LaNiO3 Research Articles

Oxygen Diode Formed in Nickelate Heterostructures by Chemical Potential Mismatch.

Deliberate control of oxygen vacancy formation and migration in perovskite oxide thin films is important for developing novel electronic and iontronic devices. Here, it is found that the concentration of oxygen vacancies (VO ) formed in LaNiO3 (LNO) during pulsed laser deposition is strongly affected by the chemical potential mismatch between the LNO film and its proximal layers. Increasing the VO concentration in LNO significantly modifies the degree of orbital polarization and drives the metal-insulator transition. Changes in the nickel oxidization state and carrier concentration in the films are confirmed by soft X-ray absorption spectroscopy and optical spectroscopy. The ability to unidirectional-control the oxygen flow across the heterointerface, e.g., a so-called "oxygen diode", by exploiting chemical potential mismatch at interfaces provides a new avenue to tune the physical and electrochemical properties of complex oxides.

Formation of PZT Structures on Silicon

Properties of thin PbZr0.52Ti0.48O3 (PZT) films on silicon substrates with Al2O3 and HfO2 dielectric barrier layers and LaNiO3 (LNO) conducting layers are studied. Barrier layers 2–10 nm thick are deposited on silicon wafers by via atomic-layer deposition (ALD). LNO layers are formed via chemical solution deposition. The critical HfO2 thickness required to prevent diffusion (upon which a perovskite phase forms in PZT films) is found to be 10 nm. The annealing temperature required for the formation of LNO crystalline structure is determined. It is shown that depositing an LNO conducting layer directly onto a silicon surface allows us to obtain PZT films with good crystallinity and electrophysical properties.

Tunability, ferroelectric and leakage studies on pulsed laser ablated (Pb0.92La0.08)(Zr0.60Ti0.40)O3 thin films

(Pb0.92La0.08)(Zr0.60Ti0.40)O3 (PLZT 8/60/40) thin films were fabricated on LNO/Si<100> substrates by using a pulsed laser deposition (PLD) technique and with in-situ crystallization. The kinetics of the subsequent pyrochlore-perovskite crystallization was found to be oxygen pressure dependent in the deposition process. Conditions for obtaining phase pure, perovskite thin films using LaNiO3 (LNO) as a bottom electrode were optimized. X-ray diffraction measurements showed well-crystallized PLZT 8/60/40 thin films on a layer of LNO which served as both a template to deposit PLZT 8/60/40 on it as well as to use as a conducting bottom electrode. Atomic force microscopy (AFM) image indicates the effect of oxygen background pressure on the morphology of the films and field emission scanning electron microscopy (FE-SEM) images are used to corroborate the same. Voltage dependent capacitance study was used for the measurement of tunability in PLZT 8/60/40 thin film and was found to be 80%. Well saturated polarization vs. electric field (P-E) hysteresis loop with a remnant polarization (Pr) of ∼13.3 μC/cm2 was observed. Leakage current studies were also done for PLZT 8/60/40 thin films.

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.

Polarization and charge-transfer effect on the transport properties in two-dimensional electron gases/LaNiO3 heterostructure

The film thickness dependent transport properties of the LaNiO3 (LNO) layer epitaxially grown on LaAlO3/SrTiO3 (LAO) 2-dimensional electronic gas (2DEG) have been investigated. The ultrathin LNO films grown on the 2DEG have a sheet resistance below the values of h/e2 in all temperature ranges. The electron density is enhanced by more than one order of magnitude by capping LNO films. X-ray photoelectron spectroscopy shows that the interface undergoes unambiguous charge transfer and electronic reconstruction, leading to modulation doping of such atomically engineered complex oxide heterointerfaces. The polar-catastrophe of the 2DEG is directly linked to the electronic structure and transport properties of the LNO. The transport properties can be well modulated by the thickness of the LAO in the 2DEG, and the data can be well fitted with the polar-catastrophe scenario. These results suggest a general approach to tunable functional films in oxide heterostructures with the 2DEG.

Exchange Bias Effect and Orbital Reconstruction in (001)-Oriented LaMnO3/LaNiO3 Superlattices.

Paramagnetic LaNiO3 (LNO)-based heterostructures have been attracting the attention of researches, especially since the interesting exchange bias (EB) effect has been observed in (111)-oriented LaMnO3 (LMO)/LNO superlattices (SLs). However, this effect is not expected to occur in the (001) direction SLs. In this paper, we report the observation of an unexpected EB effect in (001)-oriented (LMO)3/(LNO)t SLs. The orbits of interfacial Mn/Ni ions preferentially occupy the strain-stabilized x2 - y2 in ultrathin LNO layers [t ≤ 4 unit cells (u.c.)]. Conversely, as the LNO layer becomes thicker (t ≥ 6 u.c.), the EB effect is absent, and the orbits are reconstructed to form the 3z2 - r2 preferential occupancy. The absence of the EB in thicker LNO-based SLs is attributed to the interfacial charge transfer suppressed by orbital reconstruction as a consequence of the increasing LNO thickness. In the thinner LNO-based SLs, the larger charge transfer results in stronger localized magnetic moments for the cause of the EB effect. These results provide a useful interpretation of the relationship between macroscopic magnetic properties and the microscopic electronic structure in oxide-based heterostructures.

Growth of highly c-axis oriented LaNiO3 films with improved surface morphology on Si substrate using chemical solution deposition and rapid heat treatment process

LNO (LaNiO3) thin films were directly deposited onto Si substrates with a thin layer of amorphous natural oxide (SiO2) using three different precursor solutions. Effects of the constitution of precursor solution and the annealing heating rate on the surface morphology and the orientation were investigated. The LNO film derived from the mixture of a methanol solvent and an acetylacetone chelating agent had the flat surface with no cracks and pinholes. The heating rate of rapid annealing process had a critical effect on the oriented growth of the LNO film, and its c-axis orientation degree increased with the annealing heating rate. The LNO film with the heating rate of 40℃/s exhibited the highest degree of c-axis orientation (99.57%) and the lowest resistivity (9.35 × 10−4Ωcm). It would be a potential bottom electrode and/or seed layer to integrate perovskite-type films on it for functional devices.

Preparation of free-standing multilayer hemispherical shell thin film using monodisperse polymer template

A novel method to fabricate free-standing hemispherical shells of multilayer thin film is the demand of future technology to enhance the superlattices and multiferroic materials with one-dimensional quantum confinement. This is the first report to describe the fabrication of multilayer (LaNiO3 (LNO) (top electrode)/Pb(Zr,Ti)O3 (PZT)/LNO (bottom electrode)) free-standing thin film with a close-packed hemispherical shell structure. The cross-sectional investigations of the single hemispherical shell reveal the hemispherical space inside the multilayer thin film which is indeed to alleviate the clamping force from the substrate and also it represents each layer in this film has uniform thickness though it is troublesome to achieve in the case of hemispherical shell structure is noteworthy. The fabricated device made up of a thin PZT film sandwiched between the two electrodes with hemispherical close-packed structure (CPS) is the most conceivable material that would open a new window of the wide variety of applications.

Integration of c-axis oriented Bi3.15Nd0.85Ti2.95Hf0.05O12/La0.67Sr0.33MnO3 ferromagnetic-ferroelectric composite film on Si substrate

A La0.67Sr0.33MnO3 (LSMO) ferromagnetic layer and a Nd3+/Hf4+ co-substituted Bi4Ti3O12 (Bi3.15Nd0.85Ti3-xHfxO12 (BNTHx, x = 0, 0.025, 0.05, 0.1 and 0.15)) ferroelectric layer were successively deposited onto the (00 l)-oriented LaNiO3 (LNO) layer buffered (001) Si substrate via all chemical solution deposition (CSD) method. As a result, the BNTHx/LSMO ferromagnetic-ferroelectric composite films integrated on Si substrate exhibit high c-axis orientation. The Nd3+/Hf4+ co-substituted BNTHx films have the lower leakage current and the better ferroelectric properties than the mono-substituted Bi4Ti3O12 (Bi3.15Nd0.85Ti3O12 and Bi4Ti2.95Hf0.05O12) films. In particular, the BNTH0.05/LSMO/LNO film has the lowest leakage current density of 2.5 × 10−7 A/cm2 at 200 kV/cm, and the highest remnant polarization (Pr) of 27.3 μC/cm2. The BNTH0.05/LSMO/LNO composite film also exhibits the soft ferromagnetism characteristics with a high saturated magnetization of 258 emu/cm3 at 300 K, and the excellent magnetoelectric (ME) effect. The variations of ME voltage coefficient αE values with DC bias magnetic field Hbias shows that the BNTH0.05/LSMO/LNO film has the high αE value at near zero Hbias. Moreover, at Hbias = 0 Oe, the αE value gradually increases from zero with the increasing of the AC magnetic field frequency, and eventually reaches about 18.9 V/cm·Oe at 100 kHz, suggesting the existence of self-biased ME effect.

Role of 2D and 3D defects on the reduction of LaNiO3 nanoparticles for catalysis

Solid phase crystallization offers an attractive route to synthesize Ni nanoparticles on a La2O3 support. These materials have shown great promise as catalysts for methane oxidation and similar reactions. Synthesis is achieved by the reduction of a LaNiO3 (LNO) precursor at high temperatures, but the reduction pathway can follow a variety of routes. Optimization of catalytic properties such as the long-term stability has been held back by a lack of understanding of the factors impacting the reduction pathway, and its strong influence on the structure of the resulting Ni/La2O3 catalyst. Here we show the first evidence of the importance of extended structural defects in the LNO precursor material (2D stacking faults and 3D inclusions) for determining the reaction pathway and therefore the properties of the final catalyst. Here we compare the crystallization of LNO nanoparticles via two different pathways using in-situ STEM, in-situ synchrotron XRD, and DFT electronic structure calculations. Control of extended defects is shown to be a key microstructure component for improving catalyst lifetimes.

Hydrazine reduction of LaNiO3 for active materials in supercapacitors

AbstractTo improve the electric conductivity and overall performance of active materials in pseudocapacitors, we have established a novel hydrazine reduction process to transform perovskite oxides into active materials with the desired electrical conductivity and electrochemical behavior. Taking LaNiO3 (LNO) produced from chemical solution as the starting material, different durations of hydrazine reduction (e.g. from 3, 6 to 12 hours) leads to a significant increase in specific capacitance, from ~70 F·g−1 at 1 A·g−1 (LNO) to ~280 F·g−1 at 1 A·g−1 (after 12 hours reduction). The desired electrical conductivity of LNO has been retained, as shown by the overall resistance of less than 0.3 Ω in the aqueous electrolyte. The hydrazined LNO demonstrated the desired stability as electrode, where the porous structure provides better accessibility for electrolytes, which is helpful in enhancing the overall electrochemical behaviors.

Influence of annealing environment on magnetic and ferroelectric properties of chemical solution derived nanocrystalline Bi3.15La0.85Ti3O12 thin films

Bi3.15La0.85Ti3O12 (BLT) thin films grown on LaNiO3 (LNO) buffered Si (100) substrates were prepared by chemical solution deposition. The samples were annealed at 600 °C by rapid thermal annealing in oxygen and nitrogen atmosphere, respectively. X-ray diffraction results showed that the sample annealed in oxygen atmosphere exhibited pure perovskite with random orientation. Field-emission scanning electron microscopy (FE-SEM) results revealed that the average grain size of the sample is about 50 nm. The remanent polarization (Pr) and coercive electric field (Ec) values for the BLT films annealed in pure oxygen and nitrogen atmosphere were 47.9 μC/cm2 and 39.3 kV/cm, 42.8 μC/cm2 and 54.9 kV/cm, respectively. The leakage current density is 8 × 10−4 A/cm2 in oxygen atmosphere which is about one order of magnitude lower than that of BLT thin films annealing in nitrogen atmosphere. The saturation magnetizations of BLT films on Si substrate with and without LNO buffer-layer were 0.112 and 0.057 emu/cm3, respectively. The magnetic property in the BLT originates from oxygen vacancies.

Simulation of STEM-HAADF Image Contrast of Ruddlesden–Popper Faulted LaNiO3 Thin Films

LaNiO3 (LNO) thin films are widely used as electrode materials. Yet, their properties greatly depend on such parameters as strain state and defect density. In this work, we present a detailed structural characterization of epitaxial LNO thin films grown on LaAlO3(001). A noticeable lack of contrast between La/Ni ions occurs in selected areas as seen by scanning transmission electron microscope, high-angle annular dark-field imaging (STEM-HAADF). By using atomistic modelization and image simulations, we show that this effect, rather than signaling cation interfusion or other spurious effects, results from different Ruddlesden-Popper faulted combinations with 1/2a⟨111⟩ relative displacement of defect free perovskite blocks, in the LaNiO3 perovskite

Vertically arrays of Si-LaNiO3/BiFeO3/Au core-shell nano-capacitors for prominent coupled electro-optic effect

The current study delivers the first assessment of well-separated cone shaped n-type epitaxial BiFe0.9Mn0.1O3 (n-BFMO) shells integrated on LaNiO3 (LNO) buffered vertical arrays of p-type nanoporous Si nanowire cores as an absorber for high efficiency and sustainable all- oxide photovoltaic devices. The photovoltaic effect of the LNO/n-BFMO/Au radial heterojunction is investigated by registering the current-voltage curves under AM 1.5 (100 mW cm−2) illumination conditions at various ferroelectric polarization states of BFMO. The as-deposited LNO/BFMO/Au nanowire arrays fabricated by scalable Pulsed Laser deposition are completely self-polarized and produced a remarkably large open circuit photovoltage up to 0.53 V under zero poling condition. The direction of photocurrent and photovoltage is reversibly switchable in response to ferroelectric polarization switching. The short circuit photocurrent “ISC” and open circuit voltage “VOC” depict a hysteresis loop which is more or less identical to that of ferroelectric polarization and thus can be utilized as a nondestructive optical readout of the ferroelectric nonvolatile memories. By introducing special architecture for the BFO based photovoltaic device, a photoconversion efficiency ∼0.3% and External Quantum Efficiency ∼11% are achieved at zero polarization state, which can further be enhanced and modulated to ∼0.6% and 14%, respectively, at the negative poling state of BFMO.

Nanoscale investigation of ferroelectric and piezoelectric properties in (Pb,Ca)TiO3 thin films grown on LaNiO3/LaAlO3(1 0 0) and Pt/Si(1 1 1) using piezoresponse force microscopy

Single phase polycrystalline and strong textured Pb0.76Ca0.24TiO3 (PCT24) thin films have been grown on platinum coated silicon and LaAlO3(100) (LAO) substrates using LaNiO3 (LNO) as a buffer layer by chemical solution deposition. X-ray diffraction measurements showed that the PCT24 thin films crystallize in a highly a-oriented single phase on LNO/LAO(100). The effects of the LNO buffer layer, nature of the substrate, and film orientation on the ferroelectric and piezoelectric properties were investigated in the nanoscale range using piezoresponse force microscopy (PFM). Local piezoelectric hysteresis loops for PCT24/LNO/LAO(100) oriented films and PCT24/Pt/Si polycrystalline films were measured on selected grains. From these piezoloops, PCT24/LNO/LAO(100) oriented films show a higher response (maximum relative d33 value) than PCT24/Pt/Si polycrystalline films. Furthermore, the comparison of simultaneously acquired surface morphology and piezoresponse images of the PCT24/Pt/Si films revealed the presence of inactive grain regions. In contrast, highly a-oriented films showed a higher presence of active grains. Our observations suggest that the improvement of ferro/piezoelectric properties is greatly associated with the use of LNO buffer layers and the growth of highly a-oriented films.

Investigation of novel ferroelectric/gyromagnetic ferrite (Pb,Sr)TiO3/Y3Fe5O12 layered thin films with potential applications in magnetically and electrically tuning devices

We report on a novel ferroelectric/gyromagnetic ferrite layered composite thin film with two degrees of tuning freedoms. The structure was prepared by layered growth of Y3Fe5O12(YIG) ferrite, LaNiO3(LNO) electrode and (100) orientated Pb0.4Sr0.6TiO3 (PST) ferroelectric films on Si substrates by RF magnetron sputtering. LNO not only exists as an electrode, but also provides a buffer layer for the orientation growth of PST film. The PST/YIG composite thin films exhibited large magnetic tunability of μr (92.1%@600 Oe), low FMR linewidth (ΔH) of 160.7 Oe@9.1GHz and high electrical tunability (η) of 75%@360kV/cm, which shows potential applications in magnetically and electrically tuning devices.

Robust Interfacial Exchange Bias and Metal-Insulator Transition Influenced by the LaNiO3 Layer Thickness in La0.7Sr0.3MnO3/LaNiO3 Superlattices.

Artificial heterostructures based on LaNiO3 (LNO) have been widely investigated with the aim to realize the insulating antiferromagnetic state of LNO. In this work, we grew [(La0.7Sr0.3MnO3)5-(LaNiO3)n]12 superlattices on (001)-oriented SrTiO3 substrates by pulsed laser deposition and observed an unexpected exchange bias effect in field-cooled hysteresis loops. Through X-ray absorption spectroscopy and magnetic circular dichroism experiments, we found that the charge transfer at the interfacial Mn and Ni ions can induce a localized magnetic moment. A remarkable increase of exchange bias field and a transition from metal to insulator were simultaneously observed upon decreasing the thickness of the LNO layer, indicating the antiferromagnetic insulator state in 2 unit cells LNO ultrathin layers. The robust exchange bias of 745 Oe in the superlattice is caused by an interfacial localized magnetic moment and an antiferromagnetic state in the ultrathin LNO layer, pinning the ferromagnetic La0.7Sr0.3MnO3 layers together. Our results demonstrate that artificial interface engineering is a useful method to realize novel magnetic and transport properties.

Evidence of a minority monoclinic LaNiO2.5 phase in lanthanum nickelate thin films.

LaNiO3 (LNO) thin films of 14 nm and 35 nm thicknesses grown epitaxially on LaAlO3 (LAO) and (LaAlO3)0.3(Sr2TaAlO6)0.7 (LSAT) substrates are studied using High Resolution Transmission Electron Microscopy (HRTEM) and High Angle Annular Dark Field (HAADF) imaging. The strain state of the films is studied using Geometric Phase Analysis (GPA). Results show the successful in-plane adaptation of the films to the substrates, both in the compressive (LAO) and tensile (LSAT) cases. Through the systematic analysis of HRTEM superstructure contrast modulation along different crystal orientations, localized regions of the monoclinic LaNiO2.5 phase are detected in the 35 nm films.

Ferromagnetic, ferroelectric and magnetoelectric properties of (001)-oriented Pb(Zr0.52Ti0.48)O3/La0.67Sr0.33MnO3 composite films deposited on Si substrates using chemical solution deposition

Using (001)-oriented LaNiO3 (LNO) as a buffer layer, the ferromagnetic-ferroelectric layered composite film of Pb(Zr0.52Ti0.48)O3/La0.67Sr0.33MnO3 (PZT/LSMO) with a (001) orientation was deposited on a Si (100) substrate through a chemical solution deposition (CSD) method. The LNO buffer layer promotes the (001) preferential orientation and the columnar growth of the overlying LSMO and PZT layers. The oriented PZT/LSMO/LNO film has soft ferromagnetism characteristics, and a higher saturated magnetization (750.9 emu/cm3) compared with the non-oriented one. The effects of the orientation and the selection of the bottom electrode (BE) on ferroelectric properties of PZT/LSMO/LNO composite films were investigated. Using LNO as the BE, the oriented PZT/LSMO/LNO film exhibits the highest remnant polarization (Pr) of 30.0 μC/cm2 and the lowest leakage current density of 10−6 A/cm2 at 300 kV/cm. The oriented PZT/LSMO/LNO film also exhibits a good magnetoelectric (ME) effect and shows the maximum ME voltage coefficient αE of 125.9 mV/cm·Oe at room temperature. Our investigation provides an effective way to replace the expensive single-crystal substrates, and to promote the application of ferromagnetic-ferroelectric composite films into the Si-based microelectronic field.

Effects of LaNiO3 interlayer on the microstructures and electrical properties of Ba0.9Sr0.1Ti0.99Mn0.01O3 multilayer

The aim of this work was to investigate the effects of low-resistivity interlayer on the physical properties of periodic Ba0.9Sr0.1Ti0.99Mn0.01O3 (BSTM) multilayers prepared by a chemical solution deposition method. A LaNiO3 (LNO) layer was inserted into the periodic BSTM multilayer artificially to form a sandwiched configuration of BSTM/LNO/BSTM. The capacitances at low frequencies (<100 kHz) of the sandwiched multilayer are significantly enhanced compared to that of the pure BSTM multilayer. The space charge accumulated at the LNO layer was proposed to explain the enhancement based on Maxwell-Wagner (M-W) model. However, LNO interlayer leads to an increase in the leakage current. A non-Ohmic conduction region is observed for BSTM/LNO/BSTM multilayer when the electric field exceeds 100 kV/cm. The results offer a new approach to achieve dielectric films with high dielectric constant.