Structure Of Complex Oxides Research Articles

Effects of synthesis conditions on the crystal and local structures of high-entropy oxides Ln[formula omitted]O[formula omitted] (Ln = La-Yb, Y; M = Ti, Zr, Ce)

The synthesis and detailed study of six series of high-entropy complex oxides containing lanthanides (Ln) and transition metals with the general formula Ln2M2O7 (Ln = La-Yb, and Y; M = Ti, Zr, and Ce) with the number of different Ln cations not less than six in each case are reported. The influence of synthesis conditions (types of the Ln3+ and M4+ cations, calcination temperature) used in the synthesis via either coprecipitation or sol–gel method on the crystal and local structures of target materials is comprehensively surveyed. The studies were carried out using a combination of long- (s-XRD), medium- (Raman, FT-IR, SEM-EDS) and short-range (XAFS) sensitive techniques, as well as AES-ICP and STA. It was established that the ratio of the cation radii γ = r̄Ln3+/r̄M4+ is the main factor that determines the type of initially formed crystal structure. In the boundary region (γ∼ 1.42–1.47), the average radius of lanthanide cation (r̄Ln3+), along with the r̄Ln3+/r̄M4+ ratio, also plays a significant role in the type of the resulting crystal structure of the high-entropy lanthanide complex oxides. The presence of inhomogeneity in the distribution of elements in precursors significantly affects the phase composition of the resulting high-entropy oxides. An increase in the calcination temperature promotes not only the occurrence of subsequent phase transitions, but also an increase in the single-phase nature of the resulting high-entropy complex rare-earth oxides. At the same time, the cations included in the composition retain some independence, despite the fact that they occupy one crystallographic position in the resulting crystal structure.

Nanoscale chemical and structural investigation of solid solution polyelemental transition metal oxide nanoparticles

Although it has been shown that configurational entropy can improve the structural stability in transition metal oxides (TMOs), little is known about the oxidation state of transition metals under random mixing of alloys. Such information is essential in understanding the chemical reactivity and properties of TMOs stabilized by configurational entropy. Herein, utilizing electron energy loss spectroscopy (EELS) technique in an aberration-corrected scanning transmission electron microscope (STEM), we systematically studied the oxidation state of binary (Mn,Fe)3O4, ternary (Mn, Fe, Ni)3O4, and quinary (Mn, Fe, Ni, Cu, Zn)3O4 solid solution polyelemental transition metal oxides (SSP-TMOs) nanoparticles. Our findings show that the random mixing of multiple elements in the form of solid solution phase not only promotes the entropy stabilization but also results in stable oxidation state in transition metals spanning from binary to quinary transition metal oxide nanoparticles.

Effect of the Composition and Structure of Nickel-Chromium Complex Oxides on the Upgrading of Heavy Oil in Supercritical Aqueous Fluid

Effect of the Composition and Structure of Nickel-Chromium Complex Oxides on the Upgrading of Heavy Oil in Supercritical Aqueous Fluid

A solution-based route to compositionally complex metal oxide structures using high-entropy layered double hydroxides

Although complex metal oxides with tailored compositions are increasingly in demand for applications in advanced technologies, their preparation by solution-based routes, which are typically low cost and easy to scale up, is challenging. Here, we report high-entropy layered double hydroxides (HE-LDHs) having complex compositions as precursors for complex metal oxides. Furthermore, we reveal that the ionic radii are the key factors determining the incorporation of the metal cations into the hydroxide layers, which can contain up to 10 different kinds of metal cations simultaneously having a metal cation ratio inherited from the reaction solution. Furthermore, spinel-based complex oxides can be prepared by heat treating the HE-LDHs in air, and their metal cation ratios are maintained over expansive heat-treatment temperatures (up to 1,200°C). Therefore, the results reveal that complex oxides with tailored compositions can be prepared using solution-based approaches, enabling the large-scale fabrication of oxides with precisely controlled physicochemical properties for various applications.

Local-electrostatics-induced oxygen octahedral distortion in perovskite oxides and insight into the structure of Ruddlesden\u2013Popper phases

As the physical properties of ABX3 perovskite-based oxides strongly depend on the geometry of oxygen octahedra containing transition-metal cations, precise identification of the distortion, tilt, and rotation of the octahedra is an essential step toward understanding the structure–property correlation. Here we discover an important electrostatic origin responsible for remarkable Jahn–Teller-type tetragonal distortion of oxygen octahedra during atomic-level direct observation of two-dimensional [AX] interleaved shear faults in five different perovskite-type materials, SrTiO3, BaCeO3, LaCoO3, LaNiO3, and CsPbBr3. When the [AX] sublayer has a net charge, for example [LaO]+ in LaCoO3 and LaNiO3, substantial tetragonal elongation of oxygen octahedra at the fault plane is observed and this screens the strong repulsion between the consecutive [LaO]+ layers. Moreover, our findings on the distortion induced by local charge are identified to be a general structural feature in lanthanide-based An + 1BnX3n + 1-type Ruddlesden–Popper (RP) oxides with charged [LnO]+ (Ln = La, Pr, Nd, Eu, and Gd) sublayers, among more than 80 RP oxides and halides with high symmetry. The present study thus demonstrates that the local uneven electrostatics is a crucial factor significantly affecting the crystal structure of complex oxides.

A study on pyro-hydrometallurgical process for selective recovery of Pb, Sn and Sb from lead dross

This study is to propose a pyro-hydrometallurgical process for recovering Pb, Sn, and Sb from lead dross (LD), incorporating stages of roasting, leaching, and precipitation. The LD, containing 67.2% of Pb, 4.0% of Sn, and 1.4% of Sb, was first roasted at 750 °C for 2 h to oxidise the sulphide metals. Approximately 90% of Pb was oxidised from the first roasting. The LD was second roasted by mixing with 95% H2SO4 for sulphatising at 300 °C for 3 h to break the complex oxide structure of the oxyplumboromeite (Pb2Sb2O7). After the two-step roasting process, over 99% of Pb was oxidised and Sb was separated. The calcine obtained was desulphurised by 2 M Na2CO3 solution for insoluble PbSO4 to PbCO3 for selective leaching. The residue was then leached in 2.5 M HNO3 at 50 °C for 3 h and over 99% of Pb dissolved into the solution while Sn and Sb remained in the solid residue. The Pb containing solution was neutralised at pH 8 using 2 M Na2CO3 and over 99% Pb was precipitated as PbCO3 and Pb hydroxides. A residue containing Sn and Sb was leached in 7 M NaOH at 95 for 1 h and over 99% Sn was leached selectively. Sn in the solution was precipitated at pH 7 using 2 M H2SO4 as SnO2. Sb was recovered as Sb2O3 in solid reside from Sn leaching. The overall recovery rates of Pb, Sn, and Sb from the LD were 99.5%, 95.4%, and 86.3%, respectively. The proposed process is expected to contribute to recycling Pb and other metal values from LD by minimising hazardous waste emissions.

Anodizing behavior and electrochemical evaluation of accumulative roll bonded Al and Al-SiC composite

Accumulative roll bonded (ARBed) AA1050 and Al-2 vol% SiC p (AMC) samples were anodized in an H 2 SO 4 electrolyte to improve corrosion resistance. The SEM images revealed that the anodic oxide's morphology is significantly dependent on the microstructure of the ARBed bare samples, owing to high internal energy that accelerates Al consumption during anodizing process. Potentiodynamic polarization measurements and EIS evaluation showed that anodic oxide improves the corrosion resistance of both ARBed AA and AMC samples; however, the electrochemical behavior of the processed samples changed due to the formation of a complex oxide structure comprising of twisted pore channels and attack routes. • ARBed AA1050 and AA-2vol%SiCp were anodized in H 2 SO 4 . • ARB lead to a homogenous anodic oxide at higher passes. • The morphology of AAO-SiC-1P and AAO-SiC-3P comprise overgrown protuberances and wide boundaries. • Applying ARB before anodizing changes the electrochemical behavior of the anodic oxide.

Phase Equilibria and Structure of Complex Oxides in the 1/2 Nd2O3–CaO–CoO System in Air at 1373 K

X-ray powder diffraction and Rietveld full-profile analysis are used to establish the homogeneity ranges and crystalline structure of solid solutions Nd2−zCazO3−z/2 (0.0 ≤ z ≤ 0.1, space group P $$\bar {3}$$ m1) and Nd2−yCayCoO4−δ (0.7 ≤ y ≤ 1.0, space group I 4/mmm). Dependences of the unit cell parameters on the composition of solid solution Nd2−yCayCoO4−δ are obtained. It is shown that all cobaltites Nd2−yCayCoO4−δ in the temperature range of 298–1373 K in air possess virtually stoichiometric composition. Average values of thermal expansion coefficients for Nd2−yCayCoO4−δ (y = 0.8; 0.9) are calculated. An isobaric-isothermal section of the phase diagram for the 1/2Nd2O3–CaO–CoO system at 1373 K in the air has been constructed.

Phase transition of Bi5Ti3FeO15 ceramics discovered by Raman spectroscopy and in situ synchrotron XRD under stress field

Bi5Ti3FeO15 (BTFO) ceramics have been widely studied as a multiferroic material with some potential applications. However, the effect of the stress field on BTFO ceramics with complex lattice structures is unknown. Here, we use pressure-dependent Raman scattering spectroscopy to study the structure/phase transition of BTFO samples. Because the phonon mode changes significantly, there could be a phase transition in the range of 4.5–14.8 GPa. In order to further prove the occurrence of phase transition, we carried out in situ high-pressure angular dispersion x-ray diffraction (XRD), which clearly proved the structural evolution of BTFO: orthorhombic crystal A21am transformed into tetragonal I4/mmm. Note that the results from the XRD experiment are self-consistent with the data derived from Raman spectroscopy. It provides an effective method to explore the phase transition of complex oxide structures under high pressure.

Evolution of nano/submicro-scale oxide structures on Ti6Al4V achieved by an ultrasonic shot peening-induction heating approach for high-performance surface design of bone implants

Modified layers with multiscale structures have been extensively explored and rationally designed on Ti-based orthopedic implants recently, since the remarkable improvement of biomedical properties. In consideration of the inefficiency, costliness and waste products of existing technologies, herein, we proposed the ultrasonic shot peening and induction heating protocol to construct the micro-nano complex oxide structures on Ti6Al4V in term of its advantages of environmental friend, rapid heating, low-cost and easy to process. With the USP pretreatment and induction heating, the nonuniform oxide crystallites firstly appeared on smooth surface and successfully grow up into the well-distributed TiO2 nanocrystallites, and transformed to netlike structures with submicro-sized worms when subjected to high-power of shot peening, which was significantly influenced by the microstructural evolution of alloy matrix. The submicro/nano-structured oxide layers mainly contained rutile/anatase TiO2 and little Al2O3 between grain boundaries, successively enhanced the surface roughness and wettability, and tended to form the hydrophilic surfaces. The adhesion strength of the oxide layers to substrates and hardness were also distinctly increased with increasing the IHT period from 20 to 35 s. In vitro BMSCs culturing proved that the prepared submicro/nano-scale oxide layers possessed favorable cell adhesion and proliferation, and further improved the osteogenic differentiation. The novelty of this work was to explored the evolution law of submicro-and nano-scale structures in osteogenic differentiation, and further better clinical application of Ti-based biomaterials.

Magnetic and Electronic Properties of Complex Oxides from First‐Principles

The theoretical treatment of complex oxide structures requires a combination of efficient methods to calculate structural, electronic, and magnetic properties, due to special challenges such as strong correlations and disorder. In terms of a multicode approach, this study combines various complementary first‐principles methods based on density functional theory to exploit their specific strengths. Pseudopotential methods, known for giving reliable forces and total energies, are used for structural optimization. The optimized structure serves as input for the Green's function and linear muffin‐tin orbital methods. Those methods are powerful for the calculation of magnetic ground states and spectroscopic properties. Within the multicode approach, disorder is investigated by means of the coherent potential approximation within a Green's function method or by construction of special quasirandom structures in the framework of the pseudopotential methods. Magnetic ground states and phase transitions are studied using an effective Heisenberg model treated in terms of a Monte Carlo method, where the magnetic exchange parameters are calculated from first‐principles. The performance of the multicode approach is demonstrated with different examples, including defect formation, strained films, and surface properties.

Ignition and Mechanical Properties of Hot Extruded Magnesium Alloys with Trace Yttrium Additions

The ignition risk of magnesium restricts its usage in many transport applications. Yttrium has proven to be a potent alloying element to increase the ignition properties of magnesium, although large alloying quantities are generally utilized. The present work analyzes the effect of trace yttrium additions on the ignition, flammability and mechanical properties of wrought pure Mg and AZ31. A range of alloys were cast with increasing quantities of yttrium ranging from 0 wt.% to 0.2 wt.%. It was found that a concentration of 0.1 wt.% Y and above in Mg–Y binary alloys was able to increase the ignition temperature and flammability resistance. The observed increase was due to the formation of complex (MgO + Y2O3) oxide structures. However, yttrium additions lowered the ignition temperature when alloyed with AZ31. Additionally, yttrium additions were found to improve the mechanical properties when alloyed with pure Mg, although the impact on the AZ31 alloy was negligible.

Topotactic transition between perovskite and brownmillerite phases for epitaxial LaCoO3−δ films and effects thus resulted

Oxygen vacancy distribution has a direct effect on the crystal structure and physical properties of complex oxides, resulting in versatile applications. Here, we report on a reversible topotactic phase transition between the perovskite and brownmillerite structures for the LaCoO3−δ (δ = 0–0.5) epitaxial film by annealing the sample under different conditions. In the atmosphere of 2 × 10−4 Pa, LaCoO3 film is transformed from the perovskite structure to the brownmillerite structure when annealing temperature exceeds 500 °C. Meanwhile, the magnetic order transits from ferromagnetic to anti-ferromagnetic. Variable-range hopping demonstrates the electronic transport process for both phases. The incorporation of oxygen vacancies results in an upward shift of the lnρ-T−1/4 curve, without affecting the lnρ-T−1/4 slope. We found signatures for preferential distribution for oxygen vacancies; the latter prefer to appear near high spin Co3+ ions in the initial stage when they are introduced into the lattice, resulting in abnormal magnetic and transport behaviors.

Structure and calorimetric study of complex oxides based on lanthanum, tungsten, and alkaline earth elements MeLa2WO7 (Me = Mg, Ca, Sr, Ba)

As a result of citrate synthesis by the “sol–gel” method, we obtained samples of the compounds of ternary oxides with lanthanum, tungsten, and alkaline earth elements with the general formula MeLa2WO7 (Me = Mg, Ca, Sr, Ba). The structure of the samples obtained was studied by the X-ray diffraction, electron probe, and X-ray spectral microanalysis; the infrared and Raman spectra of the compounds were obtained. The results of indexing for SrLa2WO7 and BaLa2WO7 are in good agreement with the previously published crystallographic data. The heat capacity of the samples was measured by using of adiabatic calorimetry and their thermodynamic functions were calculated.

Titanium phosphonate oxo-alkoxide "clusters": solution stability and facile hydrolytic transformation into nano titania.

Titanium (oxo-) alkoxide phosphonate complexes were synthesized using different titanium precursors and tert-butylphosphonic acid (tBPA) as molecular models for interaction between phosphonates and titania surfaces and to investigate the solution stability of these species. Reflux of titanium(iv) ethoxide or titanium(iv)(diisopropoxide)bis(2,4-pentadionate) with tert-butylphosphonic acid in toluene–ethanol mixture or acetone yielded seven titanium alkoxide phosphonate complexes; [Ti5(μ3-O)(μ2-O)(μ-HOEt)2(μ-OEt)3(μ2-OEt)(μ3-tBPA)3(μ3-HtBPA)(μ2-tBPA)2(μ2-HtBPA)]·3EtOH, 1, [Ti4O(μ-OEt)5(μ2-OEt)7(μ3-tBPA)], 2, [Ti4(μ2-O)2(μ-OEt)2(μ-HOEt)2(μ2-tPBA)2(μ2-HtPBA)6]·4EtOH, 3, [Ti4(μ2-O)2(μ-OEt)2(μ-HOEt)2(μ2-tPBA)2(μ2-HtPBA)6]·2EtOH, 4, [Ti6(μ2-O)(μ3-O)2(μ2-OEt)5(μ-OEt)6(μ3-tBPA)3(μ3-HtBPA)], 5, [Ti4(μ-iOPr)4(acac)4(μ2-tBPA)4], 6 and [Ti5(μ4-O)(μ2-O)3(μ2-OEt)4(μ-OEt)6(μ-HOEt)(μ3-tBPA)]2, 7. The binding mode of tBPA to the titanium oxo-core were either double or triple bridging or a combination of the two. No monodentate or chelating coordination was observed. 31P NMR spectrometry of dissolved single crystals indicates that 1 and 5 retain their solid-state structures in solution, the latter even on moderate heating, while 6 and 7 dissolved into several other forms. The complexes were found to be sensitive towards hydrolysis, proceeding in a topotactic fashion with densification of the material into plates and lamellae resulting finally in “core–shell” nanoparticles with a crystalline core (anatase) and an amorphous outer shell upon contact with water at room temperature as observed by HRTEM and AFM analyses. 31P NMR data supported degradation after addition of water to solutions of the complexes. Hydrolysis under different conditions affords complex oxide structures of different morphologies.

Electronic structure and properties of lithium-rich complex oxides.

Lithium-rich complex transition-metal oxides Li2MoO3, Li2RuO3, Li3RuO4, Li3NbO4, Li5FeO4, Li5MnO4 and their derivatives are of interest for high-capacity battery electrodes. Here, we report a first-principles density-functional theory study of the atomic and electronic structure of these materials using the Heyd-Scuseria-Ernzerhof (HSE) screened hybrid functional which treats all orbitals in the materials on equal footing. Dimerization of the transition-metal ions is found to occur in layered Li2MoO3, in both fully lithiated and partially delithiated compounds. The Ru-Ru dimerization does not occur in fully lithiated Li2RuO3, in contrast to what is commonly believed; Ru-Ru dimers are, however, found to occur in the presence of neutral lithium vacancies caused by lithium loss during synthesis and/or lithium removal during use. We also analyze the electronic structure of the complex oxides and discuss the delithiation mechanism in these battery electrode materials.

High-Temperature Studies of the Structure of Complex Oxides Based on Bi26Mo10O69–d

Complex oxides with the general formula Bi26–2xMe2x′ Mo10O69–d, Bi26Mo10–2yMe2y′′ O69–d are synthesized by the standard ceramic technology, certified and analyzed by high-temperature X-ray and neutron diffraction techniques. Specific features of the structures of triclinic and monoclinic modifications of complex oxides are determined. It helps interpret a change in the electroconductive properties of the samples as a result of a polymorphic transition: in the monoclinic modification [MoO4–O–MoO4] clusters are detected together with a doubled amount of [(MoO4)–Bi(MoO4)–]n chains oriented along the b axis, which may affect the character of oxygen ion transfer. For Fe-substituted samples selective iron substitution for molybdenum is revealed.

Oxidation behaviour of Nimonic 263 in high-temperature supercritical water

ABSTRACTThe oxidation tests of the Nimonic 263 alloy exposed to deaerated supercritical water at 600–700°C under 25 MPa were carried out for up to 1000 h. Oxidation rate increased with an increase in temperature. The microstructure and phase composition of oxide scale were analysed by scanning electron microscopy/energy dispersive X-ray spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy. It can be seen that a complex oxide structure formed on the surface of Nimonic 263 including an outer layer of Ni–Fe/Ni–Cr spinel oxide, Ni/Co hydroxide and TiO2 and an inner layer of a mixture of NiCr2O4 and Cr2O3 while the innermost layer is made up of Cr2O3. The MoO3 can be observed at 600°C but disappeared with the increasing temperature. The growth mechanism of oxide scale was discussed.

Phase equilibria, structure and properties of complex oxides in the NdFeO3 − δ – SrFeO3 − δ – SrCoO3 − δ – NdCoO3 − δ system as potential cathodes for SOFCs

The phase equilibria in the NdFeO3−δ – SrFeO3−δ – SrCoO3−δ – NdCoO3−δ system were studied at 1373K in air. The homogeneity ranges and crystal structure of Nd1−xSrxFe1−yCoyO3−δ solid solutions were determined by the X-ray powder diffraction, the unit cell parameters were refined by the Rietveld analysis. It was found that Nd1−xSrxFe1−yCoyO3−δ with 0.0≤x≤0.6 and 0.1≤y≤0.9 possesses orthorhombic structure (sp. gr. Pbnm) that reveals O-type→O′-type→O-type structural transition. The orthorhombic distortion decreases with the increasing of strontium content, as a result Nd1−xSrxFe1−yCoyO3−δ solid solutions with 0.7≤x≤0.9 and 0.1≤y≤0.9 possess the cubic structure (sp. gr. Pm3m). Isothermal-isobaric phase diagram for the NdFeO3−δ – SrFeO3−δ – SrCoO3−δ – NdCoO3−δ system at 1373K in air has been presented. A series of samples with the overall composition Nd0.2Sr0.8Fe1−yCoyO3−δ (0.0≤y≤1.0) were characterized by the thermogravimetric analysis, iodometric titration, dilatometry and electrical conductivity measurements. The oxygen nonstoichiometry in Nd0.2Sr0.8Fe1−yCoyO3−δ (0.0≤y≤1.0) increases with increasing temperature and cobalt content. Gradual substitution of iron by cobalt in the Nd0.2Sr0.8Fe1−yCoyO3−δ oxides leads to the increase of the average thermal expansion coefficients. The electrical conductivity exhibits maximum within the range of 600–750K and significantly increased with cobalt content at T<800K. Chemical compatibility of Nd0.2Sr0.8Fe1−yCoyO3−δ with Ce0.8Sm0.2O2−δ and La0.88Sr0.12Ga0.82Mg0.12O3−δ solid electrolytes has been studied. The single cells based on the LSGM electrolyte, Sr2Ni0.75Mg0.25MoO6 anode and Nd0.2Sr0.8Fe1−yCoyO3−δ (y=0.3 and 1.0) cathode were fabricated and examined.

Высокотемпературные исследования структуры сложных оксидов на основе Bi26Mo10O69–d

Высокотемпературные исследования структуры сложных оксидов на основе Bi26Mo10O69–d