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In view of rising ecological awareness, materials development is primarily aimed at improving the performance and efficiency of innovative and more elaborate materials. However, a materials performance figure of merit should include essential aspects of materials: environmental impact, economic constraints, technical feasibility, etc. Thus, we promote the inclusion of sustainability criteria already during the materials design process. With such a holistic design approach, new products may be more likely to meet the circular economy requirements than when traditional development strategies are pursued. Using catalysts for water electrolysis as an example, we present a modelling method based on experimental data to holistically evaluate processes., In the context of a circular economy, the design process of new materials has to change. The performance‐based mindset must be replaced by a holistic approach to efficient materials. For this transition, the collaboration between materials science and sustainability assessment must be improved, and new ways of including assessments into design processes and standardized figures of sustainable merit must be defined.

The tin oxide buffer layer between the transparent conducting oxide current collector and the hematite photoelectrode causes considerable water oxidation enhancement of that electrode. The water ox...

The thermoelectric transport properties of Zr0.43Hf0.57NiSn half-Heusler compounds were investigated for samples sintered with different spark plasma sintering (SPS) periods: 8, 32 and 72 min. By means of scanning transmission electron microscopy with a high-angular annular dark-field detector (STEM-HAADF), it was found that sintering time affected the defect concentration, namely the amount of Ni interstitial atoms, and created locally ordered inclusions of full-Heusler phase. The structural information, phase composition and electrical transport properties could be consistently explained by the assumption that Ni interstitials give rise to an impurity band situated about 100 meV below the bottom of the conduction band via a self-doping behavior. The impurity band was found to merge with the conduction band for the sample with intermediate SPS time. The effect was ascribed to the gradual dissolution of full-Heusler phase inclusions and production of interstitial Ni defects, which eventually vanished for the sample with the longest sintering time. It was demonstrated that the modification of the density of states near the edge of the conduction band and enhanced overall charge carrier concentration provided by defect engineering led to overall 26% increase in the thermoelectric figure of merit (ZT) with respect to the other samples.

Bubeck, C., et al. (2020). Correction: Bandgap-adjustment and enhanced surface photovoltage in Y-substituted LataivO2N. Journal of Materials Chemistry A, 8(26). https://doi.org/10.1039/D0TA90138E The authors regret that the affiliations for author Eduardo Salas Colera were not listed correctly on the original manuscript. The corrected list of affiliations for this paper is as shown here. The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers. Perovskite-type oxynitrides AB(O,N)3 are photocatalysts for overall water splitting under visible light illumination. In the past, structurally labile perovskite-type oxynitrides (e.g. YTaON2) were predicted to be highly suitable. In this work, we tackle the challenging YTa(O,N)3 synthesis by Y-substitution in LaTaIVO2N resulting in phase-pure La0.9Y0.1TaIVO2N, La0.75Y0.25TaIVO2N, and La0.7Y0.3TaIVO2N. By using microcrystalline YTaO4 together with an unconventional ammonolysis protocol we synthesized the highest reported weight fraction (82(2) wt%) of perovskite-type YTa(O,N)3. Ta4+ in La1−xYxTaIVO2N was verified by X-ray photoelectron spectroscopy (XPS) and X-ray near edge absorption structure (XANES) analysis. Density functional theory (DFT) calculations revealed a transparent conductor-like behavior explaining the unusual red/orange color of the Ta4+-containing perovskites. In combination with crystal structure analysis the DFT calculations identified orthorhombic strain as the main descriptor for the unexpected trend of the optical bandgap (EG,x=0.3 ≈ EG,x=0 < EG,x=0.1 < EG,x=0.25). Surface photovoltage spectroscopy (SPS) of particulate La1−xYxTaIVO2N (x = 0, 0.1, 0.25, 0.3) films revealed negative photovoltages at photon energies exceeding 1.75 eV, confirming that these materials are n-type semiconductors with effective bandgaps of ∼1.75 eV irrespective of the Y content. The photovoltage values increased with the Y content, suggesting an improved carrier generation and separation in the materials. However, increasing the Y content also slowed down the timescales for photovoltage generation/decay indicating trap states in the materials. Based on our results, we suggest a significantly weaker as classically assumed impact of reduced B-site metal cations such as Ta4+ on the photovoltage and charge carrier recombination rate. This work was supported by the Deutsche Forschungsgemeinschaft within the priority program SPP 1613 "Solar H2" (WE 2803/7-1). Support for surface photovoltage spectroscopy measurements was provided by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Grant DOE-SC0015329

Monolithic, nitrogen-doped carbon sorbents were prepared from resorcinol-urea-formaldehyde resins and physically activated with CO2 for different activation times. The effect of the activation time on the water sorption behavior and the physicochemical properties were investigated. Longer activation times lead to a steeper slope of the water sorption isotherm and, due to a higher specific surface area and micropore volume, an increased water sorption capacity. It was found that, after physical activation for 3 h at 800 °C, the physically activated, nitrogen-doped carbon has a high surface area (>1000 m2/g) and a high water sorption capacity (50 wt%). In a miniaturized adsorption heat pump test stand, the best candidate material was assessed alongside commercial silica gel for reference. At a temperature swing from 90 °C → 50 °C, the CO2-activated carbon exhibits a maximal specific cooling power which is a factor of 1.7 higher in comparison with the reference silica gel (429 W/kg versus 255 W/kg). At a more applicable temperature swing, 60 °C → 30 °C, the CO2-activated carbon yields a specific cooling power 3.8 times higher than that of the silica gel reference (932 W/kg versus 240 W/kg).

The half-Heusler (HH) compound NbCoSn with 18 valence electrons is a promising thermoelectric (TE) material due to its appropriate electrical properties as well as its suitable thermal and chemical stability. Nowadays, doping/substitution and tailoring of microstructures are common experimental approaches to enhance the TE performance of HH compounds. However, detailed theoretical insights into the effects of doping on the microstructures and TE properties are still missing. In this work, the microstructure of NbCoSn was tailored through precipitating the full-Heusler phases in the matrix by changing the nominal ratio of Co and Ni on the Co sites, focusing on the resulting TE properties. Further, first-principles calculations were employed to understand the relationship between the microstructure and the TE properties from the thermodynamic point of view. Detailed analysis of the electronic structure reveals that the presence of excess Co/Ni contributes to the increasing carrier concentration. Through an increase in the electrical conductivity and a reduction in the thermal conductivity, the TE performance is improved. Therefore, the present work offers a new pathway and insights to enhance the TE properties by modifying the microstructure of HH compounds via tailoring the chemical compositions.

Correction to: Communications Chemistry https://doi.org/10.1038/s42004-019-0237-x, published online 26 November 2019. The original version of this Article incorrectly omitted the received/accepted dates of Received: 28 March 2019; Accepted: 24 October 2019. This has now been corrected in the PDF and HTML versions of the Article.

Wavelength-dependent thermoluminescence (TL) experiments were performed on SrAl2O4:Eu, SrAl2O4:Eu,B, SrAl2O4:Eu,Dy and SrAl2O4:Eu,Dy,B polycrystalline samples. Excitation at 445 nm allows to selectively excite one of the two different Eu2+ ions substituting for Sr in the crystal, whereas excitation at 375 nm excites both Eu2+ ions. Incorporation of boron generates the deepest traps which contribute to the very long afterglow in this material, while dysprosium increases significantly (by a factor of about 4–8) the total number of traps involved in the afterglow of this persistent phosphor. Increasing the temperature at which the samples are irradiated (loaded) from 173 K to 248 K reveals that many new traps can only be occupied or activated at higher temperatures, leading to a strong increase of the integrated TL intensity, in particular for the Dy-containing samples. Boron does not appear to contribute to these thermally-activated traps significantly responsible for the long afterglow of SrAl2O4:Eu,Dy,B. The results of this study reveal that the diversity of traps leading to the long afterglow is much larger than previously reported in the literature. We propose that boron stabilizes F centers (which absorb in the far UV), while the presence of dysprosium induces an excitation-induced charge-transfer reaction Eu2+ + Dy3+ → Eu3+ + Dy2+. However, the principal traps responsible for the efficient afterglow are temperature-activated and appear to be associated with the green emitting Eu2+ ion on the Sr2 site coupled to a nearby dysprosium ion.

Polycrystalline Eu 1-x Ca x TiO 3-d (0 < x < 1) samples were synthesised to investigate the interrelations among the crystal structure, local structural disorder, and thermoelectric properties. The Ca 2+ substitution is locally modifying (squeezing) the crystal structure, resulting in distinct differences between the long-range and local scales, e.g., the sample with x = 0.2 shows a cubic structure in long-range scale, while tetragonal distortions are observed locally. Additionally, the contraction of the unit cell volume with an accompanying reduction of the overall symmetry facilitates the accommodation of smaller Eu 3+ (instead of Eu 2+ ). The lattice imperfections induced by Ca 2+ substitution significantly improve electron concentration and simultaneously dramatically reduce thermal conductivity (i.e., as large as 50% compared with pristine sample) at room temperature. The average thermoelectric figure of merit of Eu 0.2 Ca 0.8 TiO 3-d is enhanced by almost 100% compared with that of the pristine EuTiO 3 . This work demonstrates that controlling lattice deformation offers new ways to enhance the thermoelectric performance of titanates.

Polycrystalline BaTiO3, BaTi(O,F)3, BaTi(N,O)3, and BaTi(N,O,F)3 powders were synthesized by a solid-state reaction and thermal ammonolysis. By powder X-ray diffraction (XRD) a tetragonal perovskite-type structure with space group P4mm was identified for all samples. Thermogravimetric analysis (TGA) revealed a gradual mass increase for the oxynitride BaTi(N,O)3 and the oxyfluoronitride BaTi(N,O,F)3 due to the nitrogen-oxygen exchange process. UV–visible diffuse reflectance spectra indicated the nitrogen incorporation into the perovskite lattice, and presumably the presence of large amounts of reduced titanium ions in BaTi(N,O,F)3. XANES spectra showed distinctive peak features for BaTi(O,F)3 and BaTi(N,O,F)3. Detailed magnetic property measurements revealed diamagnetism for BaTiO3, but weak ferromagnetism for BaTi(N,O)3 and a ferromagnetic behavior for BaTi(O,F)3 and BaTi(N,O,F)3. Enhanced magnetization of BaTi(N,O,F)3 is attributed to the synergetic effect of increased concentration of both surface/lattice defects and Ti3+.

We have measured room temperature and low temperature luminescence spectra of Eu3+ in SrAl2O4:Eu3+/2+. The powder samples were synthesized in reducing atmosphere above 1200 °C, cooled down to room temperature in the same atmosphere, and heated again to 750 °C in air. The analysis of the emission spectra of Eu3+ showed the presence of multiple sites for this ion, revealing that many different charge compensating defects are located in close vicinity to the europium ions. These defects can be positioned in each of the two void sites identified in the crystal structure of SrAl2O4. Lifetime measurements reveal the presence of very short-lived excited Eu3+ species with lifetimes around 0.7 μs, in addition to species with lifetimes around 1.6 ms. These very short lifetimes are postulated to be related to intervalence charge transfer with few remaining divalent Eu2+ ions which had not been oxidized by the thermal treatment in air. This type of intervalence charge transfer between divalent to the trivalent rare earth ion could be crucially associated to processes involved in the afterglow of the persistent phosphor SrAl2O4:Eu2+,Dy3+.

Cr-substituted and pristine Ba2In2O5·(H2O)x powders were synthesized by solid state reaction. The influence of Cr-substitution on the crystal structure, chemical composition, magnetic and optical properties were investigated. Powder X-ray diffraction (XRD), elemental analysis and TGA-MS reveal that with substitution of In for Cr, the unit cell volume and the unit cell parameter b increase together with the oxygen and hydrogen content. Magnetic property measurements indicate that Ba2In2O5·(H2O)x is diamagnetic in the temperature range of 2 K < T < 300 K becoming ferromagnetic upon Cr-substitution. In the UV–vis spectra of the Cr-substituted sample a distinctive shift of the absorption-edge energy from 430 to 690 nm was observed corresponding to a bandgap narrowing from 2.88 to 1.80 eV. The replacement of tetrahedral InO4 units by octahedral CrO6 units was found to be the main factor for the drastic change of the magnetic and optical properties.

In the present study thermoelectric properties of spark plasma sintered and subsequently air-annealed Sn 1-x Sb x O 2 (x = 0, 0.01, 0.03, 0.05) ceramic samples were characterized. It was observed that addition of Sb greatly affects density, microstructure and thermoelectric properties of SnO 2 . Grain size decreases and the microstructure becomes more homogeneous with increasing Sb content in the Sn 1-x Sb x O 2 samples from x = 0.01 to 0.05. The thermal conductivity and Seebeck coefficient of the Sb doped samples decreases with an increase in Sb concentration, while electrical conductivity increases up to a maximum at Sb doping level of x = 0.03 and then decreases at x = 0.05. The highest thermoelectric figure of merit of ZT ≈ 0.06 at 1073 K was exhibited by the sample of composition Sn 0.99 Sb 0.01 O 2 .

The dysprosium and boron effect on the emission properties of europium-doped SrAl2O4 samples has recently attracted considerable attention due to their high brightness and long afterglow. Here, the influence of both cations, Dy3+ and B3+, on the spectroscopic properties of the europium free samples SrAl2O4:Dy3+ and SrAl2O4:Dy3+, B3+ has been investigated in order to get more insights concerning the mechanism by which they enhance the afterglow. Unique features have been observed in their excitation and emission spectra that show on one hand the lattice defects induced by the replacement of Sr2+ by Dy3+ and proves the existence of different crystallography sites for the Dy3+ ions and on the other hand, the local distortion of the energy levels of Dy3+ ions in the presence of B3+.

Perovskite-type oxynitrides hold great potential for optical applications due to their excellent visible light absorption properties. However, only a limited number of such oxynitrides with modulated physical properties are available to date and therefore alternative fabrication strategies are needed to be developed. Here, we introduce such an alternative strategy involving a precursor microstructure controlled ammonolysis. This leads to the perovskite family member LaTa(IV)O2N containing unusual Ta4+ cations. The adjusted precursor microstructures as well as the ammonia concentration are the key parameters to precisely control the oxidation state and O:N ratio in LaTa(O,N)3. LaTa(IV)O2N has a bright red colour, an optical bandgap of 1.9 eV and a low (optically active) defect concentration. These unique characteristics make this material suitable for visible light-driven applications and the identified key parameters will set the terms for the targeted development of further promising perovskite family members.

Previous reports, albeit being partially contradictory, have indicated that the alloying of Ni with inexpensive transition metals, e.g. Co or Fe can affect the activity and stability of Ni-based catalysts under dry reforming conditions. In this work we critically assess the catalytic performance of Ni-based bi-metallic catalysts derived via the reduction of perovskite precursors, i.e. LaNi 0.8 M 0.2 O 3 (M = Ni, Co and Fe). In-situ XRD and energy dispersive X-ray spectroscopy techniques were employed to probe metal–metal and metal–support interactions and phase transformations under reactive conditions. Ni–Co was found to be the most active catalyst, whereas Ni–Fe showed no activity. We observed that the addition of Co increases the rate of La 2 O 2 CO 3 formation, which in turn enhances the removal of carbonaceous deposits from neighbouring active sites, thus, leading to a catalyst with an increased stability and activity. The poor activity of Ni–Fe was explained by the encapsulation of active Ni particle by LaFeO 3 .

We report herein on the development of Ni-based catalyst using activated carbon fibres (ACFs) as a structured support and its application for the three‐phase hydrogenation of nitroarenes (T = 353 K; P = 10 bar). It was shown that metallic Ni0 nanoparticles (NPs) with a mean diameter of ∼2.0 nm stabilized by the ACF microporous network were responsible for the catalytic transformation. To obtain optimum catalytic activity, the Ni/ACF catalyst must be freshly prepared and activated in situ by H2 at T > 353 K. Pre-treatment of the ACFs by nitric acid boosted the activity of the Ni/ACF catalyst, which exhibits high performance in hydrogenation of nitrobenzene to aniline (yield, Y ∼100%). The catalyst was tested for the reuse attaining a quasi-steady-state after the sixth reaction thereafter remaining relatively stable over seven consecutive runs. Near-quantitative transformation (Y > 99%) of p-chloronitrobenzene to p‐chloroaniline was achieved under mild conditions over the Ni/ACF catalyst with a ca. 20-fold higher activity than conventional Raney Ni. Thus, new catalyst reported here represents a significant step forward towards a simple, heterogeneous catalytic selective hydrogenation of nitroarenes that employs H2 as the hydrogen source.

The thermal stability of Cu/W nano-multilayers in the temperature range of 400 °C– 800 °C has been investigated by high-resolution scanning electron microcopy, X-ray photoelectron spectroscopy and X-ray diffraction. A repetition of 100 alternating nanolayers of Cu and W with individual thicknesses of 5 nm were prepared by magnetron sputter deposition on an α-Al2O3 substrate. In the as-deposited state, the nano-multilayers exhibit pronounced Cu and W textures with a Cu{111} 1 ¯ >||W{110} 1 ¯ > orientation relationship. Annealing at T ≥ 500 °C results in the appearance of a high number of line-shaped protrusions on the outer surface, which are composed of facetted Cu particles. Annealing at T ≥ 700 °C leads to a gradual degradation of the initial layered structure towards a spheroidized nanocomposite consisting of globular W particles embedded in a Cu matrix (after annealing at 800 °C). An average activation energy of 257 ± 21 kJ/mol (2.66 ± 0.22 eV) related to this degradation process is determined by in-situ high-temperature X-ray diffraction. The experimentally obtained activation energy indicates that the morphological transformation is governed by the diffusion of W along internal interfaces such as Cu/W interphase boundaries and W/W grain boundaries.

Methanol steam reforming (MSR) catalysts are derived from perovskite-type oxides LaCo1−x−yPdxZnyO3±δ by reductive pretreatment. The unsubstituted LaCoO3±δ (LCO) and LaCo1−x−yPdxZnyO3±δ (Co substituted with Pd and/or Zn) are synthesized by a citrate method and characterized by different techniques. The perovskite-type oxides exhibit a rhombohedral crystal structure and a comparable surface area (≈8.5 (±2) m2 g−1). The temperature-programmed reduction (TPR) shows low (100 °C 450 °C) temperature reduction events that correspond to partial and complete reduction of the non-rare-earth metal ions, respectively. At high temperatures, Pd–Zn alloy nanoparticles are formed exclusively on Pd- and Zn-containing LaCo1−x−yPdxZnyO3±δ, as evident from high angular annular dark-field scanning transmission electron microscopy (HAADF-STEM). The CO2-selective MSR performance of the catalysts strongly depends on the reductive pretreatment temperature, catalyst composition (i.e., the Pd : Zn molar ratio and the degree of Co substitution) and reaction temperature. Only LaCo1−x−yPdxZnyO3±δ catalysts show a low-temperature CO2 selectivity maximum between 225 and 250 °C, while all catalysts present similar high-temperature selectivity maxima at T > 400 °C. The former is missing on LCO, LaCo1−xPdxO3±δ or LaCo1−yZnyO3±δ. Pd–Zn nanoparticles facilitate Zn(OH)2 and Co(OH)2 formation exclusively on LaCo1−x−yPdxZnyO3±δ, as evident from in situ XRD under steam atmosphere. This indicates the important role of Pd–Zn nanoparticles in the low-temperature CO2 selectivity, which is improved from 0 to 76% at 225 °C on LCO and LaCo0.75Pd0.125Zn0.125O3±δ, respectively. The high-temperature CO2 selectivity is governed by the bulk catalyst composition and the occurrence of reverse water gas shift reaction.

In this work, nitrogen doped resorcinol–melamine–formaldehyde (RMF) resins were synthesized, pyrolyzed and physically activated with CO2. The influence of the activation time on the physicochemical properties and the water sorption behavior produced in this way was investigated. Furthermore, a comparison between physical activation with CO2 and chemical activation with KOH is presented. Materials performance was validated in an adsorption chiller test setup with a temperature step from 90 °C → 50 °C. The CO2 activated RMF carbon exhibits a maximal specific cooling power which is a factor of 1.7 higher in comparison to a commonly used, commercial silica gel reference material (430 W kg−1 compared to 255 W kg−1). This is surprising considering that the hydrophilicity of the CO2 activated carbon is rather low. The superior performance of carbon based sorbents is attributed to originate from the superior thermal transport properties of monolithic carbons over commercial silica gels. At a more feasible temperature swing 60 °C → 30 °C, the RMF derived carbon yields a specific cooling power 3.2 times greater than that of the silica gel reference.

Healing of micro-cracks is crucial for recovering the mechanical properties and extending the service time of bituminous materials. However, crack closure is often challenged by the efficiency and repeatability of the healing process or its technical and economic feasibility for large-scale applications. Here, we propose an innovative method to close micro-cracks in bituminous materials by using magnetically-triggered iron oxide nanoparticles as heating agents. Heating is generated through the so-called hyperthermia effect upon exposure of the nanoparticles to an external oscillating magnetic field. When mixed in a low volume fraction of 1% within bitumen, the nanoparticles generate enough heat to decrease the viscosity of the surrounding material and thus promote crack closure. Oleic acid is used to coat the iron oxide nanoparticles and enable their homogeneous distribution in the bitumen. Because of high hysteresis losses, γ-Fe2O3 nanoparticles with a mean crystallite size of 50 nm exhibited specific absorption rates (SAR) as high as 285 W/g when subjected to a magnetic field of 30 mT at 285 kHz. In contrast to the relatively slow heating of electrically-conductive additives, we find that iron oxide nanoparticles pre-embedded in bitumen allows for crack closure in a few seconds when subjected to similar magnetic field conditions. This represents a new efficient way to heal damage in thermoplastic road pavements in the presence of mineral aggregates.

Nanocrystalline Ba2(In1.8Cr0.2)O5·(H2O)δ powders were synthesized via a polymerizable-complex method in two different ways, one based on citric acid and the other additionally on 2,6-pyridinedicarboxylic acid, 2,6-diaminopyridine, and polyethylene glycol. Crystal structure, surface area, thermochemical and optical properties were analyzed. The photocatalytic activity was measured by the reduction of CO2 under H2 gas flow. CO2 adsorption at the catalyst surface is found to be a critical factor strongly affecting the reactivity. With this study, we demonstrate the importance of the surface states as a crucial parameter when developing better CO2 photo-reduction catalysts.

Ba2In2O5 is a mixed ionic–electronic conducting (MIEC) ceramic-based material offering a large number of oxygen vacancies to become an alternative material for oxygen separation membranes from gas mixtures or even a CO2 plasma. This material was selected as model system to deeper analyze the structure-property relations, while making use of a promising structure stability. In this study, partial substitution of In3+ by Cr3+ yielded single-phase Ba2In2–xCrxO5–δ (x = 0, 0.2, 0.25). This forced an altered arrangement of the oxygen vacancies and a structural change from orthorhombic (Ibm2) to tetragonal (I4cm). The highest oxygen permeability of P(O2) = 1.4 ± 0.1 mL min−1·cm−2·mm at 1223 K among all tested samples was obtained for x = 0.2. A precise adjustment of the degree of oxygen vacancy ordering and the unit cell volume in this material reduced the activation energy EA and enhanced the self-diffusion coefficient D0 of the oxygen ions boosting the oxygen permeability as demonstrated by the superior oxygen permeability at lower temperatures (~1000 K), still reaching an oxygen permeability of P(O2) = 0.72 ± 0.04 mL min−1·cm−2·mm at 773 K. This concept seems plausible for an adaption to other structurally related membrane materials.

Aiming for cost-efficiency through balanced utilization of rare-earth resources, the use of Ce, the cheapest and most abundant of all rare-earth elements, as potential candidate to substitute the expensive and resource-critical Nd in Nd2Fe14B hard magnetic alloys was tested in this work. Emphasis is put on the effects of substitution on the alloys structural properties and the related response to hydrogen treatment, one of the main processing routes in the production of Nd2Fe14B-based permanent magnets. The study follows the influence of Ce substitution on the phase structure and magnetic property development in hydrogen decrepitated and HDDR processed (Nd1-xCex)15Fe79B6 (x = 0, 0.1, …, 0.6) strip-cast alloys. Intergranular CeFe2 segregates in the as-cast alloys from x = 0.3, increases in proportion with x at the expense of the hard magnetic phase and replaces the rare-earth-rich grain boundary phase. Upon hydrogen absorption, CeFe2 transforms in amorphous CeFe2Hx which further decomposes into CeHx and α-Fe. The rare-earth components from CeHx and the rare-earth-rich hydrogenated phase melt upon hydrogen desorption, enabling the redistribution of the intergranular material among the Nd2Fe14B grains upon the desorption and recombination stage of the HDDR treatment, thus facilitating grain decoupling and coercivity development. Within a generally decreasing trend, at x = 0.2 and 0.3 Ce ratios, coercivity (μ0HC) and remanence (Br) of the HDDR powders remained rather stable despite the segregation of CeFe2 phase occurring at x = 0.3. Significant texture and very reasonable magnetic properties were obtained at x = 0.3 (μ0HC = 1.05 T and Br = 0.88 T), attributed to a favorable phase composition with Ce mainly concentrated in the intergranular material.

Correction for ‘Bandgap-adjustment and enhanced surface photovoltage in Y-substituted LaTaIVO2N’ by Cora Bubeck et al., J. Mater. Chem. A, 2020, 8, 11837–11848, DOI: 10.1039/D0TA02136A.

CaO is an effective high temperature CO2 sorbent that, however, suffers from a loss of its CO2 absorption capacity upon cycling due to sintering. The cyclic CO2 uptake of CaO-based sorbents is improved by Ca3Al2O6 as a structural stabilizer. Nonetheless, the initially rather stable CO2 uptake of Ca3Al2O6-stabilized CaO yet starts to decay after around 10 cycles of CO2 capture and sorbent regeneration, albeit at a significantly reduced rate compared to the unmodified reference material. Here, we show by a combined use of in situ XRD together with textural and morphological characterization techniques (SEM, STEM, and N2 physisorption) and solid-state 27Al NMR (in particular dynamic nuclear polarization surface enhanced NMR spectroscopy, DNP SENS) how microscopic changes trigger the sudden onset of deactivation of Ca3Al2O6-stabilized CaO. After a certain number of CO2 capture and regeneration cycles (approximately 10), Ca3Al2O6 transformed into Ca12Al14O33, followed by Al2O3 segregation and enrichment at the...

Cr-substituted polycrystalline Ba2(In2-xCrx)O5·(H2O)δ powders (0.04 ≤ x ≤ 0.60) were synthesized by solid state reaction to investigate the relation of crystal structure, thermochemical, magnetic, and optical properties. The Cr-substitution results in an unit cell expansion and formation of the higher-symmetric tetragonal phase together with increased oxygen and hydrogen contents. Magnetic property measurements reveal that the diamagnetic pristine Ba2In2O5·(H2O)δ becomes magnetically ordered upon Cr-substitution. By UV–vis spectroscopy a gradual shift of the absorption-edge energy to lower values was observed. Numerical calculations showed that the observed bandgap narrowing was ascribed to the Cr induced states near the Fermi level. The correlation between the changes of crystal chemistry, magnetic, and optical properties of Cr-substituted Ba2(In2-xCrx)O5·(H2O)δ can be explained by the replacement of In by Cr. Consequently, an enhanced photocatalytic CO2 reduction activity was observed with increasing Cr substitution, compatible with the state-of-the-art high surface area TiO2 photocatalyst (P-25).

Persistent luminescence of SrAl2O4:Eu2+ has attracted considerable attention due to their high initial brightness, long-lasting time and excellent thermal stability. Here the influence of boric acid on the persistent luminescence and thermal oxidation resistance of SrAl2O4:Eu2+ was investigated in detail. Crystal structural analysis and scanning electron microscopy revealed that with the addition of boron, the unit cell volume decreased and the morphology of the particles became more irregular with sharp edges. Thermogravimetric analysis showed better thermal oxidation resistance accompanied by a change in oxygen vacancy concentration when boron acid is used. Photoluminescence spectra and afterglow decay curves confirm an improved afterglow performance for boron-added SrAl2O4:Eu2+. Thermoluminesence allowed monitoring the changes in the trap states due to the presence of B. Our results imply that the substantial improvement of afterglow performance and the thermal stability in SrAl2O4:Eu2+ can be attributed to the incorporation of boron into the aluminate network.

Highly dense CaMn1–xMxO3−δ (with M = Nb, Mo, Ta, and W and 0 ≤ x ≤ 0.08) n-type thermoelectric materials with low electrical resistivities are prepared from nanocrystalline powders. Their room temperature power factors outperform the best reported results by 30% or more. In combination with the thermal conductivities, promising figure of merits of ZTM=Ta,x=0.04 = 0.21 and ZTM=W,x=0.04 = 0.20 were achieved at 1160 K. The relative changes and temperature dependencies of the Seebeck coefficient, the electrical resistivity, and the power factor are described with a small-polaron-hopping-based mechanism. In the limits of high temperatures and low substitution levels, the Seebeck coefficients are in good agreement with the Heikes formula. At high substitutions, the efficiency of the doping presumably decreases due to trapping states caused by the formation of bands from Jahn–Teller lowered eg orbitals of Mn3+. Jahn–Teller distortion of Mn3+ also leaves its footprints in the orthorhombic distortion of the crysta...

Redox Reactivity and structural phase transitions have a major impact on transport and me-chemical properties of thermoelectric CaMnO{sub 3−δ}. In this study series of Ca{sub 1−x}A{sub x}Mn{sub 1−y}B{sub y}O{sub 3−δ} (0≤x,y≤0.8) compounds, each with A-site (Dy{sup 3+}, Yb{sup 3+}) or B-site (Nb{sup 5+}, Ta{sup 5+} and Mo{sup 6+}, W{sup 6+}) substitution, were synthesized and crystallographically analyzed. It was found that the high-temperature oxygen content is widely independent from the substituent. Subsequently, with increasing temperature the differences in the Seebeck coefficient vanish above 1200 K. With increasing substitution the orthorhombic distortion of the perovskite-like phase increases. The orthorhombic distortion and the upper temperature limit of the stability of the orthorhombic crystal structure show an almost linear dependency. Accordingly, the mechanical stability of all-oxides thermoelectric converters at temperatures exceeding 1000 K will be increased employing materials with high substitution level and substituents inducing a high orthorhombic distortion. - Graphical abstract: Thermoelectric n-type CaMn{sub 0.98}W{sub 0.02}O{sub 3−δ}—Transport properties and expansion coefficient of: Oxygen loss (green region) and upper stability limit of the orthorhombic phase (yellow region) strongly affect the transport properties. Both features also cause lattice expansion, which leads to cracking of thermoelectric all-oxide converters. We report how the upper limit for applicationmore » can be shifted to even higher temperatures. - Highlights: • Level of Mn{sup 3+} at RT determines reduction behavior of Ca{sub 1−x}A{sub x}Mn{sub 1−y}B{sub y}O{sub 3−δ} at HT. • Differences in Seebeck coefficient vanish at T>1200 K independent from substitution. • Substitution increases orthorhombicity of Ca{sub 1−x}A{sub x}Mn{sub 1−y}B{sub y}O{sub 3−δ}. • Linear dependence of orthorhombicity and phase stability. • Design guidelines for increase of mechanical stability of all-oxide converters.« less

Li3MnO4, a lithium rich phase containing manganese (V), is a promising cathode material for Li-ion batteries due to its very high theoretical capacity (698 A h kg−1). Li3MnO4 was synthesized from freeze dried precursors at 398 K. Combined structural, morphological and chemical characterization by XRD, TGA, SEM, TEM and XPS revealed improvements in the micro- and nanostructure in comparison to the material synthesized by a standard solid state chemistry route. The average particle size decreased from 10 μm to 3.5 μm and the average crystallite size from close to 100 nm to around 30 nm. These modifications enhanced the capacity (23% at 10 A kg−1 and up to 31% at 50 A kg−1 with a maximum discharge capacity of 290 A h kg−1) and the rate capability.

Vanadium manganese oxides with Mn content up to 33 at% were synthesized by a low temperature hydrothermal route allowing for the preparation of both anodic and cathodic materials for Li-ion batteries. Low amounts of manganese (below 13 at%) lead to the formation of elongated particles of layered hydrated vanadium oxides with manganese and water intercalated between the V2O5 slabs, while for higher Mn content of 33 at%, monoclinic MnV2O6 is formed. Former materials are suitable for high energy cathodes while the latter one is an anodic compound. The material containing 10 at% Mn has the composition Mn0.2V2O5·0.9H2O and shows the best cathodic activity with 20% capacity improvement over V2O5·0.5H2O. Lithiated MnV2O6 with Li5MnV2O6 composition prepared electrochemically was evaluated for the first time as anode in a full-cell against Mn0.2V2O5·0.9H2O cathode. An initial capacity ca. 300 A h kg−1 was measured with this battery corresponding to more than 500 Wh kg−1. These results confirm the prospect of using Li5MnV2O6 anodes in lithium-ion batteries as well as high-capacity layered hydrated vanadium oxides cathodes such as V2O5·0.5H2O and Mn0.2V2O5·0.9H2O.

Absorbers for planar perovskite solar cells are often prepared by two-step deposition methods, where a thick compact PbI2 layer is deposited followed by conversion to perovskite using CH3NH3I solution. The surface of the precursor layer quickly reacts with the CH3NH3I solution, which hinders further diffusion of CH3NH3I into the layer, consequently leading to significant amounts of residual PbI2 at room temperature. Here, we report a novel concept that employs a porous nanostructured PbI2 layer consisting of nanoplates to rapidly prepare single phase perovskite layer. The non-compact nanoplate morphology is achieved in a controllable manner by thermal evaporation of PbI2 on TiO2-coated FTO substrate and allows easy penetration of CH3NH3I solution into the whole PbI2 layer, thus facilitating fast and complete conversion. The amount of PbI2 residual can be controlled by varying the CH3NH3I concentration. The growth of the nanoplates is governed by the intrinsic crystallographic structure of the deposited material, crystal characteristics of the underlying substrate, and deposition method. The introduced process enables planar perovskite solar cells with efficiency of 8.6% measured at maximum power point. This work opens a new route for rapid preparation of other three-dimensional organic–inorganic hybrid perovskites by rational tailoring the metal halide morphology.

The self-regenerative property of LaCo1–x –yPdx Zny O3±δ and LaFe1–x –yPdx Zny O3±δ solid solutions with monometallic Pd or bimetallic Pd/Zn substituents for Co or Fe is studied under a redox cycle by high angular annular dark-field scanning transmission electron microscopy (STEM-HAADF) and energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD). These results reveal that the composition of perovskites determines the self-regenerative property that occurs largely in LaCo1–x –yPdx Zny O3±δ but is limited greatly in LaFe1–x –yPdx Zny O3±δ. (© 2015 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim)

In this paper, barium titanate–nickel composite (BaTiO 3 –Ni) was synthesized using a sol–gel method and sintered by microwave furnace. Microwave sintering of BaTiO 3 –Ni (nanopowder and paste) was carried out at 1100 °C for 20 min to get dense composites. XRD was performed to confirm the phases of BaTiO 3 and Ni. The morphologies of sintered BaTiO 3 –Ni using Ni nanopowder and paste were characterized by FE-SEM. Microwave sintered BaTiO 3 –Ni nanopowder showed dielectric response of ϵ r ∼13,500 with tangent loss 0.04 at 10 kHz at room temperature being higher dielectric constant with less tangent loss as compared to BaTiO 3 –Ni paste. BaTiO 3 –Ni composites can not only be sintered densely at a lower temperature with rather shorter time, but also the grain growth can be suppressed by microwave sintering.