Refined Unit Cell Research Articles

The La2Pd3(Si, Ge)5 complete solid solution: Crystal structure, chemical bonding, and volume chemistry

The La2Pd3Si5 intermetallic and the La2Pd3(SixGe1-x)5 solid solution were targeted for structural and computational investigations. The ternary compound and quaternary alloys with varying silicon contents (x = 0.25, 0.50, 0.70, 0.75) were prepared by arc melting and turned out to crystalize with the oI40–U2Co3Si5 (Ibam, N. 72) type structure based on powder X-ray diffraction data. The crystal structure of La2Pd3Si5 was additionally solved through X-ray diffraction on single crystal grown by recrystallization in Sn flux. Chemical bonding investigations based on QTAIM effective charges and DOS/(I)COHP analysis indicate the formation of heteropolar interactions between Si and the surrounding La/Pd metals, and between La and Pd. Covalently bonded zigzag chains of Si are also formed and considered to be the main responsible for the higher melting point of La2Pd3Si5, measured by DSC, with respect to that of La2Pd3Ge5. The formation of a complete solid solution between La2Pd3Si5 and La2Pd3Ge5 was confirmed and refined unit cell parameters and volumes change linearly with composition, displaying a Vegard trend. The calculation of atomic volumes on a quantum chemical basis (QTAIM) provides detailed insights into the volume chemistry of La2Pd3(SixGe1-x)5. Through this analysis La is found to be responsible, together with the gradual substitution of Ge with Si, for the volume contraction.

Syntheses, crystal structures, and physical properties of non-centrosymmetric MgIn2Te4 and MnIn2Te4

In this study, we prepared two ternary tellurides, MgIn2Te4 and MnIn2Te4 (single crystals and bulk polycrystalline phases), by directly fusing the elements at high temperatures using the sealed tube synthesis method. Single crystal X-ray diffraction studies confirmed the non-centrosymmetric tetragonal structures (space group: I4‾ 2m) of the MgIn2Te4 and MnIn2Te4 phases with two formula units (Z = 2). Interestingly, the refined unit cell lengths of a = b = 6.2149(5) Å and c = 12.4240(19) Å for the MgIn2Te4 are slightly longer than those of the MnIn2Te4 structure (a = b = 6.1901(3) Å and c = 12.3877(7) Å). The asymmetric unit of these two MIn2Te4 (M = Mg and Mn) isostructural compounds contains three crystallographically independent sites: two disordered metal sites (M1/In1, M2/In2) and one Te1 site. Each metal atom in these structures is tetrahedrally coordinated with four Te1 atoms. Optical absorption studies for polycrystalline MgIn2Te4 and MnIn2Te4 samples showed bandgaps of 1.1(2) eV and 0.9(2) eV, respectively, consistent with these powders' black color. Seebeck studies confirm that holes are the majority of charge carriers for the MgIn2Te4 sample. The thermal conductivity (ktot) studies of the samples reveal ultralow values at 773 K: 0.37 Wm−1K−1 for the MgIn2Te4 and 0.44 Wm−1K−1 for the MnIn2Te4. Magnetic studies on the polycrystalline MnIn2Te4 show a paramagnetic behavior with a magnetic moment of 5.73 μB. Our theoretical studies indicate the possibility of achieving a high thermoelectric figure of merit (zT > 1.5) by optimizing the hole concentration in the MgIn2Te4 sample.

The dry-gel conversion synthesis of the lithium sodium borosilicate jadarite, LiNaSiB3O7(OH)

Abstract The lithium sodium borosilicate jadarite, LiNaSiB3O7(OH), was first identified in 2007 in the Jadar basin, Serbia, where it forms the principal ore mineral of one of Europe's largest Li deposits. We report the successful application of the dry-gel conversion technique (DGC) to synthesise a jadarite analogue, via a dry-gel precursor made using sol-gel synthesis and the inclusion of the structure directing agent tetraethylammonium hydroxide (TEAOH). Pawley refinement of powder X-ray diffraction (PXRD) data collected on the synthetic sample was carried out using a monoclinic unit cell in space group P21/c (Whitfield et al., 2007), and gave refined unit cell parameters of a = 6.824(3) Å, b = 13.882(5) Å, c = 7.735(3) Å and β = 124.37(1)° (Rwp = 9.22). Inductively-coupled plasma optical emission spectroscopy (ICP–OES) on the synthetic sample confirmed an empirical formula of Li1.07Na1.40Si0.79B3O7.32(OH), based on three B atoms per formula unit (apfu). The synthetic product was found to be deficient in Si compared to natural jadarite from analysis of PXRD and ICP–OES data. Fourier-transform infrared spectroscopy (FTIR) showed that synthetic jadarite has peaks at 1415 and 1342 cm–1 and between 1180 and 900 cm–1, which are attributed to the presence of trigonal (BO3) and tetrahedral (BO4) borate groups characteristic of the natural jadarite structure, as well as a broad peak at 3441 cm–1 due to the presence of residual TEAOH. Scanning electron microscopy showed similarities in the morphologies between synthetic and natural jadarite particles.

Temperature‐Dependent Interplay between Structural and Charge Carrier Dynamics in CsMAFA‐Based Perovskites

AbstractState‐of‐the‐art triple cation, mixed halide perovskites are extensively studied in perovskite solar cells, showing very promising performance and stability. However, an in‐depth fundamental understanding of how the phase behavior in Cs0.05FA0.85MA0.10Pb(I0.97Br0.03)3 (CsMAFA) affects the optoelectronic properties is still lacking. The refined unit cell parameters a and c in combination with the thermal expansion coefficients derived from X‐ray diffraction patterns reveal that CsMAFA undergoes an α–β phase transition at ≈280 K and another transition to the γ‐phase at ≈180 K. From the analyses of the electrodeless microwave photoconductivity measurements it is shown that shallow traps only in the γ‐phase negatively affect the charge carrier dynamics. Most importantly, CsMAFA exhibits the lowest amount of microstrain in the β‐phase at around 240 K, corresponding to the lowest amount of trap density, which translates into the longest charge carrier diffusion length for electrons and holes. Below 200 K a considerable increase in deep trap states is found most likely related to the temperature‐induced compressive microstrain leading to a huge imbalance in charge carrier diffusion lengths between electrons and holes. This work provides valuable insight into how temperature‐dependent changes in structure affect the charge carrier dynamics in FA‐rich perovskites.

Zeolitic germanosilicate analogue to pharmacosiderite crystallized in an acidic medium

Zeolites are typically synthesized in alkaline or fluoride-containing near-neutral media. Sophisticated organic structure-directing agents have been investigated for such systems with the aim of discovering materials with unprecedented structures and properties for novel technical applications. In contrast, zeolite crystallization in strongly acidic media has yet to be explored. This study demonstrates that a zeolitic silicate phase crystallizes from acidic gels using trimethylamine as an organic additive with the composition 1 SiO2:0.3 TMA:0.3 HCl: 0.15 HF:55 H2O:(0.1–0.4) GeO2. This phase has an interrupted four-connected framework analog to the octahedron/tetrahedron-mixed framework of the mineral family pharmacosiderite. In comparison to the pharmacosiderite-type HK3(Ge7O16)(H2O)4, the four GeO6-octahedra forming the central [HGe4O4O12]-cluster are replaced by four SiO4-tetrahedra in a [Si4O6(OH)2.89]-unit in the new phase. However, the structure is distorted and may contain connectivity and point defects; thus, healing by the occasional incorporation of GeO6-units is necessary. The refined unit cell has a cubic symmetry, space group P-43m (#215), with a = 7.7005(1) Å. Acidic-medium synthesis is a useful way to find new zeolites that move in a fundamentally different direction from sophisticated organic structure-directing agents.

Optical, structural and dielectric properties of solvothermally grown molybdenum sulfide nanosheets

MoS2 nanosheets have been synthesized by simple and conventional solvothermal methods. FEG-TEM images reveal that the produced MoS2 sample has a hexagonal crystal structure with large (2μm) nanosheets. The XRD and Raman spectra of the samples also confirm the hexagonal crystal phase. The schematic refined unit cell with electron density mapping is visualized after Rietveld refinement. The optical properties such as absorbance, PL, refractive index, extinction coefficient, dielectric constant, optical conductivity, etc. have been investigated in the wavelength range of 330nm to 1000nm. The normal dispersion (ND) and the anomalous dispersion (AD) regions have been observed in the refractive index spectrum. The estimated carrier concentration has been found to be 5×104cm−3. The temperature-dependent indirect bandgap of MoS2 has been simulated using a semi-empirical formula based on electron-phonon coupling and it decreases with increasing temperature. The calculated average lifetime of carriers is 1.17 ns. The grown MoS2 shows large dielectric constant and low tangent loss in the frequency range of 5–500 kHz. The Nyquist plot of the sample gives the NTCR (negative temperature coefficient of resistance) behaviour like a semiconductor. The activation energy (EA) has been estimated from temperature dependence AC conductivity.

New Cd(1−X)CoXO stoichiometric nanocomposite system: Synthesis, structure, magnetic and surface area properties

In this work a new nanocomposite system of Cd(1−X)CoXO (0.0 ≤ X ≤ 1.0 mol) is presented. The nanocomposite system has been synthesized using the hydrothermal method. The composition of the synthesized system is confirmed with the EDX technique. The synthesis, structure, magnetic, and surface area properties of the synthesized Cd(1−X)CoXO nanocomposite system are reported. The structure has been studied with X-ray diffraction, TEM, and SEM, which confirms the formation of the nanocomposite. The new nanocomposite system of Cd(1−X)CoXO possess fcc CdO, fcc CdCoO, and fcc Co3O4 phases. Celref Unit-Cell refinement code was used to determine the lattice parameter (a, b and c), bond length (l), cell volume (V) and theoretical density (ρ), while the average crystallite size (Dav), dislocation density (ε), and the microstrain (δ) was calculated using the Scherrer equation. The M − O (metal-oxide) bonds were investigated with the FTIR technique. In addition, we analyze the magnetization curves and the mass magnetic susceptibility (χmass) of the system. The surface area has been determined and discussed using Brunauer–Emmett–Teller method (BET). Lastly, the effect of Co2+ ions concentration on the above studies is discussed.

Quenching of spin-orbit coupling and signature of Griffiths Phase in nanocrystalline La0.6Ba0.4MnO3 perovskite manganite

The size-dependent structural and magnetic properties of nano and bulk samples of 40 ​mol% Ba2+-doped LaMnO3 (i.e., La0.6Ba0.4MnO3) manganite have been investigated in detail. The Rietveld refinement of X-ray diffraction data confirms that nano and bulk La0.6Ba0.4MnO3 manganites crystallize into ideal cubic perovskite structure with Pm3¯m space group. The refined unit cell parameters decrease with increasing calcinations temperature or particle size. The temperature dependent magnetization measurements reveal that both the bulk and nano samples exhibit paramagnetic (PM) to ferromagnetic (FM) phase transition at Curie temperature (TC). A distinct bifurcation between magnetization curves under zero-field cooled (MZFC) and field-cooled (MFC) measurements reveals the possible existence of frustrated magnetic ordering or spin glass clusters. For nano sample, a sharp downward deviation in inverse susceptibility from Curie-Weiss law is observed, which indicates the existence of Griffiths Phase. The analysis of the field dependent magnetization M(H) curves measured at 10 ​K, in terms of saturation moments, reveals that there is a coupling between spin and orbital magnetic moments, in bulk sample of La0.6Ba0.4MnO3 manganite, which can be quenched by reducing particle size of the manganite. According to the Banerjee's criterion, nano sample exhibits first-order magnetic transition and bulk sample shows second-order magnetic transition in the low magnetic field region.

Synthesis of green phosphor SrAl2O4: Eu2+, Dy3+: Rietveld refinement and optical properties

Strontium aluminate (SrAl2O4), SrAl2O4: Eu2+ and SrAl2O4: Eu2+/Dy3+ phosphors were prepared by solution combustion method. The XRD patterns of the sample were analysed using Rietveld refinement. The analysis confirmed the multiphase structure consisting of hexagonal (P63 space group) and monoclinic (P121 space group) phases. The refinement χ2 values in the range of 2.1–2.8. The crystal structure model was generated based on the refined data. The refined unit cell volume show increment after Eu and Dy doping. The estimated crystallite size is approximately 19 nm and slightly increase after calcination. The emission spectra of the Eu2+ doped SrAl2O4 sample shows a broad emission band with a peak around 500 nm, corresponding to 4f6 5d1 –4f7 transition. With additional Dy3+ doping, the emission peak shifted towards 522 nm, which emitted green light as illustrated by the CIE diagram. The synthesized compounds were also characterized by FTIR and UV-vis for their chemical bonding and energy band gap respectively.

Crystal structure and photochemistry of 5-azacytosine: experimental and theoretical study

The crystal structure of 5-azacytosine was proposed by the X-ray diffraction pattern of the compound and the performed Rietveld analysis. The crystal structure solutions were achieved with the simulated annealing procedure. The model molecule for the procedure was taken from the BLYP/aug-cc-pVDZ optimization of the N1(H) oxo-amino tautomer of the compound. The refined unit cell parameters are: a = 12.82916 Å, b = 9.47282 Å, c = 3.66363 Å, and space group P212121. The studied excited-state reaction paths of the H-detachment processes of two oxo-amino tautomers show a possibility for mutual phototransformation of the two oxo-amino tautomers: N1(H) and N5(H). The driven states of this photoreaction are the 1nσ* and 1πσ* excited states.

Altering the magnetic ordering of Fe3Ga4 via thermal annealing and hydrostatic pressure

The effects of post-synthesis annealing temperature on arc-melted samples of Fe3Ga4 has been studied to investigate changes in crystallographic and magnetic properties induced by annealing. Results show a significant trend in the evolution of the (incommensurate spin density wave) ISDW-FM (ferromagnetic) transition temperature as a function of the refined unit cell volume in annealed samples. Strikingly, this trend allowed for the tuning of the transition temperature down to room-temperature (300 K) whilst maintaining a sharp transition in temperature, opening the door to the use of Fe3Ga4 in functional devices. Crystallographic analysis through Rietveld refinement of high-resolution x-ray diffraction data has showed that arc-melted stoichiometric Fe3Ga4 is multi-phase regardless of annealing temperature with a minor phase of FeGa3 decreasing in phase fraction at higher annealing temperature. In order to validate the trend in ISDW-FM transition temperature with regard to unit cell volume, high pressure magnetometry was performed. This showed that the FM-ISDW (~ 68 K) and ISDW-FM (~ 360 K) transition temperatures could be tuned, increased and decreased respectively, linearly with external pressure. Thus, external pressure and the ensuing crystallographic changes minimize the temperature range of the stability of the ISDW pointing toward the importance of structural properties on the mechanism for the formation of the intermediate ISDW phase. These results show how this model system can be tuned as well as highlighting the need for future high-pressure crystallography and related single crystal measurements to understand the mechanism and nature of the intermediate ISDW phase to be exploited in future devices.

Plastic Crushing Failure of Bio-Inspired Cellular Hierarchical Topological Sandwich Core.

Bio-inspired self-similar hierarchical honeycombs are multifunctional cellular topologies used for resisting various loadings. However, the crushing behavior under large plastic deformation is still unknown. This paper investigates the in-plane compressive response of selective laser melting (SLM) fabricated hierarchical honeycombs. The effects of hierarchical order, relative density as well as constituent material are evaluated. The results show that at small deformation, the AlSi10Mg alloy hierarchical honeycombs show great advantages over the elastic modulus and compressive strength than 316L steel hierarchical honeycombs. As the relative density and hierarchical order increase, the failure mechanism of AlSi10Mg alloy honeycombs gradually changes from a bending-dominated mode to a fracture-dominated mode; whereas all the 316L steel honeycombs fail due to the distortion of original unit cells. At large deformation, the AlSi10Mg alloy honeycombs behave with brittle responses, while the 316L steel honeycombs exhibit ductile responses, showing a negative Poisson’s ratio behavior and gradient deformation of hierarchical unit cells. The addition of unit cell refinements improves the elastic modulus of AlSi10Mg alloy honeycombs and advances the densification of 316L steel honeycombs. In addition, the effect of constituent material on the compressive response of hierarchical honeycombs has been discussed. This study facilitates the development and future potential application of multifunctional ultra-light sandwich structures.

Syntheses of new (CdO)(1-X)(NiO)XZnO nanocomposite system: Preparation, structure, and magnetic properties

This paper presents a new nanocomposite system of (CdO)(1-X)(NiO)XZnO (0≤X≤1 mol). The proposed nanocomposite system is synthesized using a hydrothermal method to experimentally study the structure and magnetic properties of the (CdO)(1-X)(NiO)XZnO (0≤X≤1 mol) system. The formations of the nanocomposite with CdO (face-centered cubic) and ZnO (hexagonal) phases are determined using the X-ray diffraction analysis (XRD) diffractogram and they are confirmed with a high-resolution transmission electron microscope (HRTEM). In our study, we use a Celref Unit-Cell refinement code to determine the crystallization parameters, lattice parameter (a, b and c), bond length (l), cell volume (V) and theoretical density (ρ), while the average crystallite size (Dav), dislocation density (δ), and the microstrain (ɛ) are determined using the Scherrer equation. Additionally, we analyze the magnetization curves and the mass magnetic susceptibility (χmass) of the nanocomposites (CdO)(1-X)(NiO)XZnO system using a Vibrating Sample Magnetometer (VSM). Lastly, the effect of substituting Cd+2 ions by Ni+2 ions on the above properties is discussed.

Study on Local Chemical Orderings in Li3NbO4-Based Positive Electrode Materials with a Disordered Rock-Salt Structure By a Reverse Monte Carlo Modeling

1. Introduction As a positive electrode material for a lithium-ion battery, lithium-rich transition-metal oxides have drawn much attention due to the high discharge capacity. Among the oxides, we have focused on Li1+xM1-xO2 with a disordered rock-salt structure such as Li3NbO4-based solid solution [1]. It is well known that all the cations occupy a same crystallographic site in the crystals. Due to different ionic radii and electronic states of the cations, however, it can be predicted that local structures (non-periodic structures) around different cation species must be distinguishable, and such hidden strucures must affect Li+ behavior in charge and discharge processes. Therefore, some previous works tried to uncover the local structures [2], but the structures are still under debete. This is because the structures without periodicity do not show prominent Bragg peaks in a diffraction profile.From such background, this work investigated local structures of the Li3NbO4-based materials, which can be also denoted as Li1+x(Nb, M)1-xO2, with the disordered rocksalt structure by a reverse Monte Carlo (RMC) modeling using total scattering data. Especially, we paid special attention on Li1.3Nb0.3Fe0.4O2 and Li1.3Nb0.43Ni0.27O2 as typical materials. Based on the modeling results, we discuss effects of the cation species on the local structures.2. Experimental The Li3NbO4-based materials were synthesized by a conventional solid-state reaction method, according to literature [1]. Metal compositions of the samples were analyzed by an inductively coupled plasma atomic emission spectroscopy, and valences of cations were estimated by X-ray absorption near edge structures (BL14B2, SPring-8). Synchrotron X-ray Bragg profiles were collected with BL19B2 (SPring-8), and the crystal structures (average structures) were refined by a Rietveld method. We also measured neutron and synchrotron X-ray total scattering data at NOVA (J-PARC) and BL04B2 (SPring-8), respectively. By using structure factors S(Q) and reduced pair distribution functions G(r) in addition to the Bragg profiles, we performed the RMC modeling with an RMCProfile software under a bond-valence-sum (BVS) constraint. In the modeling, we optimized cation distributions by swapping the cations.3. Results We made a supercell with 1000 atoms from a refined unit cell, and then performed RMC modeling on Li1.3Nb0.3Fe0.4O2 with the disordered rock-salt structure. As a result, we could obtain an atomic configuration which could reproduce X-ray Bragg profile, neutron G(r), neutron and X-ray S(Q). From the atomic configuration, it was found that a local distortion of NbO6 was larger than those of the others (LiO6 and FeO6) in the material. The large distortion should be induced by a smaller ionic radius of Nb5+ and/or a mismatch of electronic state of Nb5+. Furthermore, it was clarified from a coordination-number analysis that Li tended to be surrounded by Nb considerably in the disordered rock-salt structure. Such a tendency was also observed in an atomic configuration of Li1.3Nb0.43Ni0.27O2. From the results, it can be concluded that Li diffusion is disturbed by a cation with a higher valence in the disordered structure.

Crystal and molecular structure of fenspiride, C15H20N2O2

The crystal and molecular structure of fenspiride, a bronchodilator and anti-inflammatory drug, are reported. Fenspiride crystallizes in the monoclinic system, with two crystallographically independent molecules in the general position of the space group P21/n (No. 14) and Z = 8. Rietveld refined unit cell parameters are a = 11.52013(8) Å, b = 5.614091(31) Å, c = 44.1567(4) Å, α = 90°, β = 93.0885(6)°, γ = 90°, and V = 2851.69(4) Å3.

Flux synthesis, crystal structure and electrochemical properties of Na2La2P4O12 material for supercapacitors

Sodium lanthanum cyclometaphosphate (Na2La2P4O12) material was synthesized using the flux method as high performance electrochemical supercapacitors. Rietveld refinement of x-ray pattern confirms that the Na2La2P4O12 material crystallizes in triclinic crystal structure with P-1 space group. The refined unit cell parameters of triclinic structure are a = 6.28124 Å, b = 6.59774 Å, c = 9.66396 Å, α = 93.2354°, β = 103.4630° and γ = 106.7750°. Na2La2P4O12 material reveals excellent electrochemical performance with high specific capacitance of ~400 F/g using 1 M NaClO4 electrolyte.

Thermal stability, low gap energy and high Temperature order–disorder Phase Transition in Hybrid Material: [N (CH3)4]2PdCl4

The crystal compound [N (CH3)4]2PdCl4 was crystallized in the orthogonal system and the space group is P4/mmm and the refined unit cell parameters are a = b = 8.831 Å, c = 11.415 Å. The structure, vibrational spectra and optical properties have been investigated. DSC studies indicate the presence of two phase transitions at higher temperature which confirm the thermal stability of the palladium‐based compound. These transitions have been studied by Raman scattering on single crystals as a function of temperature which confirmed their nature. The assignment of the observed bands is discussed based in the theoretical calculated frequencies by the density functional theory (DFT) method using B3LYP/LanL2DZ basis in the GAUSSIAN‐09 package of programs. The optical properties in the UV–visible region have been deduced and the energy gap has been determined which is equal to 3.11 eV.

Synchysite-(Ce) from Cinquevalli (Trento, Italy): Stacking Disorder and the Polytypism of (Ca,REE)-Fluorcarbonates

Synchysite-(Ce) at Cinquevalli occurs as fine needles intergrown with quartz in quartz-dikes and in association with altered K-feldspar and oxidized chalcopyrite as major constituents. Synchysite-(Ce) [Ca1.00(Ce0.43La0.26Nd0.17Y0.07Pr0.04Sm0.02Gd0.01)Σ=1.00(CO3)2(F0.58(OH)0.42)], shows an overgrowth rim of bastnäsite-(Ce) [(Ce0.34La0.25Nd0.17Pb0.07C a0.06Y0.06Pr0.04S m0.02Gd0.01)Σ=1.00C O3(F0.75(OH)0.25)]. Unit cell refinement of synchysite (C2/c) and bastnäsite (P62c) led to a = 12.272(4), b = 7.100(2), c = 18.640(5) Å, β = 102.71(5)°, and a = 7.085(1), c = 9.746(2) Å, respectively. Polysomatic faults are sporadic, but polytypic disorder is widespread. High resolution transmission electron microscopy images taken along [100] or ⟨130⟩ show an apparent order and the related diffraction patterns are streak-free. Conversely, along [010] or ⟨110⟩, a high density of stacking faults is observed and the related diffraction patterns show hhl rows with h ≠ 3n affected by streaks. No ordered domain larger than a few unit cells was detected. The stacking sequence of (Ca,REE)-fluorcarbonates can be compared with subfamily-B mica polytypes (2M2, 2O and 6H), which are characterized by n·60° (n = odd) rotations. Subfamily-A polytypes (1M, 2M1 and 3T), characterized by n·60° (n = even) rotations, should not be possible. Synchysite, characterized by ±60° rotations, can be likened to the 2M2 polytype.

Crystal Structure and Properties of a UV‐Transparent High‐Pressure Polymorph of Mg3TeO6 with Second Harmonic Generation Response

Mg3TeO6 can be synthesized at ambient pressure conditions and temperatures of 920–1070 K in a centrosymmetric, rhombohedral structure‐type (R3). By means of high‐pressure/high‐temperature synthesis at 12.5 GPa and 1570 K a new, colorless, non‐centrosymmetric high‐pressure (HP) phase of Mg3TeO6 is formed, crystallizing in the Ni3TeO6‐type structure with the following unit cell parameters and refinement results: R3, a = 513.82(7) pm, c = 1380.7(2) pm, V = 31.57(1) nm3, R1 = 0.0283, wR2 = 0.0732, and GooF = 1.096. High‐temperature PXRD measurements on HP‐Mg3TeO6 revealed exceptionally high temperature stability for a metastable high‐pressure compound of up to 1220 K. Additionally, vibrational spectra (IR/Raman) were recorded and compared to theoretical calculations obtained by Density Functional Theory. Due to the acentric crystal structure, SHG measurements on a powdery sample exhibited an SHG efficiency of 0.83 times KH2PO4 (KDP) and a wide transparency range up to an absorption edge of 260 nm was determined by UV/Vis measurements. Overall, HP‐Mg3TeO6 is therefore interesting for UV‐laser applications.

Structural Studies of Lake Baikal Natural Gas Hydrates

The structure of near-bottom gas hydrate samples obtained in Lake Baikal during the expeditions in 2005–2018 are reported. The hydrates contain mainly methane and ethane. More than 85% of the samples contain hydrate of cubic structure I (sI) with up to 4.2 mol.% ethane. The concentration of ethane in the samples containing hydrate of cubic structure II (sII) is 12–14 mol.%. Refined unit cell parameters of natural hydrates are in good agreement with the data obtained in the studies of artificially synthesized hydrates. Possible mechanisms for the formation of sII hydrates are discussed. Some arguments are provided in favor of a probable presence of dispersed gas hydrates in the near-bottom layers of Baikal sediments and the possibility of small variations in the composition of hydrate gas in different hydrate fragments taken from the same hydrate layer.