A polycrystalline sample LuCrO3 has been characterized by neutron powder diffraction (NPD) and magnetization measurements. Its crystal structure has been Rietveld refined from NPD data in space group Pnma; this perovskite contains strongly tilted CrO6 octahedra with extremely bent Cr—O—Cr superexchange angles of ∼142°. The NPD data show that below Néel temperature (T N ≃ 131 K), the magnetic structure can be defined as an A-type antiferromagnetic arrangement of Cr3+ magnetic moments, aligned along the b axis, with a canting along the c axis. A noticeable magnetostrictive effect is observed in the unit-cell parameters and volume upon cooling down across T N. The AC magnetic susceptibility indicates the onset of magnetic ordering below 112.6 K; the magnetization isotherms below T N show a nonlinear behaviour that is associated with the described canting of the Cr3+ magnetic moments. From the Curie–Weiss law, the effective moment of the Cr3+ sublattice is found to be μeff = 3.55 μB (calculated 3.7 μB) while the ΘCW parameter yields a value of −155 K, indicating antiferromagnetic interactions. There is a conspicuous increase of T N upon the application of external pressure, which must be due to shortening of the Cr—O bond length under compression that increases the orbital overlap integral.

In this work, key factors that affect catalytic activity of Ni/La-doped ceria catalysts for the reverse water gas shift reaction (RWGS) have been revealed by applying in situ advanced synchrotron techniques, such as X-ray Absorption Spectroscopy (XAS) and Near-ambient pressure X-ray Photoelectron spectroscopy (NAP-XPS). Complementary ex situ characterization techniques have been also used, adding valuable insights on different physicochemical properties of the catalysts. Lanthanum incorporates into the ceria lattice, increasing oxygen mobility, which has a role in the formation of H2O during the reaction. The optimum substitution degree of Ce by La that maximizes CO yield is close to 10 %. It is found that both bulk and surface Ce3+ proportions depend on the proportion of La, increasing with La content. At a reaction temperature of 873 K, bulk Ce3+ proportions are higher than surface ones. These differences are due to oxidative phenomena, associated to the reactive mixture that take place on the surface, such as CO2 adsorption and H2O formation. Concerning Ni phase, NiO bulk reduction to metallic Ni is very fast (in the range 573-623 K), however, Ni0 and Ni2+ species coexist on the surface during the reaction. It is found that a higher proportion of surface metallic Ni promotes the selectivity towards the RWGS, inhibiting the competing methanation reaction. On the other hand, La doping is relevant for the formation of lanthanum oxycarbonate, which has a role gasifying carbon deposits.

We report the critical behavior of the FexTi2S4 (x = 0.24, 0.42) intercalated Heideite sulfides in the vicinity of their second-order magnetic phase transition. Several methods including the modified Arrott plot, Widom scaling law, and the critical isotherm analysis reliably yield critical exponents beta = 1.105/0.442, gamma = 0.913/1.042, and delta = 1.826/3.357, in agreement with the scaling hypothesis, although slightly deviating from the conventional theoretical values. Using the renormalization group theory analysis, we conclude that the exchange distance J(r) and the correlation length critical exponent nu indicate that increasing Fe content induces a transition from localized spin interactions, described by the mean-field model, to an itinerant-electron 3D Heisenberg-like model near T-C. These features reveal a coupling between short- and long-range magnetic interactions, which are responsible for the unconventional critical behavior in FexTi2S4. Our results provide valuable insights into the magnetic nature and offer tuning mechanisms in FexTi2S4 intercalated sulfides.

Double perovskite oxides, characterized by their tunable magnetic properties and robust interconnection between the lattice and magnetic degrees of freedom, present an enticing foundation for advanced magnetic refrigeration materials. Herein, we delve into the influence of rare-earth elements on RSrCoFeO6 (R = Sm, Eu) disordered double perovskites by examining their structural, electronic, magnetic, and magnetocaloric properties. Temperature-dependent synchrotron X-ray diffraction analysis confirmed the stability of the orthorhombic phase (Pnma) across a wide temperature range. X-ray photoemission spectroscopy revealed that both Sm and Eu are in the 3+ state, whereas multiple states for Co2+/3+ and Fe3+/4+ are identified. The magnetic investigation and magnetocaloric effect (MCE) analysis brought to light the presence of a long-range antiferromagnetic (AFM) order with a second-order phase transition (SOPT) in both samples. The maximum magnetic entropy change Delta S-M(max) was approximately 0.9 J/kg K for both samples at applied field 0-7 T, manifesting prominently above Neel temperatures T-N approximate to 93 K (Sm) and 84 K (Eu). Nevertheless, different relative cooling powers (RCP) of 112.6 J/kg (Sm) and 95.5 J/kg (Eu) were observed. A detailed analysis of the temperature-dependent lattice parameters shed light on a distinct magnetocaloric effect across the magnetic transition temperature, unveiling an anisotropic thermal expansion [alpha(V) = 1.41 x 10(-5) K-1 (Sm) and alpha(V) = 1.54 x 10(-5) K-1 (Eu)] wherein the thermal expansion axial ratio alpha(Sm)(b)/alpha(Eu)(b) = 0.61 became lower with increasing temperature, which suggests that the Eu sample experiences a greater thermal expansion in the b-axis direction. At the atomic bonding level, the evidence for magnetoelastic coupling around the magnetic transition temperatures T-N was found through the anomalies along the average Co/Fe-O bond distance, formal valence, octahedral distortion, as well as an anisotropic lattice expansion.

The local atomic arrangement correlates to the short-range magnetic interactions mediated by electron hopping between Ni e g states, suggesting the occurrence of magnetoelastic coupling and magnetic frustration in Ni 0.8 Ti 2 S 4 .

Metal halide perovskites with a two-dimensional structure are utilized in photovoltaics and optoelectronics. High-crystallinity CsSn2Br5 specimens have been synthesized via ball milling. Differential scanning calorimetry curves show melting at 553 K (endothermic) and recrystallization at 516 K (exothermic). Structural analysis using synchrotron X-ray diffraction data, collected from 100 to 373 K, allows for the determination of Debye model parameters. This analysis provides insights into the relative Cs-Br and Sn-Br chemical bonds within the tetragonal structure (space group: I4/mcm), which remains stable throughout the temperature range studied. Combined with neutron data, X-N techniques permit the identification of the Sn2+ lone electron pair (5s(2)) in the two-dimensional framework, occupying empty space opposite to the four Sn-Br bonds of the pyramidal [SnBr4] coordination polyhedra. Additionally, diffuse reflectance UV-vis spectroscopy unveils an indirect optical gap of approximately similar to 3.3 eV, aligning with the calculated value from the B3LYP-DFT method (similar to 3.2 eV). The material exhibits a positive Seebeck coefficient as high as 6.5 x 10(4) mu V K-1 at 350 K, which evolves down to negative values of -3.0 x 10(3) mu V K-1 at 550 K, surpassing values reported for other halide perovskites. Notably, the thermal conductivity remains exceptionally low, between 0.32 and 0.25 W m(-1) K-1.

Spin-frustrated systems are well known for exhibiting fascinating and exotic magnetic properties and are often intertwined with other intriguing phenomena. Magnetization and specific-heat studies suggest that the spinfrustrated chiral triangular lattice compound MnGeTeO6 undergoes a long-range antiferromagnetic transition below the N & eacute;el temperature (TN) 9 K, which is further validated in the neutron powder-diffraction (NPD) study. In the absence of an external magnetic field (H), analysis of NPD data reveals a complex incommensurate spin structure, characterized by a mixture of helical and cycloidal spin orderings with a propagation vector of k = (1/3, 1/3, 0.184). Upon the application of H, this spin ordering transforms into a conical spin structure, which is manifested as a metamagnetic transition in the isothermal magnetization (M) curve when H exceeds similar to 0.9 T. Total energy calculations and estimation of various exchange-interaction energies (J) by densityfunctional theory calculations also support the formation of such a complex spin ordering. Moreover, a pronounced dielectric (e') anomaly is observed near TN, which is suppressed considerably under H. The variation of e' with increasing H closely reflects the As' cx M2 scaling behavior in the low-H regime, thus indicating a higher-order magnetoelectric coupling. Moreover, synchrotron x-ray diffraction reveals an isostructural distortion below TN, suggesting magnetoelastic coupling as a trigger for the dielectric anomaly.

Thermoelectric materials offer a promising avenue for energy management, directly converting heat into electrical energy. Among them, AgSbTe(2 )has gained significant attention and continues to be a subject of research at further improving its thermoelectric performance and expanding its practical applications. This study focuses on Ag-deficient Ag(0.7)Sb(1.12)Te(2)and Ag0.7Sb1.12Te1.95Se0.05 materials, examining the impact of compositional engineering within the AgSbTe2 thermoelectric system. These materials have been rapidly synthesized using an arc-melting technique, resulting in the production of dense nanostructured pellets. Detailed analysis through scanning electron microscopy (SEM) reveals the presence of a layered nanostructure, which significantly influences the thermoelectric properties of these materials. Synchrotron X-ray diffraction reveals significant changes in the lattice parameters and atomic displacement parameters (ADPs) that suggest a weakening of bond order in the structure. The thermoelectric characterization highlights the enhanced power factor of Ag-deficient materials that, combined with the low glass-like thermal conductivity, results in a significant improvement in the figure of merit, achieving zT values of 1.25 in Ag(0.7)Sb(1.12)Te(2 )and 1.01 in Ag0.7Sb1.12Te1.95Se0.05 at 750 K.

Among thermoelectric materials, skutterudites are the most prominent candidates in the mid-temperature range applications. In the multiple-filled Sr0.2Yb0.2Co4Sb12 skutterudite, with Sr and Yb as fillers, we have enhanced the thermoelectric performance of CoSb3 through the reduction of lattice thermal conductivity and the optimization of carrier concentration and electrical conductivity. The high-pressure synthesis of the double-filled derivative promotes filling fraction fluctuation. This is observed by high angular resolution synchrotron X-ray diffraction, showing a phase segregation that corresponds to an inhomogeneous distribution of the filler atoms, located at the 2a positions of the cubic space group Im3̅. In addition, scanning transmission electron microscopy (STEM) combined with EELS spectroscopy clearly shows a segregation of Sr atoms from the surface of the grains, which is compatible with the synchrotron X-ray powder diffraction results. Mean square displacement parameters analysis results in Einstein temperatures of ∼94 and ∼67 K for Sr and Yb, respectively, and a Debye temperature of ∼250 K. The strong effect on resonant and disorder scattering yields a significantly lower lattice thermal conductivity of 2.5 W m-1 K-1 at 773 K. Still, good weighed-mobility values were obtained, with high filling fraction of the Yb and Sr elements. This drives a reduced electrical resistivity of 2.1 × 10-5 Ω m, which leads to a peak zT of 0.26 at 773 K. The analysis and results performed for the synthesized (Sr,Yb)-double filled CoSb3, shed light on skutterudites for potential waste-heat recovery applications.

In this work, Gd-filled skutterudite GdxCo4Sb12 was prepared using one step method under high pressure in a piston-cylinder-based press at 3.5 GPa and moderate temperature of 800 °C. A detailed structural characterization was performed using synchrotron X-ray diffraction (SXRD), revealing a filling fraction of x = 0.033(2) and an average bond length of 3.3499(3) Å. The lattice thermal expansion accessed via temperature-dependent SXRD led to a precise determination of a Debye temperature of 322(3) K, from the fitting of the unit-cell volume expansion using the second order Grüneisen approximation. This parameter, when evaluated through the mean square displacements of Co and Sb, displayed a value of 265(2) K, meaning that the application of the harmonic Debye theory underestimates the Debye temperature in skutterudites. Regarding the Gd atom, its intrinsic disorder value was ~5× and ~25× higher than those of the Co and Sb, respectively, denoting that Gd has a strong rattling behavior with an Einstein temperature of θE = 67(2) K. As a result, an ultra-low thermal conductivity of 0.89 W/m·K at 773 K was obtained, leading to a thermoelectric efficiency zT of 0.5 at 673 K.

Among chalcogenide thermoelectric materials, SnTe is an excellent candidate for intermediate temperature applications, in replacement of toxic PbTe. We have prepared pure polycrystalline SnTe by arc melting, and investigated the structural evolution by temperature-dependent neutron powder diffraction (NPD) from room temperature up to 973 K. In this temperature range, the sample is cubic (space group Fm-3m) and shows considerably larger displacement parameters for Te than for Sn. The structural analysis allowed the determination of the Debye model parameters and provided information on the Sn–Te chemical bonds. SEM images show a conspicuous nanostructuration in layers below 30 nm thick, which contributes to the reduction of the thermal conductivity down to 2.5 W/m·K at 800 K. The SPS treatment seems to reduce the number of Sn vacancies, thus diminishing the carrier density and increasing the Seebeck coefficient, which reaches 60 μV K−1 at 700 K, as well as the weighted mobility, almost doubled compared with that of the as-grown sample.

In RbSn2Br5 halide, prepared by mechano-chemistry, the 5s2 lone electron pairs of Sn2+ were located from NPD and SXRD data. Among the thermoelectric properties, a huge Seebeck coefficient and an extremely low thermal conductivity are determined.

Despite the great success of hybrid CH3NH3PbI3 perovskite in photovoltaics, ascribed to its excellent optical absorption properties, its instability toward moisture is still an insurmountable drawback. All-inorganic perovskites are much less sensitive to humidity and have potential interest for solar cell applications. Alternative strategies have been developed to design novel materials with appealing properties, which include different topologies for the octahedral arrangements from three-dimensional (3D, e.g., CsPbBr3 perovskite) or two-dimensional (2D, e.g., CsPb2Br5) to zero-dimensional (0D, i.e., without connection between octahedra), as the case of Cs4PbX6 (X = Br, I) halides. The crystal structure of these materials is complex, and their thermal evolution is unexplored. In this work, we describe the synthesis of Cs4PbBr6-xIx (x = 0, 2, 4, 6) halides by mechanochemical procedures with green credentials; these specimens display excellent crystallinity enabling a detailed structural investigation from synchrotron X-ray powder diffraction (SXRD) data, essential to revisit some features in the temperature range of 90-298 K. In all this regime, the structure is defined in the trigonal R3̅c space group (#167). The presence of Cs and X vacancies suggests some ionic mobility into the crystal structure of these 0D halides. Bond valence maps (BVMs) are useful in determining isovalent surfaces for both Cs4PbBr6 and Cs4PbI6 phases, unveiling the likely ionic pathways for cesium and bromide ions and showing a full 3D connection in the bromide phase, in contrast to the iodide one. On the other hand, the evolution of the anisotropic displacement parameters is useful to evaluate the Debye temperatures, confirming that Cs atoms have more freedom to move, while Pb is more confined at its site, likely due to a higher covalency degree in Pb-X bonds than that in Cs-X bonds. Diffuse reflectance ultraviolet-visible (UV-vis) spectroscopy shows that the optical band gap can be tuned depending on iodine content (x) in the range of 3.6-3.06 eV. From density functional theory (DFT) simulations, the general trend of reducing the band gap when Br is replaced by I is well reproduced.

The development of new magnetic refrigerants demands an effective investigation of materials with a large magnetocaloric effect in a wide temperature range. Herein, we report on the structural, magnetic, and magnetocaloric properties of the two-site disordered double perovskite GdSrCoFeO6 prepared by the modified solid-state synthesis method. Temperature-dependent synchrotron X-ray diffraction analysis revealed that GdSrCoFeO6 crystallizes in the orthorhombic phase (Pnma), with Gd3+/Sr2+ and Co2+/3+/Fe3+/4+ ions randomly distributed on the A-and B-sites, respectively. An observed lattice parameter anomaly around 60 K indicates the occurrence of the magnetoelastic coupling, which coincides with the presence of ferro/ferrimagnetic (FM/FiM) ordering below T-C approximate to 65 K from the magnetic measurements. These results match well with our first-principles calculation prediction of low-temperature magnetic (FM/FiM) and electronic (insulating/metal) transitions related to a combined effect of Co and Fe short-and long-range competitions, crossings of spin state at Co ions, and the hybridization degree between Gd-4f and Co-3d states. Additionally, a modified Arrott plot and Kouvel-Fisher analysis were used to establish the nature of the magnetic phase transition in GdSrCoFeO6, yielding the critical exponent beta = 1.46(6)/1.45(6), gamma = 1.48(5)/1.17(2), and delta = 2.01(3)/1.80(5), respectively. The specific heat analysis reveals two well-defined broad peaks (similar to 10 and similar to 70 K), which match well with a Schottky anomaly (Gd-4f ) and the magnetic transition of FM/FiM to paramagnetic order, respectively. The magnetocaloric effect (MCE) analysis reveals a maximum magnetic entropy change Delta SM m a x approximate to 13 J kg(-1) K-1 (at similar to 8 K) under a field of 0-7 T. These results evidence that the Schottky anomaly and the magnetoelastic coupling seem to be key factors for driving further enhancements to the MCE in GdSrCoFeO6, making it a possible candidate for cryogenic applications.

Since superconductivity was first reported in nickelate thin films, many studies have been published about this family of materials, and different hypotheses have been proposed for explaining the mechanisms and structural dependence. Here, we report the synthesis of anchored infinite-layer LaNi0.9Al0.1O2.1 and its hole-doped derivatives by topotactic reduction from La1_xSrxNi0.9Al0.1O3 rhombohedral perovskites. LaNiO2 derivatives constitute a new family of high -temperature superconductors, with the same structure as high-Tc cuprates but based on nickel, only showing superconductivity in thin films for now. We describe a strategy to stabilize LaNiO2 derivatives in bulk: the presence of Al at the octahedral sites helps to stabilize/anchor the infinite-layer structure. The reasons for the bulk being non -superconductors are hotly debated in the literature. An important question is whether there is some hydrogen incorporated into the structure during the reduction process from LaNiO3 to LaNiO2, predicted theoretically but not reported experimentally. Our neutron powder diffraction data show that, indeed, hydrogen occupies the centers of the Ni- O squares, and spectroscopic evidence from EELS and XAS suggests that Ni is reduced to the Ni+ oxidation state, consistent with the crystallochemical data.

The RNiO3 nickelate perovskites represent a promising class of materials for spintronics applications such as in modern communication devices. This is related to the large diversity of properties shown by these compounds. Indeed, depending on the external parameters, such as temperature, pressure, or R cation size, they can exhibit para- or antiferromagnetic behavior and can transform from an insulator to a metal. Among them, PrNiO3 is one of the most important members because it exhibits tunable electronic and magnetic properties. However, our understanding of how these properties can be modified through external parameters, such as pressure and temperature, remains under debate. In this work, we characterized the structural, electronic, and magnetic properties of PrNiO3 in the range of 0-21 GPa and 10-973 K. For this purpose, we performed synchrotron X-ray diffraction (SXRD), X-ray absorption near-edge structure spectroscopy (XANES), and magnetic measurements. We compared the experimental XANES data with ab initio calculations to extract information about the electronic structure. The diffraction data demonstrated a sharp transition at the bulk level between monoclinic and orthorhombic PrNiO3 (P2(1)/n -> Pbnm) at T-IM similar to 130 K, while XANES data, which probe the medium-range and electronic structure, showed progressive changes between 90 and 130 K. The latter is in accordance with our previous EXAFS data, attesting that this transition occurs around 130 K and that it is driven at the local and medium-range scales. Between 700 and 800 K at ambient pressure, the Pbnm phase transforms into a rhombohedral phase (R3c), in agreement with a previous laboratory X-ray diffraction study. Our XANES data and ab initio simulations across this transition indicate a significant raising of the orbital overlap between Ni 3d and O 2p, suggesting superior electronic properties of the rhombohedral phase compared to the orthorhombic structure. Under isothermal cold compression, we found that the Pbnm to R3c transition is characterized by a large coexisting domain between 5.8 and 12.2 GPa. Based on the present and literature data, we proposed an extended pressure- and temperature-phase diagram of PrNiO3 and provided first-order constraints on the interplay between external parameters and properties in nickelates.

AgSbTe2 intermetallic compound is a promising thermoelectric material. It has also been described as necessary to obtain LAST and TAGS alloys, some of the best performing thermoelectrics of the last decades. Due to the random location of Ag and Sb atoms in the crystal structure, the electronic structure is highly influenced by the atomic ordering of these atoms and makes the accurate determination of the Ag/Sb occupancy of paramount importance. We report on the synthesis of polycrystalline AgSbTe2 by arc-melting, yielding nanostructured dense pellets. SEM images show a conspicuous layered nanostructuration, with a layer thickness of 25–30 nm. Neutron powder diffraction data show that AgSbTe2 crystalizes in the cubic Pm-3m space group, with a slight deficiency of Te, probably due to volatilization during the arc-melting process. The transport properties show some anomalies at ~600 K, which can be related to the onset temperature for atomic ordering. The average thermoelectric figure of merit remains around ~0.6 from ~550 up to ~680 K.

The local atomic structure of skutterudite-type compounds derived from CoSb3 plays a pivotal role in tuning their electronic and thermal properties in thermoelectric applications. For instance, the shape of the occurring [Sb-4] rings has direct consequences on the band convergence and, then, the possible enhancement of the thermoelectric efficiency. In this work, both local and electronic structures of the CoSb3 skutterudite were evaluated by the X-ray absorption technique. Extended X-rayabsorption fine-structure oscillations at the Sb K-edge were fitted in good agreement to the body-centered cubic phase. The edge shift values were taken referencing the Co and Sb foils. The standard samples were used, namely, CoO (Co2+), Co3O4 (Co2.5+), Sb2O3 (Sb3+), and Sb2O5 (Sb5+). Based on the valence state dependence of the edge shift, the valences of Co and Sb in CoSb3 were estimated as +0.8(5) for Co and -2.2(3) for Sb, which suggests a partial charge transfer from the metal to the pnictide element. From the bonding distances of Co-Sb, Sb-Sb (short), and Sb-Sb (long), the lattice parameter and fractional coordinates (y, z) were evaluated and, then, compared to those extracted from synchrotron X-ray diffraction. From temperature-dependent X-ray absorption spectroscopy data at 80-350 K, the Einstein temperatures and local coefficients of thermal expansion of those pair-bonds were properly estimated. Comparing these values with those obtained from diffraction, we have established the boundaries of both shortand long-range order techniques for structural characterization of skutterudite-based thermoelectrics.

Neutron powder diffraction and thermoelectric characterization of SnSe:K x intermetallic alloys are presented. Nanostructured ingots were prepared by arc-melting elemental tin and selenium along with potassium hydride. Up to x = 0.1 of K can be incorporated into SnSe. Rietveld refinement of the diffractograms locates potassium on the Sn site in the high-temperature Cmcm structure. However, in the low-temperature Pnma structure, K cannot be localized by difference Fourier maps, indicating the incorporation of K in a disordered form in the interlayer space. STEM-EELS indicates the incorporation of K into the SnSe grains. The resistivity upon K-doping at intermediate temperatures decreases by 1–2 orders of magnitude, but at high temperature is higher than the undoped SnSe. The Seebeck coefficient of K-doped SnSe remains p-type and almost temperature independent (400 μV/K for x = 0.1). The ultralow thermal conductivity of undoped SnSe decreases further upon K-doping to below 0.3 W/m K.

The elusive crystal structure of the socalled “antimonic acid” has been investigated by means of robust and state-of-the-art techniques. The synergic results of solidstate magicangle spinning nuclear magnetic resonance spectroscopy and a combined Rietveld refinement from synchrotron X-ray and neutron powder diffraction data reveal that this compound contains two types of protons, in a pyrochloretype structure of stoichiometric formula (H3O)1.20(7)H0.77(9)Sb2O6. Some protons belong to heavily delocalized H3O+ subunits, while some H+ are directly bonded to the oxygen atoms of the covalent framework of the pyrochlore structure, with O − H distances close to 1 Å. A proton diffusion mechanism is proposed relying on percolation pathways determined by bondvalence energy landscape analysis. Xray absorption spectroscopy results corroborate the structural data around Sb5+ ions at shortrange order. Thermogravimetric analysis and differential scanning calorimetry endorsed the conclusions on the water content within antimonic acid. Additional 0.7 water molecules per formula were assessed as moisture water by thermal analysis.