Perovskite LaNiO3 Research Articles

Sol–gel synthesis and structural characterisation of the perovskite type pseudo solid solution LaNi0.5Cu0.5O3

The composition LaNi0.5Cu0.5O3−δ has been prepared by heat treating a polyacrylamide xerogel in flowing O2. A perovskite type structure starts to crystallise at 700 °C and is achieved at 1000 °C. TGA data point to the formation of a rather strongly oxidised compound (δ ≤ 0.09). As the solid state reaction of a mixture of La2O3/NiO/CuO powder oxides never yields a perovskite, the part of the sol–gel route in this synthesis proves to be crucial. On the basis of X-ray and neutron diffraction results, the existence of a cupronickelate having a rhombohedral perovskite type structure is proved. Rather unexpectedly, an electron diffraction study of the as-prepared composition at 1000 °C reveals the presence of two sets of perovskite type cupronickelate microcrystals: a copper rich one with a fixed composition 67% Cu and a nickel rich one with a small range of compositions 59 ≤ Ni% ≤ 67. The latter microcrystals feature the rhombohedral LaNiO3 perovskite whereas the former one, due to the partial presence of Cu(II), frequently shows an orthorhombic [2ap√2 × 2ap√2 × ap] supercell. Thus, the composition LaNi0.5Cu0.5O3−δ. has to be understood in terms of a nanoscale segregated pseudo solid solution formed of two lanthanum cupronickelates, enriched in copper and nickel, respectively.

A Low Temperature LNO/PZT/LNO Ferroelectric Capacitor-Over-Interconnect (COI) FeRAM Module for Modular SOC

An embedded FeRAM module is achieved by a low temperature capacitor-over-interconnect (COI) process. A conductive perovskite LaNiO 3 (LNO) bottom electrode is used as seed layer; the crystallization temperature of in-situ sputter deposited PZT is greatly reduced to 350 C∼400C. LNO's near-perfect lattice match with PZT allows PZT to grow epitaxially at low temperature. When LNO is used as top electrode of the ferroelectric capacitor, the fatigue performance is greatly improved. The COI LNO/PZT/LNO FeRAM structure achieved by this low temperature process is completely modular and is ideal for advanced Cu/low-K SOC (System On Chip) application. The COI FeRAM has been demonstrated successfuliy in a 64Kb(2T2C)-128Kb(1T/1C) dule-mode FeRAM with a 0.5 w m CMOS logic process.

Effect of spin-polarized injection on the mixed state of YBa2Cu3O7−δ

We report measurements of the magnetic moment of YBa2Cu3O7−δ films when subjected to injection of short pulses of spin-polarized current from the colossal magnetoresistance (CMR) manganites La0.7Ca0.3MnO3 and La0.7Sr0.3MnO3, and unpolarized current from the nonmagnetic perovskite LaNiO3(LNO). We study relaxation from the Bean critical state, with and without current pulses. For pulses longer than 100 ms, the effect of injection is similar for all samples and is due to heating. Below 1 ms, we see a clear difference between the CMR and LNO samples and attribute this to the spin polarization of the current injected from the CMR materials.

Pulsed laser deposition of epitaxial PbZrxTi1−xO3 ferroelectric capacitors with LaNiO3 and SrRuO3 electrodes

It is commonly accepted that, in order to solve the fatigue problem in PbZrxTi1−xO3 (PZT) ferroelectric capacitors, oxide electrodes have to be used. However, clear criteria for the choice of an electrode material have not given yet. Here we report on the deposition and ferroelectric properties of epitaxial pulsed laser deposited PZT capacitors with SrRuO3 and LaNiO3 perovskite bottom electrodes, and aluminium top electrodes. Remarkable improvement of the ferroelectric properties, i.e. remanent polarization increasing from 7.5 to 37μC/cm2, is observed when the bottom electrode material is changed from SrRuO3 to LaNiO3. This improvement is attributed to a smoother ferroelectric/electrode interface and the formation of the tetragonal phase of PZT instead of the rhombohedral one.

Surface characterization of LaNiO 3/Ni–PVC composite

The perovskite LaNiO 3 was prepared by the sol-gel method. Electrodes of LaNiO 3/Ni–PVC were obtained by painting a conductive Ni–PVC composite substrate with a suspension of the LaNiO 3 powder in an ethanol–tetrahydrofuran mixture. They were characterized by scanning electron microscopy (SEM), X-ray powder diffraction (XRD) and energy dispersive spectroscopy (EDS). The study of the electrochemical response of this composite was performed in alkaline solutions by cyclic voltammetry, open circuit potential and by voltammetric charges. The state of the surface and the contribution of the Ni–PVC substrate in the electrochemical behavior of LaNiO 3 were studied for the same electrode after prolonged repetitive potential cycling and oxygen evolution.

Sodium Hydride as a Powerful Reducing Agent for Topotactic Oxide Deintercalation: Synthesis and Characterization of the Nickel(I) Oxide LaNiO2

The capability of sodium hydride as a reducing agent in oxide deintercalation reactions is explored. The Ni(III) perovskite LaNiO3 can be reduced topotactically to LaNiO2, isostructural with the “infinite layer” cuprates, using solid sodium hydride in a sealed evacuated tube at 190 ≤ T/°C ≤ 210, and a similar infinite-layer phase is prepared by reduction of NdNiO3. Structural characterization indicates the coexistence of incompletely reduced regions, with five-coordinate Ni centers due to the introduction of oxide anions between the NiO23- sheets, giving samples with a refined stoichiometry of LaNiO2.025(3). Neutron powder diffraction and magnetization measurements indicate that the lamellar Ni(I) phase does not show the long-range antiferromagnetic ordering characteristic of isoelectronic Cu(II) oxides. This may be due either to the influence of the interlamellar oxide defect regions or to the reduced covalent mixing of Ni 3d and O 2p levels.

Electrode effects on the low-frequency dielectric properties of (Ba, Sr)TiO3 thin films prepared by pulsed laser ablation

(Ba, Sr)TiO3(BST) thin films were prepared by pulsed laser deposition on the perovskite conductive oxide LaNiO3 (LNO), YBa2Cu3O7−δ(YBCO) films, and Pt as a bottom electrode. The crystalline structures and surface microstructrue of the BST deposited on several substrates were characterized by x-ray diffraction measurement and scanning electron microscopy, respectively. The electrode effects on low-frequency dielectric behavior of BST thin films were investigated. The complex dielectric constants of the films were measured as a function of frequency in the frequency range from 0.1 Hz to 10 MHz. BST films grown on metallic oxide substrates exhibited marked dielectric relaxation below 10 MHz. This low frequency dielectric relaxations is attributed to the ionized space charge carriers such as the oxygen vacancies and cation defects in BST film, and the interfacial polarization in the grain boundary region and the electrode/film interface.

The preparation of the single-phase perovskite LaNiO 3

There is growing use of the perovskite type mixed metal oxide materials. A host of useful properties have been well known for some time. They exhibit piezoelectricity, pyroelectricity, ferroelectricity, high temperature superconductivity and also display catalytic activity. It is, thus, important to investigate preparative routes that can yield single-phase perovskite materials free of any extraneous metal oxides. This work reports the preparation of a single-phase perovskite LaNiO 3 synthesised by co-precipitation from metal salt solutions using various organic precipitating reagents. A single perovskite phase was realised at low processing temperatures (800°C) and this was stable to 1000°C. At temperatures of 1000°C and above LaNi 2O 4 and other unidentified mixed oxide systems were observed. Evaporation and sol–gel routes were also explored but these resulted in poor homogeneity and complex multiphase oxide systems. Phase analysis was performed using powder X-ray diffraction (PXRD). Diffractograms were Rietveld refined using the trigonal space group, R-3 C, and crystallographic parameters for the oxide system are reported. Differential scanning calorimetry (DSC) was used to probe the solid-state reaction of the precipitated metal products and scanning electron microscopy (SEM) was used to examine the morphology of the resulting particles.

Ferroelectric properties of Pb(Zr 0.52Ti 0.48)O 3 thin films prepared by metal–organic decomposition process

The perovskite LaNiO 3 (LNO) and Pb(Zr 0.52Ti 0.48)O 3 (PZT) thin films were successfully prepared using metal–organic decomposition (MOD) process. Perovskite LNO phase can be obtained at temperature as low as 600°C (30 s) in rapid thermal annealing (RTA) process. However, additional furnace annealing (FA) at 650°C (60 min) is needed in order to lower the electrical resistivity of the LNO films to ρ≤30 mΩ cm. Pure perovskite PZT films can easily be obtained by either RTA or FA process. Furnace post-annealing process (650°C, 60 min) results in a PZT film possessing significantly better ferroelectric properties than the RTA process (650°C, 60 s). The best properties obtained are remanent polarization P r=11.8 μC/cm 2, coercive force E c=76.0 μC/cm 2 and leakage current density J L≤3×10 −6 A/cm 2 (for applied field≤200 kV/cm). Using LNO films as buffer layer does not increase the ferroelectric properties of PZT films, but significantly improves fatigue behavior.

TEM and AFM study of perovskite conductive LaNiO 3 films prepared by metalorganic decomposition

Perovskite conductive LaNiO 3 (LNO) films were prepared by metalorganic decomposition. The films were obtained by spin-on pyrolysis on NaCl and SrTiO 3(STO) substrates and then annealing at various temperature. The effect of different thermal treatments and annealing temperature on crystallinity, orientation and surface morphology of LNO films was studied. The results obtained by transmission electron microscopy (TEM), selected area electron diffraction (SAED) and X-ray photoelectron spectrometry (XPS) indicated that in the thermal treatment process the oxygen diffusion into the film is the critical step in the fabrication of good metallic LNO films at lower growth temperature. Epitaxial LNO films could be fabricated on STO. The surface morphology of LNO film on STO including the film roughness was recorded by atomic force microscopy (AFM).

Crystal structure and magnetism in the defect perovskite LaNiO 2.5

The fine structural features of LaNiO 2.5 have been determined from a high resolution neutron diffraction study on a powder sample with excellent crystallinity, prepared by an original method. The crystal can be described as a monoclinic 2 a 0 × 2 a 0 × 2 a 0 superstructure of perovskite, and contains one-dimensionally linked NiO 6 octahedra along the c-axis and NiO 4 square-planar units connecting the octahedra chains. The absence of magnetic ordering, revealed by neutron diffraction down to 1.5 K, is also discussed.

Approximation to the metal-insulator transition by Gd3+ doping in Pauli LaNiO3 perovskite

Abstract The effect on electrical and magnetic properties of Gd 3+ doping of LaNiO 3 was studied for Gd concentration x ⩽ 0.1. The electrical resistivity ρ increases with x , being dρ/d T > 0 for all samples studied. The magnetic susceptibilities were fitted by the function χ ( T ) = χ 0 − aT 2 + xC Gd 3+ / T . The EPR results are discussed in terms of the Gd 3+ paramagnetic moment interactions with the crystal field and with the conduction electron spins.

Preparation of perovskite conductive LaNiO3 films by metalorganic decomposition

Perovskite conductive LaNiO3 films, 250 nm thick, were prepared by metalorganic decomposition. Rutherford backscattering spectrometry was used to determine the film thickness and composition. The x-ray diffraction patterns of LaNiO3 films indicated that the lowest temperature for crystallization is about 530 °C. The measurement of resistivity as a function of annealing temperatures showed that the good metallic conductive LaNiO3 films could be obtained at 550 °C. The films with the lowest resistivity (4.0×10−4 Ω cm) were obtained on quartz by annealing in oxygen at 700 °C.

Catalytic behavior and electrical conductivity of LaNiO 3 in ethanol oxidation

The oxidation of ethyl alcohol vapor on perovskite type LaNiO 3 oxide was conducted in flowing air. Characterization of catalysts was carried out by TPD techniques and the conductivity change of the oxide during oxidation was measured to correlate catalytic properties and electrical conductivity of the material. It was demonstrated that the oxidation reaction is accompanied by transfer of charge or a loss of oxygen from the surface as well as a change in the conductivity of the oxide. The oxidation rate was found to follow the power law kinetic, r = k[O 2] 0[ethanol] 1, and the resistance R followed as R = R 0(1 + α [ethanol] β ), where α and β are the constants depending on temperature. The degree of the conductance change depended on the concentration of ethanol vapor, the oxidation circumstances, and the reaction temperature. Increase in temperature led to a change in the states of surface oxygen, O − or O 2−, and, hence, the interactions between them. The ethanol vapor showed higher conductance change in the temperature range between 250 and 350°C. Together with the study of redox mechanism, the ralations of oxidation rate and conductance as a function of reactant concentration are also discussed.

High Specific Surface Area Nickel Mixed Oxide Powders LaNiO3 (Perovskite) and NiCo2O4 (Spinel) via Sol-Gel Type Routes for Oxygen Electrocatalysis in Alkaline Media

A novel sol-gel process of preparation of oxide electrocatalysts is investigated to prepare Ni-containing mixed oxides LaNiO3 and NiCo2O4 at moderate temperatures. High surface area (20-55 m2 g-1) powders and high roughness electrodes (30-1500) were obtained. Apparent and real electrocatalytical activity are compared and discussed.

Preparation and crystal structure of the deficient perovskite LaNiO2.5, solved from neutron powder diffraction data

The deficient perovskite LaNiO2.5 has been prepared in powder form with excellent crystallinity by controlled reduction of LaNiO3 with Zr metal in evacuated ampoules at 400 °C. The neutron powder diffraction pattern could be indexed in a monoclinic unit-cell corresponding to a superstructure of perovskite with dimensions 2a0× 2a0× 2a0(a0: lattice parameter of the ideal cubic perovskite), also observed by electron diffraction. The structure was solved from the neutron powder data. The oxygen vacancies are ordered in such a way that square-planar NiO4 and NiO6 octahedra alternate in the ab plane along the [1 1 0] direction. Both kinds of Ni polyhedra are fairly distorted and tilted in order to optimize the La–O distances, giving rise to a highly strained structure of metastable character. In fact, the compound readily takes up oxygen, above 175 °C in air, to give the much more stable LaNiO3 perovskite.

Electronic properties of the metallic perovskite LaNiO3: Correlated behavior of 3d electrons.

Low-temperature electrical resistivity, specific heat, and magnetic measurements have been performed on the distorted perovskite ${\mathrm{LaNiO}}_{3}$. The electrical resistivity shows a linear temperature dependence at high temperatures and an ${\mathit{AT}}^{2}$ dependence below \ensuremath{\sim}50 K. The static paramagnetic susceptibility is nearly Pauli-like with an additional small Curie-law contribution in the range 100--300 K, and shows stronger temperature dependence at lower temperatures. The specific heat can be represented as \ensuremath{\gamma}T+\ensuremath{\beta}${\mathit{T}}^{3}$+\ensuremath{\delta}${\mathit{T}}^{3}$lnT at low temperatures. Both the Pauli magnetic susceptibility \ensuremath{\chi}=5.1\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}4}$ emu/mol and the linear temperature coefficient of the specific heat \ensuremath{\gamma}=13.7 mJ/${\mathrm{K}}^{2}$ mol are enhanced well above their electron gas values. The effective Stoner enhancement factor is S=0.58, i.e., far from the ferromagnetic instability. These results are interpreted in terms of a Fermi liquid composed of almost localized Ni 3d electrons. Thus, ${\mathrm{LaNiO}}_{3}$ represents a correlated metallic system.

Preparation of High Density Perovskite LaNiO<sub>3</sub> by Using HIP

The authors have succeeded to prepare dense sintered bodies of perovskite LaNiO3, which shows a metallic conduction, by HIPping without flux such as Na2CO3. The stoichiometric mixture of La2O3 and NiO was precalcined in air at 900°C for 5h. The ground sample was then sintered at 1100° or 1300°C in air for 20h. The sintered bodies were composed of La2NiO4 and NiO, and had the densities of up to 95%. The single phase perovskite LaNiO3 of 95% density was obtained from its presintered body by HIPping under 101MPa (in Ar gas containing 20% oxygen) and 1400°C for 2h. A very low resistivity of 2.2×10-6Ω⋅m was measured for this HIPped body of LaNiO3. The stability region for the perovskite compound LaNiO3 in P-T diagram was discussed.

LaNiO 3: A study by electron spectroscopy

The perovskite LaNiO 3 was studied using XPS, UPS and EELS. In situ oxygen annealing was used to prepare a clean, stoichiometric surface, as this material is prone to oxygen loss on heating. The results deviate somewhat from those expected from a simple band model, and are indicative of considerable correlation, in line with its magnetic properties. We discuss this in the light of similar observations on related materials.

Hot Pressing of Perovskite LaNiO<sub>3</sub>

The perovskite powder of (La, Sr)NiO3 system was prepared using acetate precursors and then reacted with Na2CO3 flux at 900°C for 24 hours to produce the perovskite single phase after washing away excess Na+ ion. The obtained powder was sintered at temperatures between 860° and 1180°C for 10 hours in the flow of O2 gas by hot press. The maximum temperature of the stability of the perovskite LaNiO3 phase is limited to the temperature at about 1040°C in this hot pressing condition. The bulk density of LaNiO3 which was sintered at 1040°C was greatly increased to 97 percentage of the theoretical value with a small amount of Na addition. The maximum stability temperature of perovskite La1-xSrxNiO3 phase seems to be lower than that of LaNiO3.