Tin selenide (SnSe) has emerged as a promising thermoelectric material with potential applications in waste heat harvesting. However, optimal performance is typically achieved in single crystals of SnSe, whose fabrication and long-term reliability under operating conditions remain challenging. Polycrystalline ceramic materials are preferred and are generally processed by spark plasma sintering (SPS), which involves high temperatures, costly equipment and intensive energy consumption. In this work, we propose a liquid-phase-assisted cold sintering process as an energy-efficient and scalable alternative to SPS that also promotes the anisotropic alignment of grains in polycrystalline SnSe. The use of a water–ethanol transient liquid phase significantly reduces interfacial friction between SnSe nanosheets, resulting in dense ceramics in which a high degree of favorable crystallite orientation is preserved. The resulting samples exhibit power factors of up to 4.6 μW cm−1K−2 at 773 K for the most textured sample, which is comparable or even superior in terms of in-plane electrical performance to those processed by SPS, demonstrating the suitability of cold sintering for high-performance SnSe thermoelectric materials.

The growth of single crystals of FeCl3, through sublimation and from the melt, is presented alongside a thorough investigation of their magnetostructural properties through a combination of DC magnetization and AC magnetic susceptibility measurements, single crystal X-ray diffraction (SCXRD), neutron powder diffraction (NPD) and small-angle neutron scattering (SANS). A new chiral polymorph of FeCl3 is identified, crystallizing in the non-centrosymmetric space group P31. NPD and SANS reveal that a weakly first-order magnetic phase transition occurs from a paramagnetic phase with significant short-range correlations to an antiferromagnetic phase at T N = 8.6 K, best described by the magnetic propagation vector k = (1/2, 0, 1/3) which differs from the previously reported magnetic structure of the well-known centrosymmetric polymorph (space group R3̄). We show that disordered crystallographic models including a large number of stacking faults are required to accurately reproduce the scattering observed in NPD patterns, preventing full determination of the magnetic structure. The magnetic field and temperature-dependent behavior of the intensities of the k = (1/2, 0, 2/3) and (1/2, 0, 5/3) magnetic Bragg peaks measured by SANS suggest that a field-induced spin reorientation occurs at H = 40 kOe when H ‖c-axis and at a significantly lower field of H ≈ 25 kOe when H ⊥c-axis. Above these magnetic fields in both cases the spins lie predominantly in the basal plane. The long-range magnetic ordering and the field-induced transitions observed in the neutron scattering experiments coincide with anomalies observed in the magnetisation versus both temperature and applied field along the principal crystal directions.

We present triple-axis neutron scattering studies of low-energy magnetic fluctuations in strongly underdoped La2-xSrxCuO4 with x = 0.05, 0.06 and 0.07, providing quantitative evidence for a direct competition between these fluctuations and superconductivity. At dopings x = 0.06 and x = 0.07, three-dimensional superconductivity is found, while only a very weak signature of two-dimensional superconductivity residing in the CuO2 planes is detectable for x = 0.05. We find a surprising suppression of the low-energy fluctuations by an external magnetic field at all three dopings. This implies that the response of two-dimensional superconductivity to a magnetic field is similar to that of a bulk superconductor. Our results provide direct evidence of a very gradual onset of superconductivity in cuprates.

Aurivillius phase Bi2LaNb1.5Mn0.5O9, derived from ferroelectric PbBi2Nb2O9 by simultaneous substitution of the A-site and B-site cations, was synthesized using a molten-salt method. Here, we discuss the structure-property relationships in detail. X-ray and neutron diffraction show that Bi2LaNb1.5Mn0.5O9 adopts an A21am orthorhombic crystal structure. Rietveld refinement analysis, supported by Raman spectroscopy, indicates that the Bi3+ ions occupy the bismuth oxide blocks, La3+ ions occupy the perovskite A-site, and Nb5+/Mn3+ ions occupy the perovskite B-site. Ferroelectric ordering takes place at 535 K, which coexists with local ferromagnetic order below 65 K. The cation disorder on the B-site results in relaxor-ferroelectric behavior, and the short-range ferromagnetic order can be attributed to Mn3+/Mn4+ double-exchange. Magnetodielectric coupling measured at 5 K and 100 kHz in a field of 5 T suggests the existence of intrinsic spin-lattice coupling with a magnetodielectric coefficient of 0.20%. These findings will provide significant impetus for further research into potential devices based on the magnetodielectric effect in Aurivillius materials.

single crystals are grown with an optimized chemical vapor transport technique using as a transport agent (TA). The optimized growth method allows to selectively produce large high‐quality single crystals. The method is shown to consistently produce crystals of maximum size 8 × 7 × 4 mm with a transport duration of around three weeks. It is found that this method, with as TA, is more efficient and simple compared with the commonly used growth techniques reported in literature with HCl gas as TA. The crystals have very high quality and their absolute structures are fully determined by simple single‐crystal X‐ray diffraction. Enantiomeric crystals with either left‐ or right‐handed chiralities are observed. The magnetization and ferromagnetic resonance data show the same magnetic phase diagram as reported earlier.

Samples of PbBi2Nb2O9, PbBi1.5La0.5Nb2O9, and PbBi1.5Nd0.5Nb2O9 have been prepared by the molten salt method. The structure, morphology, and electrical properties were investigated. All samples are singlephase and crystallize in an orthorhombic structure with A2(1)am symmetry. Neutron diffraction data indicate that the Ln(3+) cations prefer to occupy the perovskite A-site, whereas Pb/Bi occupy the perovskite A-site and the Bi2O2 layer. Changes in unit cell volume are observed on substitution and are attributed to the ionic radii of the Ln(3+) cations and also correlated to changes in the B-O bond distances in the BO6 octahedra, which are also observed in IR spectra. SEM images reveal anisotropic plate-like grains, which increase in size with the presence of Ln(3+) ions. The ferroelectric transition temperature (T-c) decreases with decreasing degree of BO6 distortion as the influence of the 6s(2) lone pair of Bi3+ is diminished. Relaxor ferroelectric behavior is observed with Ln(3+) substitution, driven by the disorder of the A-site cations. The room temperature ferroelectric polarization increases with Ln(3+) substitution, ascribed to the decreased dielectric loss. (C) 2020 Elsevier B.V. All rights reserved.

The breaking of inversion symmetry can enhance the multifunctional properties of layered hybrid organic-inorganic perovskites. However, the mechanisms by which inversion symmetry can be broken are not well-understood. Here, we study a series of MnCl4-based 2D perovskites with arylamine cations, namely, (C6H5CxH2xNH3)2MnCl4 (x = 0, 1, 2, 3), for which the x = 0, 1, and 3 members are reported for the first time. The compounds with x = 1, 2, and 3 adopt polar crystal structures to well above room temperature. We argue that the inversion symmetry breaking in these compounds is related to the rotational degree of freedom of the organic cations, which determine the hydrogen bonding pattern that links the organic and inorganic layers. We show that the tilting of MnCl6 octahedra is not the primary mechanism involved in inversion symmetry breaking in these materials. All four compounds show 2D Heisenberg antiferromagnetic behavior. A ferromagnetic component develops in each case below the long-range magnetic ordering temperature of ∼42-46 K due to spin canting.

We have grown Cu$_2$OSeO$_3$ single crystals with an optimized chemical vapor transport technique by using SeCl$_4$ as a transport agent. Our optimized growth method allows to selectively produce large high quality single crystals. The method is shown to consistently produce Cu$_2$OSeO$_3$ crystals of maximum size 8 mm x 7 mm x 4 mm with a transport duration of around three weeks. We found this method, with SeCl$_4$ as transport agent, more efficient and simple compared to the commonly used growth techniques reported in literature with HCl gas as transport agent. The Cu$_2$OSeO$_3$ crystals have very high quality and the absolute structure are fully determined by simple single crystal x-ray diffraction. We observed both type of crystals with left- and right-handed chiralities. Our magnetization and ferromagnetic resonance data show the same magnetic phase diagram as reported earlier.

The density of interfaces in spinodally decomposed Pb1−xGexTe can be controlled, allowing thermal conductivity to be optimized for thermoelectric performance.

Metastable single crystals of nonstoichiometric Pb1–xTe are obtained by rapid cooling from the melt. The composition and crystallographic morphology are studied using X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and electron backscatter diffraction. Most single crystals have cubic, pyramidal, or hemispherical shapes with sizes ranging from 50 to 400 μm. All crystals adopt the same face-centered cubic rock salt structure, and the crystal growth direction is ⟨100⟩. The bulk part of the rapidly cooled material solidifies in the form of a Te-rich polycrystalline material in which grains are separated by the PbTe–Te eutectic phase. The stabilization of nonstoichiometric Pb1–xTe provides further scope for the optimization of lead telluride-based thermoelectric materials.

The double-layer Aurivillius phase Pb0.4Bi2.1La0.5Nb1.7Mn0.3O9 was synthesized by a molten salt method using a K2SO4/Na2SO4 flux. The effect on the crystal structure, morphology, dielectric and magnetic properties of varying the molar ratio of the oxide precursors to salt flux was investigated. Single-phase products with an orthorhombic structure were obtained for oxide to salt ratios of between 1:5 and 1:9, whereas for lower concentrations of salt a pyrochlore impurity phase is found in the products. SEM showed anisotropic plate-like grains, the size of which increases for larger salt ratios. An investigation of the magnetic properties showed the presence of mixed Mn3+ and Mn4+; the unit cell volume of the single-phase products decreases as the proportion of salt increases, which implies a higher proportion of smaller Mn4+ cations. This can be explained by the oxide ion donating properties (oxobasicity) of the molten salt mixture, which produces an oxidizing environment during synthesis. The best dielectric properties are obtained for an oxide to salt ratio of 1:7, exhibiting relaxor ferroelectric behavior. This is also the ratio at which the most pronounced ferromagnetic properties are observed, resulting from double-exchange interactions between Mn3+ and Mn4+, the proportions of which are approximately equal. Pb0.4Bi2.1La0.5Nb1.7Mn0.3O9 synthesized under these conditions thus exhibits optimal multiferroic properties.

A single-phase sample of the Aurivillius compound Pb0.4Bi2.La0.5Nb1.7Mn0.3O9 was prepared by a molten salt method using K2SO4/Na2SO4 as the flux. The crystal structure, morphology, ferroelectric, and magnetic properties were investigated. Neutron powder diffraction data confirmed a non-centrosymmetric orthorhombic crystal structure with space group A2(1)am and Pb/Bi disorder in the bismuth oxide blocks, Bi/Pb/La disorder on the perovskite A-site, and Nb/Mn disorder on the perovskite B-site. The morphology of the sample showed anisotropic plate-like grains as probed by scanning electron microscopy. The dielectric constant exhibits a transition peak between 600 K and 640 K that depends on frequency, indicating relaxor ferroelectric behavior. Electrical polarization versus applied field loops are unsaturated, with a remnant polarization of 0.43 mu C/cm(2) at 40 Hz under the maximum electrical field applied of 160 kV/cm. The ferroelectricity originates from the displacement of oxygen atoms in the BO6 octahedra, resulting in a polar structural distortion. Magnetic susceptibility measurements showed the presence of mixed Mn3+ and Mn4+, resulting in short-range ferromagnetic order via double exchange interactions below 33 K. The remnant magnetization (M-r) is 0.01 emu/g at 5 K. This mixed valence of Mn cations is mainly responsible for the high electrical conductivity. Thus, Pb0.4Bi2.La0.5Nb1.7Mn0.3O9 exhibits coexisting ferroelectric and ferromagnetic properties. (C) 2019 Elsevier B.V. All rights reserved.

The double-layer Aurivillius phases Pb1-2xBi1.5+2xLa0.5Nb2-xMnxO9 (x = 0, 0.1, 0.3, and 0.5) were synthesized by a molten salt method using a mixture of K2SO4 /Na2SO4. The effect of composition on the structure, morphology and dielectric properties was investigated. X-ray diffraction showed that single-phase samples with a non-polar, orthorhombic A2(1)am structure were obtained for x = 0, 0.1 and 0.3. The unit cell becomes more orthorhombic with increasing x as the degree of distortion of the BO6 octahedra in the perovskite layer increases. Raman spectroscopy showed the typical modes of the orthorhombic double-layer Aurivillius structure and indicated that the La3+ ions prefer to occupy the perovskite A-site, Mn3+ occupies the B-site, and the Pb2+ ions are found in the Bi2O2 layer. The morphology of the samples was probed by scanning electron microscopy, which showed anisotropic, plate-like crystallites that increased in size with increasing x. The dielectric constant significantly increased with x, and the ferroelectric properties became more relaxor-like.

We report spin-singlet formation in an organic-inorganic hybrid identified as CH 3NH3Cu2Cl5. The hybrid adopts a layered structure in which Cu2Cl5− layers are separated by CH 3 NH3+ layers. The inorganic layers consist of corner- and edge-sharing CuCl6 octahedra, forming edge-sharing tetramers. Magnetic susceptibility measurements indicate strong antiferromagnetic interactions within the tetramers, whereas the coupling between the tetramers is weak. Low-temperature magnetic susceptibility data as well as electron spin resonance measurements suggest a nonmagnetic ground state with a large spin gap of ∼130K, in apparent contradiction with ferromagnetic interactions between nearest-neighbor spins. We discuss a spin-tetramer model in which antiferromagnetic next-nearest-neighbor interactions lead to a spin-singlet state.

We investigate possible mechanisms to induce electric polarization in layered organic-inorganic hybrids. Specifically, we investigate the structural phase transitions of PEA2MnCl4 (PEA = phenethylamine) using temperature dependent single-crystal X-ray diffraction analysis, including the symmetry analysis of the observed space groups. Our results show that PEA2MnCl4 transforms from a high-temperature centrosymmetric structure with space group I4/mmm to a low-temperature polar Pca21 phase via an intermediate phase with polar space group Aea2. We study the mechanism responsible for the I4/mmm to Aea2 polar phase transition and find that it is different from previously proposed mechanisms in similar systems. The transition is governed by the opening of a small dihedral angle between the phenyl ring planes of two adjacent PEA molecules, which consequently become crystallographically inequivalent in the Aea2 phase. This molecular rotation induces a significant difference in the lengths of the ethylammonium tails of the two molecules, which coordinate the inorganic layer asymmetrically and are consequently involved in different hydrogen bonding patterns. Consequently, the negatively charged chlorine octahedron that coordinates the Mn2+ cation deforms. This deformation moves the Mn2+ off-center along the out-of-plane-axis, contributing to the polar nature of the structure. Notably, the polar axis is out-of-plane with respect to the inorganic sheets. This is in contrast to other layered organic-inorganic hybrids as well as conventional layered perovskites, such as the Aurivillius phases, where in-plane polarization is observed. Our findings add to the understanding of possible mechanisms that can induce ferroelectric behavior in layered organic-inorganic hybrids.

Machteld E. Kamminga,1,* Maria Azhar,1 Julian Zeisner,2,3 Anna M. C. Maan,1 Bernd Büchner,2,3 Vladislav Kataev,2 Jacob Baas,1 Graeme R. Blake,1 Maxim Mostovoy,1 and Thomas T. M. Palstra1 1Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands 2Leibniz Institute for Solid State and Materials Research, IFW Dresden, 01069 Dresden, Germany 3Institut für Festkörperund Materialphysik, Technische Universität Dresden, 01062 Dresden, Germany

We synthesize single crystals of a new 2,5-dimethylanilinium tin iodide organic-inorganic hybrid compound and 2,5-dimethylanilinium triiodide. Single-crystal X-ray diffraction reveals that the hybrid grows as a unique rhombohedral structure consisting of one-dimensional chains of SnI6-octahedra that share corners and edges to build up a ribbon along the [111] direction. Notably, we find that hypophosphorous acid, H3PO2, is of central importance to the formation of this hybrid. In the absence of H3PO2, we synthesize 2,5-dimethylanilinium triiodide from the same starting compounds. We investigate the synthesis routes that drive the growth of these two compounds with distinct crystal structures, appearance and properties. Pulse-radiolysis time-resolved microwave conductivity measurements and density functional theory calculations reveal that both compounds have low charge carrier mobilities and very long lifetimes, consistent with their one-dimensional structural characteristics. Our findings give a better understanding of the relation between synthesis, crystal structures and charge carrier mobilities.

We use a layered solution crystal growth technique to synthesize high-quality single crystals of phenylalkylammonium lead iodide organic/inorganic hybrid compounds. Single-crystal X-ray diffraction reveals low-dimensional structures consisting of inorganic sheets separated by bilayers of the organic cations. The shortest alkyls yield two-dimensional structures consisting of inorganic sheets of corner-sharing PbI6-octahedra. However, the longer alkyls induce both corner- and face-sharing of the PbI6-octahedra, and form new compounds. Density functional theory calculations including spin-orbit coupling show quantum confinement in two dimensions for the shorter alkyls, and in one dimension for the longer alkyls, respectively. The face-sharing PbI6-octahedra create a confinement leading to effectively one-dimensional behavior. These confinement effects are responsible for the observed peak shifts in photoluminescence for the different phenylalkylammonium lead iodide hybrids. Our results show how the connectivity of the octahedra leads to confinement effects that directly tune the optical band gap.

High-quality single crystals of perovskite-like (CH3NH3)3Bi2I9 hybrids have been synthesized, using a layered-solution crystal-growth technique. The large dielectric constant is strongly affected by the polar ordering of its constituents. Progressive dipolar ordering of the methylammonium cation upon cooling below 300 K gradually converts the hexagonal structure (space group P63/mmc) into a monoclinic phase (C2/c) at 160 K. A well-pronounced, ferrielectric phase transition at 143 K is governed by in-plane ordering of the bismuth lone pair that breaks inversion symmetry and results in a polar phase (space group P21). The dielectric constant is markedly higher in the C2/c phase above this transition. Here, the bismuth lone pair is disordered in-plane, allowing the polarizability to be substantially enhanced. Density functional theory calculations estimate a large ferroelectric polarization of 7.94 μC/cm2 along the polar axis in the P21 phase. The calculated polarization has almost equal contributions of the methylammonium and Bi3+ lone pair, which are fairly decoupled.

Perovskite-based organic-inorganic hybrids hold great potential as active layers in electronics or optoelectronics or as components of biosensors. However, many of these applications require thin films grown with good control over structure and thickness--a major challenge that needs to be addressed. The work presented here is an effort towards this goal and concerns the layer-by-layer deposition at ambient conditions of ferromagnetic organic-inorganic hybrids consisting of alternating CuCl4-octahedra and organic layers. The Langmuir-Blodgett technique used to assemble these structures provides intrinsic control over the molecular organization and film thickness down to the molecular level. Magnetic characterization reveals that the coercive field for these thin films is larger than that for solution-grown layered bulk crystals. The strategy presented here suggests a promising cost effective route to facilitate the excellently controlled growth of sophisticated materials on a wide variety of substrates that have properties relevant for the high density storage media and spintronic devices.