Many compounds adopting the spinel AB(2)X(4) structure are technologically important owing to their tunable physical and chemical properties enabling diverse applications in energy storage, catalysis, magnetism, and functional ceramics. Most of them are traditionally assigned to the centrosymmetric space group Fd (3) over barm. However, the physical properties of some spinels are incompatible with centrosymmetry. This discrepancy is often accounted for by reducing the symmetry to the non-centrosymmetric space group F (4) over bar 3m, allowing thus small atomic displacements from their original position in Fd (3) over barm. In this work, we demonstrate that the loss of the inversion symmetry can occur without any atomic displacements, since the centrosymmetric Fd (3) over barm and non-centrosymmetric F4(1)32 space groups are equivalent for structure determination and refinement based on X-ray diffraction data. If consistent with experiment, only the use of an anharmonic model of atomic displacements can distinguish these space groups. This study aims to clarify certain misconceptions regarding the structural symmetry and physical properties of spinel-type compounds.

Many compounds adopting the spinel AB2X4 structure are technologically important owing to their tunable physical and chemical properties enabling diverse applications in energy storage, catalysis, magnetism, and functional ceramics. Most of them are traditionally assigned to the centrosymmetric space group Fd3m. However, the physical properties of some spinels are incompatible with centrosymmetry. This discrepancy is often accounted for by reducing the symmetry to the non-centrosymmetric space group F43m, allowing thus small atomic displacements from their original position in Fd3m. In this work, we demonstrate that the loss of the inversion symmetry can occur without any atomic displacements, since the centrosymmetric Fd3m and non-centrosymmetric F4132 space groups are equivalent for structure determination and refinement based on X-ray diffraction data. If consistent with experiment, only the use of an anharmonic model of atomic displacements can distinguish these space groups. This study aims to clarify certain misconceptions regarding the structural symmetry and physical properties of spinel-type compounds.

Many compounds belonging to the spinel AB2X4 structure play an important role due to their wide range of practical applications. Most of them are traditionally assigned to the centrosymmetric space group Fd-3m. However, the physical properties of some spinels are incompatible with centrosymmetry. This discrepancy is often accounted for by reducing the symmetry to the non-centrosymmetric space group F-43m, allowing thus small atomic displacements from their original position in Fd-3m. In this work, we demonstrate that the loss of the inversion symmetry can occur without any atomic displacements, since the centrosymmetric Fd-3m and non-centrosymmetric F4132 space groups are equivalent for structure determination and refinement based on X-ray diffraction data. If consistent with experiment, only the use of an anharmonic model of atomic displacements can distinguish these space groups. This study aims to clarify certain misconceptions regarding the structural symmetry and physical properties of spinel type compounds.

Many compounds adopting the spinel AB 2 X 4 structure are technologically important owing to their tunable physical and chemical properties enabling diverse applications in energy storage, catalysis, magnetism, and functional ceramics. Most of them are traditionally assigned to the centrosymmetric space group Fd 3 m . However, the physical properties of some spinels are incompatible with centrosymmetry. This discrepancy is often accounted for by reducing the symmetry to the non-centrosymmetric space group F 4 3 m , allowing thus small atomic displacements from their original position in Fd 3 m . In this work, we demonstrate that the loss of the inversion symmetry can occur without any atomic displacements, since the centrosymmetric Fd 3 m and non-centrosymmetric F 4 1 32 space groups are equivalent for structure determination and refinement based on X-ray diffraction data. If consistent with experiment, only the use of an anharmonic model of atomic displacements can distinguish these space groups. This study aims to clarify certain misconceptions regarding the structural symmetry and physical properties of spinel-type compounds.

Polytypism in transition metal dichalcogenides (TMDs) introduces an additional degree of freedom for tailoring the electronic properties of layered van der Waals materials. Polytypes with larger unit cells, spanning four or six layers, can be viewed as natural homostructures, since their atomic composition remains identical across the layers. The resultant crystalline environments can potentially give rise to exotic electronic states, earning these materials recent attention. In this study, we examine structural and charge transport properties of metallic and superconducting 4Ha-NbSe2. We find that the compound has a highly disordered stacking of layers, which impedes interlayer coherence, as demonstrated by detailed out-of-plane resistivity measurements, and effectively tunes the bulk system towards an atomically thin limit. The disordered structure largely accounts for the enhanced resistivity anisotropy and superconducting upper critical field, when compared to 2Ha-NbSe2. This phenomenon can be exploited to promote quasi-two-dimensional physics in bulk crystals, and our study also underscores the importance of thorough structural characterization when investigating large-unit-cell polytypes of TMDs.

In this study, we report the synthesis and characterization of a novel tetragonal polymorph of Tb-doped Pb2P2O7. Single-crystal X-ray diffraction confirms the stabilization of the P41 and P43 enantiomorphs at room temperature due to the incorporation of Tb3+ ions. Optical investigations reveal green photoluminescence from the characteristic 5D4 -> 7F j (j = 1-5) transitions of Tb3+, with each emission split due to the crystal field effect, indicating the presence of Tb3+ in multiple coordination environments. The power dependence of the PL intensity follows a linear power-law behavior, suggesting a one-photon excitation process. Temperature-dependent PL measurements show an initial increase in intensity up to 125 degrees C, attributed to energy transfer from structural defects, followed by thermal quenching above this temperature. Structural stability at elevated temperatures is confirmed via high-temperature X-ray diffraction, showing no phase transitions before melting at approximately 800 degrees C. These findings highlight the potential of tetragonal Tb-doped Pb2P2O7 as a new class of photoluminescent material.

The formation and characteristics of magnetic skyrmions are strongly governed by the symmetry of the underlying crystal structure. In this study, we report the discovery of a new trigonal polymorph of Cu2OSeO3, observed exclusively in nanoparticles. Electron diffraction and density functional theory calculations confirm its R3m space group, sharing C3v symmetry with Néel-type skyrmion hosts. This polymorph is likely stabilized by surface effects, suggesting that size-induced structural changes may drive a transformation from Bloch-type to Néel-type skyrmions in Cu2OSeO3. This hypothesis could be consistent with prior unexplained observations of Néel-type skyrmions at the surfaces of bulk crystals, which may result from surface-specific structural distortions. Overall, these findings provide insights into the interplay between size, structure, and magnetism, opening pathways for controlling skyrmionic properties in nanoscale systems.

The newly synthesized compound Fe[SeO 4 ]OH belongs to the kieserite-like structure. Using the superspace approach, possible polytypes are predicted for R[MO 4 ]Z, where R = Mg, Fe, Ni, Co, Zn, Mn, Al, V, Sb, Y; M = S, Se, P, As; Z = OH, H 2 O, F, O.

The synthesis and X-ray structural study of the new family of compounds Ba4Fe4ClO9.5-x with tunable structural modulation are reported. The framework of the structure has the Ba2Fe4O9.5-x composition, with open hexagonal channels extending along the c-axis. The channels are filled with linear [Ba-Cl-Ba] triplets. The oxygen stoichiometry and the oxidation state of iron both are controlled by the redox conditions during crystal preparation. The modulation of the crystal structure arises from the distribution of the oxygen atoms in the framework and iron coordination polyhedra are a combination of FeO4-tetrahedra, FeO5-bipyramids, and FeO6-octahedra. The structure modulation also originates from the ordered or disordered distribution of the [Ba-Cl-Ba] triplets filling the channels which is also affected by the conditions of the thermal treatment of the crystals. The structure investigation reveals a composition variation from Ba4Fe4ClO9.5 (x = 0), in which Fe exhibits a 3+ oxidation state, to Ba4Fe4ClO8 (x = 1.5) with the framework built exclusively of FeO4 tetrahedra.

An environmentally friendly analog of the prominent methylammonium lead halide perovskite, methylammonium bismuth bromide (MA3Bi2Br9), was prepared and investigated in the form of powder, single crystals and nanowires. Complete characterization via synchrotron X-ray diffraction data showed that the bulk crystal does not incorporate water into the structure. At the same time, water is absorbed on the surface of the crystal, and this modification leads to the changes in the resistivity of the material, thus making MA3Bi2Br9 an excellent candidate for use as a humidity sensor. The novel sensor was prepared from powder-pressed pellets with attached carbon electrodes and was characterized by being able to detect relative humidity over the full range (0.7–96% RH) at ambient temperature. Compared to commercial and literature values, the response and recovery times are very fast (down to 1.5 s/1.5 s).

X-ray photon detection is important for a wide range of applications. The highest demand, however, comes from medical imaging, which requires cost-effective, high-resolution detectors operating at low-photon flux, therefore stimulating the search for novel materials and new approaches. Recently, hybrid halide perovskite CH3NH3PbI3 (MAPbI3) has attracted considerable attention due to its advantageous optoelectronic properties and low fabrication costs. The presence of heavy atoms, providing a high scattering cross-section for photons, makes this material a perfect candidate for X-ray detection. Despite the already-successful demonstrations of efficiency in detection, its integration into standard microelectronics fabrication processes is still pending. Here, we demonstrate a promising method for building X-ray detector units by 3D aerosol jet printing with a record sensitivity of 2.2 × 108 μC Gyair-1 cm-2 when detecting 8 keV photons at dose rates below 1 μGy/s (detection limit 0.12 μGy/s), a 4-fold improvement on the best-in-class devices. An introduction of MAPbI3-based detection into medical imaging would significantly reduce health hazards related to the strongly ionizing X-rays' photons.

A detailed synchrotron X-ray diffraction (XRD) study performed with a single crystal of BaVS3 (barium vanadium trisulfide) in the temperature range between 10 and 295 K is reported. Aside from the known tetragonal–orthorhombic (240 K) and orthorhombic–monoclinic (69 K) phase transitions, in the 130 < T ≤ 295 K range the overall structure can be viewed as a host–guest (H–G) composite. The BaS3 matrix is the host, while the V-chains form the guest. The two subsystems lock in at T LOCK = 130 ± 20 K. This temperature is marked by a symmetry change from orthorhombic to monoclinic. This results in the formation of twins, implying a structural phase transition identified here for the first time. From the refined structural data, it is possible to follow, starting already at 295 K downwards, the stepwise transformation of VS6 octahedra into VS5 tetragonal pyramids as the origin of the structure evolution. The new findings will yield a better understanding of the complex electronic phase diagram of BaVS3.

Layered transition metal dichalcogenides (TMDs) are commonly classified as quasi-two-dimensional materials, meaning that their electronic structure closely resembles that of an individual layer, which results in resistivity anisotropies reaching thousands. Here, we show that this rule does not hold for 1T-TaS2-a compound with the richest phase diagram among TMDs. Although the onset of charge density wave order makes the in-plane conduction non-metallic, we reveal that the out-of-plane charge transport is metallic and the resistivity anisotropy is close to one. We support our findings with ab initio calculations predicting a pronounced quasi-one-dimensional character of the electronic structure. Consequently, we interpret the highly debated metal-insulator transition in 1T-TaS2 as a quasi-one-dimensional instability, contrary to the long-standing Mott localisation picture. In a broader context, these findings are relevant for the newly born field of van der Waals heterostructures, where tuning interlayer interactions (e.g., by twist, strain, intercalation, etc.) leads to new emergent phenomena.

Controversy in the description/identification of so-called intermediate phase(s) in PbHfO3, stable in the range ∼420-480 K, has existed for a few decades. A synchrotron diffraction experiment on a partially detwinned crystal allowed the structure to be solved in the superspace group Imma(00γ)s00 (No. 74.2). In contrast to some previously published reports, in the pure compound only one distinct phase was observed between Pbam PbZrO3-like antiferroelectric and Pm3m paraelectric phases. The modulation vector depends only slightly on temperature. The major structure modulation is associated with the displacement of lead ions, which is accompanied by a smaller amplitude modulation for the surrounding O atoms and tilting of HfO6 octahedra. Tilting of the octahedra results in a doubling of the unit cell compared with the parent structure.

The crystals of a novel family of rare-earth borate-nitrate compounds, Ln7(BO3)3(NO3)N3O (Ln = Pr, Nd), were grown at high-pressure in KAs flux and their crystal structure was determined. The new type of the crystalline structure consists of parallel chains of Ln6 octahedra connected by common faces and forming the channels with the NO3 triangular planar motifs in the center, and isolated OLn4 tetrahedra separated from each other by N3 triangular motifs. Each NO3 triangle is in fact a part of rather unusual (NB3O12) block consisting of 3 distorted BO4 tetrahedra around central nitrogen atom. Under near-infrared (NIR) (λex = 1064 nm) excitation, both compounds revealed a strong signal of second harmonic generation (SHG) at half the excitation wavelength (λem = 532 nm), which is in agreement with their noncentrosymmetric structure. In addition, a photon up-conversion (UC) emission at λem = 880 nm was observed for microcrystals of Nd7(BO3)3(NO3)N3O, which was assigned to the UC process occurring within the 4f electronic manifold of Nd3+ ions. The dual-emission (SHG/UC) properties of Nd7(BO3)3(NO3)N3O microcrystals, concomitant with the absence of photobleaching, makes them prospective candidates for microscopic probes in biological studies.

Single crystal growth by chemical vapour transport has resulted samples with Fe1.35Ge stoichiometry. Structural study has shown that the large number of vacancies introduces an incommensuately modulated structure. The electrical resistivity is in the 200 mu Omega cm range at room temperature, and although the ferromagnetic transition temperature at 425 K is clearly visible, it hardly varies down to 4.2 K. It is suggested that the large number of vacancies (and the incommensurate modulation) introduce a strong backscattering, and the system is at the brink of a Mooij correlation. The thermal conductivity and Seebeck coefficient carry also the consequences of the high concentration of vacancies. (c) 2019 Elsevier B.V. All rights reserved.

Layered metallic transition-metal dichalcogenides are conventionally seen as two-dimensional conductors, despite a scarcity of systematic studies of the interlayer charge transport conducted in a well-defined geometry. Here, we reveal c-axis-oriented quasi-one-dimensional electronic states in 1T-TaS2, a layered system hosting a plethora of diverse phases, by probing its out-of-plane electrical resistivity using focused-ion-beam-tailored crystals. While the in-plane conduction appears non-metallic due to presence of a unique nanoarray of charge density wave (CDW) domains, the interlayer resistivity has a metallic temperature dependence with the anisotropy close to one, as a result of intertwining of the orbital and CDW orders. The compound is known for what was believed to be a Mott-type localisation below 150 K, yet with our data, supplemented by ab-initio calculations, we interpret the transition as a Peierls-like instability of the quasi-one-dimensional electronic structure. Our findings present a very unintuitive behaviour in a van der Waals crystal.

The photovoltaic perovskite, methylammonium lead triiodide [CH3NH3PbI3 (MAPbI3)], is one of the most efficient materials for solar energy conversion. Various kinds of chemical and physical modifications have been applied to MAPbI3 towards better understanding of the relation between composition, structure, electronic properties and energy conversion efficiency of this material. Pressure is a particularly useful tool, as it can substantially reduce the interatomic spacing in this relatively soft material and cause significant modifications to the electronic structure. Application of high pressure induces changes in the crystal symmetry up to a threshold level above which it leads to amorphization. Here, a detailed structural study of MAPbI3 at high hydrostatic pressures using Ne and Ar as pressure transmitting media is reported. Single-crystal X-ray diffraction experiments with synchrotron radiation at room temperature in the 0-20 GPa pressure range show that atoms of both gaseous media, Ne and Ar, are gradually incorporated into MAPbI3, thus leading to marked structural changes of the material. Specifically, Ne stabilizes the high-pressure phase of NexMAPbI3 and prevents amorphization up to 20 GPa. After releasing the pressure, the crystal has the composition of Ne0.97MAPbI3, which remains stable under ambient conditions. In contrast, above 2.4 GPa, Ar accelerates an irreversible amorphization. The distinct impacts of Ne and Ar are attributed to differences in their chemical reactivity under pressure inside the restricted space between the PbI6 octahedra.

Optoelectronic devices and solar cells based on organometallic hybrid perovskites have to operate over a broad temperature range, which may contain their structural phase transitions. For instance, the temperature of 330 K, associated with the tetragonal–cubic transformation, may be crossed every day during the operation of solar cells. Therefore, the analysis of thermal cycling effects on structural and electronic properties is of significant importance. This issue is addressed in the case of methylammonium lead iodide (CH 3 NH 3 PbI 3 ) across both structural phase transitions (at 160 and 330 K). In situ synchrotron radiation X‐ray diffraction (XRD) data recorded between 140 and 180 K show the emergence of a boundary phase between the orthorhombic and tetragonal phases, which becomes more abundant with successive thermal cycles. At high temperatures, around 330 K, an incommensurately modulated tetragonal phase is formed upon repeated crossings of the phase boundary between tetragonal and cubic phases. These alterations, which indicate a gradual evolution of the material under operating conditions of photovoltaic devices, are further documented by electrical resistivity and heat capacity measurements.