Neutron Powder Diffraction Data Research Articles

Seeing the Unseen: The Structural Influence of the Lone Pair Electrons in PbWO4.

Pair distribution function (PDF) analysis of the scheelite-type material PbWO4 reveals previously unidentified short-range structural distortions in the PbO8 polyhedra and WO4 tetrahedra not observed in the similarly structured CaWO4. These local distortions are a result of the structural influence of the Pb2+ 6s2 lone pair electrons. These are not evident from the Rietveld analysis of synchrotron X-ray or neutron powder diffraction data, nor do they strongly influence the X-ray PDF (XPDF). This illustrates the importance of neutron PDF (NPDF) in the study of such materials. First-principles density function theory (DFT) calculations show that the Pb2+ 6s2 electrons are hybridized with the O2- 2p electrons near the Fermi level. The presence of local-scale distortions has previously been neglected in studies of structure-functionality relationships in PbWO4 and other scheelite-structured photocatalytic materials, including BiVO4, and this observation opens new avenues for their optimization.

Nanostructured Niobium and Titanium Carbonitrides as Electrocatalyst Supports.

Nanostructured niobium-titanium carbonitrides, (Nb,Ti)C1-xNx, with the cubic-rock salt structure are prepared without the use of reactive gases via thermal treatment (700-1200 °C) under nitrogen of mixtures of guanidine carbonate and ammonium niobate (V) oxalate hydrate, with addition of ammonium titanyl oxalate monohydrate as a titanium source. The bulk structure and chemical composition of the materials are characterized using powder X-ray diffraction (XRD) and powder neutron diffraction, elemental homogeneity is studied using energy dispersive spectroscopy (EDS) mapping using transmission electron microscopy (TEM), and surface chemical analysis is examined using X-ray photoelectron spectroscopy (XPS). Nanoscale crystallites of between 10 and 50 nm are observed by TEM, where EDS reveals the homogeneity of metal distribution for the mixed-metal materials. Titanium carbonitrides are found to be air sensitive, reacting with air under ambient conditions, while titanium-niobium carbonitrides are found to degrade in aqueous sulfuric acid. The niobium carbonitrides, however, show some stability toward acidic solutions. Materials are produced with composition NbC1-xNx with x between 0.35 and 0.45, and more carbon-rich materials (x ≈ 0.35) are found as the synthesis temperature is increased, as proven by Rietveld refinement of crystal structure against powder neutron diffraction data. Despite phase purity seen by diffraction and negligible bulk carbon content, XPS shows a complex surface chemistry for the NbC1-xNx materials, with evidence for Nb2O5-like oxide species in a carbon-rich environment. The NbC1-xNx prepared at 900 °C has a surface area around 50 m2 g-1, making it suitable as a catalyst support. Loading with iridium provides a material active for the oxygen evolution reaction in 0.1 M sulfuric acid, with minimal leaching of either Nb or Ir after 1000 cycles.

A New Family of High Oxidation State Antiperovskite Nitrides: La3MN5 (M = Cr, Mn and Mo).

Three new nitrides La3MN5 (M = Cr, Mn, and Mo) have been synthesized using a high pressure azide route. These are the first examples of ternary Cs3CoCl5-type nitrides, and show that this (MN4)NLa3 antiperovskite structure type may be used to stabilise high oxidation-state transition metals in tetrahedral molecular [MN4]n- nitridometallate anions. Magnetic measurements confirm that Cr and Mo are in the M6+ state, but the M = Mn phase has an anomalously small paramagnetic moment and large cell volume. Neutron powder diffraction data are fitted using an anion-excess La3MnN5.30 model (space group I4/mcm, a = 6.81587(9) Å and c = 11.22664(18) Å at 200 K) in which Mn is close to the +7 state. Excess-anion incorporation into Cs3CoCl5-type materials has not been previously reported, and this or other substitution mechanisms may enable many other high oxidation state transition metal nitrides to be prepared.

A New Family of High Oxidation State Antiperovskite Nitrides: La3MN5 (M = Cr, Mn and Mo)

Three new nitrides La3MN5 (M = Cr, Mn, and Mo) have been synthesized using a high pressure azide route. These are the first examples of ternary Cs3CoCl5‐type nitrides, and show that this (MN4)NLa3 antiperovskite structure type may be used to stabilise high oxidation‐state transition metals in tetrahedral molecular [MN4]n‐ nitridometallate anions. Magnetic measurements confirm that Cr and Mo are in the M6+ state, but the M = Mn phase has an anomalously small paramagnetic moment and large cell volume. Neutron powder diffraction data are fitted using an anion‐excess La3MnN5.30 model (space group I4/mcm, a = 6.81587(9) Å and c = 11.22664(18) Å at 200 K) in which Mn is close to the +7 state. Excess‐anion incorporation into Cs3CoCl5‐type materials has not been previously reported, and this or other substitution mechanisms may enable many other high oxidation state transition metal nitrides to be prepared.

Ruddlesden-Popper Oxyfluorides La2Ni1-xCuxO3F2 (0 ≤ x ≤ 1): Impact of the Ni/Cu Ratio on the Structure.

Ruddlesden-Popper oxyfluorides La2Ni1-xCuxO3F2 (0 ≤ x ≤ 1) were obtained by topochemical reaction of oxide precursors La2Ni1-xCuxO4, prepared by citrate-based soft chemistry synthesis, with polyvinylidene fluoride (PVDF) as the fluorine source. Systematic changes of the crystal structure in the oxide as well as the oxyfluoride substitution series were investigated. For 0.2 ≤ x ≤ 0.9, the oxyfluorides adopt the monoclinic (C2/c) structural distortion previously solved for the x = 0.8 compound based on neutron powder diffraction data, whereas the sample with a lower Cu content of x = 0.1 crystallizes in the orthorhombic (Cccm) structure variant of La2NiO3F2. The orthorhombic-to-monoclinic structural transition was found to be the result of an additional tilt component of the Jahn-Teller elongated CuO4F2 octahedra. The structural transitions were additionally studied by DFT calculations, confirming the monoclinic space group symmetry. The "channel-like" anionic ordering of the endmembers La2NiO3F2 and La2CuO3F2 was checked by 19F MAS NMR experiments and was found to persist throughout the entire substitution series.

Thermal multiferroics in all-inorganic quasi-two-dimensional halide perovskites.

Multiferroic materials, particularly those possessing simultaneous electric and magnetic orders, offer a platform for design technologies and to study modern physics. Despite the substantial progress and evolution of multiferroics, one priority in the field remains to be the discovery of unexplored materials, especially those offering different mechanisms for controlling electric and magnetic orders1. Here we demonstrate the simultaneous thermal control of electric and magnetic polarizations in quasi-two-dimensional halides (K,Rb)3Mn2Cl7, arising from a polar-antipolar transition, as evidenced using both X-ray and neutron powder diffraction data. Our density functional theory calculations indicate a possible polarization-switching path including a strong coupling between the electric and magnetic orders in our halide materials, suggesting a magnetoelectric coupling and a situation not realized in oxide analogues. We expect our findings to stimulate the exploration of non-oxide multiferroics and magnetoelectrics to open access to alternative mechanisms, beyond conventional electric and magnetic control, for coupling ferroic orders.

Hydride-Ion Conduction in AELiH3 (AE = Sr, Ba)

Hydride ions (H–) are expected to conduct fast in solids owing to their monovalent state, appropriate ionic radius for conduction, and large polarizability. Thus, H– is a promising class of the charge carrier with high mobility, and may be applicable to the electrochemical reaction in batteries and fuel cells. The K2NiF4–type structure, wherein the perovskite KNiF3 and the rock-salt KF layers are stacked along the c-axis, has been the most researched material as a hydride-ion conductor, e.g., K2NiF4–type oxyhydrides of La2–x–y Sr x +y LiH1–x+y O3–y [1]. In this study, we focused on perovskite-type hydrides, AELiH3 (AE = Ca, Sr, Ba). A simple perovskite structure is expected to have high ionic conductivity, because it ensures a three-dimensional diffusion pathway for the anion species [2-6].First, the migration energy of H– ions in the AELiH3 materials were evaluated using nudged elastic band (NEB) calculations. The migration pathway between adjacent H– sites via vacancies was considered. First-principles calculations were performed using the projector-augmented wave method and PBEsol functional as implemented in the VASP code. The H– diffusivity of sodium-doped SrLiH3 was investigated using density functional theory molecular dynamics. AELiH3 were experimentally synthesized using a mechanochemical method, and their ionic conductivities were evaluated using electrochemical impedance spectroscopy. To further improve the ionic conductivity of these materials, hydride-ion vacancies were introduced by replacing the A-site cation with the monovalent cation of Na+. Neutron powder diffraction (NPD) data were collected at room temperature using a time-of-flight diffractometer (BL09 SPICA) at the J-PARC facility. The distribution of the nuclear scattering length density was analyzed by the maximum entropy method (MEM) using the Z-MEM code. The effect of the alkali-earth element at A-site on the migration energy of H– was evaluated using NEB. The migration energy are estimated to be 24, 35, and 39 kJ mol–1 for CaLiH3, SrLiH3, and BaLiH3, respectively. These low migration energy (< 40 kJ mol–1) suggest that the perovskite-type AELiH3 are suitable substances for hydride-ion conduction. AELiH3 (AE = Sr, Ba) were synthesized via mechanical milling process. The X-ray diffraction patterns of SrLiH3 and BaLiH3 were attributed to a cubic perovskite structure with the space group Pm–3m. For CaLiH3, the starting materials of CaH2 and LiH remained in the product, and the perovskite-type CaLiH3 could not be synthesized. The ionic conductivities of SrLiH3 and BaLiH3 at 100 °C were 4.6 × 10–7 and 6.7 × 10–9 S cm–1, respectively. This clearly denotes the characteristic of hydride ion; a smaller ionic radius of the A-site cation results in a lower migration energy and a higher ionic conductivity. Solid solutions of Sr1–x Na x LiH3–x were obtained in the range of 0 ≤ x ≤ 0.075. The ionic conductivity was enhanced upon Na-doping. The highest conductivity was observed for Sr0.925Na0.075LiH2.925 (x = 0.075) with a bulk conductivity of 5.0 × 10–6 S cm–1 at 25.6 °C. The figure shows the refined crystal structure of Sr0.925Na0.075LiH2.925 obtained by a Rietveld analysis of the NPD data, in addition to the isosurface plot of the nuclear density obtained by MEM. Rietveld analysis confirmed the presence of H defects and a remarkable anisotropy of the thermal oscillations of H. The negative nuclear density at the H sites showed broadening along the {100} direction. These structural features suggest that hydride ions conduct via vacancies between their adjacent sites. The choice of small cations at the A sites and the presence of hydrogen vacancies in perovskite-type hydrides resulted in high hydride-ion conductivity. [1] Kobayashi et.al., Science, 351, 1314–1317(2016). [2] Bai, Q. et.al., ACS Appl. Energy Mater., 1, 1626–1634(2018). [3] Ishihara, T. et.al., J. Am. Chem. Soc., 116, 3801–3803(1994). [4] Li, M. et.al., Nat. Mater., 13, 31–35(2014). [5] Hull, S. et.al., J. Phys.: Condens. Matter, 11, 5257–5272(1999). [6] Yamane, Y. et.al., Solid State Ionics, 179, 605–610(2008). Figure 1

Ba12 [BN2 ]6.67 H4 : A Disordered Anti-Skutterudite filled with Nitridoborate Anions.

Skutterudites are of high interest in current research due to their diversity of structures comprising empty, partially filled and filled variants, mostly based on metallic compounds. We herein present Ba12 [BN2 ]6.67 H4 , forming a non-metallic filled anti-skutterudite. It is accessed in a solid-state ampoule reaction from barium subnitride, boron nitride and barium hydride at 750 °C. Single-crystal X-ray and neutron powder diffraction data allowed to elucidate the structure in the cubic space group Im (no. 204). The barium and hydride atoms form a three-dimensional network consisting of corner-sharing HBa6 octahedra and Ba12 icosahedra. Slightly bent [BN2 ]3- units are located in the icosahedra and the voids in-between. 1 H and 11 B magic angle spinning (MAS) NMR experiments and vibrational spectroscopy further support the structure model. Quantum chemical calculations coincide well with experimental results and provide information about the electronic structure of Ba12 [BN2 ]6.67 H4 .

Ba12[BN2]6.67H4: A Disordered Anti‐Skutterudite filled with Nitridoborate Anions

AbstractSkutterudites are of high interest in current research due to their diversity of structures comprising empty, partially filled and filled variants, mostly based on metallic compounds. We herein present Ba12[BN2]6.67H4, forming a non‐metallic filled anti‐skutterudite. It is accessed in a solid‐state ampoule reaction from barium subnitride, boron nitride and barium hydride at 750 °C. Single‐crystal X‐ray and neutron powder diffraction data allowed to elucidate the structure in the cubic space group Im (no. 204). The barium and hydride atoms form a three‐dimensional network consisting of corner‐sharing HBa6 octahedra and Ba12 icosahedra. Slightly bent [BN2]3− units are located in the icosahedra and the voids in‐between. 1H and 11B magic angle spinning (MAS) NMR experiments and vibrational spectroscopy further support the structure model. Quantum chemical calculations coincide well with experimental results and provide information about the electronic structure of Ba12[BN2]6.67H4.

Structure and bonding in TiNiSi type LaMgSnH intermetallic hydride

The work was aimed on reaching a better understanding of the effect of magnesium as a component of the hydride-forming LaMgSn intermetallic compound crystallising with the orthorhombic TiNiSi type of structure on the hydrogenation behaviours, crystal structure and bonding interactions with hydrogen. The LaMgSn structure is significantly expanded as compared to the earlier studied isotypic LaNiSn H storage material (volume expansion of 23%), as a result of a substitution of the smaller Ni atoms by much larger Mg atoms. This significantly affects the chemistry of the interaction of the intermetallic compound with hydrogen because a transition metal, Ni, in replaced by an active hydride-forming metal, Mg. The work involved computational studies of the electronic structure of the intermetallic compound and its hydride, and experimental studies of the hydrogenation behaviour and thermal stability of the formed hydride LaMgSnH, its structural characterisation by SR XRD and neutron powder diffraction, and Mössbauer spectroscopic studies of the stannide and its hydride. These studies showed that in the system LaMgSn-H2 a monohydride LaMgSnH is a thermodynamically favourable hydride composition. PDOS levels show that hydrogen and all constituting elemental metals, La, Mg and Sn, have peaks of electron density in the range between − 6 and − 4 eV indicating their hybridisation. The results show the hybridization of H atoms not only with bonded La and Mg atoms forming H-filled tetrahedra La3Mg, but also with Sn despite its atoms do not have bonding interactions with H. This explains the high stability of the metal substructure which does not disproportionate into the binary hydrides of La and Mg even when heated to 200 °C @ 20 bar H2, but instead forms an insertion type hydride. Formation of the monohydride LaMgSnH (Sp.gr. Pnma; a=8.1628(4); b= 4.5555(3); c= 9.2391(5) Å; V= 343.56(5) Å3) causes a small (1.26%) expansion of the unit cell volume compared to LaMgSn, and mainly proceeds along the [100] direction. Hydrogen absorption-desorption cycle results in a reversible formation of the initial compound LaMgSn, with the peak of hydrogen release occurring in vacuum at 355 °C, which is intermediate between the temperatures for the vacuum decomposition of the dihydrides MgH2 and LaH2. From the combined refinements of the Synchrotron (SR) XRD and Neutron Powder Diffraction (NPD) data, deuterium atoms completely and in an ordered way fill a half of the available La3Mg interstitial sites with metal-H/D distances of Mg-D= 2.026 Å; La-D= 2.381 and 2.502 Å. The occupied La3Mg sites are smaller in size than the vacant Mg3La tetrahedra. Sn and D exhibit a nonbonding interaction with the closest Sn-D separation of 3.033 Å. 119Sn Mössbauer spectra of LaMgSn and LaMgSnH show isomer shifts of 1.98(2) and 1.99(1) mm/s which are typical for the chemically similar stannides.

Magnetic structure of the S = ½ staircase kagome lattice PbCu3TeO7

The crystal and magnetic structure characterization of geometrically distorted PbCu3TeO7 with S=1/2 Cu2+ spins forming a staircase kagome lattice was investigated using x-ray and neutron diffraction on a powder sample. The distorted kagome lattice of antiferromagnet PbCu3TeO7 exhibits a quasi-two-dimensional spin network. The x-ray diffraction data show that PbCu3TeO7 crystallizes in the orthorhombic system in the space group Pnma (No. 62). The lattice parameters a = 10.488(1) Å, b = 6.353(1) Å, and c = 8.814(2) Å. Our temperature-dependent x-ray diffraction data show that there is no structure phase transition between 12 and 298 K. From our powder neutron diffraction data at 2 K, we observed two distinct magnetic Bragg peaks at low angles, confirming the magnetic transition to the ordered state at low temperatures. In previous work, the ordering vector for the magnetic structure was determined using simulations to be (0,1/3,0). However, in this work, we found that based on the neutron diffraction data the ordering vector is in fact (0,1/3,1/3). The magnetic structure of PbCu3TeO7 exhibiting an antiferromagnet with noncollinear spin order is proposed.

Combining Nitridoborates, Nitrides and Hydrides—Synthesis and Characterization of the Multianionic Sr6N[BN2]2H3

AbstractMultianionic metal hydrides, which exhibit a wide variety of physical properties and complex structures, have recently attracted growing interest. Here we present Sr6N[BN2]2H3, prepared in a solid‐state ampoule reaction at 800 °C, as the first combination of nitridoborate, nitride and hydride anions within a single compound. The crystal structure was solved from single‐crystal X‐ray and neutron powder diffraction data in space group P21/c (no. 14), revealing a three‐dimensional network of undulated layers of nitridoborate units, strontium atoms and hydride together with nitride anions. Magic angle spinning (MAS) NMR and vibrational spectroscopy in combination with quantum chemical calculations further confirm the structure model. Electrochemical measurements suggest the existence of hydride ion conductivity, allowing the hydrides to migrate along the layers.

Combining Nitridoborates, Nitrides and Hydrides-Synthesis and Characterization of the Multianionic Sr6 N[BN2 ]2 H3.

Multianionic metal hydrides, which exhibit a wide variety of physical properties and complex structures, have recently attracted growing interest. Here we present Sr6 N[BN2 ]2 H3 , prepared in a solid-state ampoule reaction at 800 °C, as the first combination of nitridoborate, nitride and hydride anions within a single compound. The crystal structure was solved from single-crystal X-ray and neutron powder diffraction data in space group P21 /c (no. 14), revealing a three-dimensional network of undulated layers of nitridoborate units, strontium atoms and hydride together with nitride anions. Magic angle spinning (MAS) NMR and vibrational spectroscopy in combination with quantum chemical calculations further confirm the structure model. Electrochemical measurements suggest the existence of hydride ion conductivity, allowing the hydrides to migrate along the layers.

Incommensurate magnetic structure of CrAs at low temperatures and high pressures.

The magnetic structure of chromium arsenide CrAs is studied with neutron powder diffraction at ambient pressure in the temperature range 1.5-300 K as well as with neutron single-crystal diffraction at 2 K and 0.12 GPa. The material undergoes an anti-isostructural phase transition at TN = 267 K and atmospheric conditions, in which both orthorhombic phases have the same space-group symmetry (Pnma, Z = 4) but different distortions of the parent hexagonal structure of the NiAs type (P63/mmc, Z = 2). The magnetic structure below TN is incommensurate with the propagation vector k = (0, 0, kc). At ambient pressure, the component kc decreases from kc = 0.3807 (7) at 260 K to kc = 0.3531 (6) at 50 K. Below this temperature, it is basically constant. With increasing pressure at 2 K, kc is also constant within standard uncertainties [kc = 0.353 (2)]. For the analysis of the magnetic structure, a group-theoretical approach based on the space group of the nuclear structure and its subgroups is used. To avoid falling into false minima in the refinements, a random search for magnetic moments in the models is implemented. In the literature, the magnetic structure has been determined on the basis of powder diffraction data as a double helix propagating along the c axis. Although this double-helical model leads to satisfactory agreement factors for our powder data, it does not reproduce the intensities of the magnetic satellite reflections measured on single-crystal data in a satisfactory way and can therefore be discarded. Instead, several other models are found that lead to better agreement. Each of them is spiral-like with directional components in all three directions and with no spin-density wave character that would cause a non-constant magnetic moment. In all these models, the ordering of the spins is neither a pure helix nor a pure cycloid. Instead, the unit vectors of the spin rotation planes make an angle α, 0° < α < 90°, with respect to the c* direction. The model in superspace group P21.1'(α0γ)0s yields the best agreement factors in the refinements of the neutron single-crystal and powder diffraction data. This model is unique as it is the only one in which all the magnetic moments rotate with the same chirality.

Lithium‐Filled Skutterudites by Intercalation at Ambient‐Temperature

AbstractThe incorporation of lithium as a filler species in Co1‐2xFexNixSb3 skutterudites was accomplished by intercalation at 60 °C, using n‐BuLi as a reducing agent. Solid state 7Li NMR and ICP‐MS analysis confirm the presence of lithium in the product phases and provide an estimate of the lithium content. The maximum uptake of lithium increases as cobalt is progressively substituted by an equimolar mixture of iron and nickel. Difference Fourier maps, calculated during Rietveld structure refinement using powder neutron diffraction data, locate the lithium cations at the 2a (0,0,0) sites within the cavities of the skutterudite framework. The intercalation of lithium results in reductions in thermal conductivity of up to 47 %, indicative of phonon glass electron crystal (PGEC) type behaviour. Charge transfer from lithium to the framework that accompanies intercalation results in a substantial decrease in electrical resistivity in lithiated phases and a more metal‐like temperature dependence. The increased carrier concentration also decreases the Seebeck coefficient, with the consequence that modest increases in the figure of merit occur, despite the reduced thermal conductivity.

Magnetic structure of α-U3O8: a DFT and experimental study

The magnetic ordering of α-U3O8 remains a puzzling question for a long time. Recent inelastic neutron scattering study exhibited magnetic peaks at (0.5,1,1) and (0.5,2,2) but without intensity at (0.5,0,0). The magnetic propagation vector could still be k = (0.5,0,0), as the probability that the magnetic moments are perpendicular to the reflection plane (0.5,0,0) leading to zero intensity should be not ruled out. Magnetic symmetry analysis leads to 4 distinct magnetic structures, and the first-principles calculations show that the possible ground state of U3O8 could be collinear antiferromagnetic (AFM) ordering (m∣∣a-axis). Only one paramagnetic-AFM phase transition at T 1 = 24 K in magnetization curves has been confirmed, which shifts to lower temperatures as the magnetic field increases. At T = 1.8 K, no hysteresis loop around zero field has been observed which could exclude ferromagnetic ground state in this compound. Neutron powder diffraction data have been collected at several temperatures (300, 40, 15 and 5 K), and the absence of visible magnetic reflections makes the unusual magnetic properties even more mysterious.

Understanding Lithium-Ion Transport in Selenophosphate-Based Lithium Argyrodites and Their Limitations in Solid-State Batteries

To develop solid-state batteries with high power and energy densities, solid electrolytes with fast Li+ transport are required. Superionic lithium argyrodites have proven to be a versatile system, in which superior ionic conductivities can be achieved by elemental substitutions. Herein, we report the novel selenophosphate-based lithium argyrodites Li6–xPSe5–xBr1+x (0 ≤ x ≤ 0.2) exhibiting ionic conductivities up to 8.5 mS·cm–1 and uncover the origin of their fast Li+ transport. Rietveld refinement of neutron powder diffraction data reveals a better interconnection of the Li+ cages compared to the thiophosphate analogue Li6PS5Br, by the occupation of two additional Li+ sites, facilitating fast Li+ transport. Additionally, a larger unit cell volume, lattice softening, and higher structural disorder between halide and chalcogenide are unveiled. The application of Li5.85PSe4.85Br1.15 as the catholyte in In/LiIn|Li6PS5Br|LiNi0.83Co0.11Mn0.06O2:Li5.85PSe4.85Br1.15 solid-state batteries leads to severe degradation upon charging of the cell, revealing that selenophosphate-based lithium argyrodites are not suitable for applications in lithium nickel cobalt manganese oxide-based solid-state batteries from a performance perspective. This work further expands on the understanding of the structure–transport relationship in Li+ conducting argyrodites and re-emphasizes the necessity to consider chemical and electrochemical stability of solid electrolytes against the active materials when developing fast Li+ conductors.

Evidence of Long-Range and Short-Range Magnetic Ordering in the Honeycomb Na3Mn2SbO6 Oxide

We present a comprehensive study of the synthesis, structure, and magnetic properties of the honeycomb oxide Na3Mn2SbO6 supported by neutron diffraction, heat capacity, and magnetization measurements. The refinements of the neutron diffraction patterns (150, 50, and 45 K) using the Rietveld method confirm the monoclinic (S. G. C2/m) structure. Temperature-dependent magnetic susceptibilities measured at varying fields along with the heat capacity measurements demonstrate the coexistence of long-range ordering (∼42 K) and short-range ordering (∼65 K). The field-dependent isothermal magnetization measurements at 5 K indicate a spin-flop transition around 5 T. Rietveld refinements of the low-temperature (below 45 K) neutron diffraction data further confirm the long-range magnetic ordering. In addition, the temperature variation of the lattice parameters obtained from the neutron powder diffraction analysis exhibited a distinct anomaly near the antiferromagnetic transition temperature. The appearance of the concomitant broadened backgrounds in the neutron powder diffraction data collected at 80, 50, and 45 K supports the short-range ordering. The resultant magnetic structure consists of spins that are aligned antiparallel with the nearest neighbors and also with the spins of the adjacent honeycomb layers. The occurrence of a fully ordered magnetic ground state (Neel antiferromagnetic (AFM)) in Na3Mn2SbO6 consolidates the significance of fabricating new honeycomb oxides.

Competing magnetic interactions, structure and magnetocaloric effect in Mn3Sn1-xZnxC antiperovskite carbides

Structural, magnetic and magnetocaloric properties of Mn3Sn1-xZnxC antiperovskite carbides have been studied. With increasing Zn content the first-order magnetic transition (FOMT) is weakened. The Curie temperature (TC) reduces first from 273 to 197 K and when x > 0.3, TC increases, reaching its maximum of 430 K for x = 1.0. An increase in TC is accompanied by pronounced changes in magnetic behaviour and a significant rise in magnetization from 21.82(4) to 76.2(2) Am2kg−1 for x = 0.8 in the maximum applied magnetic field of 5 T. Neutron powder diffraction (NPD) was employed to study the magnetic structure of Mn3Sn1-xZnxC compounds. The refinement of the NPD data for x = 0.3 revealed a magnetic structure with propagation vector k = (½,½,0) with a decrease in the canted antiferromagnetic (AFM) moment, which results in a reduction of the negative volume change at the magnetic transition and a decrease in the magnetocaloric effect (MCE). For x = 0.4, the magnetic structure is described by a propagation vector k = (½,½,½) for the AFM moment which dominates at low temperature, with the presence of a minor ferromagnetic (FM) component with a k = (0, 0, 0) propagation vector, which confirms the presence of the ferrimagnetic (FiM) state. For a higher Zn content (x = 0.6), the magnetic moment originates mainly from the FM component found on three independent Mn positions and an additional AFM moment oriented in the a-b plane. The results presented confirm the presence of competing AFM-FM interactions in Mn3Sn1-xZnxC antiperovskite carbides.

Structure and Anharmonicity of α- and β-Sb2O3 at Low Temperature

Antimony oxides are important materials for catalysis and flame-retardant applications. The two most common phases, α-Sb2O3 (senarmontite) and β-Sb2O3 (valentinite), have been studied extensively. Specific focus has been placed recently on their lattice dynamics properties and how they relate to the α-β phase transformation and their potential anharmonicity. However, there has not been any direct investigation of anharmonicity in these systems, and a surprising lack of low-temperature structural information has prevented further study. Here, we report the powder neutron diffraction data of both phases of Sb2O3, as well as structural information. α-Sb2O3 behaved as expected, but β-Sb2O3 revealed a small region of zero thermal expansion along the c axis. Additionally, while the β phase matched well with reported atomic displacement parameters, the α phase displayed a marked deviation. This data will enable further investigations into these systems.