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International audience; The Aurivillius layered compounds with predominant fraction of paramagnetic transition metals are an emerging playground for discovery of magnetoelectric or multiferroic compounds. This aim was recently achieved by incorporating Fanions in the perovskite layer of the (Bi2O2)(CoF4) compound, only described so-far in a disordered model (unit cell : ap, ap, c). Here we report the investigation on the representative compounds (Bi2O2)(MF4) (M = Fe, Ni) using single crystal, synchrotron, neutron and electron diffraction. These reveal that the crystallographic average cell (2xap, 2xap, c) is orthorhombic, polar and accompanied by versatile (in)commensurate modulations. The supercell model was fully refined for (Bi2-xO2)(FeF4) (q = (0, ½, 0)) in the P2111 polar space group with transverse Fe-displacements relative to q. Bi-deficiency is compensated by a mixed Fe 2.5+ valence, but, the ideal stoichiometry is preserved for (Bi2O2)(NiF4). Both compounds are antiferromagnetic below TN = 89 K (Fe) and 45 K (Ni) with moments lying in the (ac) plane and a weak ferromagnetic component along the b-axis. DFT calculations validate a strongly anisotropic distribution of magnetic exchanges (Jab/Jc > 10). A broad anomaly on the dielectric constant at TN and a polarization loop at room temperature were obtained on (Bi2-xO2)(FeF4) single crystals, revealing multiferroism with magneto electric couplings.

International audience; We report bulk dilatometry and diffraction data through the T MIT = 427 K metal-insulator transition of the n = 3 member of the V n O 2n-1 Magnéli series. Besides VO 2 , V 3 O 5 is the only other vanadium oxide with a potentially useful MIT transition above room temperature. A narrow (ΔT = 10 K) abrupt negative thermal expansion of α L =-21.4 x 10-6 (dilatometry) and α V =-213 x 10-6 K-1 (crystallographic) is observed. We argue that the combination of the MIT along with the simultaneous vanadium charge ordering are responsible for such large values. The low temperature magnetic properties are also clarified and neutron diffraction measurements show a k = [½ ½ 0] magnetic structure at 1.5 K. DFT calculations of the exchange interactions support the low dimensionality and allow modelling the magnetic susceptibility.

Funding Information: The authors thank Christoph Wallach for Raman measurements and Sabine Zeitz for UV/Vis absorption spectroscopy. A. M. and M. B. thank Leonhard Dorsch for packing of the MAS rotors. Bircan Dilki is thanked gratefully for conducting the elemental analysis. We would like to thank the Institut Laue-Langevin for beam time allocated on D2B; https://doi.org/10.5291/ILL-DATA.5-21-1170 and https://doi.org/10.5291/ILL-DATA.EASY-725 . A. M. and N. K. thank the DFG for funding (project number 245845833) within International Research Training Group IRTG 2022—Alberta Technical University of Munich School for Functional Hybrid Materials (ATUMS). A. M. thanks the International Graduate School for Science and Engineering (IGSSE) for support. A. J. K. thanks Academy of Finland for funding (grant 324973) and CSC, the Finnish IT Center for Science for computational resources. Publisher Copyright: © 2022 The Royal Society of Chemistry The four compounds A3MO4H (A = Rb, Cs; M = Mo, W) are introduced as the first members of the new material class of the transition oxometalate hydrides. The compounds are accessible via a thermal synthesis route with carefully controlled conditions. Their crystal structures were solved by neutron diffraction of the deuterated analogues. Rb3MoO4D, Cs3MoO4D and Cs3WO4D crystallize in the antiperovskite-like K3SO4F-structure type, while Rb3WO4D adopts a different orthorhombic structure. 2H MAS NMR, Raman spectroscopy and elemental analysis prove the abundance of hydride ions next to oxometalate ions and experimental findings are supported by quantum chemical calculations. The tetragonal phases are direct and wide band gap semiconductors arising from hydride states, whereas Rb3WO4H shows a unique, peculiar valence band structure dominated by hydride states.

The chemical bonding, structural and magnetic properties of EuPdSn2 have been investigated by DFT, synchrotron X-ray and neutron powder diffraction and 151Eu Mössbauer spectroscopy.

We present a comprehensive structural and magnetic characterization of the barlowite family of S = 1/2 kagomé magnets, Cu4(OH)6FX, where X = Cl, Br, or I. Through high-resolution synchrotron X-ray and neutron powder diffraction measurements, we reveal two sources of structural complexity within this family of materials, namely, compositional disorder of the halide species that occupy sites in between the kagomé layers and the positional disorder of the interlayer Cu2+ ions that persists well into the Pnma structural ground state. We demonstrate that understanding these inherent structural disorders is key as they correlate with the degree of partial order in the magnetic ground states of these quantum frustrated magnets.

Aliovalent anion substitution 2 O2− ⇒ N3− + H− in LiLa2HO3 yields the heteroanionc hydrides LiLa2NH2O and LiLa2N1.5H2.5.

We report two new rare-earth (R) ternary intermetallic compounds—Ho2Ni0.8T1.2 with T = Si and Ge—that correspond to the R5Ni2T3 phase earlier reported to form in Dy–Ni–T and Ho–Ni–T ternary systems. The compounds crystallize in a filled version of the orthorhombic Zr2Ni1–xP-type structure with x = 0.52; their stoichiometry, determined from both single-crystal and powder X-ray diffraction data, is centered on Ho2Ni0.8T1.2 with a narrow solid solubility range for the silicide, while the germanide appears to be a line phase. In addition to R = Dy and Ho, R2Ni0.8T1.2 compounds also form for R = Y and Tb, representing the first examples of rare-earth-based compounds adopting the Zr2Ni1–xP structural prototype. Bulk magnetization data reveal the main transitions of the ferrimagnetic or ferromagnetic type at TC = 38 K for Ho2Ni0.8Si1.2 and TC = 37 K for Ho2Ni0.8Ge1.2, which are followed by subsequent magnetic reordering at lower temperatures. Neutron diffraction shows complex magnetic structures below TC with both ferromagnetic and antiferromagnetic components and magnetic propagation vector κ1 = [0, 0, 0]. Below TN ≅ 24 K (22 K) for the silicide (germanide), an additional antiferromagnetic coupling following an incommensurate magnetic propagation vector κ2 = [κx, 0, 0] appears to coexist with the first magnetic structure., The crystal structure of Ho2Ni0.8Si1.2 (and Ho2Ni0.8Ge1.2) [Zr2Ni0.48P-type (oP32-Pnma)] viewed along the b axis is given. The Ho, Ni1, Ni2/Si, Si1 and Si2 atoms are represented as red, turquoise, blue, light-gray, and dark-gray spheres, respectively. The distinctive structural fragment is built up of five differently oriented trigonal prisms. The magnetic structure of Ho2Ni0.8Ge1.2 with the antiferromagnetic component in the c direction and the ferromagnetic component along the a axis.

Nitride perovskites ABN 3 are extremely rare with only two known instances of bulk-phase materials, ThTaN 3 and LaReN 3 . Here, we present a powder neutron diffraction study of the recently-reported nitride perovskite LaReN 3 . A full structural model of LaReN 3 at 300 K ( [[EQUATION]] , a = 5.58523(5), b = 5.59297(5), c = 7.90419(6) Å, α = 89.9170(8), β = 90.1729(7), γ = 90.1709(7)°) has been refined simultaneously against powder neutron and previously-collected synchrotron X-ray diffraction data. This indicates that the triclinic distortion is due to cooperative electronic distortions of ReN 6 octahedra, and also demonstrates that all nitrogen positions are fully occupied so the sample is stoichiometric LaReN 3 . Lattice strains derived from fits to variable temperature powder neutron data from 5 to 300 K indicate that LaReN 3 undergoes structural transitions to higher symmetry perovskite tilt structures between 300 and 350 K.

Magnetic frustration results from competing magnetic interactions and leads to unusual ground states, ranging from non-collinear magnetic orders to spin liquids (SLs), opening the path to new physics and emerging properties. We report the engineered magnetic interaction design and synthesis of the new ternary nitride MnTa2N4 with a normal spinel structure, where the magnetic cations Mn2+ occupy exclusively the tetrahedral sites forming a diamond lattice. Although the magnetic interactions are strongly antiferromagnetic (θCW ≈ -140 K), a long-range magnetic order is not established, but a smooth magnetic anomaly is observed at T∗ ≈ 5.1 K, fingerprinting a large magnetic frustration. A short-range helicoidal magnetic order emerges at low temperatures. The ordered moment is ≈70% of the expected magnetic moment of Mn2+ ions and a large part (≈28%) of the spin entropy remains at 400 mK, signaling the coexistence of a helicoidal order with spin-glass-like or SL textures. First-principles calculations unveil an unexpected large direct Mn-Mn exchange interaction that balances the superexchange and accounts for the magnetic frustration. These findings open new avenues toward the design of quantum materials., This work was supported by the Ministerio de Ciencia e Innovación, Spain (PID2020-113805GB-I00, PID2020-118479RB-I00 (AEI/FEDER, EU), PGC2018-096955-B-C44 ,PGC2018-093863-B-C22, CEX2019-000917-S and MDM-2017-0767) and from Generalitat de Catalunya (2017SGR1377, 2017SGR581, 2017SGR1506, and 2017SGR1289). We thank Alba and ILL for beam time provision (experiments 2019023454 and 5-31-2713, respectively), Dr. François Fauth for assistance in data collection at Alba, and Dr. Bernat Bozzo (ICMAB-CSIC) for performing magnetic measurements. The authors acknowledge the use of Servicio General de Apoyo a la Investigación-SAI, Universidad de Zaragoza., With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).

Cation ordering in ABX

We present the synthesis of a novel binary metal oxide material: Ba

We present the synthesis of a novel binary metal oxide material: Ba7Mn4O15. The crystal structure has been investigated by high-resolution powder synchrotron X-ray diffraction in the temperature range of 100–300 K as well as by powder neutron diffraction at 10 and 80 K. This material represents an isostructural barium-substituted analogue of the layered material Sr7Mn4O15 that forms its own structural class. However, we find that Ba7Mn4O15 adopts a distinct magnetic ordering, resulting in a magnetoelectric ground state below 50 K. The likely magnetoelectric coupling mechanisms have been inferred from performing a careful symmetry-adapted refinement against the powder neutron diffraction experiments, as well as by making a comparison with the nonmagnetoelectric ground state of Sr7Mn4O15.

CaMnFeTaO6 has been synthesized at 1200 °C under 10 GPa pressure. Powder neutron diffraction shows that CaMnFeTaO6 adopts a double double perovskite structure (tetragonal space group P42/n, lattice parameters a = 7.683(3) and c = 7.685(7) Å) with cation disorder at all transition-metal sites. Magnetization measurements reveal an apparent ferro- or ferrimagnetic transition at Tm1 = 51 K and a susceptibility peak at Tm2 = 20 K, but no long-range magnetic order is observed by neutron diffraction down to 1.5 K. This is attributed to the formation of superparamagnetic clusters of ferrimagnetically ordered spins below Tm1 that freeze into a cluster spin glass at Tf = Tm2. ac magnetization measurements confirm the cluster spin glass ground state. Disorder from the substitution of Fe2+ for Mn2+ and Fe3+/Ta5+ inversion disrupts the network of superexchange interactions leading to the cluster spin glass ground state, in contrast to other P42/n double double perovskites where long-range magnetic order is stabilized.

The first representative of a novel class of mixed-anionic compounds, the sulfate hydride Na3SO4H, and the corresponding deuteride Na3SO4D were obtained from the solid-state reaction of NaH or NaD with dry Na2SO4. Precise reaction control is required, because too harsh conditions lead to the reduction of sulfate to sulfide. A combined X-ray and neutron diffraction study revealed that the compound crystallizes in the tetragonal space group P4/nmm with the lattice parameters a=7.0034(2) Å and c=4.8569(2) Å. The sole presence of hydride and absence of hydroxide ions is proven by vibrational spectroscopy and comparison with spectra predicted from quantum chemical calculations. 1H and 23Na MAS NMR spectra are consistent with the structure of Na3SO4H: a single 1H peak at 2.9 ppm is observed, while two peaks at 15.0 and 6.2 ppm for the inequivalent 23Na sites are observed. Elemental analysis and quantum chemical calculations further support these results.

Herein we report the second transition-metal-only triple perovskite Mn3MnTa2O9, from high pressure-high temperature transformation of Mn4Ta2O9. It shows 1 : 2 Mn : Ta B-site order and a complex antiferromagnetic behavior with a collinear structure that modulates into a spin density wave. The high pressure phase presents a 25% band gap reduction compared to its multiferroic precursor, recoverable above 625 °C.

Die ersten Vertreter einer neuen Klasse gemischt‐anionischer Verbindungen, das Sulfathydrid Na3SO4H und das entsprechende Deuterid Na3SO4D, werden durch die Festkörperreaktion von NaH bzw. NaD mit trockenem Na2SO4 erhalten. Hierfür wird eine genaue Reaktionskontrolle benötigt, da zu harsche Reaktionsbedingungen zur Reduktion des Sulfats zum Sulfid führen. Eine kombinierte Auswertung von Röntgen‐ und Neutronendiffraktometrie zeigt, dass die Verbindung tetragonal mit der Raumgruppe P4/nmm und den Zellparametern a=7.0034(2) Å and c=4.8569(2) Å kristallisiert. Die alleinige Anwesenheit von Hydridionen und die Abwesenheit von Hydroxidionen wird durch Schwingungsspektroskopie im Vergleich zu Spektren, erhalten durch quantenchemische Berechnungen, bewiesen. 1H‐ und 23Na‐Festkörper‐NMR‐Spektren entsprechen der Struktur von Na3SO4H: ein 1H‐Signal bei 2.9 ppm sowie zwei Signale bei 15.0 und 6.2 ppm für zwei ungleiche 23Na‐Positionen. Zusätzlich stützen Elementaranalyse und quantenchemische Berechnungen die experimentellen Befunde.

We present Mn2LiReO6 synthesised at high pressure in two different polymorphs. They are the only A-site manganites with an ideal +/7+ charge distribution over the B/B′ sites. The lower pressure polymorph crystallises in a polar R3 ordered-ilmenite type structure (OIL) with a calculated 26.9 μC cm−2 electrical polarisation. It shows a cluster spin glass behaviour due to Li/Mn anti-site mixing. The well-ordered higher-pressure double-perovskite polymorph (DPv, P21/n) develops weak-ferromagnetism with giant magnetic coercivity (HC = 6.9 T at 2 K) due to magnetocrystalline anisotropy enhanced by symmetry-restricted exchange interactions but in the absence of spin–orbit coupling.

High resolution and high intensity neutron powder diffraction is used to study the ground state magnetic order and the spin reorientation transition in the orthoferrite DyFeO

The unprecedented borate hydride Sr5 (BO3 )3 H and deuteride Sr5 (11 BO3 )3 D crystallizing in an apatite-related structure are reported. Despite the presence of hydride anions, the compound decomposes only slowly in air. Doped with Eu2+ , it shows broad-band orange-red emission under violet excitation owing to the 4f6 5d-4f7 transition of Eu2+ . The observed 1 H NMR chemical shift is in good agreement with previously reported 1 H chemical shifts of ionic metal hydrides as well as with quantum chemical calculations and very different from 1 H chemical shifts usually found for hydroxide ions in similar materials. FTIR and Raman spectroscopy of different samples containing 1 H, 2 H, nat B, and 11 B combined with calculations unambiguously prove the absence of hydroxide ions and the sole incorporation of hydride ions into the borate. The orange-red emission obtained by doping with Eu2+ shows that the new compound class might be a promising host material for optical applications.

The hydrothermally synthesized chain molecular magnets [{Fe(Δ)Fe(Λ)}1-x{Cr(Δ)Cr(Λ)}x(ox)2(phen)2]n (x =0, 0.1, and 0.5) have been investigated using neutron diffraction. The structural analysis rev...

The potential of the perovskite system Nd1-xSrxCoO3-δ (x = 1/3 and 2/3) as cathode material for solid oxide fuel cells (SOFCs) has been investigated via detailed structural, electrical, and electrochemical characterization. The average structure of x = 1/3 is orthorhombic with a complex microstructure consisting of intergrown, adjacent, perpendicularly oriented domains. This orthorhombic symmetry remains throughout the temperature range 373-1073 K, as observed by neutron powder diffraction. A higher Sr content of x = 2/3 leads to stabilization of the cubic perovskite with a homogeneous microstructure and with a higher oxygen vacancy content and cobalt oxidation state than the orthorhombic phase at SOFC operation temperature. Both materials are p-type electronic conductors with high total conductivities of 690 and 1675 S·cm-1 at 473 K in air for x = 1/3 and 2/3, respectively. Under working conditions, both compounds exhibit similar electronic conductivities, since x = 2/3 loses more oxygen on heating than x = 1/3, associated with a greater loss of p-type charger carriers. However, composite cathodes prepared with Nd1/3Sr2/3CoO3-δ and Ce0.8Gd0.2O2-δ present lower ASR values (0.10 Ω·cm2 at 973 K in air) than composites prepared with Nd2/3Sr1/3CoO3-δ and Ce0.8Gd0.2O2-δ (0.34 Ω·cm2). The high activity for the oxygen electrochemical reaction at intermediate temperatures is likely attributable to a large disordered oxygen-vacancy concentration, resulting in a very promising SOFC cathode for real devices.

Several different mechanisms of magnetoresistance (MR) have been observed in 1111 LnMnAsO1–xFx oxypnictides (Ln = lanthanide) as a result of magnetic coupling between the Mn and Ln. Such phases als...

A new CaFe3O5-type phase NiFe3O5 (orthorhombic Cmcm symmetry, cell parameters a = 2.89126(7), b = 9.71988(21) and c = 12.52694(27) Å) has been synthesised under pressures of 12–13 GPa at 1200 °C. NiFe3O5 has an inverse cation site distribution and reveals an interesting evolution from M2+(Fe3+)2Fe2+O5 to Fe2+(M2+ 0.5Fe3+ 0.5)2Fe3+O5 distributions over three distinct cation sites as M2+ cation size decreases from Ca to Ni. Magnetic susceptibility measurements show successive transitions at 275, ∼150, and ∼20 K and neutron diffraction data reveal a series of at least three spin-ordered phases with evolving propagation vectors k = [0 0 0] → [0 k y 0] → [½ ½ 0] on cooling. The rich variety of magnetically ordered phases in NiFe3O5 likely results from frustration of Goodenough-Kanamori exchange interactions between the three spin sublattices, and further interesting magnetic materials are expected to be accessible within the CaFe3O5-type family.

We report the results of magnetization, heat capacity, and neutron diffraction measurements on (Mo

International audience; Mixed anion compounds AFe3(SeO3)2F6 (A=K, Rb) have been synthesized by hydrothermal reactions. Prior results obtained for the isostructural Cs analog have revealed original 2D-ferrimagnetic (FI) blocks, antiferromagnetically (AFM) ordered around 120 K. Surprisingly, the whole series orders at a nearly constant TN temperature with similar field-induced magnetization steps, despite significant changes of the interlayer thickness. The metamagnetic transition from AFM to FI on oriented single crystals and Cp measurements prove an in-plane easy-magnetic axis confirmed by neutron powder diffraction (NPD). The ferrimagnetic alignment [Fe(1)↑−Fe(2)↓−Fe(1)↑] in each 2D subunit is robust, but the AFM-ordering between them is broken under weak field leaving field-aligned 2D-macrospins, with weak magnetocrystalline anisotropy. DFT+U calculations validate the exchange ratio Jinter/Jintra of 5.10-3 for all compounds and the relatively high TN value is well predicted by a modified random-phase approximation (RPA) like relation, established for Quasi-Low-Dimensional Heisenberg Antiferromagnets. However, our calculations of intralayer magnetic dipole-dipole (MDD) interactions indicate a non-neglectable values and suggest the latter to assist the in-plane spin orientation below TN. At TN, under field a 3D-Heisenberg model was deduced for the AFM →FI transition from the critical behavior using modified Arrott plots.

and presentation of a contributed talk at the MRS 2022 Spring Meeting in Symposium SF01: Materials Research Needs to Advance Nuclear Fuels, Structural Materials and Wasteforms ---Abstract--- The principal type of nuclear fuel material, which remains widely used today, is uranium dioxide (UO2). After discharge from a nuclear reactor some sort of disposal scenario needs to be considered to manage the spent fuel in a sustainable and safe way during extensive periods of time. However, in most countries which employ(ed) commercial nuclear energy, no political decision has yet been made, leading to prolonged intermediate storage periods up to several decades. As a result, oxidation and corrosion reactions due to accidental interaction between air, water, or moisture and the spent fuel need to be considered and understood. The response of conventional nuclear fuel to oxidation and corrosion is determined mainly by the physico-chemical properties of uranium. The binary uranium-oxygen system displays a very complex landscape of oxide phase fields. At temperatures below about 450 °C two single-valence compounds, uranium(IV) oxide (UO2) and uranium(VI) oxide (UO3), and several mixed-valence compounds (U4O9, U3O7, U3O8) can occur [1-4], characterized by particular associations of oxygen interstitials and vacancies. At higher temperature, long-range correlations among defects become less effective and the phase diagram becomes simpler, displaying a wide phase domain of nonstoichiometric UO2±x [5]. A characteristic feature of these higher oxide compounds lies in their crystallographic modifications, which occur almost exclusively in the anion sublattice, where point defects arrange into larger clusters to form complex long-range ordered structures [6-8]. However, despite sustained efforts for almost a century, the transition and structural relations between the different compounds is yet to be fully understood. New perspectives on the oxidation behavior of UO2 were obtained by investigating the kinetic mechanisms of these materials at the nanoscale, where fundamental differences were reported compared to the macroscale observations. Recent breakthroughs were made possible by using nanoscale imaging techniques like transmission electron microscopy [9], and by evaluating atomistic models of crystal structures [8,10,11]. A key instrument has been the application of neutron scattering techniques, owing to its sensitivity towards the anion sublattice [10], and its selectivity in probing magnetic transitions [12] and the local structure [13]. In this contribution we will report our current understanding of the uranium oxide systems U3O7 and U3O8 in ground state, based on latest neutron scattering data and ab-initio calculations. References [1] Grenthe I., et al., "Uranium", in: Morss L.R., Edelstein N.M., F. J. (Eds.) The Chemistry of the Actinide and Transactinide Elements, Springer, Dordrecht, 2008. [2] K.O. Kvashnina, et al., Phys. Rev. Lett., 111 (2013) 253002. [3] D.A. Andersson, et al., Inorg. Chem., 52 (2013) 2769. [4] S.D. Conradson, et al., Phys. Rev. B, 96 (2017) 125114. [5] P.Y. Chevalier, et al., J. Nucl. Mater., 303 (2002) 1. [6] B.T.M. Willis, J. Chem. Soc., Faraday Trans. II, 83 (1987) 1073. [7] L. Desgranges, et al., Inorg. Chem., 48 (2009) 7585. [8] G. Leinders, et al., Inorg. Chem., 55 (2016) 9923. [9] G. Leinders, et al., Inorg. Chem., 55 (2016) 3915. [10] G. Leinders, et al., Inorg. Chem., 60 (2021) 10550. [11] A. Soulié, et al., Inorg. Chem., 58 (2019) 12678. [12] A. Miskowiec, et al., Phys. Rev. B, 103 (2021) 205101. [13] L. Desgranges, et al., Inorg. Chem., 56 (2017) 321., {"references":["Grenthe I., et al., \"Uranium\", in: Morss L.R., Edelstein N.M., F. J. (Eds.) The Chemistry of the Actinide and Transactinide Elements, Springer, Dordrecht, 2008.","K.O. Kvashnina, et al., Phys. Rev. Lett., 111 (2013) 253002.","D.A. Andersson, et al., Inorg. Chem., 52 (2013) 2769.","S.D. Conradson, et al., Phys. Rev. B, 96 (2017) 125114.","P.Y. Chevalier, et al., J. Nucl. Mater., 303 (2002) 1.","B.T.M. Willis, J. Chem. Soc., Faraday Trans. II, 83 (1987) 1073.","L. Desgranges, et al., Inorg. Chem., 48 (2009) 7585.","G. Leinders, et al., Inorg. Chem., 55 (2016) 9923.","G. Leinders, et al., Inorg. Chem., 55 (2016) 3915.","G. Leinders, et al., Inorg. Chem., 60 (2021) 10550.","A. Soulié, et al., Inorg. Chem., 58 (2019) 12678.","A. Miskowiec, et al., Phys. Rev. B, 103 (2021) 205101.","L. Desgranges, et al., Inorg. Chem., 56 (2017) 321."]}

Pyrophosphates of the general formula A2BP2O7 (A = alkali metal and B = transition metal) find applications in several technological fields, including rechargeable Na-ion batteries. They present a rich polymorphism vs composition, which may strongly influence their functional properties. Therefore, to selectively obtain a specific structure is crucial for applications. Here, we combine structural investigation techniques (solid-state NMR, X-ray and neutron diffraction, and DFT calculations) to investigate the crystal chemistry of the series Na2(M/M’)P2O7 with couples M/M’ = Co/Zn and Co/Fe. For both the series, a phase transition vs composition is observed. A tetragonal to orthorhombic phase transition is found for the Zn/Co series, and an orthorhombic to triclinic phase transition is found for the Co/Fe series. Such changes are interpreted in view of the different electronic structures of the transition metal ion. In addition, with the support of modeling, short- and long-range structural analysis, we show that the coexistence of two polymorphs for a given composition is possible, suggesting that the final structures may be strongly dependent upon the synthesis procedure.

We report the results of magnetization, heat capacity, and neutron diffraction measurements on (Mo2/3RE1/3)(2)AlC with RE = Dy and Tb. Temperature and field-dependent magnetization as well as heat capacity were measured on a powder sample and on a single crystal allowing the construction of the magnetic field-temperature phase diagram. To study the magnetic structure of each magnetic phase, we applied neutron diffraction in a magnetic field up to 6 T. For (Mo2/3Dy1/3)(2)AlC in zero field, a spin density wave is stabilized at 16 K, with antiferromagnetic ordering at 13 K. Furthermore, we identify the coexistence of ferromagnetic and antiferromagnetic phases induced by magnetic fields for both RE = Tb and Dy. The origin of the field induced phases is resulting from the competing ferromagnetic and antiferromagnetic interactions. Funding Agencies|Knut and AliceWallenberg (KAW) FoundationKnut & Alice Wallenberg Foundation [KAW 2020.0033]; Deutsche Forschungsgemeinschaft (DFG)German Research Foundation (DFG) [CRC/TRR 270, 405553726]; ANR projectFrench National Research Agency (ANR) [ANR-18-CE09-0041]; government of the Russian Federation [075-15-2019-1886]; Flag-ERA JTC 2017

International audience; Cation ordering in ABX3 perovskites is important to structural, physical and chemical properties. Here we report discovery of CaCuFeReO6 with the tetragonal AA′BB′O6 double double perovskite structure that was previously only reported for A′=Mn compositions. CaCuFeReO6 occurs in the same phase field as CaCu3Fe2Re2O12 demonstrating that different A-cation ordered peroskites may be obtained in the same chemical system. CaCuFeReO6 has ferrimagnetic order of Fe, Re and Cu spins below TC=567 K, in contrast to Mn analogues where the Mn spins order separately at much lower temperatures. The magnetoresistance of CaCuFeReO6 displays low-field “butterfly” hysteresis with an unusual change from negative to positive values as field increases. Many more AA′BB′O6 double double perovskites may be accessible for A′=Cu and other divalent transition metals at high pressure, so the presently known phases likely represent only the “tip of the iceberg” for this family.

Mixed-valent transition-metal compounds display complex structural, electronic and magnetic properties, which often intricately coexist. Here, we report the new ternary oxide GaV

Consolidating a microscopic understanding of magnetic properties is crucial for a rational design of magnetic materials with tailored characteristics. The interplay of 3d and 4f magnetism in rare-earth transition metal antimonides is an ideal platform to search for such complex behavior. Here the synthesis, crystal growth, structure, and complex magnetic properties are reported of the new compound Pr3Fe3Sb7 as studied by magnetization and electrical transport measurements in static and pulsed magnetic fields up to 56 T, powder neutron diffraction, and Mößbauer spectroscopy. On cooling without external magnetic field, Pr3Fe3Sb shows spontaneous magnetization, indicating a symmetry breaking without a compensating domain structure. The Fe substructure exhibits noncollinear ferromagnetic order below the Curie temperature TC ≈ 380 K. Two spin orientations exist, which approximately align along the Fe–Fe bond directions, one parallel to the ab plane and a second one with the moments canting away from the c axis. The Pr substructure orders below 40 K, leading to a spin-reorientation transition (SRT) of the iron substructure. In low fields, the Fe and Pr magnetic moments order antiparallel to each other, which gives rise to a magnetization antiparallel to the external field. At 1.4 K, the magnetization approaches saturation above 40 T. The compound exhibits metallic resistivity along the c axis, with a small anomaly at the SRT.

The development of new synthetic methodologies of perovskite oxynitrides is challenging but necessary for the search of new compounds and the investigation of new properties. Here, we report a new method of preparation of the perovskite LaTaON

The most common MXene composition Ti3C2Tx (T = F, O) shows outstanding stability as anode for sodium ion batteries (100% of capacity retention after 530 cycles with charge efficiency >99.7%). However, the reversibility of the intercalation/deintercalation process is strongly affected by the synthesis parameters determining, in turn, significant differences in the material structure. This study proposes a new approach to identify the crystal features influencing the performances, using a structural model built with a multitechnique approach that allows exploring the short-range order of the lamella. The model is then used to determine the long-range order by inserting defective elements into the structure. With this strategy it is possible to fit the MXene diffraction patterns, obtain the structural parameters including the stoichiometric composition of the terminations (neutron data), and quantify the structural disorder which can be used to discriminate the phases with the best electrochemical properties.

Transition metal compounds can feature different types of magnetic anisotropy. By studying a honeycomb-lattice material with disconnected transition-metal octahedra, the authors reveal the crucial role of the single-ion anisotropy term that arises despite the nominally quenched orbital moment of the ${d}^{3}$ magnetic ion. Their findings suggest that the effect of single-ion anisotropy should not be ignored when searching for signatures of Kitaev interactions in spin-3/2 honeycomb magnets.

The first triple perovskite with Mn in A- and 1 : 2 B-site order Mn

The realization of magnetic frustration in a metallic van der Waals (vdW) coupled material has been sought as a promising platform to explore novel phenomena both in bulk matter and in exfoliated devices. However, a suitable material platform has been lacking so far. Here, we demonstrate that CeSiI hosts itinerant electrons coexisting with exotic magnetism. In CeSiI, the magnetic cerium atoms form a triangular bilayer structure sandwiched by van der Waals stacked iodine layers. From resistivity and magnetometry measurements, we confirm the coexistence of itinerant electrons with magnetism with dominant antiferromagnetic exchange between the strongly Ising-like Ce moments below 7 K. Neutron diffraction directly confirms magnetic order with an incommensurate propagation vector k ~ (0.28, 0, 0.19) at 1.6 K, which points to the importance of further neighbor magnetic interactions in this system. The presence of a two-step magnetic-field-induced phase transition along c axis further suggests magnetic frustration in the ground state. Our findings provide a novel material platform hosting a coexistence of itinerant electron and frustrated magnetism in a vdW system, where exotic phenomena arising from rich interplay between spin, charge and lattice in low dimension can be explored., 15 pages, 9 figures

Two M