Catalytic ammonia decomposition is a sustainable chemical route for hydrogen production. Transition metal nitrides have emerged as promising and effective catalysts for this reaction. In this study, we revisit the synthesis, crystal structure, optoelectronic properties, and catalytic performance of antifluorite-derived Li7MnN4. Phase-pure Li7MnN4 powder is synthesized from Li3N and metallic Mn at 800 °C in a tantalum ampoule, resulting in a highly crystalline cubic phase with space group P4̄3 n (no. 218), a lattice parameter of a = 9.5598(8) Å, and a unit cell volume of 873.66(14) Å3. Rietveld refinement results show excellent residual factors (R wp = 1.71, S = 1.38), confirming the ordered arrangement of [MnN4]7- tetrahedra and five symmetrically distinct Li sites. The experimental data are complemented by density functional theory calculations, revealing weak spin coupling consistent with a paramagnetic ground state. Strong absorption in the UV-visible region corresponds to an experimental optical band gap of ∼2.76 eV, while Raman and infrared spectra are dominated by MnN4 tetrahedral vibrations. X-ray absorption spectroscopy indicates a high Mn oxidation state and a well-defined Mn-N/Li coordination. Catalytic tests show that Li7MnN4 and Li7MnN4 : LiNH2 (1 : 1 molar ratio) exhibit activities comparable to a Ni-based reference catalyst, with apparent activation energies of 364.4 kJ mol-1 and 256.0 kJ mol-1, respectively, highlighting the beneficial effect of LiNH2 incorporation. Thermogravimetry coupled with mass spectrometry identifies decomposition pathways involving LiNH2/Li2NH intermediates and forming Li3N and manganese nitrides. These results demonstrate that Li7MnN4 is a catalytically promising nitride for ammonia decomposition, with potential for further optimization through compositional tuning and mechanistic insights.

Five phases of Fe3-xCoxMo3N were synthezised and characterized by energy-dispersive X-ray spectroscopy, hot gas extraction analyses and X-ray diffraction. The catalytic activity for the decomposition of ammonia was investigated. The data was compared with the results for Fe3Mo3N. Co3Mo3N and Fe3Mo3N show a higher activity than the solid solutions.

High-velocity oxygen fuel (HVOF) spraying enables the deposition of particulate ceramic materials, producing dense coatings in the micrometer to millimeter range that are particularly suitable for coating metallic parts for demanding environments. Alumina (Al2O3) is one of the most commonly used feedstocks for thermal spray coatings because it has good dielectric properties, excellent hardness, and corrosion resistance while being costeffective. In this work, alumina coatings from two aqueous suspensions with different particle size distributions were processed by HVOF spraying. Rietveld refinements of the X-ray diffraction (XRD) data were used to quantitatively determine the phase content within the as-sprayed coatings. The phase composition was further explored using the electron backscatter diffraction (EBSD) method. Our work provides strong evidence for the higher retention of the thermodynamically stable alpha-Al2O3 phase in suspension HVOF-sprayed coatings compared to the powder counterpart. In addition, the impact of key processing parameters was studied, providing guidance for the production of particular phase compositions and microstructures tailored to specific application requirements.

Catalytic ammonia (NH3(g)) decomposition is a carbon-neutral chemical process for hydrogen generation. Transition metal nitrides are particularly promising in this regard due to their unique catalytic properties. This study takes a closer look at the crystal structure, explores the thermal behavior under NH3, and evaluates the catalytic activity of Li2ZrN2 for ammonia decomposition. Phase-pure Li2ZrN2, synthesized via solid-state reaction at 900 °C, crystallizes in the La2O3#CaAl2Si2-type structure in space group P3̅m1 (No. 164). Rietveld refinements and atomic parameters align well with previous studies. The unit cell parameters obtained are a = 3.2826(3) Å and c = 5.4611(5) Å. First-principles density-functional theory (DFT) calculations reveal an optical band gap of 2.50 eV, consistent with the experimentally determined value of 2.46 eV, and a low lattice thermal conductivity (1.52 W·m-1·K-1), suggesting its suitability for energy applications. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy confirm the ionic Li-N and covalent Zr-N bonding in Li2ZrN2. In situ X-ray diffraction analysis and thermogravimetric analysis coupled with mass spectrometry (TG-MS) reveal complex decomposition pathways of Li2ZrN2 under NH3, impacting catalytic activity. Ammonia decomposition initiates above 500 °C and improves with successive heating-cooling cycles, likely due to the formation of active sites.

In this work, the synthesis of phase-pure Ag 2 CdSnSe 4 by a mechanochemical approach and a subsequent annealing step in an evacuated ampoule is presented. A detailed analysis of the X-ray diffraction pattern of the product revealed the presence of weak reflections, that cannot be observed in the previously proposed crystal structure with space group Cmc 2 1 . Our structural investigation led to the assumption that Ag 2 CdSnSe 4 crystallizes in the wurtzstannite-type structure with space group Pmn 2 1 (a structure type derived from Cmc 2 1 ). The aim of this contribution is to discuss the crystal structure of Ag 2 CdSnSe 4 using Rietveld refinements in space group Cmc 2 1 and its possible subgroups.

Ag2CdGeSe4 - a I-2-II-IV-VI4 quaternary chalcogenide - was synthesized by a mechanochemical synthesis route with a subsequent annealing step inside of a glass ampoule. Detailed analysis and structural investigation using X-ray powder diffraction (PXRD) indicate that Ag2CdGeSe4 crystallizes in the wurtzstannite-type structure with space group Pmn2(1). For Rietveld refinements, all cubic diamond/sphalerite- and hexagonal diamond/wurtzite-related structure types including all subgroups of the wurtzstannite-type structure were considered. Quantum-chemical calculations were carried out at density-functional theory (DFT) level. The results do not allow an unambiguous verification of the experimentally observed Ag2CdGeSe4 type, due to the small energy differences between the structures. Comparison of calculated and measured UV/Vis data, however, support the results of the Rietveld refinement.

A new member of the A(2)B(5)C(5)X(16) family of compounds - the first one containing Se - has been synthesized. Following a one-step mechanochemical synthesis route, starting from the binary selenides and Mg metal, Cu2Mg5Sn5Se16 has been obtained. Structural evaluation was carried out using X-ray diffraction with subsequent Rietveld refinement. Cu2Mg5Sn5Se16 adopts the spinel type with space group Fd (3) over barm and exhibits a statistical distribution of Cu, Mg, and Sn on Wyckoff position 16d whereas Wyckoff position 8a is only occupied by Mg. Despite the fact that structures containing MgSe4 tetrahedra are rare in the literature, it appeared to be the most plausible way of distributing the cations in this compound.

Ammonia is an efficient compound for hydrogen transportation. The release of hydrogen from ammonia at the point of use is accomplished by the catalytic decomposition of ammonia using commercially available catalysts. Transition metal nitrides with properties similar to those of well-known precious metal-based catalysts exhibit outstanding catalytic activity in ammonia decomposition. Particularly, the cyclical formation and decomposition of certain lithium-based ternary metal nitrides result in improved catalytic activity in the decomposition of ammonia. Since the stability of lithium metal nitride oxides generally exceeds that of lithium metal nitrides, catalysts based on lithium metal nitride oxides are of particular interest for future practical applications. Therefore, this study aims at revisiting the synthesis, crystal structure, and stability from the theoretical perspective of Li14Cr2N8O, as a member of the lithium-based transition metal nitride oxide family. A one-step method is applied to successfully synthesize single-phase Li14Cr2N8O in powder form with high crystallinity. The crystal structure of Li14Cr2N8O is determined to adopt the Na14Mn2O9-type structure. The group-subgroup relation between the antifluorite-type structure and Li14Cr2N8O with the Na14Mn2O9-type structure is elucidated by applying the Barnighausen formalism. Rietveld refinements and atomic parameters from the literature show equally satisfactory results. The unit-cell parameters obtained for Li14Cr2N8O are a = 5.7936(6) & Aring; and c = 8.20634(11) & Aring; (trigonal crystal system). Theoretical studies by density functional theory (DFT) are conducted to explore the stability of Li14Cr2N8O with respect to anion order and exchange, the magnetic ground state, and the oxidation state of chromium. The findings of this study pave the way for Li14Cr2N8O to be further explored as an important catalyst for the decomposition of ammonia to generate hydrogen.

Ni2Mo3N was synthesized by ammonolysis of NiMoO4, prepared by a sol-gel-based modified Pechini route. X-ray powder diffraction measurements confirmed that Ni2Mo3N crystallizes in a filled beta-Mn type (cubic space group P4(1)32) with a lattice parameter of a = 6.6338 & Aring;. Group theoretical methods were applied to elucidate the relation between the crystal structure of Ni2Mo3N and that of the rock salt type. The high-temperature behavior was investigated in-situ by X-ray diffraction measurements in flowing ammonia gas at temperatures up to 875 degrees C. Ni2Mo3N exhibits significant catalytical activity for ammonia decomposition, which is critically discussed in comparison to literature.

Abstract A metastable polymorph of Ti3Sn (called c-Ti3Sn) exhibiting the cubic Cr3Si-type structure was prepared by a mechanochemical route. At temperatures of about 450 °C, it transforms to the well-known hexagonal phase (Ni3Sn type, called h-Ti3Sn). 0.5% of iron was incorporated into the material originating from the steel beaker and the steel balls. However, quantum-chemical calculations show that this should not lead to a stabilization of the Cr3Si type. c-Ti3Sn shows a single signal at an isomer shift of δ = 1.70(1) mm s−1 in its 119Sn Mössbauer spectrum at 78 K.

Fe3Mo3N was synthesized successfully via ammonolysis out of an oxidic precursor prepared by a modified Pechini route. Rietveld refinement using X-ray powder data confirmed that the compound crystallizes in space group Fd (3) over barm with a lattice parameter of alpha = 11.0777 angstrom Group theoretical methods were applied to elucidate the relation between the crystal structure of Fe3Mo3N and that of the copper type. The high temperature behavior of Fe3Mo3N in ammonia gas was investigated by in situ powder X-ray diffraction. In addition, the catalytic activity of our iron molybdenum nitride for ammonia decomposition was measured and compared to the activity of an industrial ironbased catalyst. Both catalysts show similar performances.

Quaternary kesterite-type (KS) compounds have attracted worldwide attention from the scientific community as promising materials for solar cells. On the route to optimizing their performance, the effect of stress and strain constitutes a critical factor when it comes to thin film applications. Following a recent theoretical study, we report here joint experimental and computational high-pressure investigations on the KS Ag2ZnSnS4 and wurtz–kesterite (WZ–KS)-type Ag2CdSnS4 compounds. Our results reveal that both materials undergo successive transformations, first into a GeSb-type and then toward a CrN-type modification at ambient temperature. Our theoretical calculations predict a metallic character for all Ag2ZnSnS4 and Ag2CdSnS4 high-pressure phases. In addition, structural disorder is observed in KS Ag2ZnSnS4 upon moderate compression, prior to its KS → GeSb-type transition. Decompression leads to the recovery of a disordered zinc blende-type structure in the latter, whereas Ag2CdSnS4 retains the disordered GeSb-type modification. The similarities and deviations from the archetypical KS Cu2ZnSnS4 are discussed.

Phase-pure and highly crystalline Na2ZnSnS4 was prepared via a mechanochemical synthesis route. It crystallizes in the kesterite-type structure. The unusual large Debye-Waller factors of the sodium atoms were analyzed in detail, respecting also group-theoretical aspects. The results point to the existence of static disorder, mainly to the presence of various patterns of sodium ordering on a local scale. This is confirmed by quantum-chemical calculations at hybrid density-functional theory level. The dynamic atomic displacements due to phonons are much smaller than the observed Debye-Waller factors.

Abstract Ag2CdSnS4 was synthesized by a two step mechanochemical synthesis route. From a detailed analysis of the observed reflections in the X-ray powder diffraction pattern, the crystal structure proposed in the literature (space group Cmc21 [E. Parthé, K. Yvon, R. H. Deitch, Acta Crystallogr.1969, B25, 1164–1174; O. V. Parasyuk, I. D. Olekseyuk, L. V. Piskach, S. V. Volkov, V. I. Pekhnyo, J. Alloys Compd.2005, 399, 173–177]) is questionable. Our structural investigations presented in this contribution point to the fact that Ag2CdSnS4 crystallizes in the monoclinic wurtzkesterite-type structure (space group Pn). At around T = 200°C, a phase transition to the orthorhombic wurtzstannite-type structure (space group Pmn21) is observed.

The presence of defects, which act as the recombination hubs for photogenerated charge carriers, hinders the improvement of photocatalytic activity for oxygen evolution reaction of LaTiO2N under visible light irradiation via a four-electron-transfer reaction pathway. Here, we involve titanium nitride (TiN) in a varying content (0–17.8%) to improve the efficiency of charge separation and transport, influencing the photoelectrochemical performance of LaTiO2N. The characterization results confirm the formation of a strong contact between orthorhombic-LaTiO2N and cubic-TiN particles. The photoelectrochemical (PEC) measurements reveal the inverse dependence between electron transfer phenomena and charge carrier recombination, which allows to understand the trend when modifying LaTiO2N with TiN. In fact, the incorporation of 17.8% TiN in the LaTiO2N:TiN material results in a higher photocurrent. Open-circuit potential (OCP) decay and transient absorption spectroscopy (TAS) studies confirm longer lifetimes of charge carriers for increasing amounts of TiN in the synthesized materials. Thus, the main role of TiN is to improve the properties of the semiconductor-electrolyte interface, having verified its impact on the separation and transport of photogenerated charge carriers. Furthermore, computational studies predict that the adsorption of water molecules is favored at the LaTiO2N:TiN surface compared to the individual TiN and LaTiO2N surfaces.

Abstract We have examined the effect of composition on the Raman-active vibrational response of the Cu2(Fe x Zn1−x )SnS4 and Cu2(Mn x Zn1−x )SnS4 solid solution series at ambient conditions. Based on these results we were able to identify the phase boundaries of the respective kesterite-type and stannite-type structures adopted by these compounds as a function of composition. In the case of Cu2(Fe x Zn1−x )SnS4, our observations correlate very well with earlier reports. For the Cu2(Mn x Zn1−x )SnS4 series, on the other hand, we were able to clearly pinpoint the kesterite↔stannite transition for intermediate compositions for the first time, indicating that Raman spectroscopy can serve as an efficient method for monitoring subtle structural transitions in these systems.

Oxygen-defective ceria, e.g. Gd-doped ceria, shows giant electromechanical properties related to a complex local rearrangement of its lattice. Although they are not entirely identified, the electroactive mechanisms arise from cation and oxygen vacancy (VO) pairs (i.e. Ce-VO), and the local structural elastic distortion in their surroundings. Here, we study the geometry and behaviour of Ce-VO pairs in a grain boundary-free bulk Ce0.9Gd0.1O1.95 single crystal under an AC electric field of ca. 11 kV cm-1. The analysis was carried out through X-ray absorption spectroscopy (XAS) techniques at the Ce L-III edge. Using Density Functional Theory (DFT) calculations, we investigated the effects of the strain on density of states and orbitals at the valence band edge. Our research indicates that electrostriction increases at low temperatures. The electromechanical strain has a structural nature and can rise by one order of magnitude, i.e., from 5 × 10-4 at room temperature to 5 × 10-3 at -193 °C, due to an increase in the population of the electrically active pairs. At a constant VO concentration, the material can thus configure heterogeneous pairs and elastic nanodomains that are either mechanically responsive or not.

Exploring alternatives to the Cu2ZnSnS4 kesterite solar cell absorber, we have calculated first principle enthalpies of different plausible structural models (kesterite, stannite, P4¯ and GeSb type) for Cu2FeSnS4 and Cu2MnSnS4 to identify low and high pressure phases. Due to the magnetic nature of Fe and Mn atoms we included a ferromagnetic (FM) and anti-ferromagnetic (AM) phase for each structural model. For Cu2FeSnS4 we predict the following transitions: P4¯ (AM) →16.3GPa GeSb type (AM) →23.0GPa GeSb type (FM). At the first transition the electronic structure changes from semi-conducting to metallic and remains metallic throughout the second transition. For Cu2MnSnS4, we predict a direct AM (kesterite) to FM (GeSb-type) transitions at somewhat lower pressure (12.1 GPa). The GeSb-type structure also shows metallic behaviour.

Abstract Ag2FeGeS4 was synthesized as a phase-pure and highly crystalline product by mechanochemical milling from the binary sulfides and iron metal, followed by annealing in H2S atmosphere. The structure evaluation was carried out using X-ray powder diffraction with subsequent Rietveld refinements. As Fe and Ge atoms are not distinguishable using conventional X-ray methods, the chalcopyrite-type structure (space group I 4 ‾ 2 d $I‾{4}2d$ ), exhibiting a statistical distribution of Fe and Ge on Wyckoff position 4b, was considered. However, quantum-chemical calculations at hybrid density-functional level indicate that mechanochemically prepared Ag2FeGeS4 crystallizes in the kesterite-type structure (space group I 4 ‾ $I‾{4}$ ) where the cations are arranged in an ordered way. Ag2FeGeS4 is a further example of a mechanochemically prepared compound differing structurally from the commonly known polymorph exhibiting the stannite type (solid-state route).