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In nuclear fusion reactors, the first wall is the name given to the surface which is in direct contact with the plasma. A part of it is the divertor which is a device that removes fusion products from the plasma and impurities that have entered into it from the vessel lining. It is covered with water cooled tiles which have to withstand high temperatures and high heat fluxes. Moreover, resistance to neutron bombardment, low tritium absorption and low hydrogen permeation are additional demands. One materials concept under research is the application of a Reduced Activation Ferritic Martensitic Steel (RAFM) as a structural material with a tungsten protective coating. Since there is a considerable thermal mismatch between, a functional-graded materials concept was proposed.As the formation of undesired intermetallic Fe-W phases as well as oxidation should be avoided, cold gas spraying was chosen as manufacturing process. Two powder blends of EUROFER97 RAFM steel and a fine tungsten powder cut on the one hand and a coarser one on the other hand were tested in different ratios. The coatings were characterized with respect to their porosity and surface structure. Furthermore, the deposition efficiencies for steel and tungsten were determined each. It turned out that the deposition process is a complex mixed situation of bonding and erosion mechanisms as the deposition windows of these very different materials obviously diverge. Thus, a lower working gas temperature and pressure was advantageous in some cases. Unexpectedly, the coarser tungsten powder in general enabled to achieve better results.

Nine commercial and experimental powders from the MgO/Al2O3 system have been investigated in the present project. The composition ranged from MgO/MgAl2O4 composites with more than 70% MgO to an alumina-rich spinel powder (94% Al2O3). The powders were fused and crushed or agglomerated and sintered. The influence of the composition, the manufacturing route as well as the particle size distribution on the microstructure and the phases in the produced coatings have been investigated. For several of the powders, detailed design of experiment plans have been made and properties such as deposition efficiency, hardness and porosity were optimized. With optimized spray conditions coatings have been produced from all powders which were characterized in depth. Here, the results of microstructure, porosity values and thermal cyclic tests will be presented in more detail.

Two types of solid electrolytes have reached technological relevance in the field of sodium batteries: s/s"-aluminas and NaSICON-type materials. Today, significant attention is paid to room-temperature stationary electricity storage technologies and all-solid-state Na batteries used in combination with these solid electrolytes are an emerging research field besides sodium-ion batteries. In comparison, NaSICON materials can be processed at lower sintering temperatures than the s/s"-aluminas and have a similarly attractive ionic conductivity. Since Na2 O-SiO2 -ZrO2 -P2 O5 ceramics offer wider compositional variability, the series Na3 Zr3-x Si2 Px O11.5+x/2 with seven compositions (0≤x≤3) was selected from the quasi-quaternary phase diagram in order to identify the predominant stability region of NaSICON within this series and to explore the full potential of such materials, including the original NaSICON composition of Na3 Zr2 Si2 POl2 as a reference. Several characterization techniques were used for the purpose of better understanding the relationships between processing and properties of the ceramics. X-ray diffraction analysis revealed that the phase region of NaSICON materials is larger than expected. Moreover, new ceramic NaSICON materials were discovered in the system crystallizing with a monoclinic NaSICON structure (space group C2/c). Impedance spectroscopy was utilized to investigate the ionic conductivity, giving clear evidence for a dependence on crystal symmetry. The monoclinic NaSICON structure showed the highest ionic conductivity with an optimum ionic conductivity of 1.22×10-3 at 25 °C for the composition Na3 Zr2 Si2 PO12 . As the degree of P5+ content increases, the total ionic conductivity is initially enhanced until x=1 and then decreases again. Simultaneously, the increasing amount of phosphorus leads a decrease in the sintering temperatures for all samples, which was confirmed by dilatometry measurements. The thermal and microstructural properties of the prepared samples are also evaluated and discussed.

Yttria stabilized zirconia (YSZ) has been for several decades the state of the art material for thermal barrier coating (TBC) applications in gas turbines. Although the material has unique properties, further efficiency improvement by increasing the temperature is limited due to its maximum temperature capability of about 1200°C. Above this temperature the deposited metastable tetragonal (t´) phase undergoes a detrimental phase transformation as well as enhanced sintering. Both processes promote the failure of the coatings at elevated temperatures and this early failure has been frequently observed in gradient tests. In this paper we now experimentally shown for the first time that under typical cycling conditions not the time at elevated temperatures leads to the reduced lifetime but the transient cooling rates. If cooling rates were reduced to 10K/s, TBC systems could be operated in a burner rig at a surface temperature well above 1500°C without showing a lifetime reduction. The explanation of these astonishing findings is given by the evaluation of energy release rate peaks during fast transient cooling in combination with the phase evolution during cooling with the used cooling rates.

The garnet-type Li

Yb-silicate is used as volatilization barrier material in environmental barrier coating applications. In this study, metastable to stable phase transformation in highly amorphous atmospheric plasma sprayed Yb-silicate coating was investigated during post-heat treatment. High-temperature X-ray diffraction (HT-XRD) was used to analyze the phase composition of the coating at elevated temperatures. Three metastable phases (Yb2Si2O7 (P-1), Yb2SiO5 (P21/c), Yb4.67Si3O13 (P63/m)) and two stable phases (Yb2Si2O7 (C2/m), Yb2SiO5 (I2/a)) preferentially crystallized from the amorphous coating starting at 1000 °C. Metastable phases transformed into stable Yb2Si2O7 and Yb2SiO5 at higher temperatures. HT-XRD data were used to estimate the volume expansion in the coating due to the phase transformation and the results were compared to the dilatometry measurements. The estimated expansion from HT-XRD data was larger than the measured expansion in dilatometry. Microstructural investigation revealed crack healing in the coating during the measurements which was associated with the lower expansion measured in dilatometry

Garnet-based all-solid-state batteries (ASBs) with high energy density require composite cathodes with high areal loading and high-capacity cathode active materials. While all ceramic cathodes can typically be manufactured via cosintering, the elevated temperatures necessary for this process pose challenges with respect to material compatibility. High-capacity cathode active materials like Ni-rich LiNixCoyMn1–x–yO2 (NCM) show insufficient material compatibility toward the solid electrolyte Li6.45Al0.05La3Zr1.6Ta0.4O12 (LLZO:Ta) during cosintering, leading to the formation of highly resistive interphases. We investigated this secondary phase formation both experimentally and via density functional theory calculation to get a mechanistic understanding of the cosintering behavior of LLZO:Ta with NCM111 and Ni-rich NCM811. Furthermore, we employed B doping of both NCM materials in order to assess its impact on the cation interchange and subsequent secondary phase formation. While secondary phases were formed for all four NCM materials, their onset temperature, nature, and amount strongly depend on the NCM composition and doping. Surprisingly, Ni-rich NCM811 turned out to be the most promising cathode active material for the combination with garnet-type LLZO:Ta. As proof of concept, fully inorganic, ceramic all-solid-state lithium batteries featuring only a Li-metal anode, an LLZO:Ta separator, and a composite cathode, consisting of LLZO:Ta, Li3BO3, and NCM811, were prepared by conventional sintering. The purely inorganic full cells delivered a high specific areal discharge capacity of 0.7 mA h cm–2 in the initial cycle.

Doping of Ni-rich cathode active materials with boron is a promising way to improve their cycling stability and mitigate their degradation, but it is still not understood how this effect is achieved and where the boron is located. To receive deeper insights into the impact of doping on atomic and microscale properties, B-doped Li[Ni0.8Co0.1Mn0.1]O2 (NCM811) cathode materials were synthesized by a hydroxide coprecipitation as a model compound to verify the presence and location of boron in B-doped, Ni-rich NCM, as well as its impact on the microstructure and electrochemical properties, by a combined experimental and theoretical approach. Besides X-ray diffraction and Rietveld refinement, DFT calculation was used to find the preferred site of boron absorption and its effect on the NCM lattice parameters. It is found that boron shows a trigonal planar and tetrahedral coordination to oxygen in the Ni layers, leading to a slight increase in lattice parameter c through an electrostatic interaction with Li ions. Therefore, B-doping of NCM811 affects the crystal structure and cation disorder and leads to a change in primary particle size and shape. To experimentally prove that the observations are caused by boron incorporated into the NCM lattice, we detected, quantified, and localized boron in 2 mol % B-doped NCM811 by ion beam analysis and TOF-SIMS. It was possible to quantify boron by NRA with a depth resolution of 2 μm. We found a boron enrichment on the agglomerate surface but also, more importantly, a significant high and constant boron concentration in the interior of the primary particles near the surface, which experimentally verifies that boron is incorporated into the NCM811 lattice.

The garnet-type Li7La3Zr2O12 (LLZO) ceramic solid electrolyte combines high Li-ion conductivity at room temperature with high chemical stability. Several all-solid-state Li batteries featuring the LLZO electrolyte and the LiCoO2 (LCO) or LiCoO2–LLZO composite cathode were demonstrated. However, all batteries exhibit rapid capacity fading during cycling, which is often attributed to the formation of cracks due to volume expansion and the contraction of LCO. Excluding the possibility of mechanical failure due to crack formation between the LiCoO2/LLZO interface, a detailed investigation of the LiCoO2/LLZO interface before and after cycling clearly demonstrated cation diffusion between LiCoO2 and the LLZO. This electrochemically driven cation diffusion during cycling causes the formation of an amorphous secondary phase interlayer with high impedance, leading to the observed capacity fading. Furthermore, thermodynamic analysis using density functional theory confirms the possibility of low- or non-conducting secondary phases forming during cycling and offers an additional explanation for the observed capacity fading. Understanding the presented degradation paves the way to increase the cycling stability of garnet-based all-solid-state Li batteries.

A rapid photonic sintering process (rapid thermal processing) was used to obtain compact films of cathode active material of lithium batteries. LiCoO2 (LCO) thick films were screen-printed on a steel substrate followed by a contactless thermal processing at 1000 °C in only 90 s. A homogenous densification of such layers could be verified by scanning electron microscopy, while the structural consistency of the LCO phase in these layers could be detected by X-ray diffraction and Raman spectroscopy. Furthermore, electrochemical activity of the layer was confirmed by electrochemical cell tests with a liquid electrolyte.

The materials typically used for oxygen transport membranes, Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) and La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) tend to decompose due to their low thermochemical stability under reducing atmosphere. Fe- and Co-doped SrTiO3 (SrTi1-x-yCoxFeyO3-δ, x + y ≤ 0.35) (STCF) materials showing an oxygen transport comparable to LSCF have great potential for application in ion-transport-devices. In this study, the thermochemical stability of pure perovskite-structured STCF was investigated after annealing in a syngas atmosphere at 600–900 °C. The phase composition of the materials after annealing was characterized by means of X-ray diffraction (XRD). The thermodynamic activities of SrO, FeO, and CoO in the STCF materials were evaluated using Knudsen effusion mass spectrometry (KEMS). Co-doped SrTiO3 (STC) materials were not stable after annealing in the syngas atmosphere above 5 mol% Co-substitution. Ruddlesden-Popper-like phases and SrCO3 were detected after annealing at 600 °C. In contrast, Fe substitution (STF) showed good stability after annealing in syngas upto 35 mol% substitution.

Titanium silicon carbide (Ti3SiC2) powder was synthesized by molten salt shielded synthesis route of elemental reactants. Potassium bromide (KBr) was used for gas-tight encapsulation of the consolidated reaction mixture for further high temperature processing. The synthesis of Ti3SiC2 powder was carried out in air, the salt cladding and molten salt pool provided for the protection of the material against oxidation both at low and high temperature. The process yielded free flowing Ti3SiC2 powders without the need of a milling step. Al addition to the reaction mixture resulted in a high purity (96 wt. %) of Ti3SiC2 at a synthesis temperature of 1250 °C. The synthesized micro-metric Ti3SiC2 can be milled to nano-metric powders.

The present article describes aspects of the cold gas spray processability of the intermetallic Ti-48Al-2Cr-2Nb (at. %) alloy, which is employed as a structural material in gas turbine engines. The effects of processing parameters, namely, gas pressure, gas temperature, spray distance, as well as the gas atomized feedstock particle size (d50 = 30 and 42 μm, respectively) and phase composition on deposition, were investigated. The results showed that when the highest available gas pressure (40 bar) and temperature (950 °C) were combined with a short spray distance (20 mm), well-adhering coatings could be deposited regardless of the investigated particle size. However, the maximum coating thickness could be achieved was about 30 μm with a deposition efficiency of 1%. Phase composition of the gas atomized feedstock was investigated with HT-XRD and according to the findings, heat treatment of the feedstock under vacuum was carried out. With this treatment, non-equilibrium, disordered α phase of the atomized powder was transformed into an α, α2 and γ phase mixture. At the same time, an increase in the hardness and oxygen content of the powder was detected. Swipe test performed with the heat treated powder revealed no improvement in terms of deposition, in fact, the number of adhering particles on the substrate was decreased in comparison with that of the untreated powder.

By Plasma Spray-Physical Vapor Deposition (PS-PVD), major fractions of the powder feedstock can be evaporated so that the coating builds up mainly from vapor phase. In this work, the deposition mechanisms at different PS-PVD conditions were investigated. Depending on the plasma flow conditions and the substrate temperature, the columns in the coatings possess successively pyramidal, cauliflower, and lamellar shaped tops. In addition, the different microstructures show characteristic crystallographic textures, in which different in-plane and out-of-plane orientations were observed by pole figures. Based on investigations by electron back-scatter diffraction (EBSD), the overall coating growth process can be roughly divided into three subsequent stages: equiaxed growth, competitive growth, and preferential growth. Influences of diffusion and shadowing on final coating microstructure and orientation were discussed. The formation of equiaxed grains was proposed to be caused by high nucleation rates, which are probably induced by large undercooling and super-saturation at the beginning of deposition. The preferential growth orientation was preliminarily explained based on an evolutionary selection mechanism.

Highly pure Cr2AlC powders were synthesized and deposited for the first time by cold spray technology on stainless steel substrates. The Cr2AlC coatings were relative dense, up to 91%, and present high purity (> 98%) since only small traces of Cr2Al, Al2O3 and Cr2O3 were detected by XRD, SEM and EDX. The microstructure of the coatings is homogeneous, although some preferential orientation in the basal plane was observed by XRD pole figures. The adhesion between the coating and the substrate is strong, and compressive residual stresses up to 300 MPa in the coating were determined by XRD. Furthermore, a conventional YSZ Thermal Barrier Coating (TBCs) was deposited by Atmospheric Plasma Spray (APS) on top of the cold sprayed Cr2AlC coating in order to demonstrate the processing feasibility of Cr2AlC MAX phases as a bond-coat layer.

Low-temperature NOx storage materials for lean NOx traps based on nanocomposites containing perovskite-type oxides of La0.5Sr0.5Fe1-xMxO3-δ (M = Ti, Nb or Zr; x = 0.25 or 0.5) are prepared in a highly porous alumina with different loadings of 15−25 wt. %. The resulting storage materials are characterised by X-ray diffraction, BET and transmission electron microscopy with coupled ASTAR system for crystallite phase mapping. For all nanocomposites high surface areas around 100 m²/g are found. With perovskite loadings of 20 wt. % the platinised composites reveal NOx storage capacities between 120–164 μmol/g below 300 °C with a performance ranking of Zr > Ti > Nb. After hydrothermal ageing at 750 °C only for the Nb and Zr containing composites a decrease of the NSC up to 20 % can be observed. The NSC of the LSFT system can be improved by decreasing the perovskite loading to 15 wt. %.

One of the necessary prerequisites to advance the electrochemical performance of Li7La3Zr2O12 (LLZ) based all-solid-state lithium batteries is the manufacturing of dense composite cathodes from cathode active material (CAM) and the LLZ ceramic solid electrolyte. However, free co-sintering of LLZ and CAM mixtures requires temperatures above 1000 °C which often leads to decomposition and secondary phase formation, especially for high energy CAMs. In our study we present a completely dry processing route which is fast, free of any sintering additives and coatings and suitable to fabricate dense mixed cathodes, pure LLZ separators and multilayers of the two. Through application of high mechanical pressure during Field-Assisted Sintering we were able to reduce the sintering temperature down to 675–750 °C with dwell times as low as 10 min, while still obtaining 95% theoretical density for LCO/LLZ mixtures. The low sintering temperature is suitable for high energy CAMs, but leads to a significant effect of surface impurities, especially from powder handling in air, and affects the crystallinity of the CAM/LLZ interface. In the present paper we investigate the impact of resulting interfaces on the ionic conductivity, the interfacial impedance and the cycling stability of produced cells and propose the optimization strategy.

In this work, silicon–hafnia (Si-HfO2, 80/20 mol. %) feedstock was plasma sprayed for Environmental Barrier Coating bond coat application. In the as-sprayed coating, hafnium disilicide (HfSi2), HfO2 tetragonal (t), and cubic (c) phases with a total volume of ~20 % were detected together with Si and HfO2 monoclinic (m). The temperature-dependent evolution of these phases was analyzed and paired with microstructural observations. It was found that above 700 °C, HfSi2 oxidizes and HfO2 (t) and (c) transforms into (m) polymorph. Up to this temperature, as-sprayed coating showed a non-linear expansion behavior. Estimated volume expansion at ~750 °C was 3.6 % based on dilatometry measurement. The primary and secondary mechanisms leading to the expansion in the coating were identified as oxidation of HfSi2 and polymorphic phase transitions in HfO2, respectively. As a consequence of the volume expansion, the coating was extensively cracked during cyclic oxidation and hence not protective anymore. After 100 h at 1300 °C, the volume fraction of oxidation product SiO2 was significant in the coating (0.34), while HfO2 was largely consumed (0.1) in the formation of HfSiO4 (0.56). This result suggested that reversible α↔β phase transitions in SiO2-cristobalite could be another factor contributing to the cracking in the coating during cyclic oxidation.

Journal of thermal spray technology : JTST (2020). doi:10.1007/s11666-020-01139-x, Published by Springer, Boston, Mass.

Journal of the American Ceramic Society (2020). doi:10.1111/jace.17582, Published by American Ceramic Society, Westerville, Ohio

Dense protective layers are needed to reduce chromium-related degradation in SOFC stacks. In particular, atmospheric plasma sprayed (APS) Mn1.0Co1.9Fe0.1O4 (MCF) coatings demonstrated low degradation rates in stack tests. We show that short-term annealing in air induces crack healing within these coatings. Parallel to this effect, a phase transformation is observed originating from oxidation that proceeds by solid state-diffusion. The present contribution reveals the basic mechanisms of the microstructural and phase changes of coatings in long-term annealing tests of up to 10,000 h at 700 °C. The layer develops differently at the air-facing surface and in the bulk. Due to cation deficiency, oxidation is dominated by cation outward diffusion, leading to a Co-enriched surface layer. The bulk displays a fine distribution of the initial (rock salt) and the final (spinel) phases. Understanding the mechanisms leading to these irreversible changes enables predictions to be made concerning durable protectivecoatings in SOFCs.

During the last decade, Suspension Plasma Spraying (SPS) attracted a lot of interest as an alternative process to produce columnar Thermal Barrier Coatings (TBCs). In this study, columnar TBCs were deposited with SPS. After spraying, samples were isothermally annealed at 1373 K for 1 h, 3 h, 10 h and 50 h, respectively. Microstructures and mechanical properties of the ceramic coatings were investigated as a function of annealing time. Annealing resulted in healing of micro-cracks, coarsening of pores, growth of domain size, companied with a decrease of porosity within columns. The change of coating microstructure led to change of mechanical properties. In addition, residual stress in SPS coatings was also investigated. Furthermore, as-sprayed coatings and pre-annealed coatings were subjected to burner rig tests. Short time pre-annealing allowed to enhance thermal cycling lifetime of such SPS coatings. The thermal cycling results were related to microstructure modifications of coatings.

The thermal stability of LiCoMnO4 and LiCoMnO4 with 1 wt.-% LiF as an additive was compared upon heating in air. The stoichiometries of samples heat-treated at 700, 800, 900 and 1000 °C were analyzed by means of inductively coupled plasma optical emission spectroscopy for cation contents, inert gas fusion analysis for oxygen, and nuclear reaction analysis for fluorine contents, revealing that the sample chemistries remain constant except for oxygen. The oxygen content of the samples correlates with the Li2MnO3 secondary phase fraction, which forms upon heating, as is shown by X-ray powder diffraction. For each temperature, a greater amount of Li2MnO3 is formed in the samples with LiF addition than in the single LiCoMnO4 samples. In situ high-temperature X-ray powder diffraction between 650 and 950 °C demonstrates that LiCoMnO4 with LiF addition exhibits the same kind of decomposition reactions upon heating and cooling as the sample without LiF addition. However, for the samples with LiF addition, the formation of the decomposition product, Li2MnO3, is accelerated due to the excess Li through LiF addition, i.e. the stability of the spinel phase decreases due to the supply of lithium. Since lithium is consumed by Li2MnO3 formation and fluorine remains in the samples, we can also conclude that the fluorine anion is incorporated into the spinel or Li2MnO3 phase upon heating LiCoMnO4 and LiF together.

The formation and decomposition of aluminum titanate (Al2TiO5, tialite) in feedstock powders and coatings of the binary Al2O3-TiO2 system are so far poorly understood. A commercial fused and crushed Al2O3-40%TiO2 powder was selected as the feedstock for the experimental series presented in this paper, as the composition is close to that of Al2TiO5. Part of that powder was heat-treated in air at 1150 and 1500 °C in order to modify the phase composition, while not influencing the particle size distribution and processability. The powders were analyzed by thermal analysis, XRD and FESEM including EDS of metallographically prepared cross sections. Only a maximum content of about 45 wt.% Al2TiO5 was possible to obtain with the heat treatment at 1500 °C due to inhomogeneous distribution of Al and Ti in the original powder. Coatings were prepared by plasma spraying using a TriplexPro-210 (Oerlikon Metco) with Ar-H2 and Ar-He plasma gas mixtures at plasma power levels of 41 and 48 kW. Coatings were studied by XRD, SEM including EDS linescans of metallographically prepared cross sections, and microhardness HV1. With the exception of the powder heat-treated at 1500 °C an Al2TiO5-Ti3O5 (tialite–anosovite) solid solution Al2−xTi1+xO5 instead of Al2TiO5 existed in the initial powder and the coatings.

We report on the materials interaction of gadolinium doped ceria (GDC) and yttria stabilized zirconia (YSZ) in the context of high temperature sintering during manufacturing of anode supported solid oxide fuel cells (AS-SOFC). While ceria-based anodes are expected to show superior electrochemical performance and enhanced sulfur and coking tolerance in comparison to zirconia-based anodes, we demonstrate that the incorporation of a Ni-GDC anode into an ASC with YSZ electrolyte decreases the performance of the ASC by approximately 50% compared to the standard Ni-YSZ cell. The performance loss is attributed to interdiffusion of ceria and zirconia during cell fabrication, which is investigated using powder mixtures and demonstrated to be more severe in the presence of NiO. We examine the physical properties of a GDC-YSZ mixed phase under reducing conditions in detail regarding ionic and electronic conductivity as well as reducibility, and discuss the expected impact of cation intermixing between anode and electrolyte. This article is protected by copyright. All rights reserved.

Dense, crack-free, uniform, and well-adhered environmental barrier coatings (EBCs) are required to enhance the environmental durability of silicon (Si)-based ceramic matrix composites in high pressure, high gas velocity combustion atmospheres. This paper represents an assessment of different thermal spray techniques for the deposition of Yb2Si2O7 EBCs. The Yb2Si2O7 coatings were deposited by means of atmospheric plasma spraying (APS), high-velocity oxygen fuel spraying (HVOF), suspension plasma spraying (SPS), and very low-pressure plasma spraying (VLPPS) techniques. The initial feedstock, as well as the deposited coatings, were characterized and compared in terms of their phase composition. The as-sprayed amorphous content, microstructure, and porosity of the coatings were further analyzed. Based on this preliminary investigation, the HVOF process stood out from the other techniques as it enabled the production of vertical crack-free coatings with higher crystallinity in comparison with the APS and SPS techniques in atmospheric conditions. Nevertheless, VLPPS was found to be the preferred process for the deposition of Yb2Si2O7 coatings with desired characteristics in a controlled-atmosphere chamber.

Double layer thermal barrier coatings (TBCs) consisting of a Gd2Zr2O7 (GZO) top and an ytrria stabilized zirconia (YSZ) interlayer have been tested in a burner rig facility and the results compared to the ones of conventional YSZ single layers. In order to gain insight in the high temperature capability of the alternative TBC material, high surface temperatures of up to 1550 °C have been chosen while keeping the bond coat temperature similar. It turned out that the performance of all systems is largely depending on the microstructure of the coatings especially reduced porosity levels of GZO being detrimental. In addition, it was more difficult in GZO than in YSZ coatings to obtain highly porous and still properly bonded microstructures. Another finding was the reduced lifetime with increasing surface temperatures, the amount of reduction is depending on the investigated system. The reasons for this behavior are analyzed and discussed in detail.

In situ high‐temperature powder X‐ray diffraction analysis (HT‐XRD) was carried out in the temperature range from 25°C‐1430°C to investigate the crystal structure of double perovskites, La2(Al1/2MgTa1/2)O6 (LAMT) and its phase transitions. This complex perovskite is a promising candidate for application in thermal barrier coating systems. Rietveld analysis shows a rock‐salt type ordering of the B‐site cations in the monoclinic space group symmetry, P21/n at room temperature. Upon heating, a structural phase transition occurs at ~855°C, and the crystal structure becomes rhombohedral with the space group symmetry urn:x-wiley:00027820:media:jace16740:jace16740-math-0001. On further heating, LAMT transforms to the ideal cubic phase at ~1390°C with the space group symmetry urn:x-wiley:00027820:media:jace16740:jace16740-math-0002. Both of the structural phase transitions are completely reversible, and were confirmed through complementary differential scanning calorimetry and thermogravimetry measurements. With increasing temperature, the degree of the octahedral tilting decreases and the variance of the different B–O bond lengths is reduced, until in the cubic phase, no tilting is present, and almost equal B–O bond lengths are obtained.

The practical use of Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) prototypical oxygen-transport membrane for air separation is currently hampered by the decomposition of the cubic perovskite into a variant with hexagonal stacking at intermediate temperatures of ≤850 °C, which impairs the oxygen transport. Here, we report the development of a W-doped BSCF composite that contains Fe-rich single perovskite (SP) and W-rich double perovskite (DP) phases with different crystallographic parameters. In contrast to BSCF, the BSCFW SP/DP composite maintains its cubic structure at 800 °C for 200 h, demonstrating its structural stability at intermediate temperatures. We use X-ray diffraction, scanning electron microscopy, and high-resolution transmission electron microscopy to show that the enhanced phase stability of the composite is associated with a temperature-induced SP–DP dynamic interaction, which involves W and Fe interdiffusion between the SP and DP phases, dynamically adjusting the chemical composition and limiting structural distortion and new phase formation. The composite exhibits a stable permeation performance in the oxygen-transport membrane during over 150 h operation at 800 and 700 °C, confirming the potential of intermediate-temperature oxygen-transport membranes for air separation and providing insight for designing thermally stable composite oxides.

With the aim of improving the electrochemical properties of the LiCoMnO4 high-voltage spinel for lithium ion battery applications, LiCoMnO4-yFy (y = 0, 0.05, 0.1) compounds were synthesized by a two-step solid-state reaction at 800 °C. The stoichiometry of the samples was verified by nuclear reaction analysis for the fluorine stoichiometry, inert gas fusion analysis for the oxygen stoichiometry, and inductively coupled plasma optical emission spectroscopy for the cation stoichiometry. X-ray diffraction analysis and scanning electron microscopy revealed increasing phase purity and changing microstructure upon fluorine incorporation. Electrochemical characterizations were carried out in battery test cells using a liquid electrolyte. The samples show poor coulombic efficiency, due to liquid electrolyte decomposition. However, fluorinated spinels demonstrated significantly improved capacities of up to 18% and improved cycling stability of up to 20%, compared to their non-fluorinated counterparts.

Rechargeable oxide batteries (ROB) comprise a regenerative solid oxide cell (rSOC) and a storage medium for oxygen ions. A sealed ROB avoids pumping loss, heat loss, and gas purity expenses in comparison with conventional rSOC. However, the iron oxide base storage medium degrades during charging–discharging cycles. In comparison, CaFe3O5 has improved cyclability and a high reversible oxygen storage capacity of 22.3 mol%. In this study, we analyzed the redox mechanism of this compound. After a solid-state synthesis of CaFe3O5, we verified the phase composition and studied the redox reaction by means of X-ray diffraction, Mossbauer spectrometry, and scanning electron microscopy. Results show a great potential to operate the battery with this storage material during multiple charging–discharging cycles.

Chromium evaporation barriers are frequently used in solid oxide fuel cells to protect the porous cathode from chromium poisoning. Volatile chromium species are generated at the operation temperature of about 600–900 °C in a humid atmosphere for chromia scale forming steels as interconnect materials. In order to reduce this effect, barrier coatings are applied, often by atmospheric plasma spraying. However, also in these coatings microstructural changes as densification and in parallel formation of large pores have been observed. In order to clarify these mechanisms plasma sprayed Mn1.0 Co1.9Fe0.1O4 (“MCF”) are deposited on ferritic steels and furthermore coated with a perovskite based contact layer as used in stack build-up. These coatings are annealed in air up to 1000 h and the microstructural changes and bending of the samples are studied. The results show increasing bending with increasing aging time. High temperature curvature measurements indicate that the amount of bending is not significantly dependent on temperature. As an explanation the creep deformation of the substrate/coating system at high temperatures due to compressive stress levels in the coating is given. The origin of the stress is related to phase changes in combination with the oxidation of the coatings. In addition, interdiffusion and densification processes are discussed.

The characteristics of a polymer electrolyte membrane (PEM) are crucial for the success of PEM based fuel cells and electrolyzers. Membranes play a significant role regarding ohmic losses, fuel permeability and mechanical stability. For the resulting catalyst coated membrane (CCM), it is important to create an ideal contact between membrane and electrode to avoid gaps and enhance interfacial surface area. Production of CCMs for fuel cells or electrolyzers is mainly based on two techniques: Decal Transfer: Fabrication of an electrode onto a carrier substrate and subsequent transfer by hot-pressing it onto a membrane [1]. Direct deposition: Spray-deposition onto heated and vacuum fixed membranes [2] or doctor-blade coating onto pre-swollen membranes [3]. Both techniques bear several problems: During hot-pressing membranes are exposed to high temperatures and pressure. This can lead to deformations or cracks within the membrane. At the same time, transfer of electrode material can be insufficient and membrane electrode interface can suffer from delamination which causes gaps in terms of proton conductivity. Direct deposition of electrode material onto membranes entails difficult processing. Swelling and shrinking during coating and drying can result in inhomogeneous electrodes. Instead of coating membranes with electrodes, ultrasonic spray-deposition was employed to produce self-standing membranes. Being able to produce membranes allows the consecutive fabrication of all layers in a CCM and makes commercial membranes obsolete. It also reduces problems when an electrode is spray-deposited because the membrane is usually produced just before the electrode that is supposed to be spray-deposited. Thus, the membrane is attached to either a carrier substrate (PTFE) or another electrode that was spray-deposited at the very beginning. Fabricating membranes by spray-deposition gives freedom in terms of several processing aspects: Modification of the ionomer solution composition. The following variations were used: Solutions based on water/alcohol and water/alcohol + high boiling point solvents such as ethylene glycol, dimethyl sulfoxide, dimethylformamide and dimethylacetamide. Application of thermal treatments Variation of the membrane thicknesses This approach reveals possibilities that would not be available with commercial Nafion membranes with predefined properties. Self-standing Nafion membranes, based on different ionomer solution compositions and thermal treatments were produced (120-130 µm). All samples were employed for CCM fabrication (Anode: 3.0 mg/cm² PtRu; Cathode: 0.7 mg/cm² PtNi). Further, they were characterized, regarding hydrogen permeability, ohmic resistances and single-cell polarization curves in direct methanol fuel cell (DMFC) operation. All samples were compared to commercial Nafion 115 membranes. With some samples the performances of CCMs using spray-deposited membranes could be matched with Nafion 115. At the same time they showed lower ohmic resistances and partly lower hydrogen crossover values. Additionally, thinner membranes equivalent to Nafion 212 (50 µm) and Nafion 211 (25 µm) were fabricated and tested. They showed even better performances. While 50 µm thick membranes had moderate permeability levels comparable to 127 µm thick membranes, 25 µm samples showed high permeabilities. To reach high performances with relatively low permeation values, thin composite membranes (25 µm) were produced. These consisted of Nafion and graphene oxide, where graphene oxide was supposed to work as a blocking layer against permeation [4] while supporting proton conductivity. It is also possible to deposit Nafion solutions or Nafion (composite) dispersions directly onto electrodes instead of producing self-standing membranes [5]. This would allow the fabrication of a whole CCM consecutively [6]. Even though this technique was used for fabrication of CCMs for DMFCs, it can also be transferred to hydrogen-based fuel cells (PEMFC) [6] or water-electrolysis (PEMWE) [7]. X. Ren, M. Wilson, S. Gottesfeld, J. Electrochem. Soc., 143 (1996) L12–L15. L. Sun, R. Ran, Z. Shao, Int. J. Hydrogen Energy, 35 (2010) 2921–2925. I.-S. Park, W. Li, A. Manthiram, J. Power Sources, 195 (2010) 7078–7082. L. Sha Wang, A. Nan Lai, C. Xiao Lin, Q. Gen Zhang, A. Mei Zhu, Q. Lin Liu, J. Memb. Sci., 492 (2015) 58–66. M. Klingele, M. Breitwieser, R. Zengerle, S. Thiele, J. Mater. Chem. A, 3 (2015) 11239–11245. M. Klingele, B. Britton, M. Breitwieser, S. Vierrath, R. Zengerle, S. Holdcroft, S. Thiele, Electrochem. Commun., 70 (2016) 65–68. P. Holzapfel, M. Bühler, C. Van Pham, F. Hegge, T. Böhm, D. McLaughlin, M. Breitwieser, S. Thiele, Electrochem. Commun., 110 (2020) 106640. Figure 1

Although photovoltaic–electrochemical (PV–EC) water splitting is likely to be an important and powerful tool to provide environmentally friendly hydrogen, most developments in this field have been conducted on a laboratory scale so far. In order for the technology to make a sizeable impact on the energy transition, scaled up devices must be developed. Here a scalable (64 cm2 aperture area) artificial PV–EC device composed of triple-junction thin-film silicon solar cells in conjunction with an electrodeposited bifunctional nickel iron molybdenum water-splitting catalyst is shown. The device shows a solar to hydrogen efficiency of up to 4.67% (5.33% active area, H2 production rate of 1.26 μmol H2/s) without bias assistance and wire connection and works for 30 min. The gas separation is enabled by incorporating a membrane in a 3D printed device frame. In addition, a wired small area device is also fabricated in order to show the potential of the concept. The device is operated for 127 h and initially 7.7% solar to hydrogen efficiency with a PV active area of 0.5 cm2 is achieved.

Despite numerous studies and decades of industrial application, there is still a lack of understanding about the formation and the impact of aluminum titanate (Al2TiO5) in Al2O3-TiO2 thermal spray coatings. Especially the influence of the feedstock powder characteristics on the phase composition has only crudely been investigated so far. Therefore, in this work we have characterized commercial fused and crushed Al2O3-TiO2 feedstock powders: three of them containing 13 wt.% TiO2 and three containing 40 wt.% TiO2. The effect of the varying phase compositions of the powders and their relevance on the deposition efficiency, the phase compositions, the porosity, and the hardness of the respective APS coatings is described in detail. While detrimental to the mechanical properties of 40 wt.% TiO2 coatings, we have found an enhancement of the hardness for 13 wt.% TiO2 coatings with a high Al2TiO5/Al6Ti2O13 content in the feedstock powder. Furthermore, it was found that Al2TiO5 may reform during APS when sprayed from an Al2TiO5-free powder.

Atmospheric plasma sprayed (APS) Al2O3 TiO2 coatings have found a wide range of industrial application due to their favorable properties in combination with low costs and a high availability. However, the detailed effect of the phase composition and the element distribution of the feedstock powders on the coating properties and the spraying process has only crudely been investigated so far. Here the impact of aluminum titanate (Al2TiO5) on the microstructural features and mechanical properties of Al2O3 40 wt.% TiO2 APS coatings is demonstrated by investigating the detailed phase composition and the distribution of aluminum and titanium in three different fused and crushed feedstock powders and the respective coatings. Thereby, a direct influence of the Al2TiO5 on the deposition efficiency, the porosity, the elastic modulus, and the hardness of the coatings is revealed. In particular, the feedstock powder had a stronger effect on the coating properties than increasing the stand off distance from 150 to 350 mm. Furthermore, Al2TiO5 coatings were found to exhibit a strong texture. The obtained results emphasize the need for a more detailed specification of commercial Al2O3 TiO2 feedstock powders in terms of their phase composition and elemental homogeneity to ensure a high reliability of the coating process and ultimately the coating properties.

This work presents a systematic study of the lanthanum tungstate (LaWO) ceramic layers formation on porous metallic substrates as a function of the PS-PVD processing parameters including plasma characteristics, support type and temperature, as well as addition of O2 during the spraying. Through precise control of the PS-PVD parameters, a set of processing conditions were found that led to He gas-tight purely cubic LaWO layers with negligible secondary phase precipitations. Being dependent on process conditioning, the formation and evolution of the cubic La6−xWO12−δ (x = 0.3-0.6) as the main phase of functional importance and of the undesired secondary phases (La2O3 and La6W2O15) was strongly affected by the cation and oxygen stoichiometries. The rapid cooling of the feedstock at particle impact on the substrate led to the formation of highly La-saturated compositions which exhibited significant lattice expansion in comparison with conventionally processed LaWO and is considered beneficial in terms of material performance. And indeed, the H2 permeation performance of the PS-PVD processed LaWO ceramic layers shown earlier by our group was 0.4 ml/min∙cm2 at 825 °C for 60 µm thickness of the functional layer, the highest value reported for this type of proton conducting ceramics, so far.

The purpose of this research was to investigate the corrosion behavior of the low/high Yb2SiO5 containing Yb2Si2O7 coatings under high-velocity water vapor flow. To that end, Yb2Si2O7 and Si coatings were deposited by atmospheric plasma spraying on SiC substrates. The corrosion tests were performed in the burned natural gas under atmospheric pressure, with a gas flow velocity of 100 m/s at 1200 °C for 200 h. After the test, a 25 mm thick, porous corrosion layer at the surface of the Yb2Si2O7 rich coatings was found accompanied with a mass reduction, whereas samples with Yb2SiO5 rich coatings showed mass gain indicating the greater resistance of Yb2SiO5 against water vapor. A comparison of the Yb2Si2O7 rich coatings tested in this work and Yb2Si2O7 bulk samples tested in an earlier work at the same facility revealed significantly different recession rates. Possible mechanisms responsible for this distinct behavior are discussed in the manuscript.

La0.58Sr0.4Co0.2Fe0.8O3− δ (LSCF) deposited on a metallic porous support by plasma spray-physical vapor deposition is a promising candidate for oxygen-permeation membranes. Ionic transport properties are regarded to depend on the fraction of perovskite phase present in the membrane. However, during processing, the LSCF powder decomposes into perovskite and secondary phases. In order to improve the ionic transport properties of the membranes, spraying was carried out at different oxygen partial pressures p(O2). It was found that coatings deposited at lower and higher oxygen partial pressures consist of 70% cubic/26% rhombohedral and 61% cubic/35% rhombohedral perovskite phases, respectively. During annealing, the formation of non-perovskite phases is driven by oxygen non-stoichiometry. The amount of oxygen added during spraying can be used to increase the perovskite phase fraction and suppress the formation of non-perovskite phases.

To increase the efficiency of turbines for the power generation and the aircraft industry, advanced thermal barrier coatings (TBCs) are required. They need to be long-term stable at temperatures higher than 1200 °C. Nowadays, yttria partially stabilized zirconia (YSZ) is applied as standard TBC material. But its long-term application at temperatures higher than 1200 °C leads to detrimental phase changes and sintering effects. Therefore, new materials have to be investigated, for example, complex perovskites. They provide high melting points, high thermal expansion coefficients and thermal conductivities of approx. 2.0 W/(m K). In this work, the complex perovskite La(Al1/4Mg1/2Ta1/4)O3 (LAMT) was investigated. It was deposited by the suspension plasma spraying (SPS) process, resulting in a columnar microstructure of the coating. The coatings were tested in thermal cycling gradient tests and they show excellent results, even though some phase decomposition was found.

The hydrogen bond in K3H(SO4)2 was investigated using a neutron single crystal diffraction technique at room temperature and 2.3 K. The title compound crystallizes in the monoclinc space group A12/...

Impedance measurements were performed on single crystals of (NH4)3H(SO4)2 in the temperature range of 295–441 K. Anisotropy of protonic conductivity was found in the monoclinic room-temperature phase (space group C2/c) as well as in the rhombohedral high-temperature phase (space group R 3 ¯ m ). Above the high-temperature phase transition at 413 K, conductivity in the hexagonal (001) plane yields a value of ~ 10− 2 S cm− 1, which is typical for superionic conductors. A verification of a sample quality after the impedance measurements, using X-ray powder diffraction, showed minor additional peaks of (NH4)2(SO4). This suggests a beginning of thermal decomposition at high temperature. The possible pathways of proton conduction were discussed according to crystal structure analyses by single-crystal neutron diffraction method.

Dense coatings on metallic interconnectors are necessary to suppress chromium poisoning of SOFC cathodes. Atmospherically plasma sprayed (APS) Mn1.0Co1.9Fe0.1O4 (MCF) protective layers demonstrated reduced chromium related degradation in laboratory and stack tests. Previous analyses revealed strong microstructural changes comparing the coating's as-sprayed and operated condition. This work concentrates on the layer-densification and crack-healing observed by annealing APS-MCF in air, which simulates the cathode operation conditions. The effect is described by a volume expansion induced by a phase transformation. Reducing conditions during the spray process lead to a deposition of the MCF in a metastable rock salt configuration. Annealing in air activates diffusion processes for a phase transformation to the low temperature stable spinel phase (T < 1050 °C). This transformation is connected to an oxygen incorporation which occurs at regions facing high oxygen partial pressures, as there are the sample surface, cracks and pore surfaces. Calculations reveal a volume expansion induced by the oxygen uptake which seals the cracks and densifies the coating. The process decelerates when the cracks are closed, as the gas route is blocked and further oxidation continues over solid state diffusion. The self-healing abilities of metastable APS coatings could be interesting for other applications.

From the literature, it is known that due to their glass formation tendency, it is not possible to deposit fully-crystalline silicate coatings when the conventional atmospheric plasma spraying (APS) process is employed. In APS, rapid quenching of the sprayed material on the substrate facilitates the amorphous deposit formation, which shrinks when exposed to heat and forms pores and/or cracks. This paper explores the feasibility of using a high-velocity oxygen-fuel (HVOF) process for the cost-effective fabrication of dense, stoichiometric, and crystalline Yb2Si2O7 environmental barrier coatings. We report our findings on the HVOF process optimization and its resultant influence on the microstructure development and crystallinity of the Yb2Si2O7 coatings. The results reveal that partially crystalline, dense, and vertical crack-free EBCs can be produced by the HVOF technique. However, the furnace thermal cycling results revealed that the bonding of the Yb2Si2O7 layer to the Silicon bond coat needs to be improved.

[EN] Hydrogen permeation membranes are a key element in improving the energy conversion efficiency and decreasing the greenhouse gas emissions from energy generation. The scientific community faces the challenge of identifying and optimizing stable and effective ceramic materials for H-2 separation membranes at elevated temperature (400-800 degrees C) for industrial separations and intensified catalytic reactors. As such, composite materials with nominal composition BaCe0.8Eu0.2O3-delta:Ce0.8Y0.2O2-delta revealed unprecedented H-2 permeation levels of 0.4 to 0.61 mL center dot min(-1)center dot cm(-2) at 700 degrees C measured on 500 mu m-thick-specimen. A detailed structural and phase study revealed single phase perovskite and fluorite starting materials synthesized via the conventional ceramic route. Strong tendency of Eu to migrate from the perovskite to the fluorite phase was observed at sintering temperature, leading to significant Eu depletion of the proton conducing BaCe0.8Eu0.2O3-delta phase. Composite microstructure was examined prior and after a variety of functional tests, including electrical conductivity, H-2-permeation and stability in CO2 containing atmospheres at elevated temperatures, revealing stable material without morphological and structural changes, with segregation-free interfaces and no further diffusive effects between the constituting phases. In this context, dual phase material based on BaCe0.8Eu0.2O3-delta:Ce0.8Y0.2O2-delta represents a very promising candidate for H-2 separating membrane in energy-and environmentally-related applications, This work has been conducted with the financial support by the Helmholtz Association under the Research Programme Energy Efficiency, Materials and Resources. Financial funding from the Spanish Government (ENE2014-57651 and SEV-2012-0267 grants) is also gratefully acknowledged. ZEA-3 at FZJ is gratefully acknowledged for performing the ICP-OES analysis.

Hydrogen permeation membranes are a key element in improving the energy conversion efficiency and decreasing the greenhouse gas emissions from energy generation. The scientific community faces the challenge of identifying and optimizing stable and effective ceramic materials for H2 separation membranes at elevated temperature (400–800 °C) for industrial separations and intensified catalytic reactors. As such, composite materials with nominal composition BaCe0.8Eu0.2O3-δ:Ce0.8Y0.2O2-δ revealed unprecedented H2 permeation levels of 0.4 to 0.61 mL·min−1·cm−2 at 700 °C measured on 500 μm-thick-specimen. A detailed structural and phase study revealed single phase perovskite and fluorite starting materials synthesized via the conventional ceramic route. Strong tendency of Eu to migrate from the perovskite to the fluorite phase was observed at sintering temperature, leading to significant Eu depletion of the proton conducing BaCe0.8Eu0.2O3-δ phase. Composite microstructure was examined prior and after a variety of functional tests, including electrical conductivity, H2-permeation and stability in CO2 containing atmospheres at elevated temperatures, revealing stable material without morphological and structural changes, with segregation-free interfaces and no further diffusive effects between the constituting phases. In this context, dual phase material based on BaCe0.8Eu0.2O3-δ:Ce0.8Y0.2O2-δ represents a very promising candidate for H2 separating membrane in energy- and environmentally-related applications.

[EN] La0.58Sr0.4Co0.2Fe0.8O3-delta (LSCF), deposited on a metallic porous support by plasma spray -physical vapor deposition (PS-PVD) is a promising candidate for oxygen -permeation membranes. However, after O-2 permeation tests, membranes show vertical cracks leading to leakage during the tests. In the present work, one important feature leading to crack formation was identified. More specifically; membrane residual stress changes during thermal loading were found to be related to a phase transformation in the support. In order to improve the performance of the membranes, the metallic support was optimized by applying an appropriate heat treatment. The observed oxygen fluxes during permeation tests had infinite selectivity and were amongst the highest fluxes ever measured for LSCF membranes in the thickness range of 30 mu m, supported by LSCF porous substrates. (C) 2016 Elsevier B.V. All rights reserved., The authors gratefully acknowledge Mr. Ralf Laufs for his help with the use of the PS-PVD facility, the preparation of the SEM and EDS investigations by Dr. Doris Sebold and Mr. P. Terberger for calculations and discussion of Thermocalc phase diagrams (Forschungszentrum Julich, IEK-1). The work on membranes by PS-PVD was part of the DEMOYS Project funded from the European Community's Seventh Framework Program, FP7/2007-2013, under grant agreement No. 241309.