O3 Phase Research Articles

Exploring Li Substituted O3-Structured Layered Oxides As Promising Cathode Materials for Rechargeable Na Batteries

Na-ion batteries have recently gained increasing recognition as intriguing candidates for next-generation large scale energy storage systems, owing to significant cost advantages stemming from the high natural abundance and broad distribution of Na resources. Although in terms of absolute energy density, Na-ion battery materials are not comparable with their Li-ion counterparts which are one of the dominating energy technologies in this decade. In particular, Na-ion batteries operating at room temperature could be suitable for applications where specific volumetric and gravimetric energy density requirements are not as stringent as in EVs, namely in electrical grid storage of intermittent energy produced via renewable sources.1 This would also contribute to a significant reduction of the costs connected to the use of renewable sources, which could then penetrate the energy market more easily and make Na-ion technology complementary to Li-ion batteries for stationary storage.2-4 A new O3 - Na0.78Li0.18Ni0.25Mn0.583Ow is obtained by the electrochemical Na-Li ion exchange process of Li1.167Ni0.25Mn0.583O2. The new material shows exceptionally high discharge capacity of 240 mAh g-1 in the voltage range of 1.5-4.5 V, (Fig. 1) thus the total energy density at the materials level reaches 675 Wh kg-1. When cycled between 1.5-4.2 V, the discharge capacity is well maintained around 190 mAh g-1 after 30 cycles. The O3 phase is kept through ion-exchange and cycling process, as confirmed by SXRD (Fig. 2). The stabilized O3 phase could be related to the tetrahedral Li formed upon initial lithiation, and breaks through the critical limitation for most of the O3 compounds. XAS results show that Ni2+/Ni4+ is the main active redox couple during cycling while Mn ions basically stay at tetravalent state. The Na full cell utilizing Na0.78Li0.18Ni0.25Mn0.583Ow as cathode delivers 430 Wh kg-1energy density. Later, the new Li substituted Na layered oxide with pure O3 phase is successfully synthesized by hydroxide co-precipitation method. It demonstrates a considerably high reversible capacity, and excellent rate performance. The phase is stabilized throughout the cycling, which could be the main reason for its good electrochemical properties. Ni2+/Ni4+ is the main active redox couple during cycling, and Co3+/Co4+partially contributes to the charge compensation while Mn ions basically stay at tetravalent state. The findings would contribute to the future improvement and design of practical cathode materials for Na-ion batteries. Fig. 1: (a) Electrochemical profiles of initial delithiation and initial sodiation for Na0.78Li0.18Ni0.25Mn0.583Ow in half cell. (b) Cycling performance for Na0.78Li0.18Ni0.25Mn0.583Ow with 125 mA g-1 current density. Inset is the corresponding electrochemical profile of Na0.78Li0.18Ni0.25Mn0.583Ow during the 1st, 2nd, 10th, 20th, 30th cycles in Na-ion batteries.5 Fig. 2: (a) Ex situ SXRD for Li1.167Ni0.25Mn0.583O2 and Na0.78Li0.18Ni0.25Mn0.583Ow at different states. (b) Schematic of the typical O3 structure. (c) Schematic of the proposed mechanism for sodiation. (In the schematic, transition metal ions are blue, Li+ is red, and Na+ is green.)5 Acknowledgements J. Xu and Y.S.Meng are grateful for the seed funding support from the Northeastern Center for Chemical Energy Storage, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Basic Energy Sciences, with Award Number DE-SC0012583. The follow up work have been carried out by H. Liu and C. M with other private funding source. H. Liu acknowledges the financial support from China Scholarship Council under Award Number 2011631005. The authors appreciate the kind assistance from Dr Baihua Qu for anode SnS2/rGO synthesis at National University of Singapore (NUS). The XAS and SXRD were collected on 20-BM-B and 11-BM respectively at Advanced Photon Source in Argonne National Laboratory. Reference 1. B. L. Ellis and L. F. Nazar, Current Opinion in Solid State & Materials Science, 2012, 16, 168-177. 2. H. L. Pan, Y. S. Hu and L. Q. Chen, Energy & Environmental Science, 2013, 6, 2338-2360. 3. V. Palomares, M. Casas-Cabanas, E. Castillo-Martinez, M. H. Han and T. Rojo, Energy & Environmental Science, 2013, 6, 2312-2337. 4. M. Valvo, F. Lindgren, U. Lafont, F. Bjorefors and K. Edstrom, Journal of Power Sources, 2014, 245, 967-978. 5. H. D. Liu, J. Xu, C. Z. Ma and Y. S. Meng, Chem Commun, 2015, 51, 4693-4696. Figure 1

Crystalline structure, thermal expansion, and electrotransport properties of Bi0.91Ln0.09FeO3, BiFe0.91Mn0.09O3, and Bi0.91Ln0.09Fe0.91Mn0.09O3 (Ln = Nd, Ho) multiferroics

Bi0.91Ln0.09FeO3, BiFe0.91Mn0.09O3 and Bi0.91Ln0.09Fe0.91Mn0.09O3 (Ln = Nd, Ho) solid solutions have been synthesized, the parameters of their crystalline structure have been determined, and thermal expansion, electrical conductivity and thermal EMF have been studied at temperatures higher than the ambient temperature. It has been established that the solid solutions have a rhombohedral structure (space group R3c) and are semiconductors of the p-type, whose electrical conductivity is higher than that of nonsubstituted bismuth ferrite BiFeO3, the coefficient of thermal EMF sharply decreases at the partial substitution of iron with manganese, and the coefficient of linear thermal expansion varies in the ranges of (9.22–13.4) × 10–6 K–1. The parameters of charge carriers transfer in the (Bi,Ln)(Fe,Mn)O3 (Ln = Nd, Ho) phases have been determined.

Effect of ZnO Addition on Dielectric and Piezoelectric Properties of (Ba0.85Ca0.15)(Ti0.915Zr0.085)O3 Ceramics

Lead-free (Ba0.85Ca0.15)(Ti0.915Zr0.085)O3 + x wt%ZnO piezoelectric ceramics were synthesized using a conventional solid state sintering method and the effect of ZnO addition on their piezoelectric and dielectric properties was investigated. The X-ray diffraction date exhibited that ZnO diffuses into the lattice of (Ba0.85Ca0.15)(Ti0.915Zr0.085)O3 (abbreviated as BCTZ) and pure perovskite structure phase was formed at all the specimens, And no secondary phases are observed in the measurement range of XRD. In addition, all the specimens showed tetragonal phase structure. The Curie temperature of BCTZ ceramics decreases with increasing the ZnO content. At the 0.2 wt% ZnO added (Ba0.85Ca0.15)(Ti0.915Zr0.085)O3 ceramics sintered at 1360°C, the optimized piezoelectric properties were obtained; piezoelectric constant(d33) = 348 [pC/N], dielectric constant(ϵr) = 3263, mechanical quality factor(Qm) = 267, electromechanical coupling factor(kp) = 0.41, respectively.

On the Origin of the Improvement of Electrodeposited MnOx Films in Water Oxidation Catalysis Induced by Heat Treatment.

Manganese oxides (MnOx ) are considered to be promising catalysts for water oxidation. Building on our previous studies showing that the catalytic activity of MnOx films electrodeposited from aqueous electrolytes is improved by a simple heat treatment, we have explored the origin of the catalytic enhancement at an electronic level by X-ray absorption spectroscopy (XAS). The Mn L-edge XA spectra measured at various heating stages were fitted by linear combinations of the spectra of the well-defined manganese oxides-MnO, Mn3 O4 , Mn2 O3 , MnO2 and birnessite. This analysis identified two major manganese oxides, Mn3 O4 and birnessite, that constitute 97 % of the MnOx films. Moreover, the catalytic improvement on heat treatment at 90 °C is related to the conversion of a small amount of birnessite to the Mn3 O4 phase, accompanied by an irreversible dehydration process. Further dehydration at higher temperature (120 °C), however, leads to a poorer catalytic performance.

Lithium-Ion solid electrolytes Li8La3Zr2–0.75x Al x O12.5 and Li9La3Zr2–0.75x Al x O13

New solid lithium-conducting electrolytes of nominal composition Li8La3Zr2–0.75xAlxO12.5 and Li9La3Zr2–0.75xAlxO13 (x = 0.05–0.30) were obtained. It is shown that the superionic cubic phase can be stabilized for compositions with x > 0.5 by annealing at 1150°C. The electrical conductivity of the electrolytes under study grows with increasing content of Al3+ and reaches the maximum value of 5.9 × 10–5 S cm–1 (at (25°C) at the point x = 0.20 for the Li8La3Zr2–0.75xAlxO12 system and 2.2 × 10–5 S cm–1 at the point x = 0.15 for the Li9La3Zr2–0.75xAlxO13 system. No further rise in the conductivity is observed with increasing x because of the formation of the LaAlO3 and La2Li0.5Al0.5O4 phases. The activation energy of conductivity is approximately constant for all compositions with stabilized cubic structure and is close to 35.8 ± 0.7 kJ mol–1 (Li8La3Zr1.85Al0.20O12.5 composition). The smaller values of the conductivity, compared with the Li7La3Zr2–0.75xAlxO12, are due to the filling of vacant lithium sites in the structure of the cubic LLZ and, accordingly, to the blocking of conduction paths.

High frequency reciprocating sliding wear behavior and mechanisms of quaternary metal oxide coatings

Wear resistant coatings based on quaternary metal oxides were studied with comparisons made to more traditional ternary metal oxides. While much is known about ternary metal oxide wear behavior and mechanisms from room to higher temperatures, little is known about quaternary oxides; for instance, the role of the fourth element in determining the coating crystalline state and defect structure and how they control tribological properties. To this end, the system (ZnTiZr)xOy was deposited by atomic layer deposition (ALD) and compared to previously studied wear resistant nanocrystalline ALD ZnTiO3 coatings. X-ray diffraction determined that both as-deposited and ex situ 550°C annealed ternary and quaternary coatings exhibit ZnTiO3 phase or solid solution Zn(Ti,Zr)O3 phase only, respectively. However, the coatings have completely different growth structures where the ternary ZnTiO3 coatings exhibit textured (104) nanocolumnar grains and the quaternary Zn(Ti,Zr)O3 coatings are predominantly amorphous with some nanocrystalline grains. High frequency reciprocating sliding on these coatings revealed that the growth structure did not influence the wear rate (~1×10−6mm3/Nm). However, the crystal structure-dependent deformation mechanisms were different as revealed by FIB–SEM and HRTEM analyses inside worn surfaces. It was determined that both coatings show surface deformation due to ductile layering/smearing with no evidence of brittle fracture. Wear reduction of the ZnTiO3 coating was due to nanoscale sliding-induced plastic deformation when (104) stacking faults were sheared along the sliding direction resulting in an intrafilm shear velocity accommodation mode. Conversely, wear reduction in the quaternary Zn(Ti,Zr)O3 coating was a result of a tribofilm/mechanically mixed layer, composed of amorphous transferred silica from the sliding Si3N4 counterface and refined nanocrystalline Zn(Ti,Zr)O3 grains from the coating. Both wear surfaces contained solid cylindrical rolls or roll-ups often found in ceramic–ceramic reciprocating sliding. New insights revealed that the rolls originate in the tribofilm, with similar composition and structure, and evolve to the surface with continued sliding.

Electrochemical Performance of a Layered-Spinel Integrated Li[Ni1/3Mn2/3]O2 as a High Capacity Cathode Material for Li-Ion Batteries

Li[Ni1/3Mn2/3]O2 was synthesized by a self-combustion reaction (SCR), characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Raman spectroscopy, and studied as a cathode material for Li-ion batteries at 30 °C and 45 °C. The structural studies by XRD and TEM confirmed monoclinic Li[Li1/3Mn2/3]O2 phase as the major component, and rhombohedral (LiNiO2), spinel (LiNi0.5Mn1.5O4), and rock salt Li0.2Mn0.2Ni0.5O as minor components. The content of the spinel phase increases upon cycling due to the layered-to-spinel phase transition occurring at high potentials. A high discharge capacity of about 220 mAh g–1 is obtained at low rate (C/10) with good capacity retention upon cycling. However, LiNi0.5Mn1.5O4 synthesized by SCR exhibits a discharge capacity of about 190 mAh g–1 in the potential range of 2.4–4.9 V, which decreases to a value of 150 mAh g–1 after 100 cycles. Because of the presence of the spinel component, Li[Ni1/3Mn2/3]O2 cathode materi...

Microwave dielectric properties of (1 − x)Mg(Sn0.05Ti0.95)O3–x(Ca0.8Sr0.2)TiO3–y wt% ZnNb2O6 ceramics with near-zero temperature coefficient

The microstructures and the microwave dielectric properties of (1 − x)Mg(Sn0.05Ti0.95)O3–x(Ca0.8Sr0.2)TiO3−y wt% ZnNb2O6 (x = 0.05–0.08, y = 2–8) ceramics system prepared by conventional solid-state route were investigated. The crystalline phases and the microstructures of the ceramics were characterized by means of X-ray diffraction and scanning electron microscopy. Zn2+ partially replaced Mg2+ in Mg(Sn0.05Ti0.95)O3 and formed the ilmenite-type (Mg1−δZnδ)(Sn0.05Ti0.95)O3 phase. Second phase (Mg1−δZnδ)(Sn0.05Ti0.95)2O5 increased remarkably when excess ZnNb2O6 added. ZnNb2O6 as additives could not only effectively lower the sintering temperature of the ceramics to 1320 °C, but also promote the densification. The microwave dielectric properties of specimens were strongly related to ZnNb2O6 and (Ca0.8Sr0.2)TiO3 content. The optimized microwave dielectric properties with e r ~ 22.13, Q × f value ~60,613(at 7 GHz) and τ f value ~0.4 ppm/ °C were achieved for (1 − x)Mg(Sn0.05Ti0.95)O3–x(Ca0.8Sr0.2)TiO3–y wt% ZnNb2O6 (x = 0.07, y = 4) sintered at 1320 °C for 2 h.

Structure and Properties of the Bi<sub>0.85</sub>Nd<sub>0.15</sub>FeO<sub>3</sub>, BiFe<sub>0.85</sub>Mn<sub>0.15</sub>O<sub>3</sub>, and Bi<sub>0.85</sub>Nd<sub>0.15</sub>Fe<sub>0.85</sub>Mn<sub>0.15</sub>O<sub>3</sub> Multiferroics Solid Solutions

The Bi0.85Nd0.15FeO3, BiFe0.85Mn0.15O3, and Bi0.85Nd0.15Fe0.85Mn0.15O3 ferrites solid solutions were synthesized and their crystal structure, magnetic susceptibility, thermal expansion, electrical conductivity, thermo-EMF and dielectric properties were studied. It was found that Bi0.85Nd0.15FeO3 and BiFe0.85Mn0.15O3 had rhombohedral structure (space group R3c), but Bi0.85Nd0.15Fe0.85Mn0.15O3 one had orthorhombic structure (space group Pnma) and all the complex oxides studied were the antiferromagnetic semiconductors of p-type, which electrical conductivity values were larger than for unsubstituted bismuth ferrite BiFeO3, Neel temperature and thermo-EMF coefficient sharply decreased at partial substitution of iron by manganese and linear thermal expansion coefficient values varied within (10.0-13.4)·10 - 6 K -1 . The values of charge carriers transfer parameters in (Bi,Nd)(Fe,Mn)O3 phases were calculated.

A study of room-temperature LixMn1.5Ni0.5O4 solid solutions.

Understanding the kinetic implication of solid-solution vs. biphasic reaction pathways is critical for the development of advanced intercalation electrode materials. Yet this has been a long-standing challenge in materials science due to the elusive metastable nature of solid solution phases. The present study reports the synthesis, isolation, and characterization of room-temperature LixMn1.5Ni0.5O4 solid solutions. In situ XRD studies performed on pristine and chemically-delithiated, micron-sized single crystals reveal the thermal behavior of LixMn1.5Ni0.5O4 (0 ≤ x ≤ 1) cathode material consisting of three cubic phases: LiMn1.5Ni0.5O4 (Phase I), Li0.5Mn1.5Ni0.5O4 (Phase II) and Mn1.5Ni0.5O4 (Phase III). A phase diagram capturing the structural changes as functions of both temperature and Li content was established. The work not only demonstrates the possibility of synthesizing alternative electrode materials that are metastable in nature, but also enables in-depth evaluation on the physical, electrochemical and kinetic properties of transient intermediate phases and their role in battery electrode performance.

Electrochemical and structural study of layered P2-type Na(2/3)Ni(1/3)Mn(2/3)O2 as cathode material for sodium-ion battery.

P2-type Na(2/3)Ni(1/3)Mn(2/3)O2 was synthesized by a controlled co-precipitation method followed by a high-temperature solid-state reaction and was used as a cathode material for a sodium-ion battery (SIB). The electrochemical behavior of this layered material was studied and an initial discharge capacity of 151.8 mA h g(-1) was achieved in the voltage range of 1.5-3.75 V versus Na(+)/Na. The retained discharge capacity was found to be 123.5 mA h g(-1) after charging/discharging 50 cycles, approximately 81.4% of the initial discharge capacity. In situ X-ray diffraction analysis was used to investigate the sodium insertion and extraction mechanism and clearly revealed the reversible structural changes of the P2-Na(2/3)Ni(1/3)Mn(2/3)O2 and no emergence of the O2-Ni(1/3)Mn(2/3)O2 phase during the cycling test, which is important for designing stable and high-performance SIB cathode materials.

Emergence of novel phase of solid oxygen in ultrahigh magnetic Held

Faraday discovered the magnetism of molecular oxygen in 1850, and since then, oxygen has attracted significant interests as a ubiquitous but exotic molecular magnet. In solid oxygen, the magnetic energy through the exchange interaction is comparable to the van der Waals cohesive energy, resulting in a strong spin-lattice correlation. We reported the discovery of a magnetic-field-induced phase transition of solid oxygen using ultrahigh magnetic fields up to 186 T. This is the first experiments demonstrating the phase control through the spin by applying a magnetic field. Magneto-optical absorption measurements of the α phase at low temperatures revealed that visible light absorption suddenly ceases and the background transparency dramatically improves above the critical field. The large hysteresis in these data indicates a first-order transition with a relaxation time on the order of microseconds. The results strongly suggest the reconstruction of the O2 molecular geometry by the magnetic field, which causes that the antiferromagnetic phase collapses and the field-induced phase should have an isotropic crystal structure. Since all of the known phases of O2 are induced in high pressure, the discovery of a field-induced phase is noteworthy in the long history of solid O2 studies.

Growth Rate, Microstructure and Phase Composition of Oxide Scales for Three Typical Steels in Simulated Continuous Casting Process

Growth rate, microstructure and phase composition of scale layer formed during oxidation in 56% H2O-9%O2-N2 and following continuous cooling in ambient air were experimentally investigated by means of optical microscopy, scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS) and X-ray diffraction (XRD) for 45, 20CrMnTi and TTS443M steels respectively, to examine the effects of strand surface temperature and steel composition on the scale formation in simulated continuous casting process. The growth rates were found to be approximately parabolic and the calculated activation energy of TTS443M steel is much higher than those of the two other steels. For 45 and 20CrMnTi steels, the scale layers were looser and a distinct gap formed at the scalc-sub-strate interface at higher strand surface temperature. The dominant phases within the scale were iron oxides except for FeO • Cr2 O3 phase simultaneously existing in the oxide scale of 20CrMnTi steel. On the other hand, the scale layer formed on TTS443M steel was compact and tightly attached to the steel surface. At both lower and higher strand surface temperature, iron oxide was main phase in external layer of the scale, while chromia was dominant in inner layer with an appreciable Cr enrichment.

Cobalt-manganese-based spinels as multifunctional materials that unify catalytic water oxidation and oxygen reduction reactions.

Recently, there has been much interest in the design and development of affordable and highly efficient oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) catalysts that can resolve the pivotal issues that concern solar fuels, fuel cells, and rechargeable metal-air batteries. Here we present the synthesis and application of porous CoMn2 O4 and MnCo2 O4 spinel microspheres as highly efficient multifunctional catalysts that unify the electrochemical OER with oxidant-driven and photocatalytic water oxidation as well as the ORR. The porous materials were prepared by the thermal degradation of the respective carbonate precursors at 400 °C. The as-prepared spinels display excellent performances in electrochemical OER for the cubic MnCo2 O4 phase in comparison to the tetragonal CoMn2 O4 material in an alkaline medium. Moreover, the oxidant-driven and photocatalytic water oxidations were performed and they exhibited a similar trend in activity to that of the electrochemical OER. Remarkably, the situation is reversed in ORR catalysis, that is, the oxygen reduction activity and stability of the tetragonal CoMn2 O4 catalyst outperformed that of cubic MnCo2 O4 and rivals that of benchmark Pt catalysts. The superior catalytic performance and the remarkable stability of the unifying materials are attributed to their unique porous and robust microspherical morphology and the intrinsic structural features of the spinels. Moreover, the facile access to these high-performance materials enables a reliable and cost-effective production on a large scale for industrial applications.

A temperature stable microwave dielectric material Ni0.35Zn0.65TiNb2O8

A temperature stable, high quality, low sintering temperature microwave dielectric material Ni0.35Zn0.65TiNb2O8 was investigated for the first time. The compounds were prepared by a conventional mixed-oxide route and sintered at the temperature range of 1,060–1,140 °C. The microstructure and microwave dielectric properties were investigated systematically. The X-ray diffraction results show that the Ni0.35Zn0.65TiNb2O8 ceramics contained two phase: ZnTiNb2O8 phase and Zn0.17Nb0.33Ti0.5O2 phase. With increase in temperature, the amount of ZnTiNb2O8 phase decreased and that of Zn0.17Nb0.33Ti0.5O2 increased. The microwave dielectric properties of Ni0.35Zn0.65TiNb2O8 were mainly affected by the variation of content and crystal structure of each phase. With increasing temperature, the content of Zn0.17Nb0.33Ti0.5O2 phase increased, resulting in the increasing dielectric constant and τ f , and decreasing Qf value. In addition, the dielectric constant increased with increasing bulk density, the Qf value were related to the cell volume of each phase, and the τ f value had correlation with the bond valence of each phase. Outstanding microwave dielectric properties of e = 40.9, Qf = 40,870 GHz, especially near-zero τ f = 0.62 × 10−6/°C were obtained sintered at 1,100 °C for 6 h. With the relatively low sintering temperature and excellent dielectric properties in microwave range, this material is very promising for electronic devices application.

Interplay between the ferromagnetic and ferroelectric phases on the magnetic and impedance analysis of (x)Pb(Zr0.52Ti0.48)O3–(1 − x)CoFe2O4 composites

Magnetoelectric (ME) composites with the composition (x)PbZr0.52Ti0.48O3+(1−x)CoFe2O4 where x=0.0, 0.5 and 1.0 are synthesized by ball milling method. X-ray diffraction (XRD) analysis revealed the presence of both PbZr0.52Ti0.48O3 (PZT) and CoFe2O4 (CFO) pure phases in the PZT–CFO composite. Scanning electron micrographs (SEM) showed distribution of constituent phases throughout the sample. Magnetic hysteresis loop showed ferromagnetic like behaviour of the composite with a coercive field larger than cobalt ferrite. Impedance (Z′ and Z″) and electrical modulus (M′ and M″) spectra suggested two distinct electrical responses which are observed in the temperature range of 300–370K. These contributions are arising due to the coexistence of two relaxation processes: one is attributed to the high resistive (PZT) phase; while the second one is due to the comparatively conductive (CFO) phase in the PZT–CFO composite, respectively. The electrical conduction and dipolar relaxation are dominated by small polaron hopping (SPH) model, whereas the activation energies calculated from SPH model suggested that p-type carriers are responsible for the conduction in the PZT–CFO composite. Furthermore, ion hopping and conduction mechanism are discussed using an ac conductivity analysis.

Effects of Nd on the properties of CeO2–ZrO2 and catalytic activities of three-way catalysts with low Pt and Rh

A series of Ce0.35Zr0.65−xNdxO2−x/2 (x=0.05, 0.10, 0.15, 0.20 and 0.25) were prepared, and the combinational effects of Nd and noble metals on the catalytic activities of monolithic cordierite honeycomb catalysts were elucidated. The results showed that the BET surface area and pore volume of CZN3F reach a maximum, 97m2/g and 0.19ml/g, but all aged samples undergo a sharp decline. The CZN2 has more oxygen vacancy and higher oxygen storage capacity (OSC) before and after ageing, but OSC of the samples with high Nd content decreases. All fresh samples have cubic Ce0.40Zr0.60O2 phase with nano-size, but the aged samples with low Nd content still exhibit cubic Ce0.40Zr0.60O2 phase. When Nd content (CZN4A) is 20mol% after ageing at 1000°C, small Ce0.60Nd0.40O1.80 is segregated from CeO2–ZrO2 cubic phase; when the doped Nd increases to 25mol% (CZN5A), the CeO2–ZrO2 cubic phase completely converts into Nd050Zr0.50O1.75 cubic phase with 12.4nm, accompanying a sharp decline of OSC; and O2 pretreatment can change the reductive behavior and H2 consumption of samples because of oxygen absorbed. Noble metals can influence the reduction of Ce0.35Zr0.65−xNdxO2−x/2. Ce0.35Zr0.65−xNdxO2−x/2 shows important differences in the TPR and H2 consumption and can change the dispersion and sintering of noble metals, resulting in different catalytic activities. The light-off temperature (T50%) of catalysts containing CZN2F (C2F) can be as low as 160°C for CO, 211°C for NO and 259°C for C3H8, indicating that appropriate Nd doping is helpful for the improving catalytic activity.

TEM study of microstructural development during heating in a nanolaminated amorphous ZrAlCuFe/crystalline CuCoFeNi composite structure

A nanolaminated amorphous/crystalline composite structure with a mean lamellar thickness of around 10nm was fabricated on a Cu plate. The crystalline phase was a multicomponent non-equilibrium face-centered cubic (fcc) Cu(CoFeNi) solid solution, and the amorphous phase was a Zr-based compound containing Al, Cu, and Fe. The composite’s thermal stability and microstructural transformation was studied over the temperature range of 200–900°C. The lamellae maintained their shape during heating up to 600°C. Transformation of the structure began with separation of the elements inside the crystalline lamellae. In early stages of the transformation, hardening occurred. At 600°C, an interconnected CoFe phase started to appear with an ordered body-centered cubic (bcc) crystal structure. When the temperature was increased further, the nanolaminated structure degraded and the bcc CoFe phase grew. At 750°C, the bcc CoFe phase formed a complex network that surrounded the formerly amorphous regions, and the bcc CoFe phase started transforming to the fcc configuration. The Cu atoms segregated to the grain boundaries of the fcc CoFe(Ni) phase. The amorphous phase gradually crystallized into nanometer-sized polycrystalline grains that were attributed to the Zr(Al)O2 phase. As a result of these transformations, heating at 900°C produced a morphologically complex nanocomposite structure consisting of branched grains of Zr(Al)O2 and fcc CoFe(Ni) with Cu inclusions. When the nanolaminated structure had completely transformed, the layer was softer than it had been in the initial annealing steps, but was still almost five times as hard as the initial Cu plate.

The Al2O3–Zr(Hf)O2–La2O3 Phase Diagrams as a Scientific Basis for Developing New Thermal Barrier Coatings

Comparison of the isothermal sections in similar Al2O3–ZrO2–La2O3 and Al2O3–HfO2–La2O3 systems shows that equilibria between the α-Al2O3, Hf(Zr)O2, La2Zr2O7, La2Hf2O7, and LaAlO3 phases in these systems differ fundamentally. While the ZrO2−LaAlO3 equilibrium is observed in the system with ZrO2, the alternative La2Hf2O7–Al2O3 equilibrium takes place in the system with HfO2. The triangulation in the system with HfO2 changes. This phenomenon is probably due to higher thermodynamic stability of the La2Hf2O7 phase (melting point 2420°C) compared to the similar La2Zr2O7 phase (melting point 2280°C). Other equilibria in both systems are of the same type. Lanthanum hafnate can be directly deposited onto the binding coating without reacting with α-Al2O3 or destroying the thermal barrier coating. Stable performance of the lanthanum hafnate coating is expected.

Platinum uptake and Ba2CePtO6 formation during in situ BaCe(1-x)M(x)O(3-δ) (M = La, In) formation.

We report the formation, structures, temperature-dependent phase transitions, and high-temperature reactivity of the potential proton and oxide ion conductors BaCe(1-x)M(x)O3 (M(3+) = In(3+), La(3+)). The present in situ diffraction studies show oxidative platinum uptake at temperatures as low as 950 °C into BaCeO3, forming the cubic Ba2CePtO6 double perovskite. The transient B-site double perovskite expels platinum at around 1200-1250 °C. Platinum oxidation via BaCeO3 is investigated by in situ powder X-ray and neutron diffraction experiments in various atmospheres. Doped BaCe(1-x)M(x)O3 phases show the formation of Ba2CePtO6 without incorporating the M(3+) dopant. Oxidative platinum uptake is also observed during the synthesis of BaCeO3 on platinum metal. We report the reaction pathway for the low-temperature oxidative formation of Ba2CePtO6 and the subsequent liberation of platinum for the barium cerate system. The findings are supported by ambient-temperature X-ray diffraction, in situ powder X-ray, and powder neutron diffraction as well as XPS.