from the interaction between a spatially varying spin susceptibility within the LNO and interfacial charge transfer that creates localized Ni2+ states. This provides a new approach to engineering non-collinear spin textures in metallic oxide heterostructures that can be exploited in devices based on both spin and charge transport.

The effect of LaNiO3 thickness on the magnetoelectric response of Pb(Zr0.52Ti0.48)O3 film-on-CoFe2O4 ceramic composites

A magnetoelectric composite of Pb(Zr0.52Ti0.48)O3 film-on-CoFe2O4 ceramic was prepared by spin-coating Pb(Zr0.52Ti0.48)O3 films of 300 nm in thickness on the LaNiO3-buffered highly dense CoFe2O4 ceramics. The X-ray diffraction, ferroelectric loops, piezoelectric curves, and magnetoelectric coupling effects were all measured at room temperature to investigate the effect of LaNiO3 thickness on the magnetoelectric response of the composites. The introduction of the metallic oxide LaNiO3 efficiently enhanced the magnetoelectric coefficient α E by improving the electric-related outputs. However, too thick LaNiO3 layer would also hinder the strain (stress) transferring across the interface between the Pb(Zr0.52Ti0.48)O3 and CoFe2O4 phases. A peak α E value was obtained in the sample with a LaNiO3 thickness of about 60 nm, which was 2.5 times larger than that in the composite of Pb(Zr0.52Ti0.48)O3 film on the CoFe2O4 ceramic without the LaNiO3 layer. Further enhancement could be anticipated by optimizing the LaNiO3 layer and/or Pb(Zr0.52Ti0.48)O3 films.

Strain-Controlled Transport Mechanism in Strongly Correlated LaNiO3

A density functional theory + Hubbard U (DFT + U) method is employed to investigate the effect of strain on the electronic and transport properties of the correlated metal LaNiO3. LaNiO3 without strain is characterized by a low temperature Fermi liquid behaviour of resistivity, a negative Seebeck coefficient and a positive Hall coefficient. Density of states, resistivity, thermopower and Hall coefficient obtained within the DFT + U approach reveal that LaNiO3 under both compressive and tensile strain is more metallic compared to the unstrained system. However, LaNiO3 under tensile strain is found to be more strongly correlated than that under compressive strain. Electron localization function calculation shows that there is a substantial increase in the covalent part of the chemical bonding, which corroborates an increase in the resistivity for LaNiO3 under tensile strain. Our first-principle–based calculation clearly demonstrates that the transport properties of LaNiO3 can be tuned by applying suitable strain.

Interlayer coupling through a dimensionality-induced magnetic state.

Dimensionality is known to play an important role in many compounds for which ultrathin layers can behave very differently from the bulk. This is especially true for the paramagnetic metal LaNiO3, which can become insulating and magnetic when only a few monolayers thick. We show here that an induced antiferromagnetic order can be stabilized in the [111] direction by interfacial coupling to the insulating ferromagnet LaMnO3, and used to generate interlayer magnetic coupling of a nature that depends on the exact number of LaNiO3 monolayers. For 7-monolayer-thick LaNiO3/LaMnO3 superlattices, negative and positive exchange bias, as well as antiferromagnetic interlayer coupling are observed in different temperature windows. All three behaviours are explained based on the emergence of a (¼,¼,¼)-wavevector antiferromagnetic structure in LaNiO3 and the presence of interface asymmetry with LaMnO3. This dimensionality-induced magnetic order can be used to tailor a broad range of magnetic properties in well-designed superlattice-based devices.

Engineered Mott ground state in a LaTiO(3+δ)/LaNiO3 heterostructure.

In pursuit of creating cuprate-like electronic and orbital structures, artificial heterostructures based on LaNiO3 have inspired a wealth of exciting experimental and theoretical results. However, to date there is a very limited experimental understanding of the electronic and orbital states emerging from interfacial charge transfer and their connections to the modified band structure at the interface. Towards this goal, we have synthesized a prototypical superlattice composed of a correlated metal LaNiO3 and a doped Mott insulator LaTiO3+δ, and investigated its electronic structure by resonant X-ray absorption spectroscopy combined with X-ray photoemission spectroscopy, electrical transport and theory calculations. The heterostructure exhibits interfacial charge transfer from Ti to Ni sites, giving rise to an insulating ground state with orbital polarization and eg orbital band splitting. Our findings demonstrate how the control over charge at the interface can be effectively used to create exotic electronic, orbital and spin states.

Built-in Electric Field Induced Mechanical Property Change at the Lanthanum Nickelate/Nb-doped Strontium Titanate Interfaces.

The interactions between electric field and the mechanical properties of materials are important for the applications of microelectromechanical and nanoelectromechanical systems, but relatively unexplored for nanoscale materials. Here, we observe an apparent correlation between the change of the fractured topography of Nb-doped SrTiO3 (Nb:STO) within the presence of a built-in electric field resulting from the Schottky contact at the interface of a metallic LaNiO3 thin film utilizing cross-sectional scanning tunneling microscopy and spectroscopy. The change of the inter-atomic bond length mechanism is argued to be the most plausible origin. This picture is supported by the strong-electric-field-dependent permittivity in STO and the existence of the dielectric dead layer at the interfaces of STO with metallic films. These results provided direct evidence and a possible mechanism for the interplay between the electric field and the mechanical properties on the nanoscale for perovskite materials.

Elastic properties of rhombohedral, cubic, and monoclinic phases of LaNiO3 by first principles calculations

By applying density functional theory (DFT) approximations, we present a first principles investigation of elastic properties for the experimentally verified phases of a metallic perovskite LaNiO3. In order to improve the accuracy of calculations, at first we select the most appropriate DFT approaches according to their performance in reproducing the low-temperature crystalline structure and the electronic density of states. Then, we continue with the single-crystal elastic constants and mechanical stability for the most common rhombohedral as well as high-temperature cubic and strain-induced monoclinic phases. Together with the calculated single-crystal elastic constants, the deduced polycrystalline properties, including bulk, shear, and Young’s moduli, Poisson’s ratio, Vickers hardness, sound velocities, Debye temperature, and anisotropy indexes, remedy the existing gap of knowledge about the elasticity of LaNiO3, at least from a theoretical standpoint. It turns out that all three considered structures are mechanically stable, behave in a ductile manner, and their overall anisotropy is not strongly pronounced. Besides, rhombohedral and monoclinic phases show a similar polycrystalline behavior indicating that LaNiO3 is able to retain its bulk mechanical properties when grown in thin-film form.

Insulating-layer formation of metallic LaNiO3 on Nb-doped SrTiO3 substrate

We investigated the electronic structures of strongly correlated metallic LaNiO3 (LNO) and semiconducting Nb-doped SrTiO3 (Nb:STO) heterostructures by varying the LNO film thickness using in situ photoemission spectroscopy. We found that, contrary to other interfaces with SrTiO3 and LaAlO3, insulating LNO layers are formed between metallic LNO layers and Nb:STO. Such behavior seems to be related with an electron transfer from Nb:STO to LNO due to Schottky-barrier formation at the interface.

Latent instabilities in metallic LaNiO3 films by strain control of Fermi-surface topology.

Strain control is one of the most promising avenues to search for new emergent phenomena in transition-metal-oxide films. Here, we investigate the strain-induced changes of electronic structures in strongly correlated LaNiO3 (LNO) films, using angle-resolved photoemission spectroscopy and the dynamical mean-field theory. The strongly renormalized eg-orbital bands are systematically rearranged by misfit strain to change its fermiology. As tensile strain increases, the hole pocket centered at the A point elongates along the kz-axis and seems to become open, thus changing Fermi-surface (FS) topology from three- to quasi-two-dimensional. Concomitantly, the FS shape becomes flattened to enhance FS nesting. A FS superstructure with Q1 = (1/2,1/2,1/2) appears in all LNO films, while a tensile-strained LNO film has an additional Q2 = (1/4,1/4,1/4) modulation, indicating that some instabilities are present in metallic LNO films. Charge disproportionation and spin-density-wave fluctuations observed in other nickelates might be their most probable origins.

Electromagnetic wave absorption and dielectric-modulation of metallic perovskite lanthanum nickel oxide

Metallic LaNiO3 powder shows excellent EM absorption due to arc-discharge effect, which can modulate the complex permittivity of LNO–FeCo/C composites.