Relationship Between Electronic Structures and Capacitive Performance of the Electrode Material IrO2–ZrO2

First‐principles calculations were employed to study the effects of the addition of ZrO₂ on the electrochemical activity and structure of Ir–Zr binary oxide. In the computation model employed, Zr atoms replaced Ir atoms in IrO₂ supercells, so as to form a rutile‐type solid solution of Ir_1?xZr_xO₂ (0 ≤ x ≤ 1). IrO₂–ZrO₂ oxide coatings were prepared on Ti substrates by thermal decomposition. X‐ray diffraction (XRD) analyses, cyclic voltammetry, and galvanostatic charge/discharge tests were performed to investigate the effects of the Zr content on the structure and capacitive performance of the synthesized Ti/IrO₂–ZrO₂ electrodes. As the Zr content was increased, the density of state of Ir_1?xZr_xO₂ moved to a higher energy level, and a forbidden band was formed, which reduced its electronic conductivity. The XRD analyses showed that ZrO₂ restrained the crystallization of IrO₂. Thus, the extent of the amorphous phase increased with the increase in the ZrO₂ content, indicating that the proton conductivity of the binary oxide coating increased with the ZrO₂ content. When the ZrO₂ content was higher than 50 mol%, the IrO₂–ZrO₂ coating exhibited a relatively narrow energy band gap (0.42eV) and a “amorphous/crystalline” structure, as well as the highest charge capability, indicating that its electronic and protonic conductivities had reached an equilibrium. This was in accordance with the sudden variation in the length of the M‐O bond and the change in the bulk modulus.     

The Influence of ZrO2 Additions on Al2O3 Evaporation and AlN Crystal Growth by Thermal Nitridation of Al2O3–ZrO2 Pellets

The effects of ZrO₂ additions to Al₂O₃ were investigated to improve the evaporation rate of Al₂O₃ for bulk AlN crystal growth. The evaporation rate of Al₂O₃ increased concomitantly with increasing ZrO₂ concentration under a nitrogen gas stream at 2223 K. The ZrO₂ was predominantly nitrided. The nitridation of ZrO₂ kept the local oxygen partial pressure high at the pellet surface, which suppressed the nitridation of Al₂O₃. The nitridation of ZrO₂ caused the outward diffusion of ZrO₂ (Zr⁴⁺ and O^2?) in the pellet, which was accelerated further by the presence of Al₂O₃–ZrO₂ liquid phase in grain boundaries, leading to the prompt formation of ZrN porous layer on the pellet surface. The suppressed nitridation of Al₂O₃ and the formation of porous ZrN layer were the reasons for the enhanced evaporation of Al₂O₃, leading to enhanced bulk AlN growth.     

Volcanic Ash‐Induced Decomposition of EB‐PVD Gd2Zr2O7 Thermal Barrier Coatings to Gd‐Oxyapatite,Zircon, and Gd,Fe‐Zirconolite

The resistance of EB‐PVD Gd₂Zr₂O₇ thermal barrier coatings against high‐temperature infiltration and subsequent degradation by molten volcanic ash is investigated by microstructural analysis. At 1200°C, EB‐PVD Gd₂Zr₂O₇ coatings with silica‐rich, artificial volcanic ash (AVA) overlay show a highly dynamic and complex recession scenario. Gd₂O₃ is leached out from Gd₂Zr₂O₇ by AVA and rapidly crystallizes as an oxyapatite‐type solid‐solution (Ca,Gd)₂(Gd,Zr)₈(Si,Al)₆O₂₆. The second product of Gd₂Zr₂O₇ decomposition is Gd₂O₃ fully stabilized ZrO₂ (Gd‐FSZ). Both reaction products are forming an interpenetrating network filling open coating porosity. However, first‐generation Gd‐oxyapatite and Gd‐FSZ are exhibiting chemical evolution in the long term. The chemical composition of Gd‐oxyapatite does evolve from Ca,Zr enriched to Gd‐rich. AVA continuously leaches out Gd₂O₃ from Gd‐FSZ followed by destabilization to the monoclinic ZrO₂ polymorph. Finally, zircon (ZrSiO₄) is formed. In addition to the prevalent formation of Gd‐oxyapatite, a Gd‐, Zr‐, Fe‐, and Ti‐rich oxide is observed. From chemical analysis and electron diffraction it is concluded that this phase belongs to the zirconolite‐type family (zirconolite CaZrTi₂O₇), exhibiting an almost full substitution Ca²⁺ + Ti⁴⁺ <> Gd³⁺ + Fe³⁺. As all Gd₂Zr₂O₇ decomposition products with the exception of ZrSiO₄ exhibit considerable solid solubility ranges, it is difficult to conclusively assess the resistance of EB‐PVD Gd₂Zr₂O₇ coatings versus volcanic ash attack.     

Oxygen‐ion conduction in scandia‐stabilized zirconia‐ceria solid electrolyte (xSc2O3–1CeO2–(99−x)ZrO2, 5 ≤ x ≤ 11)

Solid oxide fuel cells (SOFCs) operating at intermediate temperature (500°C‐700°C) provide advantages of better durability, lower cost, and wider target application market. In this work, we have studied Sc₂O₃ (5‐11 mol%) stabilized ZrO₂–CeO₂ as a potential solid electrolyte for application in IT‐SOFCs. Lower Sc₂O₃ doping range than the traditional 11 mol% Sc₂O₃‐stabilized ZrO₂ is an interesting research topic as it could potentially lead to an electrolyte with reduced oxygen vacancy ordering, lower cost, and higher mechanical strength. XRD and Raman spectroscopy was used to study the phase equilibrium in ZrO₂–CeO₂–Sc₂O₃ system and impedance spectroscopy was done to estimate the grain, grain boundary, and total ionic conductivities. Maximum for the grain and grain‐boundary conductivities as well as the tetragonal‐cubic phase boundary was found at 8‐9 Sc₂O₃ mol% in ZrO₂‐1 mol% CeO₂ system. It is suggested that the addition of 1 mol% CeO₂ in the ZrO₂ host lattice has improved the phase stability of high‐conductivity cubic and tetragonal phases at the expense of low‐conductivity t′‐ and β‐phases.     

Phase evolution mechanism of non‐oxide bonded Al–Al2O3–MgO–ZrO2 composites at 1873 K in flowing nitrogen

In flowing nitrogen, non‐oxides such as Al₄O₄C, Al₂OC, Zr₂Al₃C₄, and MgAlON bonded Al₂O₃‐based composites were successfully prepared by a gaseous phase mass transfer pathway using aluminum, zirconia, alumina, and magnesia as raw materials at 1873 K, after an Al–AlN core‐shell structure was formed at 853 K. Resin bonded Al–Al₂O₃–MgO–ZrO₂ composites after sintering were characterized and analyzed by X‐ray diffraction (XRD), scanning electron microscope (SEM) and, energy dispersive spectrometer (EDS), and the influence of the MgO content on the sintered composites was studied. The results show that after sintering, the phase composition of the Al–Al₂O₃–ZrO₂ composite is Al₂O₃, Al₄O₄C, Al₂OC, and Zr₂Al₃C₄, while the phase composition of the Al–Al₂O₃–ZrO₂ composite with the addition of MgO 6 wt% and MgO 12 wt% is Al₂O₃, MgAlON, Al₄O₄C, Al₂OC, and Zr₂Al₃C₄ as well as Al₂O₃, MgAlON, Al₂OC, and Zr₂Al₃C₄, respectively. The addition of MgO changed the phase composition and distribution for the resin bonded Al–Al₂O₃–MgO–ZrO₂ system composites after sintering. When the added MgO content is equal to or more than 12 wt%, the Al₄O₄C in the resin bonded Al–Al₂O₃–MgO–ZrO₂ system composites is unable to exist in a stable phase.     

Catalytic Effect of CeO2‐Stabilized ZrO2 Ceramics with Strong Shock‐Heated Mono‐ and Di‐Atomic Gases

The reducibility of synthesized ceria‐stabilized zirconia (CSZ) with strong shock‐heated test gases is investigated. Free piston‐driven shock tube operating at hypersonic speed at Mach number of 6–8 has been used to heat the ultrahigh pure test gases like Ar to ~12800 K, N₂ to ~7960 K, and O₂ to ~5500 K at a medium reflected shock pressure (5.0–7.4 MPa) for a short duration of 1–2 ms test time. Under this extreme thermodynamic condition, test gases undergo real gas effects. The structural and spectroscopic investigations of CSZ (Ce₂Zr₂O₈) after interaction with shock‐heated argon gas show pyrochlore structure of Ce₂Zr₂O_7?δ which is observed to be black in color. In presence of shock‐heated N₂ gas, CSZ remains in fluorite structure by changing its color to pale green as nitrogen atoms fill oxygen vacancies. After O₂ interaction with the shock wave, CSZ remains pale yellow but the X‐ray diffraction pattern shows the presence of monoclinic ZrO₂ due to phase separation. During reduction process, Ce⁴⁺ has been reduced to Ce³⁺ which is an unusual effect. In this study, the catalytic and surface recombination effects of CSZ due to shock‐induced compression in millisecond timescale are presented.     

Phase composition of TiO2-coated ZrO2/Si3N4 composite

The effect of TiO₂ coating on the phase composition of ZrO₂/Si₃N₄ composites was investigated both with pressureless-sintered samples and with hot-pressed ones. The formation of ZrN could be suppressed by increasing in the amount of TiO₂ coated on 3Y–ZrO₂. However, the existence of TiO₂ did little to accelerate the transformation of α- to β-Si₃N₄. When combined with small addition of Y₂O₃, the formation of ZrN could be further suppressed and the α to β-Si₃N₄ transformation could also be improved. The compositional variation of TiN grains with a rise in temperature was analyzed by using TEM and EDS. There was some solubility of zirconium ion into the TiN lattice. It increased with sintering temperature and caused the XRD peaks of TiN towards lower angles. ©     

Phase Structure Evolution and Thermo‐Physical Properties of Nonstoichiometry Nd2−xZr2+xO7+x/2 Pyrochlore Ceramics

Nonstoichiometry pyrochlore composites of Nd_2?xZr_2+xO_7+x/2 (x = 0, 0.1, 0.2) were synthesized by chemical‐coprecipitation and calcination method. The phase structure evolution and thermo‐physical properties of Nd_2?xZr_2+xO_7+x/2 were investigated. Structural analysis by Raman spectroscopy showed that Nd_2?xZr_2+xO_7+x/2 underwent an ordering degree decrease and a lattice distortion increase with increasing x value. Nd_1.9Zr_2.1O_7.05 and Nd_1.8Zr_2.2O_7.1 exhibited lower thermal conductivities than Nd₂Zr₂O₇, which might be related to the lower ordering degree and the enhanced phonon scattering due to lattice distortion. As ZrO₂ content increasing, the thermal expansion coefficients of Nd_2?xZr_2+xO_7+x/2 increased, which possibly arised from the decreased crystal energy due to reduced ordering degree.     

Densification and Thermal Stability of Hot‐Pressed Si3N4–ZrB2 Ceramics

Densification and thermal stability of hot‐pressed Si₃N₄–ZrB₂ ceramics with and without additives were investigated in N₂ atmosphere. The addition of MgO–Yb₂O₃, MgO–Y₂O₃, and Al₂O₃–Yb₂O₃ resulted in significant increase in relative density of the ceramics hot‐pressed at 1500°C from 48.5% to 98.0%, 97.3%, and 95.6%, respectively. There was weak reaction of ZrB₂ with N₂ to form ZrN in hot‐pressed ceramics. Then heat treatment at 1550°C resulted in the further reactions to produce ZrN, ZrSi₂, and BN. The Si₃N₄–ZrB₂ ceramics with MgO–Yb₂O₃ showed much better thermal stability as compared to the ceramics with Al₂O₃–Yb₂O₃. The small difference in density led to the obvious difference in thermal stability. Therefore, Si₃N₄–ZrB₂ ceramics should be densified to full density, to obtain high thermal stability.     

Preparation,Structural Characterization,and Enhanced Electrical Conductivity of Pyrochlore‐type (Sm1–xEux)2Zr2O7 Ceramics

(Sm_1–xEu_x)₂Zr₂O₇ (0 ≤ x ≤ 1.0) samples are prepared by solid state reaction method using Sm₂O₃, Eu₂O₃, and ZrO₂ as starting materials. The phase composition and microstructure of (Sm_1–xEu_x)₂Zr₂O₇ ceramics are investigated by X‐ray diffraction (XRD), scanning electron microscopy, high‐resolution transmission electron microscopy (HRTEM) coupled with selected area electron diffraction and Raman spectroscopy. XRD and TEM show that all the samples exhibit a single pyrochlore‐type structure. HRTEM observation indicates that the whole grain interior of Sm₂Zr₂O₇ ceramic is a perfect crystal free of any dislocation. Raman spectroscopy reveals that the degree of structural disorder of (Sm_1–xEu_x)₂Zr₂O₇ ceramics increases gradually with increasing Eu content. The electrical conductivity of (Sm_1–xEu_x)₂Zr₂O₇ ceramics is investigated by impedance spectroscopy in the air and hydrogen atmospheres, respectively. The electrical conductivity of (Sm_1–xEu_x)₂Zr₂O₇ ceramics increases with increasing Eu content at identical temperature levels. Both the activation energy E_g and the pre‐exponential factor σ_0g for the grain conductivity gradually increase with increasing Eu content. As the ionic conductivity shows no obvious change in both air and hydrogen atmospheres, the conduction of (Sm_1–xEu_x)₂Zr₂O₇ is purely ionic with negligible electronic conduction.     

Fabrication of pressureless sintered dense β-SiAlON via a reaction-bonding route with ZrO2 addition

A reaction-bonding and post-sintering process was applied to fabricate pressureless sintered β-Si_6?ZAl_ZO_ZN_8?Z (Z = 1–3) ceramics with monoclinic ZrO₂ added to the starting powder. Samples with ZrO₂ showed enhanced nitridation and achieved near theoretical density following post-sintering, although this could not be achieved in the samples produced without ZrO₂. Thus the ZrO₂ is effective in both enhancing the nitridation of Si and as a sintering additive for densification of β-SiAlON. Part of the added monoclinic ZrO₂ was transformed to tetragonal ZrO₂, and the ZrN phase was also formed due to reaction with nitrogen during the reaction-bonding process. After the post-sintering process, the ZrN phase remained only in the Z = 3 composition. In the other compositions the ZrN reacted with SiO₂ to form both tetragonal and monoclinic ZrO₂ phases. These differences are explained in terms of the increasing densification and grain growth for Al₂O₃ rich compositions and the ZrN being trapped inside such grains in the case of the Z = 3 sample.     

Transient and steady states of Gd2Zr2O7 and 2ZrO2∙Y2O3 (ss) interactions with calcium magnesium aluminium silicates

Reactions between calcium magnesium aluminium silicates (CMAS) and Gd₂Zr₂O₇ or 2ZrO₂?Y₂O₃ (ss) are investigated within a temperature range of 1200–1300 °C and for durations of 1 h–100 h. The evolution of CMAS penetration depth in Gd₂Zr₂O₇ and 2ZrO₂?Y₂O₃ (ss) pellets varies considerably depending on the interaction time. A quantitative analysis of the nature and composition of phases observed in stationary conditions (powder/powder interaction) is performed by SEM-FEG coupled with WDS analyses using micro-agglomerated nanoparticles of Gd₂Zr₂O₇ and 2ZrO₂?Y₂O₃. Faster kinetics of the gadolinium-based system are illustrated through an analysis of the morphology of the reaction area and of the resulting CMAS tightness of reaction products. The compositions and quantities of reaction products observed at equilibrium are very similar for the two systems, but transient states are significantly different.     

Evaluation of Rare‐Earth Modified ZrB2–SiC Ablation Resistance Using an Oxyacetylene Torch

Rare‐earth modified ZrB₂–SiC coatings were prepared via mechanical mixing Sm₂O₃ or Tm₂O₃ powders with spray‐dried ZrB₂, or by chemically doping samarium ions into spray‐dried ZrB₂. In either approach, SiC powders were also added and coatings were fabricated via shrouded air plasma spray. An oxyacetylene torch was utilized to evaluate the coatings under high heat flux conditions for hold times of 30 and 60 s. The resulting phases and microstructures were evaluated as a function of rare‐earth type, modification approach, and ablation time. A brittle m‐ZrO₂ scale was observed in the ZrB₂/SiC‐only coating after ablative tests; during cooling this scale detached from the unreacted coating. In contrast, rare‐earth modified coatings formed a protective oxide scale consisting primarily of either Sm_0.2Zr_0.8O_1.9 or Tm_0.2Zr_0.8O_1.9, along with small amount of m‐ZrO₂. These rare‐earth oxide scales displayed high thermal stability and remained adhered to the unreacted coating during heating and cooling, offering additional oxidation protection.     

Synthesis of nickel catalysts supported on Zr-doped ordered mesoporous Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and their catalytic performance for low-temperature CO<Subscript>2</Subscript> reforming of CH<Subscript>4</Subscript>

A series of Zr-doped ordered mesoporous Al₂O₃ with various Zr contents were synthesized by evaporation-induced self-assembly strategy and the Ni-based catalysts supported on these Al₂O₃ materials were prepared by impregnation method. These catalysts with large specific surface area, big pore volume, uniform pore size possess excellent catalytic performance for the low-temperature carbon dioxide reforming of methane. The activities of these catalysts were tested in carbon dioxide reforming of methane reaction with temperature increasing from 500 to 650?°C and the stabilities of these catalysts were evaluated for long time reaction at 650?°C. It was found that when Zr/(Zr?+?Al) molar ratio?=?0.5%, the Ni/0.5ZrO₂–Al₂O₃ catalyst showed the highest activity, and exhibited superior stabilization compared to the Ni-based catalyst supported on traditional ordered mesoporous Al₂O₃. The “confinement effect” from mesoporous channels of alumina matrix is helpful to stabilize the Ni nanoparticles. As a promoter, Zr could stabilize the ordered mesoporous framework by reacting with Al₂O₃ to form ZrO₂–Al₂O₃ solid solution. Since ZrO₂ enhances the dissociation of carbon dioxide, more oxygen intermediates are given to remove the carbon formed during the reaction.     

In Situ Diffraction from Levitated Solids Under Extreme Conditions—Structure and Thermal Expansion in the Eu2O3–ZrO2 System

The accurate determination of structure and thermal expansion of refractory materials at temperatures above 1500°C is challenging. Here, for the first time, we demonstrate the ability to reliably refine the structure and thermal expansion coefficient of oxides at temperatures to 2200°C using in situ synchrotron diffraction coupled with aerodynamic levitation. Solid solutions in the Eu₂O₃–ZrO₂ binary system were investigated, including the high‐temperature order–disorder transformation in Eu₂Zr₂O₇. The disordered fluorite phase is found to be stable above 1900°C, and a reversible phase transition to the pyrochlore phase is noticed during cooling. Site occupancies in Eu₂Zr₂O₇ show a gradual increase in disorder on both cation and anion sublattices with increasing temperature. The thermal expansion coefficients of all cubic solid solutions are relatively similar, falling in the range 8.6–12.0 × 10^?6 C^?1. These studies open new vistas for in situ exploration of complex structural changes in high‐temperature materials.     

High lithium ionic conductivity in the garnet‐type oxide Li7−2xLa3Zr2−xMoxO12 (x=0‐0.3) ceramics by sol‐gel method

Lithium garnet‐type oxides Li_7?2xLa₃Zr_2?xMo_xO₁₂ (x=0, 0.1, 0.2, 0.3) ceramics were prepared by a sol‐gel method. The influence of molybdenum on the structure, microstructure and conductivity of Li₇La₃Zr₂O₁₂ were investigated by X‐ray diffraction, scanning electron microscopy, and impedance spectroscopy. The cubic phase Li₇La₃Zr₂O₁₂ has been stabilized by partial substitution of Mo for Zr at low temperature. The introduction of Mo (x≥0.1) can accelerate densification. Li_6.6La₃Zr_1.8Mo_0.2O₁₂ sintered at lower temperature 1100°C for 3 hours exhibits highest total ionic conductivity of 5.09 × 10^?4 S/cm. Results indicate that the Mo doping LLZO synthesized by sol‐gel method effectively lowers its sintering temperature and improves the ionic conductivity.     

Production of Al2O3‐Stabilized Tetragonal ZrO2 Nanoparticles for Thermal Barrier Coating

Al₂O₃‐stabilized tetragonal ZrO₂ nanoparticles were obtained through hot‐air spray pyrolysis and characterized after postsynthesized treatments. The produced nanoparticles were 26 nm in size with surface area of 59 m²/g. A multilayer thermal barrier coating of nanostructured Al₂O₃‐ZrO₂‐embedded silicate was applied to the mild steel (EN3) specimen using spin‐coating technique and characterized comprehensively employing X‐ray diffraction and scanning electron microscope. The Al₂O₃‐stabilized ZrO₂ with silicate matrix facilitates the formation of zirconium silicate nanostructured surface‐protective coating on EN3 specimen. The Al₂O₃‐ZrO₂/SiO₂ matrix‐based hybrid inorganic coating shows effective thermal barrier for EN3 after firing at a high temperature of 600°C.     

ZrB2–ZrCxN1−x Eutectic Composites Produced by Melt Solidification

Ceramic eutectics are naturally occurring in‐situ composites and can offer superior mechanical properties. Here, ZrB₂–ZrC_xN_1?x quasi‐binary ceramic eutectic composites were produced by arc‐melting a mixture of ZrB₂, ZrC, and ZrN powders in an N₂ atmosphere. The arc‐melted ZrB₂–ZrC_xN_1?x composites containing 50 mol% of ZrB₂ (irrespective of the ZrC/ZrN ratio) showed rod‐like eutectic structures, where ZrC_xN_1?x single‐crystalline rods were dispersed in the ZrB₂ single‐crystalline matrices. Multiple orientation relationships between the ZrC_xN_1?x rods and the ZrB₂ matrices were observed, and one was determined as ZrB₂ {} //Zr_xN_1?x {111} and ZrB₂ < > //ZrC_xN_1?x < > . The rod‐like eutectic composites had higher hardness than the hypo‐ and hypereutectic composites and the 50ZrB₂–40ZrC–10ZrN (mol%) eutectic composite showed the highest Vickers hardness (H_v) of 19 GPa.     

Synthese und Charakterisierung von O2S2 — und N2S2‐Übergangsmetallkomplexen ausgehend von β‐Chlor) β‐trifluormethylvinylaldehyden

Synthesis and Characterization of O₂S₂ — and N₂S₂‐Transition Metal Complexes Starting from β‐Chloro‐β‐trifluoromethyl Vinylaldehydes The syntheses of complexes 4 and 5 with O₂S₂ ‐and N₂S₂ — donor atom sets are described as one‐step procedures. Their structures were confirmed by NMR, IR, UV‐ VIS and MS spectroscopy. One nickel complex 5a was determined by X‐ray structure analysis whereas the Cu^II complexes were studied by EPR spectroscopy.