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Materials by the modified proteic method based on calcium doped LaMnO3 and LaNiO3, with perovskite structure were prepared. The X-ray diffraction patterns revealed the presence of the perovskite phase in all materials, whose specific surface area values varied between 27 and 37 m2.g-1. The materials presented efficiency for the removal of Congo red dye and those with site B occupied by nickel presented better adsorptive efficiency. The incorporation of calcium on LaMnO3 or LaNiO3 materials caused an improvement in the performance of the materials for the dye removal from water. The materials maintained perovskite structure after the adsorption tests, allowing their reuse in new adsorption tests with high efficiency.

Perovskite-type oxides with transition elements offer promising potential as catalysts in total oxidation reactions. The present work reports the synthesis of crystalline lanthanum nickelates and cobaltates and their intermediate nanomaterials compositions LaNi1-XCoXO3 (x = 0.3, 0.5, and 0.7) at 800 ºC by co-precipitation precursor technique for structural, morphological, and total propylene oxidation catalytic activity. The evolution of the crystal structure and formation of the perovskite phase were analyzed by X-ray diffraction, Thermo Gravimetry Analysis (TGA) / Differential Scanning Calorimetry (DSC), Fourier Transformed Infra-Red (FTIR), Atomic Absorption Spectroscopy (AAS), Scanning Electron Microscopy (SEM), Brunauer–Emmett–Teller (BET), Electron Spin Resonance (ESR) techniques. The terminal compounds LaNiO3, LaCoO3, and their intermediates compositions were identified to be single-phase and are indexed to rhombohedral structures. The bonding characteristics were studied by FTIR spectroscopy. On substitution of Ni with Co in B-site, the slight distortion in XRD diffraction peaks were observed. These compounds show a considerable increase in the activity of propylene oxidation to carbon dioxide. This study aims at understanding the effect of B– site substitution in the lattice of LaNiO3 and their influence on catalytic propylene oxidation efficiency.

The direct magnetoelectric (ME) coupling of Pb(Zr0.52Ti0.48)O3/LaNiO3/Ni (PZT/LNO/Ni) heterostructure was studied, which is prepared with the combination of sol–gel spin-coating method (for PZT) and off-axis magnetron sputtering (for LNO). LNO served as the buffer layer for the ferroelectric film and effective stress transfer can be realized between Ni foil and PZT film. Structural and morphological characterization was carried out for the as-grown PZT/LNO/Ni film-electrode-substrate heterostructure. Well-defined ferroelectric and magnetic hysteresis loops demonstrated the good ferroelectric and magnetic property. A large voltage ME coefficient of 560 mV cm− 1 Oe− 1 was observed at the relatively low bias magnetic field (Hdc) (~ 65 Oe) with LNO buffer layer thickness of ~ 15 nm in PZT/LNO/Ni heterostructures, which is 2 times higher than that observed in the PZT/Ni composite and provides great opportunities for the new generation sensor apparatuses that depend on direct ME effect. The results indicated the strain-mediated magnetoelectric coupling between ferroelectric PZT film and magnetic Ni foil.

Recently, due to the unique advantage in ionic conductivity, semiconductor–ionic conductor composite (SIC) has been widely applied as electrolyte for solid oxide fuel cell (SOFC), and the suitable anode and cathode should be chosen to match the SIC electrolyte. Inspired by this ideology, the semiconductor lanthanum nitrate (LaNiO3) with perovskite structure was prepared by sol-gel method and then composed with ionic conductor yttrium-stabilized zirconia (YSZ) to form LaNiO3-YSZ SIC, which was applied as electrolyte membrane, simultaneously the Li2CO3–LaNiO3 composite and Ni0.8Co0.15Al0.05LiO2 (NCAL) were respectively utilized as anode and cathode for fuel cell construction. Through optimizing the electrolyte composition, such device based on LaNiO3-YSZ electrolyte and Li2CO3–LaNiO3 anode received a supreme performance of 505 mW/cm2 at 550 °C, and the maximum power density can also maintain at 350 mW/cm2 even as the temperature dropped to 475 °C. The excellent performance is attributed to the decent ionic conductivity of LaNiO3-YSZ electrolyte and the outstanding catalysis activity of electrodes. In addition, we have found that the addition of Li2CO3 component into anode can substantially enhance the cell performance. Our result demonstrates that the multifunctional LaNiO3 can be simultaneously applied as electrolyte and anode for low-temperature SOFC.

Nature materials 20, 674–682 (2021). doi:10.1038/s41563-020-00877-1, Published by Nature Publishing Group, Basingstoke

Enhanced magnetoelectric effects in two-dimensional multiferroics promise greater interests for fundamental understanding and for device applications. To ameliorate properties and multifunctionality of magnetoelectric materials, highly ordered multiferroic thin films ought to be optimally designed with a high surface area and with a minimum contact area between the substrate and the films. Fabrication of hierarchically ordered, hemispherical close-packed free-standing multiferroic thin film structures of CoFe2O4 (CFO)/Pb(Zr0.52Ti0.48)O3 (PZT)/La0.6Sr0.4MnO3 (LSMO)/LaNiO3 (LNO) on a Pt/Ti/SiO2/Si substrate using a RF magnetron sputtering technique is reported here. The hemispherical space inside the shell structures, inherited from the spherical polymer, are shown by the cross-sectional scanning transmission electron microscopy. Importantly, the observed enhancement of remanent polarization is elucidated based on the facts, like the generation of a high level of compressive stress, a large thermal expansion coefficient of LSMO, and a minimal lattice mismatch with the PZT thin film.

The high tunability range of capacitive sensors can be achieved by the use of ferroelectric materials due to its perovskite structure. Thin films provide better utilization of properties comparative to bulk but greatly affect by the surface on which it deposited. In this work thin films of BaxSr1−xTiO3 (BST) and PbxSr1−xTiO3 (PST) are developed with x = 0.3 & 0.7. Thin films without doping of Sr are also developed for comparison. The capacitors Al/Si/BST/Al and Al/Si/PST/Al are fabricated in parallel plate structure using the sol–gel processing technique with Al as metal electrodes and BST/PST as the dielectric material. A new parallel plate capacitor with the introduction of Lanthanum Nickel Oxide (LNO) thin film with the preferred (100) orientation between Si substrate and BST/PST is proposed in this work. Crystallinity and orientation of BST/PST on Si and BST/PST over LNO are observed by X-ray diffraction (XRD). The average grain size and uniformity of thin films are confirmed by scanning electron microscopy (SEM) images. The capacitances are measured at 50 mV and 70 mV using LCR meter. The highest capacitance of 79.6pF is observed for Al/Si/LNO/BST/Al. Impedance spectroscopy reveals the decrement in impedance with doping of Sr and tunability range of LNO based BST/PST capacitor is much higher compared to non-LNO capacitors. Tunability with BST material reaches 57% at frequency 2.98 kHz and the PST attains a value of 33.8% at frequency 1.44 KHz.

The composite catalyst of crystalline Co(OH)2 modified rare-earth perovskite-type LaNiO3 was synthesized by physical precipitation-sol high temperature calcination method. The ratio between La/Ni and between Co(OH)2/LaNiO3 added presence obvious impact on hydrogen production performance. Under the illumination of the cut-off filter (≥ 420 nm), when the molar ratio between La/Ni is 2:1, the hydrogen production amount at 5 h reached 70.89 μmol. The hydrogen production of Co(OH)2/LaNiO3 under the optimal catalytic conditions was 4.5 times higher than of pure LaNiO3. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) showed good crystallinity of the sample and successful synthesis of the material. TEM and SEM were used to detect the appearance of the catalytic material. The Photoluminescence spectrum (PL), ultraviolet–visible spectroscopy (UV–Vis) and electrochemical workstations were used to characterize the catalytic performance, which is consistent with the hydrogen production results. It is indicated that the bulk Co(OH)2 acts as an electron collector in the catalytic process, which significantly increases the transfer rate of photoelectrons, enhance the hydrogen production performance.

Using ion-implanted $^{8}\mathrm{Li} \ensuremath{\beta}$-detected NMR, we study the evolution of the correlated metallic state of ${\mathrm{LaNiO}}_{3}$ in a series of ${\mathrm{LaNiO}}_{3}/{\mathrm{LaAlO}}_{3}$ superlattices as a function of bilayer thickness. Spin-lattice relaxation measurements in an applied field of $6.55\phantom{\rule{0.16em}{0ex}}\mathrm{T}$ reveal two equal amplitude components: one with metallic ($T$ linear) $1/{T}_{1}$ and a second with a more complex $T$ dependence. The metallic character of the slow relaxing component is only weakly affected by the ${\mathrm{LaNiO}}_{3}$ thickness, while the fast component is much more sensitive, exhibiting the opposite temperature dependence (increasing toward low $T$) in the thinnest, most magnetic samples. The origin of this bipartite relaxation is discussed in terms of electronic phase separation.

Here we study the transport properties of a nickelate compound, namely LaNiO2 using density functional theory (DFT) in conjunction with dynamical mean field theory (DMFT). An interacting multi-orbital spin-resolved scenario for LaNiO2 yields a metallic ground state with ferromagnetic correlations. The latter contrasts an antiferromagnetic order reported earlier. The metallic behaviour persists even at large values of the interaction energies. Further support of the metallic state is provided by the angular resolved photoemission spectroscopy (ARPES) data., Comment: 6 pages, 6 figures

The inside of the electrical double layer at perovskite oxide heterointerfaces is examined. Here, we report the local polarization and valence distribution in ${\mathrm{LaNiO}}_{3}$/${\mathrm{LaMnO}}_{3}$ and ${\mathrm{LaMnO}}_{3}$/${\mathrm{LaNiO}}_{3}$ bilayers on a ${\mathrm{SrTiO}}_{3}$ (001) substrate. Simultaneous measurements of two aspects of the structure are realized by using Bayesian inference based on resonant- and nonresonant-surface x-ray diffraction data. The results show that the average Mn valences are ${\mathrm{Mn}}^{3.12+}$ and ${\mathrm{Mn}}^{3.19+}$ for the two samples. The intensity of their local electric field is $\ensuremath{\sim}1$ GV/m and the direction of the field points from ${\mathrm{LaMnO}}_{3}$ to ${\mathrm{LaNiO}}_{3}$.

Sonicated sol-gel method was used to prepare LaNiO3from lanthanum nitrate hexahydrate La(NO3)3.6H2O(LN), nickel nitrate Ni(NO3)3.6H2O(NN), glycine and urea. Nanocrystalline LaNiO3powder was formed after heating at 175 °C in 5 min. Particle size of LaNiO3nanopowder was determined by Debay Scherrer’s equation and was found 48 nm. Prepared nanocatalyst characterized with the help of XRD, TGA, SEM, IR, BET surface area, EDX. Surface area of LaNiO3was 9.22 m2/g. We have reported first time good antibacterial activity of LaNiO3forStaphylococcus aureus. Zone of inhibition for LaNiO3was 13 mm studied with the help of agar cup method.

Herein, Pt/Nb:SrTiO3/LaNiO3(Pt/NSTO/LNO) heterostructures are prepared by the sol–gel method, and the resistive switching (RS) characteristics of NSTO films are studied under different preparation conditions and Nb-doping content. It is shown from SEM images that the grain size of NSTO decreases with the increase of Nb-doping content. It is observed from electrical tests and analysis that the RS phenomenon of the Pt/NSTO/LNO structure can be attributed to the migration of internal oxygen vacancies, which are formed during the material preparation. J–V curves of Pt/NSTO/LNO, prepared under different heat treatment atmospheres, exhibit that pure nitrogen atmosphere results in optimal RS performance. In addition, the RS performance has shown an increasing trend with Nb content up to a threshold limit, followed by a gradual decrease. Furthermore, the RS performance of Pt/NSTO/LNO, prepared at different heat treatment temperatures, was investigated. The results demonstrate that the hysteresis window of RS for the Pt/NSTO/LNO structure first increased with increasing temperature, followed by a decrease. Moreover, the optimal RS performance is achieved at the heat treatment temperature of 700 °C.

No-precious bifunctional catalysts with high electrochemical activities and stability were crucial to properties of rechargeable zinc-air batteries. Herein, LaNiO3 modified with Ag nanoparticles (Ag/LaNiO3) was prepared by the co-synthesis method and evaluated as the bifunctional oxygen catalyst for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Compared with LaNiO3, Ag/LaNiO3 demonstrated the enhanced catalytic activity towards ORR/OER as well as higher limited current density and lower onset potential. Moreover, the potential gap between ORR potential (at −3 mA·cm−2) and OER potential (at 5 mA·cm−2) was 1.16 V. The maximum power density of the primary zinc-air battery with Ag/LaNiO3 catalyst achieved 60 mW·cm−2. Furthermore, rechargeable zinc-air batteries operated reversible charge-discharge cycles for 150 cycles without noticeable performance deterioration, which showed its excellent bifunctional activity and cycling stability as oxygen electrocatalyst for rechargeable zinc-air batteries. These results indicated that Ag/LaNiO3 prepared by the co-synthesis method was a promising bifunctional catalyst for rechargeable zinc-air batteries.

Nonpolar ZnO films are deposited on (100) Si substrate using LaNiO3 conducting buffer layer by radio frequency sputtering. X-ray diffraction results show that ZnO films are (110) and (002) orientation with and without LaNiO3 buffer layer. The current behavior of ZnO/LaNiO3 heterojunction exhibits ohmic conduction which is different from the diode-like rectification current behavior of ZnO film using insulated buffer layers. The photoluminescence properties indicate that the (110)-oriented nonpolar ZnO film has better band-edge emission than that of (002)-oriented polar ZnO film. It is suggested that LaNiO3 buffer layer can be used to deposit silicon-based ZnO film with well ohmic contact electrode in optoelectronic devices.

This work reports the growth of 170 nm to 400 nm thick tetragonal {001}-textured Nb-doped Pb(Zr,Ti)O 3 (PNZT) thin films on AISI 304 stainless steel substrates by pulsed laser deposition. Al 2 O 3 and LaNiO 3 buffer layers prevent substrate oxidation and act as growth template to promote the PNZT thin film texture. The thin films have a dielectric constant of 390 at 1 kHz, with dielectric losses below 0.05. After P-E loop measurements, permittivity increases up to 430 with a remanent polarization of 31.3E-6 C/cm2 and a coercive field of 164 kV/cm1. As compared to previously reported PZT thin films on stainless steel substrates, the improved ferroelectric properties of these PNZT thin films make them promising candidates for future piezoelectric MEMS applications requiring non-brittle substrates, especially for sensing purposes.

The recent observation of superconductivity in infinite-layer Nd$_{1-x}$Sr$_x$NiO$_2$ thin films has attracted a lot of attention, since this compound is electronically and structurally analogous to the superconducting cuprates. Due to the challenges in the phase stabilization upon chemical doping with Sr, we synthesized artificial superlattices of LaNiO$_3$ embedded in insulating LaGaO$_3$, and used layer-selective topotactic reactions to reduce the nickelate layers to LaNiO$_{2}$. Hole doping is achieved via interfacial oxygen atoms and tuned via the layer thickness. We used electrical transport measurements, transmission electron microscopy, and x-ray spectroscopy together with ab initio calculations to track changes in the local nickel electronic configuration upon reduction and found that these changes are reversible. Our experimental and theoretical data indicate that the doped holes are trapped at the interfacial quadratic pyramidal Ni sites. Calculations for electron-doped cases predict a different behavior, with evenly distributed electrons among the layers, thus opening up interesting perspectives for interfacial doping of transition metal oxides., 12 pages, 10 figures

Magnetic interlayer coupling is a key ingredient in designing magnetic multilayers with functionalities that reach out to the realm of applications. In epitaxial ferromagnetic (FM) oxide multilayers, the magnetic interlayer coupling is, however, less studied and its prediction is often a challenging task. Ultrathin FM ${\mathrm{SrRuO}}_{3}$ epitaxial films with perpendicular magnetic anisotropy, interfaced with suitable oxides, may be susceptible of forming skyrmions. Hence, a strong FM interlayer coupling would be beneficial to achieve uniform switching behavior of a ${\mathrm{SrRuO}}_{3}$-based multilayer. Previous studies reported that the coupling of two ${\mathrm{SrRuO}}_{3}$ layers separated by a non-FM oxide spacer is at best weakly FM and the two FM layers switch at markedly different fields. Here we study the magnetic interlayer coupling between two FM ${\mathrm{SrRuO}}_{3}$ layers separated by ultrathin ${\mathrm{LaNiO}}_{3}$ in epitaxial heterostructures grown on ${\mathrm{SrTiO}}_{3}$(100) single crystals. We found that FM ${\mathrm{SrRuO}}_{3}$ layers separated by 2 monolayers (MLs) thick ${\mathrm{LaNiO}}_{3}$ show weak FM interlayer coupling of about $106\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{J}/{m}^{2}$ at 10 K. The coupling becomes strongly FM for four MLs thick (about 1.6 nm) ${\mathrm{LaNiO}}_{3}$ spacers and the two ${\mathrm{SrRuO}}_{3}$ layers reverse their magnetization at a common value of the perpendicular magnetic field. This is likely due to a transition of the ${\mathrm{LaNiO}}_{3}$ spacer from insulating to metallic, as its thickness increases.

The recent discovery of superconductivity in doped infinite-layer nickelates has stimulated intensive interest, especially for similarities and differences compared to that in cuprate superconductors. In contrast to cuprates, although earlier magnetization measurement reveals a Curie-Weiss-like behavior in undoped infinite-layer nickelates, there is no magnetic ordering observed by elastic neutron scattering down to liquid helium temperature. Until now, the nature of the magnetic ground state in undoped infinite-layer nickelates was still elusive. Here, we perform a nuclear magnetic resonance (NMR) experiment through 139La nuclei to study the intrinsic spin susceptibility of infinite-layer LaNiO2. First, the signature for magnetic ordering or freezing is absent in the 139La NMR spectrum down to 0.24 K, which unambiguously confirms a paramagnetic ground state in LaNiO2. Second, a pseudogap-like behavior instead of Curie-Weiss-like behavior is observed in both the temperature-dependent Knight shift and nuclear spin-lattice relaxation rate (1/T1), which is widely observed in both underdoped cuprates and iron-based superconductors. Furthermore, the scaling behavior between the Knight shift and 1/T1T has also been discussed. Finally, the present results imply a considerable exchange interaction in infinite-layer nickelates, which sets a strong constraint for the proposed theoretical models., 14 pages, 4 figures, accepted by Physical Review Letters

Employing first-principles density functional theory calculations and Wannierization of the low-energy band structure, we analyze the electronic structure of undoped, infinite-layer nickelate compounds ${\mathrm{NdNiO}}_{2},$ ${\mathrm{PrNiO}}_{2},$ and ${\mathrm{LaNiO}}_{2}$. Our study reveals the important role of the nonzero $f$-ness of Nd and Pr atoms, as opposed to the ${f}^{0}$ occupancy of La. The nonzero $f$-ness becomes effective in lowering the energy of the rare-earth $5d$ hybridized axial orbital, thereby enhancing the electron pockets and influencing the Fermi surface topology. The Fermi surface topology of ${\mathrm{NdNiO}}_{2}$ and ${\mathrm{PrNiO}}_{2}$ is strikingly similar, while differences are observed for ${\mathrm{LaNiO}}_{2}$. This difference shows up in computed doping-dependent superconducting properties of the three compounds within a weak coupling theory, which finds two-gap superconductivity for ${\mathrm{NdNiO}}_{2}$ and ${\mathrm{PrNiO}}_{2}$, and the possibility of a single-gap superconductivity for ${\mathrm{LaNiO}}_{2}$ with the strength of superconductivity suppressed by almost a factor of 2, compared to the Nd or Pr compound.

While defects such as oxygen vacancies in correlated materials can modify their electronic properties dramatically, understanding the microscopic origin of electronic correlations in materials with defects has been elusive. Lanthanum nickelate with oxygen vacancies, ${\mathrm{LaNiO}}_{3\ensuremath{-}x}$, exhibits the metal-to-insulator transition as the oxygen vacancy level $x$ increases from the stoichiometric ${\mathrm{LaNiO}}_{3}$. In particular, ${\mathrm{LaNiO}}_{2.5}$ exhibits a paramagnetic insulating phase, also stabilizing an antiferromagnetic state below ${T}_{N}\ensuremath{\simeq}152\phantom{\rule{0.28em}{0ex}}\mathrm{K}$. Here, we study the electronic structure and energetics of ${\mathrm{LaNiO}}_{3\ensuremath{-}x}$ using first principles. We find that ${\mathrm{LaNiO}}_{2.5}$ exhibits a ``site-selective'' paramagnetic Mott insulating state at $T\ensuremath{\simeq}290\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ as obtained using density functional theory plus dynamical mean field theory ($\mathrm{DFT}+\mathrm{DMFT}$). The Ni octahedron site develops a Mott insulating state with strong correlations as the Ni ${e}_{g}$ orbital is half-filled while the Ni square-planar site with apical oxygen vacancies becomes a band insulator. Our oxygen vacancy results cannot be explained by the pure change of the Ni oxidation state alone within the rigid band-shift approximation. Our $\mathrm{DFT}+\mathrm{DMFT}$ density of states explains that the peak splitting of unoccupied states in ${\mathrm{LaNiO}}_{3\ensuremath{-}x}$ measured by the experimental x-ray absorption spectra originates from two nonequivalent Ni ions in the vacancy-ordered structure.

Using SrNiO${}_{2}$ as a reference system, the authors find multiorbital Hund's metal behavior in the new Ni-based superconductor Nd${}_{1\ensuremath{-}x}$ SrxNiO${}_{2}$ by many-body $a\phantom{\rule{0}{0ex}}b$ $i\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}o$ calculations. They show that both the weights of Ni 3$d$ multiplets and total Ni 3$d$ occupancy are barely changed from the typical Hund's metal SrNiO${}_{2}$ to LaNiO${}_{2}$ in spite of the large charge-carrier doping. The calculations are well justified by existing experiments with important implications on the pairing mechanism.

We present an ab initio $GW$ self-energy calculation of the electronic structure of ${\mathrm{LaNiO}}_{2}$. With respect to density-functional theory, we find that in $GW$ the La $4f$ states undergo an important $+2$ eV upward shift from the Fermi level, while the O $2p$ states are pulled down by $\ensuremath{-}1.5$ eV, thus reinforcing the charge-transfer character of this material. However, $GW$ many-body effects leave the $d$-like bands at the Fermi level almost unaffected, so that the Fermi-surface topology is preserved, unlike in cuprates.

Reflection high-energy electron diffraction (RHEED) is a ubiquitous in situ molecular beam epitaxial (MBE) characterization tool. Although RHEED can be a powerful means for crystal surface structure determination, it is often used as a static qualitative surface characterization method at discrete intervals during a growth. A full analysis of RHEED data collected during the entirety of MBE growths is made possible using principle component analysis (PCA) and k-means clustering to examine significant boundaries that occur in the temporal clusters grouped from RHEED data and identify statistically significant patterns. This process is applied to data from homoepitaxial SrTiO$_{3}$ growths, heteroepitaxial SrTiO$_{3}$ grown on scandate substrates, BaSnO$_{3}$ films grown on SrTiO$_{3}$ substrates, and LaNiO$_{3}$ films grown on LaAlO$_{3}$ substrates. This analysis may provide additional insights into the surface evolution and transitions in growth modes at precise times and depths during growth, and that video archival of an entire RHEED image sequence may be able to provide more insight and control over growth processes and film quality., 12 pages, 12 figures

Correlated electrons give rise to both exotic electronic and magnetic properties in rare-earth nickelates. Here we present evidence of the interfacial coupling between two nickelate systems, EuNiO_{3} (ENO) and LaNiO_{3} (LNO), with different electronic and magnetic properties but with compatible structural registry giving rise to an electrostructural transition, unobserved in each constituent. Nominally, LNO remains in a paramagnetic-metallic R3[over ¯]c phase while orthorhombic ENO undergoes antiferromagnetic and insulating transitions. However, the ENO/LNO heterostructure displays a uniform rotational symmetry set by an entwined interface. This leads to an anomalous reduction of bond disproportionation in the ENO layer through the metal to insulator transition and concomitantly charge disproportionation opens the gap accompanied by antiferromagnetic ordering. Our results resolve a long-standing question in the physics of rare-earth nickelates, herein demonstrating that charge and bond disproportionation are competing mechanisms for the charge localization process in the rare-earth nickelate system.

Calculations of the electronic structure of NdNiO${}_{2}$, recently found to be superconducting, reveal important similarities and differences to cuprates, which may shed light on the origin of cuprate high-temperature superconductivity.

Throughout this chapter, parts of which are based on Bluschke et al. Phys. Rev. Lett. 118, 207203 (2017) [52], we explore the concept of combining two magnetic systems in an epitaxial relationship, with the goal of producing novel magnetic structures with properties inherited from both of the constituent materials. In this study we choose two complementary systems. The first, antiferromagnetic LaNiO\(_3\), hosts a closed shell A-site cation and the strongly correlated nickel and oxygen bands support strong superexchange interactions amongst the Ni spins. The second material, DyScO\(_3\), hosts a closed shell B-site cation and a large, strongly localized magnetic moment of about 9 \(\mu _B\) on the rare-earth Dy\(^{3+}\) site. In contrast to the Ni magnetism of the LaNiO\(_3\) layers, the Dy spins experience weak mutual exchange fields and, instead, a rather strong magneto-crystalline anisotropy associated with the reduced symmetry of their local crystal field environment. The resulting structure, when these two systems are integrated, hosts strong antiferromagnetic correlations on the Ni sites with an anisotropy which is adopted from the nearby Dy ions. As a test case we compared our study of the coupled LaNiO\(_3\)-DyScO\(_3\) system with the closely related system LaNiO\(_3\)-GdScO\(_3\). By replacing Dy with Gd we allow the antiferromagnetic Ni spins to couple to a large rare-earth moment, similar to Dy, but without an additional coupling to the lattice, i.e. no magneto-crystalline anisotropy. These \(\text {LaNiO}_{3}\)-based heterostructures constitute a new and insightful model system for the interaction between 3d and 4f magnetic moments.

Throughout the remainder of this thesis we will explore nickelate based heterostructures in which ultrathin nickelate layers are epitaxially integrated with a chemically distinct and approximately isostructural material in order to manipulate the magnetic properties of the Ni sublattice. In Chap. 7 we report a comprehensive study of superlattices composed of alternating layers of LaNiO\(_{3}\) and DyScO\(_{3}\) or GdScO\(_{3}\) in which the 3d Ni sublattice couples to the magnetic 4f rare-earth sublattice across the epitaxial interface. In order to introduce concepts necessary for understanding the results of Chap. 7, the current chapter provides a brief review of previous studies of antiferromagnetism in ultrathin nickelate layers with a particular focus on work performed at the Max-Planck-Institute for Solid Sate Research.

In this study, we reported that a porous perovskite LaNiO 3 prepared by a precipitation-combustion method exhibited significant catalytic effect on hydrogen storage properties of Mg. It is demonstrated that the optimal H-absorption property was achieved on the composite containing 10 wt.% porous LaNiO 3 with a milling time of 10 h, 5.1 wt.% hydrogen can be absorbed within 1.0 min at 200 °C. The activation energy of hydrogenation of the composite is ca. 7.05 kJ/mol H 2 and the rate-controlling step is controlled by H-diffusion at a temperature higher than 200 °C. SEM, XRD and XPS results indicated that the prominent hydrogen storage properties of MgH 2 catalyzed by the porous LaNiO 3 are resulted from the uniform distribution of porous LaNiO 3 with high BET surface in the matrix of MgH 2 as well as the synergistic catalytic effect of LaH 3 and Mg 2 NiH 4 formed in situ at the hydrogenation process.

Over the last few decades, manipulating the metal-insulator (MI) transition in perovskite oxides (ABO3) via an external control parameter has been attempted for practical purposes, but with limited success. The substitution of A-site cations is the most widely used technique to tune the MI transition. However, this method introduces unintended disorder, blurring the intrinsic properties. The present study reports the modulation of MI transitions in [10 nm-NdNiO3/t-LaNiO3/10 nm-NdNiO3/SrTiO3 (100)] trilayers (t = 5, 7, 10, and 20 nm) via the control of the LaNiO3 thickness. Upon an increase in the thickness of the LaNiO3 layer, the MI transition temperature undergoes a systematic decrease, demonstrating that bond disproportionation, the MI, and antiferromagnetic transitions are modulated by the LaNiO3 thickness. Because the bandwidth and the MI transition are determined by the Ni-O-Ni bond angle, this unexpected behavior suggests the transfer of the bond angle from the lower layer into the upper. The bond-angle transfer eventually induces a structural change of the orthorhombic structure of the middle LaNiO3 layer to match the structure of the bottom and the top NdNiO3, as evidenced by transmission electron microscopy. This engineering layer sequence opens a novel pathway to the manipulation of the key properties of oxide nickelates, such as the bond disproportionation, the MI transition, and unconventional antiferromagnetism with no impact of disorder.

Formation of La-based perovskite compounds, LaBO 3 (B: Fe, Al, Mn, Co and Ni), in supercritical water was examined using a batch-type reactor vessel. Investigations of processing conditions revealed that the heat treatment of the equimolar nitrate solution of La and Fe with pH 8 at 450 °C and 30 MPa for 15 min was optimal for obtaining LaFeO 3 as a single phase. Analysis of the products prepared under the conditions of the lower reaction temperature or the shorter reaction time elucidated the formation mechanism of LaFeO 3 ; it was formed from a reaction of intermediate products of LaOOH and Fe 2 O 3 at 450 °C, and LaOOH was formed via La 2 (OH) 5.1 (NO 3 ) 0.9 at the lower temperature. Adjustment of the pH of the nitrate solution to 8 by the addition of the KOH solution was important for the effective formation of the LaOOH intermediate and for the decrease in the formation of La 2 (OH) 5.1 (NO 3 ) 0.9 or La(OH) 3 , which had a poor reactivity with Fe 2 O 3 or other iron-related compound at 450 °C and 30 MPa and remained as the secondary phase in the final product. The optimum conditions were applied to the synthesis of LaAlO 3 , LaMnO 3 , LaCoO 3 and LaNiO 3 , and it was observed that a single phase of LaAlO 3 was formed, while LaMnO 3 was formed with several secondary phases, and LaCoO 3 and LaNiO 3 could not be formed at all. The ease of the formation of the La-based perovskites was mostly related to the sum of first, second and third ionization energies of B-site cations, which may mean that it is easy to form a B ion with a + 3 valence (Fe 3+ , Al 3+ , Mn 3+ , Co 3+ and Ni 3+ ) in supercritical water.

Na0.5Bi0.5(Ti,W,Ni)O3 (NBTWN) thin films were fabricated on the pure and Bi(Fe,Mn)O3 buffered Pt/TiO2/SiO2/Si and LaNiO3(100)/Si substrates by chemical solution deposition, respectively. The crystallization, surface morphology, and electrical properties of the four films are mainly investigated. The films, which are grown on the Pt/TiO2/SiO2/Si substrates, exhibit similar polycrystalline structure. Whereas for films deposited on the LaNiO3 (100)/Si substrates, strong (l00) orientations are observed. Compared with the NBTWN film on pure Pt/TiO2/SiO2/Si, the introduction of Bi(Fe,Mn)O3 buffer layer and LaNiO3 oxide electrode can promote the grain growth of the NBTWN resulting in larger grain size. Large remanent polarization and breakdown strength can be observed in films with Bi(Fe,Mn)O3 buffer layers. Furthermore, the combination of low leakage current and good energy storage capacity, together with high dielectric tunability is achieved in NBTWN/Bi(Fe,Mn)O3/LaNiO3(100)/Si heterostructure. The enhancement in electrical properties may be attributed to the preferred crystalline orientation and optimized grain size depending on both the buffer layer and the electrode that are used.

The preparation of nanoparticles and nanofibers of bimetallic oxides containing f block element perovskites of the type LaNiO 3 , SmCoO 3 and DyFeO 3 was undertaken. They were obtained by electrospinning and its formation simply tuneable in the subsequent oxidation step-heating rate. These bimetallic oxides were tested as catalysts in the partial oxidation of methane aiming the production of syngas. The best results were those obtained over the nickel-based catalysts, which have an activity and selectivity comparable to that of a commercial catalyst used as reference (5 wt% Pt / Al 2 O 3 ). The catalysts present also an unusual long catalytic stability in the gaseous stream. These perovskites type bimetallic oxides were characterized by different techniques (XRD, SEM/EDS, H 2 -TPR). To our knowledge, it is the first time that these results are reported in the literature.

LNO (LaNiO 3 ) thin films were directly deposited onto Si substrates with a thin layer of amorphous natural oxide (SiO 2 ) 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 −4 Ω cm). It would be a potential bottom electrode and/or seed layer to integrate perovskite-type films on it for functional devices.

The material class of rare earth nickelates with high Ni$^{3+}$ oxidation state is generating continued interest due to the occurrence of a metal-insulator transition with charge order and the appearance of non-collinear magnetic phases within this insulating regime. The recent theoretical prediction for superconductivity in LaNiO$_3$ thin films has also triggered intensive research efforts. LaNiO$_3$ seems to be the only rare earth nickelate that stays metallic and paramagnetic down to lowest temperatures. So far, centimetre-sized impurity-free single crystal growth has not been reported for the rare earth nickelates material class since elevated oxygen pressures are required for their synthesis. Here, we report on the successful growth of centimetre-sized LaNiO$_3$ single crystals by the floating zone technique at oxygen pressures of up to 150 bar. Our crystals are essentially free from Ni$^{2+}$ impurities and exhibit metallic properties together with an unexpected but clear antiferromagnetic transition., Nature Communications 9 (1), 43, S. 1 - 7 (2018)

The compositionally graded BiFe 1-X Mn X O 3 (0.0 ≤ x ≤ 0.3) thin film was deposited on LaNiO 3 coated Si (100) substrate via pulsed laser deposition technique to investigate multiferroic properties. This thin film had a ( l 00) oriented perovskite structure without any secondary phases. Compared with the pure BiFeO 3 film, the graded film not only exhibits out of plane magnetic anisotropy but also increases ferroelectric polarization and dielectric tunability. A large remanent polarization of P r ∼69.47 μC/cm 2 and coercive field of H C ∼86.95 kV/cm are observed in such a graded thin film. These improved responses could be due to spontaneous and induced polarization of individual layers. Moreover, electrostatic coupling, polarization gradient and elastic integration between layers also contributed for the enhancement of multiferroic properties in graded thin film. This work presents a feasible way to design a new kind of electronic devices based on graded multiferroic for developing high power and energy density applications.

Two-dimensional (2D) perovskite-type metal oxides with ultrathin feature of nanosheets are highly promising for electrochemical energy storage applications. Here, 2D perovskite LaNiO3 nanosheet assemblies with rich pores are prepared by facile sol-gel method and subsequent heating treatment. The crystal structure, morphology and electrochemical performance of LaNiO3can be simply tuned by adjusting the heating temperature and time. The optimized sample exhibited uniform sheet-like morphology with a thickness of ∼50 nm and a large surface area and pore volume, which achieves a high specific capacitance of 139.2 mAh g−1 at a current density of 1.0 A g−1, a good rate capability and an excellent cycle stability. What's more, the LaNiO3//graphene asymmetric supercapacitor device demonstrates a high energy density of 65.8 Wh kg−1 at a power density of 1.8 kW kg−1 and an outstanding cycling stability performance with 92.4% specific capacitance retention after 10000 cycles, which represents a critical step forward toward practical applications.

A series of La1−xCexNi1−yFeyO3 (x, y = 0.00–0.25) NPs was fabricated via micro-emulsion route and effect of doping was investigated on the basis of optical, photocatalytic and structural properties. The as-synthesized NPs were characterized via XRD, Raman analysis, SEM and UV–visible techniques. The XRD results confirmed the rhombohedral perovskite phase particles with particles of 60–80 nm range. UV–vis absorption edge showed significant red shift thereby tuning the band gap from 2.77 to 2.64 eV. The photocatalytic effectiveness of LaNiO3 and La0.80Ce0.20Ni0.80Fe0.20O3 catalysts was performed by degrading Congo red (CR) dye under visible light exposure. Substituted catalyst exhibited superior photodegradation by showing 97% degradation in comparison to pristine LaNiO3 (63% only) in 120 min. Degradation of CR followed the pseudo fist order kinetics. In addition, the catalyst dose effect, dye concentration and pH variation was studied for Cr dye degradation. Enhanced photocatalytic activity and narrow bandgap of Ce and Fe doped LaNiO3 introduce such materials as efficient visible active photocatalysts to be utilized in dye removal application from waste water and in photovoltaic applications, respectively.

In this study, nano catalyst LaNiO3 with perovskite structure was synthesized using the citrate sol–gel method in the combined methane reforming with CO2 and O2 (CRM). The effects of increasing the surface area of the LaNiO3 perovskite on the catalytic activity were investigated by changing the method of preparing and creating holes in the surface of the samples. Physical and chemical properties of the samples, before and after the reactor test, were determined through ICP, AA, XRD, TGA, TPR, BET, SEM, EDX and TEM techniques. The results of XRD, ICP, AA, SEM, EDX and TEM tests indicated that the citrate sol–gel method is a good way to prepare a homogeneous perovskite LaNiO3 sample on a scale of nanometers. The results of the TPR test showed using etching in the citrate sol–gel method can produce samples with high stability. The BET results indicated that the surface area of the LaNiO3 sample tripled with the method suggested in this paper. Changes in preparation method lead to induction time decreasing and temperature increasing. Use of etching in the citrate sol gel method had no significant effect in the results of activity tests versus time reaction at a temperature of 800 °C. TGA curves revealed no production of coke over the process for the produced samples.