High-entropy materials are complex, multifunctional materials that have reshaped the design of advanced functional materials. Their chemically diverse compositions enable access to a broader compositional space than conventional solid solutions, while simultaneously posing significant challenges for fundamental structure-property understanding. In this study, we introduce a new high-entropy spinel oxide with an exceptionally low coercivity of 1.8 Oe at room temperature, among the lowest reported for bulk spinel oxides, and a high electrical resistivity (1560 ohm cm). Neutron powder diffraction (NPD) and magnetic measurements reveal long-range collinear ferrimagnetic ordering (k = 0, 0, 0) with a transition temperature at 420 K. This rare combination of ultra-soft magnetic behavior, robust ferrimagnetic ordering well above room temperature, and high resistivity highlights its strong potential as an advanced soft-magnetic oxide for low-loss, high-frequency applications. Furthermore, X-ray absorption spectroscopy (XAS), Mössbauer spectroscopy, and NPD analyses were combined to determine the cation distribution and site selectivity across the tetrahedral and octahedral sites of the complex structure.

We report on the high-pressure synthesis of a CrS_2 phase in the form of single-crystalline nanorods. A structural refinement of Precession Electron Diffraction Tomography data confirms the nominal CrS_2 composition and unveils a ladder-type structure formed by portions of 1T-type CrS_2 layers characteristic of two-dimensional (2D) dichalcogenides connected by chains of edge-sharing CrS_6 octahedra characteristic of 3D dichalcogenides with marcasite structure. Ab initio density functional theory calculations of the relaxed structure confirm the stability of this structure and indicate a strong overlap of the 3d states of Cr with the 3p states of S, thus suggesting strong covalent Cr-S bonds and metallic behavior. Electrical resistivity, ϱ, measurements on single nanorods confirm this behavior and yield ϱ∼ 2-20 mΩ cm at 4 K. The proposed ladder-like structure of CrS_2 forms open channels along the chain direction, which may be suitable for ionic conduction.

Synthesis, structural and transport properties of Ni 7− δ SnS 2 : signatures of structural modulation were evidenced by TEM and the intergrowth structure leads to a moderate value of thermal conductivity in this metal-rich sulfide.

A polycrystalline sample of Co3Sn2S2 shandite was synthesized using spark plasma sintering for its densification. The unit cell parameters, a = 5.3688(1) angstrom and c = 13.1797(1) angstrom, refined from room temperature X-ray diffraction data, confirm the R -3m shandite structure. The frustrated nature of the Co magnetic network is invoked to explain the low effective paramagnetic moment of Co, mu eff = 1.04 mu B/Co, whereas the ferromagnetic Curie temperature, TC = 175K, determined from Tdependent magnetic susceptibility corresponds to the metal to metal transition at that temperature. Interestingly, the residual resistivity ratio and resistivity values indicate that the electronic transport is driven by the in -plane contribution. This behaviour close to that of ab-plane transport of Co3Sn2S2 crystal fits well with the measurement of an anomalous Nernst effect (ANE). The latter reaches at T = 100K a maximum value Sxy = +1.5 mu V K-1, i.e. a reduction by a factor of approximate to 2 as compared to crystal, explained by the reduction for the magnetization, M, of the former. This is also demonstrated by the H -dependent Sxy and M loops that match very well. Similarly, a hysteresis is found for the thermal conductivity demonstrating the existence of an anomalous thermal Hall effect of about 5 % of the total thermal conductivity. This study shows that ANE can be also measured in ceramics of Weyl ferromagnets.

CoV2O6, a Brannerite-type material, exists in both monoclinic (α) and triclinic (γ) forms. α- CoV2O6 exhibits quasi-1D ferromagnetic chains of octahedrally-coordinated Co2+ions in the higher spin state. Fe2+ doped α-CoV2O6 (3 mol%) single crystals were synthesized using high temperature melt method. The motivation is to investigate whether disruption of 1D Co2+ ferromagnetic chains by small Fe3+ substitution alters the antiferromagnetic ground state and lead to stronger spin-frustration. In this paper, we report the magnetic and magnetodielectric properties of Fe doped α-CoV2O6 in detail. The strongly anisotropic nature of magnetic and magnetodielectric characteristics were captured well in the data through orientation dependent measurements with H being parallel to a and c axes of the crystal. Relative dielectric permittivity (εr) exhibited sharp peaks coinciding with the plateau edges Hc1 ∼2.2 T and Hc2 ∼4.4 T in the magnetization curves (M-H) for applied H parallel to a-axis. For dielectric measurements under applied H parallel to c-axis, relative dielectric permittivity exhibited sharp peak around Hc2 ∼3.1 T, again coinciding with the M-H behavior. Such closely related magnetic field induced dielectric transitions reflected in both M(H) and εr(H) measurements is a rare phenomenon and representative of strong spin-lattice coupling in this phase.

We present electrical and thermal transport measurements in single crystals of the metallic oxide RuO$_2$. The resistivity and Seebeck coefficient measured up to 970K confirm the metallic nature of transport. Magnetoresistance and Hall effect measurements as a function of orientation can be most easily described by a multiband transport model. We find that the ordinary Hall effect dominates any anomalous Hall signal in single crystals.

Triple doping of CaMnO3 in different stoichiometric proportions has been studied in bulk sintered materials. They were prepared through the classical ceramic route using planetary milling to decrease the precursors particle sizes. It has been found that particle sizes decrease with the amount of dopant, both in the pre-cursors and in the sintered bodies. XRD patterns showed that all samples were nearly single phase, with small amounts of CaMn2O4 phase. SEM and TEM observations revealed a homogeneous distribution of dopants in the CaMnO3 phase, while EDX showed a composition close to the nominal one. However, HREM imaging has shown some dark regions in the crystallites, with different Ca(Y,La,Yb)/Mn ratios found through STEM image-chemical mapping, which points out to the coexistence of CaMnO3 and CaMn2O4-type do-mains in the crystallites. Electrical resistivity, absolute Seebeck coefficient and thermal conductivity have been drastically decreased with doping. The highest PF values at 800 degrees C have been achieved in 0.02(Y,La,Yb) doped samples (-0.37 mW/K2m), which is among the best reported values in literature. On the other hand, lattice thermal conductivity is dramatically decreased with doping due to the phonon scattering produced by the dopants, the decrease in the grain sizes, and the strains present inside the crystallites, reaching the minimum values at 800 degrees C in 0.03(Y,La,Yb) doped samples (-0.8 W/K m). Consequently, ZT reaches the maximum values (-0.29) in 0.03(Y,La,Yb) doped samples due to their very low thermal conductivity, being higher than the best ZT reported values in the literature. (c) 2023 Elsevier B.V. All rights reserved.

Codoped (Tb,Eu) ZnO films grown by magnetron sputtering on a silicon substrate and annealed up to 1200 degrees C showed intense photoluminescence (PL) emission from Eu3+ ions. The high-temperature annealing led to diffusion and segregation of rare earth (RE) elements toward the bottom of the film, which induced the formation of nanometric Zn-free inclusions responsible for remarkable PL emission intensity. Combined electron diffraction, chemical contrast imaging, and optical studies of these nanometric phases have been carried out. Large inclusions of zinc silicates and RE silicates a few hundreds of nanometers in size were observed, embedded in a silica phase. The structural determination of these RE-rich inclusions was carried out by combining atomic Z contrast imaging (high-angle annular dark-field imaging) and precession electron diffraction data. Upon annealing at 1200 degrees C, it appeared that the structure was related to an F-type disilicate structure. Energy-dispersive X-ray spectroscopy and electron energy loss spectroscopy experiments were carried out to determine the ratios between elements and the oxidation states of the RE elements in the abovementioned inclusions. A (Tb,Eu)(2)Si2O7 formulation is proposed from dynamical precession electron diffraction tomography refinements, leading to a +III valence state for the RE species in agreement with spectroscopic results. PL modeling is also in good agreement with the experimental data. These results complete those obtained at 1100 degrees C for which the inclusions were identified as some RE10-x(SiO4)(6)O2-x oxyapatite structures and pointed out a combined structural and PL properties' evolution between 1100 and 1200 degrees C annealing temperatures.

This paper reports the effect of Na doping Cu2ZnSnS4 powders on the structural, morphological and optical properties. CZTS powders were synthesized by direct melting method of the constituent elements with different sodium doping concentrations from 0.5% to 2%. The resulting CZTS:Na powders were characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, scanning transmission electron microscopic and UV-visible-NIR spectrophotometer. X-ray diffraction and scanning transmission electron microscopic analysis confirmed the formation of CZTS:Na with kesterite structure and preferential orientation along (112) plane. SEM results shown the microstructure with large grains with increasing the Na doping concentration. Optical mea-surements revealed that the band gap of CZTS decreases from 1.66 to 1.53 eV by increasing Na-doping. In addition, electrical investigations indicated that all ingots exhibit p-type conductivity.

H. Rotella, 2 O. Copie, 3 A. Pautrat, ∗ P. Boullay, A. David, D. Pelloquin, C. Labbé, C. Frilay, and W. Prellier Laboratoire CRISMAT, CNRS UMR 6508, ENSICAEN et Université de Caen, 6 Bd Maréchal Juin, 14050 Caen Cedex 4, France. NUSNNI-NanoCore, National University of Singapore, Singapore 117411. CEA, DSM/IRAMIS/SPEC, F-91191 Gif-sur-Yvette Cedex, France. Laboratoire CIMAP, CNRS UMR 6252, CEA, ENSICAEN et Université de Caen, 6 Bd Maréchal Juin, 14050 Caen Cedex 4, France. (Dated: February 28, 2022)

(Tb,Eu)-doped ZnO-annealed films at 1100 °C showed intense photoluminescense (PL) emission from Eu and Tb ions. The high-temperature annealing led to a chemical segregation and a secondary Zn-free phase formation that is suspected to be responsible for the high PL intensity. Large faceted inclusions of rare-earth (RE) silicates of a size of few hundred nanometers were observed. Owing to various advanced electron microscopy techniques, a detailed microstructural study of these nanometric inclusions combining atomic Z contrast imaging (STEM) and precession electron diffraction tomography (PEDT) data was carried out and resulted in the determination of a hexagonal P63/m-type (Tb,Eu)9.43(SiO4)6O2-δ structure related to an oxy-apatite structure. Chemical analyses from spectroscopic data (energy-dispersive X-ray mapping and electron energy loss spectroscopy) at the atomic scale showed that both RE elements sitting on two independent (4f) and (6h) atomic sites have three-fold oxidation states, while refinements of their occupancy sites from PEDT data have evidenced preferential deficiency for the first one. The deduced RE-O distances and their corresponding bond valences are listed and discussed with the efficient energy transfer from Tb3+ toward Eu3+.

Magneto-caloric materials offer the possibility to design environmentally friendlier thermal management devices compared to the widely used gas-based systems. The challenges to develop this solid-state based technology lie in the difficulty of finding materials presenting a large magneto-caloric effect over a broad temperature span together with suitable secondary application parameters such as low heat capacity and high thermal conductivity. A series of compounds derived from the PbFCl structure is investigated using a combination of computational and experimental methods focusing on the change of cell volume in magnetic and non-magnetic ground states. Scaling analysis of the magnetic properties determines that they are second order phase transition ferromagnets and that the magnetic entropy change is driven by the coupling of magneto-elastic strain in the square-net through the magnetic transition determined from neutron and synchrotron X-ray diffraction. The primary and secondary application related properties are measured experimentally, and the c/a parameter is identified as an accurate proxy to control the magnetic transition. Chemical substitution on the square-net affords tuning of the Curie temperature over a broad temperature span between 252 and 322 K. A predictive machine learning model for the c/a parameter is developed to guide future exploratory synthesis.

We report the aperiodic titanate Ba10Y6Ti4O27 with a room-temperature thermal conductivity that equals the lowest reported for an oxide. The structure is characterised by discontinuous occupancy modulation of each of the sites and can be considered as a quasicrystal. The resulting localisation of lattice vibrations suppresses phonon transport of heat. This new lead material for low-thermal-conductivity oxides is metastable and located within a quaternary phase field that has been previously explored. Its isolation thus requires a precisely defined synthetic protocol. The necessary narrowing of the search space for experimental investigation was achieved by evaluation of titanate crystal chemistry, prediction of unexplored structural motifs that would favour synthetically accessible new compositions, and assessment of their properties with machine-learning models.

The magnetism, magnetotransport, and Seebeck coefficients (S) for three ruthenates Ba1-delta M2+xRu4-xO11 (delta = 0.06; M = Mn, Co; x = 0.4) and Sr1-delta M2+xRu4-xO11 (delta = 0.02; M = Fe; x = 0.7) compositions have been studied. Their crystallographic structures contain three metal sites, edge-sharing octahedra forming kagome lattices, face-shared octahedra with the shortest Ru(M)-Ru(M) distance, and MO5 trigonal bipyramids. These three compositions have been selected for their transport behavior exhibiting small resistivity values (similar to m Omega cm) together with a complex ferrimagnetic behavior, with localization increasing from M = Co to M = Fe. This enabled the thermopower to be measured in hexagonal ruthenates in which the conducting kagome layers are more or less diluted by three different magnetic cations substituted for Ru. The positive Seebeck coefficient of the three compounds is found to increase up to 750 K to values in the range of 22 to 35 mu V K-1. Such values, similar to those of perovskite ruthenates, reveal a Seebeck coefficient dominated by the Ru network at high temperature whatever the foreign magnetic cation is. In addition, below about 50 K, the values of S are very small for M = Mn and Co, and the S(T) curves of the Ba1-delta M2.4Ru3.6O11 compounds exhibit similarities with that of ruthenium metal. This is interpreted by shorter Ru-Ru distances as compared with perovskite ruthenates allowing a metallic direct exchange. The ferrimagnetism associated with the M cation does not seem to play a major role in transport, as there is almost no impact of the magnetic ordering on thermopower and electrical resistivity and the values of magnetoresistance remain very small, reaching at most -1% in 9 T at 5 K for M = Mn, and -0.4% at T-C for M = Co. The present results obtained in these phases containing hexagonal Ru networks show that Hund's metal model developed to describe the thermopower of perovskite ruthenates with a Ru square lattice can have a broader range of validity.

(Tb, Eu)-co-doped ZnO films with about 3 at.% total doping rate were grown by magnetron sputtering on Si substrate. Post annealing treatments were performed at 973-1373 K in continuous nitrogen flow to investigate the transformation of microstructural and optical characteristics by means of X-ray diffraction, transmission electron microscopy, photoluminescence and electroluminescence. For annealing temperatures lower than 1073 K, segregation of Eu and Tb was observed mainly at the film/substrate junction. For temperatures higher than 1173 K, additional phases appeared, namely, Zn2SiO4 and rare earth silicates. For the highest temperature investigated (1373 K), only silica and rare earth silicates remained in the film due to Zn evaporation. PL measurements indicated a very intense Eu emission associated with the presence of rare earth silicate inclusions. Energy transfer from Tb towards Eu was evidenced in this secondary phase. At last, based on these preliminary works, a (Tb, Eu)-co-doped ZnO/Si electroluminescent structure was produced and showed very promising results paving the way for very thin ZnO based light emitting diodes.

2D materials exhibiting alternating ferro- and non-ferromagnetic layers are highly sought due to their potential for applications. In this work, we demonstrate, through the use of robust methodolog...

AbstractIn this work we benefited from recent advances in tools for crystal‐structure analysis that enabled us to describe an exotic nanoscale phenomenon in structural chemistry. The Mn0.60Ni0.40As sample of the Mn1−xNixAs solid solution, exhibits an incommensurate compositional modulation intimately coupled with positional modulations. The average structure is of the simple NiAs type, but in contrast to a normal solid solution, we observe that manganese and nickel segregate periodically at the nano‐level into ordered MnAs and NiAs layers with thickness of 2–4 face‐shared octahedra. The detailed description was obtained by combination of 3D electron diffraction, scanning transmission electron microscopy, and neutron diffraction. The distribution of the manganese and nickel layers is perfectly described by a modulation vector q=0.360(3) c*. Displacive modulations are observed for all elements as a consequence of the occupational modulation, and as a means to achieve acceptable Ni–As and Mn–As distances. This modulated evolution of magnetic MnAs and non‐magnetic NiAs‐layers with periodicity at approximately 10 Å level, may provide an avenue for spintronics.

Herein, a new class of high entropy spinel material with composition (Mg0.2Co0.2Ni0.2Cu0.2Zn0.2)Cr2O4 is introduced. Detailed structural and microstructural characterizations highlight that the sample crystallizes in a cubic spinel structure with an excellent chemical homogeneity at the nanoscale. A peak in the dielectric measurement is observed at the antiferromagnetic ordering temperature (35 K), indicating the possibility of magneto-electric coupling at that temperature. Our study, for the first time, highlights the feasibility to accommodate multiple elements onto a single sublattice in a complex spinel structure and opens new possibilities to design and tailor functional properties in high entropy stabilized correlated electron systems.

Recent advances in tools for crystal structure analysis enabled us to describe a new phenomenon in structural chemistry, which, to this day, has remained hidden. Here we describe a crystal structure with an incommensurate compositional modulation, Mn0.6Ni0.4As. The sample adopts the NiAs type structure, but in contrast to a normal solid solution, we observe that manganese and nickel separate into layers of MnAs and NiAs with thickness of 2-4 face-shared octahedra. Experimentally, results are obtained by combination of 3D electron diffraction, scanning transmission electron microscopy and neutron diffraction. The distribution of octahedral units between the manganese and nickel layers is perfectly described by a modulation vector q = 0.360(3) c*. An additional periodicity is thus present in the compound. Positional modulation is observed of all elements as a consequence of the occupational modulation.