Space Group R3 Research Articles

Structural analysis and properties of two novel pharmaceutical salts of letermovir

Two novel pharmaceutical salts of letermovir (LM) were successfully achieved by a slow reaction in solution containing LM with ethylenediamine (EDA) and diisopropylamine (DIPA). In this article, crystal structure, X-ray diffraction, thermal properties, 1H NMR, 13C NMR, HPLC analysis, stability and solubility of salt 1 and salt 2 have been discussed. Salt 1 crystalized in R3 space group and salt 2 crystalized in P3221 space group. The formation of salt was proved by pKa rule and single crystal determination. From the perspective of crystal structure, for salt 1 and salt 2, the strong hydrogen bond makes the crystal structure more stable. The weak interaction between molecules is further studied by Hirshfeld surface and 2D-fingerprint plots. Notably, this is the first report of a single crystal structure of LM, which could contribute to the development of corresponding drugs. In addition, salt 1 and salt 2 showed better solubility and stability under wet conditions, and had the potential to replace the bulk drug.

Structural and electrical studies of B3+-and-In3+-ion co-doped Li1.3Al0.3Ti1.7(PO4)3 solid electrolytes

In this study, B3+ and In3+ ions were co-doped at the Al3+ sites of Li1.3Al0.3Ti1.7(PO4)3 electrolyte using a solid-state reaction with the goal of obtaining electrolytes with remarkable Li-ion conductivities. B3+-ion doping enhanced the densification of Li1.3Al0.3-yByTi1.7(PO4)3 electrolytes, and Li1.3Al0.22B0.08Ti1.7(PO4)3 electrolyte delivered the highest relative density of 97.6%. Subsequent In3+-ion doping further enhanced densification, and Li1.3Al0.21B0.08In0.01Ti1.7(PO4)3 electrolyte delivered the highest relative density of 98.2%. However, the electrolyte densification diminished rapidly upon further increasing the In3+-ion content. The peaks in the X-ray diffraction patterns of the Li1.3Al0.3-yByTi1.7(PO4)3 and Li1.3Al0.22-xB0.08InxTi1.7(PO4)3 electrolytes were indexed to rhombohedral NASICON-type LiTi2(PO4)3 with the space group R3¯c with trace amounts of LiTiPO5 secondary phase. Upon incorporating In3+ ions into the lattice of Li1.3Al0.3Ti1.7(PO4)3 solid electrolyte, the cell volume and the transport channels for Li+ ions were expanded, while B3+-ion incorporation slightly contracted the cell. The scanning electron microscopy and Raman spectroscopy results indicated that B3+-ion substitution into the Li1.3Al0.3Ti1.7(PO4)3 lattice to obtain Li1.3Al0.3-yByTi1.7(PO4)3 electrolytes, which led to the increase in the structural order of the lattices and promoted the formation of microstructures with superior crystallinity and smaller and more uniform grain sizes. Further, B3+ and In3+-ions co-doped Li1.3Al0.22-xB0.08InxTi1.7(PO4)3 electrolytes showed lower structural order, larger grain size, lower grain-size uniformity, and more pore contents than those of undoped Li1.3Al0.3Ti1.7(PO4). The ionic conductivities of the Li1.3Al0.3-yByTi1.7(PO4)3 electrolytes increased with increasing concentration of B3+-ion dopant and reached a maximum of 8.35× 10−4 S/cm for Li1.3Al0.22B0.08Ti1.7(PO4)3. Among the Li1.3Al0.22-xB0.08InxTi1.7(PO4)3 electrolytes, Li1.3Al0.21B0.08In0.01Ti1.7(PO4)3 presented the highest ionic conductivity of 1.08 × 10−3 S/cm, which was closely correlated to its high relative density. The contribution of electronic conductivity to total conductivity was found to be trivial.

Structure redetermination, transport and thermal properties of the YNi3Al9 compound

Single crystals of completely ordered variant of the YNi3Al9 compound were grown by self-flux method with excess of aluminum. The crystal structure of the title compound was redetermined from single crystal X-ray diffraction data. The structure adopts ErNi3Al9 type, space group R32, parameters of the unit cell a ​= ​7.2838(2) Å, c ​= ​27.4004(8) Å. The growth of relatively large single crystals of the YNi3Al9 compound, having completely ordered structure, indicates possible existence of region on phase diagram, where the title compound is in equilibrium with liquid. Comparison with the results in the literature on the investigations of the same and related compounds shows trend towards formation of more ordered structures in flux grown samples and more disordered ones in arc melted samples.Physical properties of the title compound - electrical resistivity, magnetoresistance and heat capacity - were measured for the first time. It shows metallic-like behavior with very high values of magnetoresistance up to 420% at low temperatures without presence of magnetic elements. Therefore electronic structure calculations were carried out. The phonon heat capacity reveals major Debye and minor Einstein contributions at the intermediate temperatures, and total heat capacity approaches Dulong-Petit limit at high temperatures. The calculated Debye temperature from the whole temperature range θD ​= ​480(6) K is typical for aluminium-rich compounds. Corresponding Einstein temperature is θE ​= ​198(8) K. The estimations of electron-phonon coupling constant λ ​= ​0.092 show very weak coupling and absence of superconducting transition.

Y-Substitution effects in the crystal field of the trigonal YxRE1−xNi3Ga9 (RE = Tb, Dy, and Ho)

Multipolar ordering arising from the interplay between crystalline electric field (CEF) effects and magnetic interactions has been gaining more attention in 4f systems. In this work, we explore this possibility in the chiral magnets RENi3Ga9 (RE = Tb, Dy and Ho; x = 0.15 and 0.30) through Y-dilution. We present temperature-dependence of the M∕H curves, isothermal magnetization and heat-capacity experiments. Single crystalline samples grown by Ga self flux allow us to measure the magnetic properties for different crystallographic directions. X-ray diffraction patterns analyzed by Rietveld method indicate that all samples crystallize in a trigonal ErNi3Al9-type structure with space group R32. Our results are consistent with an antiferromagnetic order with transition temperatures TN< 20 K for all the studied samples, which decrease gradually with Y-substitution. By using a mean field model including anisotropic near- and next-near-neighbors magnetic interactions and the trigonal CEF Hamiltonian, we are able to study in detail the evolution of the crystal-field scheme and magnetic couplings for these compounds. We show that the spatial charge distribution between the compounds are in agreement, increasing the confidence of the obtained CEF schemes. Finally, we compare our fittings with disorder simulations assuming that CEF effects should not evolve as a function of Y-substitution. Our results show that only disorder effects do not fully describe the experimental data, which may indicate that quadrupolar degrees of freedom indeed have a role in the magnetic properties of this family.

NaRb6(B4O5(OH)4)3(BO2) Featuring Noncentrosymmetry, Chirality, and the Linear Anionic Group BO2.

Noncentrosymmetric (NCS) structures are of particular interest owing to their symmetry-dependent physical properties, e.g., pyroelectricity, ferroelectricity, piezoelectricity, and nonlinear optical (NLO) behavior. Among them, chiral materials exhibit polarization rotation and host topological properties. Borates often contribute to NCS and chiral structures via their triangular [BO3] and tetrahedral [BO4] units and their numerous superstructure motifs. However, no chiral compound with the linear [BO2] unit has been reported to date. Herein, an NCS and chiral mixed-alkali-metal borate, NaRb6(B4O5(OH)4)3(BO2), with a linear BO2- unit in the structure was synthesized and characterized. The structure features a combination of three types of basic building units (BBUs), [BO2], [BO3], and [BO4] with sp-, sp2-, and sp3-hybridization of boron atoms, respectively. It crystallizes in the trigonal space group R32 (No. 155), one of the 65 Sohncke space groups. Two enantiomers of NaRb6(B4O5(OH)4)3(BO2) were found, and their crystallographic relationships are discussed. These results not only expand the small family of NCS structures with the rare linear BO2- unit but also prompt recognition to the fact that NLO materials have generally overlooked the existence of two enantiomers in achiral Sohncke space groups.

Crystalline and vitreous Na3.89Ca0.67Al0.23Ti0.77(PO4)3 : Synthesis, crystal structure, vibrational and UV–Visible spectra

Na3.89Ca0.67Al0.23Ti0.77(PO4)3 phosphate exists in both crystalline and vitreous forms. It has been synthesized as microcrystalline powder, single crystals and glass. The structure of the crystalline form, belonging to Nasicon family with M(1)M(2)3A2(PO4)3 formula, was solved by single crystal X-ray diffraction (Space group R32, Z = 6, ah = 8.9976(1) Å, ch = 21.8312(3) Å, R1 = 0.03, wR2 = 0.06). A Rietveld refinement was also performed. The structure is formed by a 3D network of PO4 tetrahedra and AO6 (A= Na/Ca and Al/Ti) octahedra sharing corners. One of the two positions of A sites is statistically occupied by Na+ and Ca2+, the other position is statistically occupied by Al3+ and Ti4+. The remaining sodium atoms occupy totally M(1) and partially M(2) interstitial sites. Raman and infrared spectra show for the crystalline powder, broad peaks attributed principally to monophosphate PO4 modes. The structure of the glass contains PO4 and P2O7 groups and short -Ti-O-Ti-O- chains. UV–Visible spectra consist of strong bands at high energy assigned to O-Ti and O-Al electronic charge transfers.

Single-Layer MoS2: A Two-Dimensional Material with Negative Poisson’s Ratio

Negative Poisson’s ratio (NPR) materials have broad applications such as heat dissipation, vibration damping, and energy absorption because of their designability, lightweight quality, and high strength ratio. Here, we use first-principles calculations to find a two-dimensional (2D) auxetic material (space group R3¯m), which exhibits a maximum in-plane NPR of −0.0846 and a relatively low Young’s modulus in the planar directions. Calculations show that the NPR is mainly related to its unique zigzag structure and the strong interaction between the 4d orbital of Mo and the 3p orbital of S. In addition, molecular dynamics (MD) simulations show that the structure of this material is thermodynamically stable. Our study reveals that this layered MoS2 can be a promising 2D NPR material for nanodevice applications.

Spark Plasma Sintering of Ceramics Based on Solid Solutions of Na1+2xZr2−xCox(PO4)3 Phosphates: Thermal Expansion and Mechanical Properties Research

The structure, microstructure, coefficient of thermal expansion (CTE), and mechanical properties of Na1+2xZr2−xCox(PO4)3 ceramics (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5) were studied. Na1+2xZr2−xCox(PO4)3 submicron powders with the NaZr2(PO4)3 structure (NZP, kosnarite type) were obtained by the solid-phase method. The starting reagents (NaNO3, ZrOCl2·8H2O, NH4H2PO4, CoCl2·6H2O, ethanol) were mixed with the addition of ethyl alcohol. The resulting mixtures were annealed at 600 °C (20 h) and 700 °C (20 h). The obtained phosphates crystallized in the expected structure of the NaZr2(PO4)3 type (trigonal system, space group R3¯c). Thermal expansion of the powders was studied with high-temperature X-ray diffraction at temperatures ranging from 25 to 700 °C. CTEs were calculated, and their dependence on the cobalt content was analyzed. Na1+2xZr2−xCox(PO4)3 ceramics with high relative density (93.67–99.70%) were obtained by Spark Plasma Sintering (SPS). Ceramics poor in cobalt (x = 0.1) were found to have a high relative density (98.87%) and a uniform fine-grained microstructure with a grain size of 0.5–1 µm. Bigger cobalt content leads to a smaller relative density of ceramics. During the sintering of ceramics with high cobalt content, anomalous grain growth was observed. The powder compaction rate was shown to be determined by creep and diffusion intensity in the Na1+2xZr2−xCox(PO4)3 crystal lattice. SPS activation energy in ceramics increased as the cobalt content grew. The microhardness and fracture toughness of ceramics did not depend on their cobalt content.

Characterization, room and low temperature photoluminescence of yttrium aluminium borate activated with Sm3+ ions

In this study, the combustion method assisted by urea that is ideally suited to economic and time saving was used for the synthesizing of reddish orange emitting YAl3(BO3)4 phosphor samples doped with various Sm3+ ions (from 0.01 wt% to 7wt%). A detailed study of the structural and luminescence properties at room/low temperature of the synthesized samples was performed. XRD analysis revealed a rhombohedral structure with an R32 space group (155). The particle size was determined by the Scherrer's method to be 48 nm. The visible PL emission spectra upon excitation at 359 nm are recorded and four emission peaks around 564, 599, 646, and 707 nm with transitions 4G5/2 → 6H5/2, 4G5/2 → 6H7/2, 4G5/2 → 6H9/2 and 4G5/2 → 6H11/2 are observed. Concentration quenching was mainly caused by dipole-dipole interactions between neighbouring trivalent Sm3+ ions. Through the CIE chroma coordinates (0.606, 0.382), the optimized sample (x = 0.03) demonstrates admirable luminous performance. YAl3(BO3)4:Sm3+ can be a good candidate for use as a red component for lighting applications.

Electronic and optical properties of the R3 Ni3TeO6 compound described by the modified Becke-Johnson exchange potential

Calculations based on the density functional theory (DFT) have been realized to study the electronic and optical properties of the Ni3TeO6 compound with a hexagonal crystal structure (R3 space group). Exchange and correlation electronic effects were described by a modified Becke-Johnson (mBJ) potential in its semiconductor variance form. The collinear antiferromagnetic state of the R3 Ni3TeO6 compound was simulated. The calculated spin magnetic moment of the Ni atoms (1.65 μB) was found to be in good agreement with the experimental result (2.03 μB). Moreover, the calculated optical band gap (2.8 eV) agreed well with the experimental prediction (2.5 eV). These facts suggest a reliable electronic structure description of the material. Hence, we also calculated the complex dielectric function, optical absorption spectrum, refractive index, and extinction coefficient. The optical absorption spectrum was interpreted based on the determined electronic structure. The direct optical absorption edge of the material was characterized by the electronic transitions from O 2p states to Te 5s states and from Ni 3d states to O 2p states. This description did not agree with previous ones based on DFT + U calculations or those made based on the electronic structure of the Ni3V2O8 compound. Thus, an alternative description of the electronic structure of the R3 Ni3TeO6 compound in its antiferromagnetic state using the DFT + mBJ calculations has been suggested, and consequently a new origin for the optical absorption observed around the optical band gap.

New Series of Red-Light Phosphor Ca9-xZnxGd0.9(PO4)7:0.1Eu3+ (x = 0-1).

In this study, a new series of phosphors, Ca9−xZnxGd0.9(PO4)7:0.1Eu3+ (x = 0.00−1.00, step dx 0.05), was synthesized, consisting of centro- and non-centrosymmetric phases with β-Ca3(PO4)2-type structure. Crystal structures with space groups R3c (0.00 ≤ x < 0.35) and R3¯c (x > 0.8) were determined using X-ray powder diffraction and the method of optical second harmonic generation. In the region 0.35 ≤ x ≤ 0.75, phases R3c and R3¯c were present simultaneously. Refinement of the Ca8ZnGd(PO4)7 crystal structure with the Rietveld method showed that 71% of Gd3+ ions are in M3 sites and 29% are in M1 sites. A luminescent spectroscopy study of Ca9−xZnxGd0.9(PO4)7:0.1Eu3+ indicated the energy transfer from the crystalline host to the Gd3+ and Eu3+ luminescent centers. The maximum Eu3+ luminescence intensity corresponds to the composition with x = 1.

Crystal structure of a new europium(III) compound based on thio-phene-acrylic acid.

A europium(III) coordination compound based on thio-phene-acrylic acid (Htpa), tri-aqua-tris-[3-(thio-phen-2-yl)prop-2-enoato-κ2 O,O']europium(III)-3-(thio-phen-2-yl)prop-2-enoic acid (1/3), [Eu(C7H5O2S)3(H2O)3]·3C7H6O2S or [Eu(tpa)3(H2O)3]·3(Htpa) (1), where tpa is the conjugate base of Htpa, has been synthesized and structurally characterized. Compound 1 crystallizes in the trigonal space group R3. The structure of 1 consists of a discrete mol-ecular complex [Eu(tpa)3(H2O)3] species and the Htpa mol-ecule. In the crystal, the two components are involved in O-H⋯O [ring motif R 2 2(8)] and C-H⋯π hydrogen-bonding inter-actions. These inter-actions were further investigated by Hirshfeld surface analysis, which showed high contributions of H⋯H, H⋯C/C⋯H and H⋯O/O⋯H contacts to the total Hirshfeld surfaces.

Investigations of the structural, magnetic, mechanical, electronic and ferroelectric properties of Mn2MnWO6 double corundum oxide

Materials exhibiting both ferroelectric and ferromagnetic or antiferromagnetic (FM or AFM) ordering are exceptional and are desired for promising applications in future electronic devices. A ferroelectric material Mn2MnWO6 corundum double oxide with AFM magnetic spin order is investigated using density functional theory (DFT). The structure relaxations and optimization confirmed that the non-centrosymmetric (space group R3) is the most stable ground state structure of the compound. The compound is found semiconductor with band gap value 1.8 eV in spin up and 2.47 eV in spin down channel. The electric polarization arises due to d0 electronic configuration of W atom, and the magnetization occurs due to unpaired dn orbital configuration of Mn atom. The large value of polarization 61.98 μC/cm2 and magnetic moments 5.96μB/f.u (f.u = formula unit) of Mn2MnWO6 make it suitable candidate for magneto-electric and ferroelectric applications. The elastic and mechanical calculations show that Mn2MnWO6 is mechanically stable in rhombohedral phase. The calculated piezoelectric coefficient d33 = 528 pC/N is comparable to those of lead based piezoelectric materials.

Selsurtite, (H3O)12Na3(Ca3Mn3)(Na2Fe)Zr3□Si[Si24O69(OH)3](OH)Cl⋅H2O, a new eudialyte-group mineral from the Lovozero alkaline massif, Kola Peninsula, Russia

AbstractThe new eudialyte-group mineral selsurtite, ideally (H3O)12Na3(Ca3Mn3)(Na2Fe)Zr3□Si[Si24O69(OH)3](OH)Cl⋅H2O, was discovered in metasomatic peralkaline rock from the Flora mountain, northern spur of the Selsurt mountain, Lovozero alkaline massif, Kola Peninsula, Russia. The associated minerals are aegirine, albite and orthoclase, as well as accessory lorenzenite, calciomurmanite, natrolite, lamprophyllite and sergevanite. Selsurtite occurs as brownish-red to reddish-orange, equant or flattened on (0001) crystals up to 2 mm across and elongate crystals up to 3 cm long. The main crystal forms are {0001}, {11$\bar{2}$0}, and {10$\bar{1}$1}. Selsurtite is brittle, with the Mohs’ hardness of 5. No cleavage is observed. Parting is distinct on (001). D(meas) = 2.73(2) and D(calc) = 2.722 g⋅cm–3. Selsurtite is optically uniaxial (–), with ω = 1.598(2) and ɛ = 1.595(2). The chemical composition is (wt.%, electron microprobe): Na2O 6.48, K2O 0.27, MgO 0.10, CaO 6.83, MnO 4.73, FeO 1.18, SrO 1.88, La2O3 0.57, Ce2O3 1.07, Pr2O3 0.20, Nd2O3 0.44, Al2O3 0.29, SiO2 50.81, ZrO2 13.50, HfO2 0.45, TiO2 0.61, Nb2О5 1.10, Cl 1.01, SO3 0.29, H2O 8.10, –O≡Cl –0.23, total 99.68. The empirical formula is H25.94Na6.03K0.16Mg0.07Ca3.51Sr0.52Ce0.19La0.10Nd0.08Pr0.03Mn1.91Fe0.47Ti0.22Zr3.16Hf0.06Nb0.24Si24.40Al0.16S0.10Cl0.82O79.13. The crystal structure was determined using single-crystal X-ray diffraction data and refined to R = 0.0484. Selsurtite is trigonal, space group R3, with a = 14.1475(7) Å, c = 30.3609(12) Å, V = 5262.65(7) Å3 and Z = 3. Infrared and Raman spectra show that hydronium cations are involved in very strong hydrogen bonds and form Zundel- and Eigen-like complexes. The strongest lines of the powder X-ray diffraction pattern [d, Å (I, %)(hkl)] are: 11.38 (56)(101), 7.08 (59)(110), 5.69 (36)(202), 4.318 (72)(205), 3.793 (36)(303), 3.544 (72)(027, 220, 009), 2.970 (100)(315) and 2.844 (100)(404). The mineral is named after the discovery locality.

A comparative study on the structural, optical, and magnetic behavior of transition metal (Co and Mn) ions substituted Cr2O3 nanoparticles

A comparative study on structural, optical, and magnetic properties of TMxCr2−xO3 (TM = Co and Mn) nanoparticles was synthesized using a simple co-precipitation method with subsequent heat treatment. The structural characterizations of as-prepared nanoparticles were performed using X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. XRD pattern revealed the formation of rhombohedral Cr2O3 phase with space group R3¯c. The FTIR spectra illustrated the shifting of absorption bands of Cr2O3 nanoparticles with Co and Mn substitution due to strain induced within the crystal lattice. X-ray photoelectron spectroscopy (XPS) confirmed the presence of a mixed oxidation state of Cr and oxygen defects in the prepared nanoparticles. Furthermore, XPS spectra also demonstrated the presence of Co and Mn having +2 oxidation state. The reduction in optical band gap of host material was observed with Co and Mn substitution. The magnetic properties of as-synthesized nanoparticles were recorded using a SQUID magnetometer and temperature-dependent magnetic measurements illustrated the decrease of Neel temperature with Co and Mn substitution. It was also demonstrated that magnetization increases below about ∼ 120 K due to spin canting and spin frustration for both TM ions substituted Cr2O3 nanoparticles and is fitted using the 3D spin-wave model with Curie-Weiss law. The magnetic studies revealed the mixed paramagnetic (PM) and antiferromagnetic (AFM) order at room temperature and AFM mix with ferromagnetic (FM) order at low temperature explained using the bound magnetic polarons (BMP) model.

Linear and nonlinear optical properties of trigonal borate crystals K7MIn2−xYbx(B5O10)3 (M = Ca, Sr, Ba; x = 0…2) with isolated B5O10 units

Noncentrosymmetric borates K7MIn2−xYbx(B5O10)3 (M = Ca, Sr, Ba; x = 0…2) were synthesized by the solid state reaction and the crystals were successfully grown by the top seeded solution growth method using the K2O-B2O3-MF2 flux. According to Rietveld refinement, the crystal structure belongs to the noncentrosymmetric R32 space group. Also, the octahedrally coordinated In atoms are located at wide ranges ∼8 Å which may be promising for phosphor and laser applications. Samples with ytterbium show a characteristic emission band in the range of 950–1050 nm related to the 2F5/2 → 2F7/2 transition of Yb3+ ions that is commonly used for laser generation. IR, Raman and absorption spectra were obtained for the samples as well. The short cut edge of UV absorption, SHG intensity comparable with KDP and low concentration quenching of luminescence suggest that the K7MIn2−xYbx(B5O10)3 borates are promising self-frequency doubling materials.

Sol-gel synthesis and structural evolution in solid solutions of InGaZn1-xCoxO4 (0 ≤ x ≤ 1)

Complete solid solutions InGaZn1-xCoxO4 (0 ​≤ ​x ​≤ ​1) were synthesized via the citrate sol-gel method and structurally characterized by powder X-ray diffraction. All oxides adopt the LuFe2O4-type layered structure and crystallize in the space group R3¯m. The successful cationic doping can be first confirmed by the linear changes in a- and c-axes lengths, then investigated by careful Rietveld refinements. The Co2+-to-Zn2+ replacement induces the structural changes in the [MO]2 (M ​= ​Ga, Zn, Co) layers exclusively, where M locates in the trigonal bipyramidal (TBP) coordination. In detail, three M-Obasal bond exhibit a gentle expansion, and two apical M-O bonds show opposite variations (a minor expansion and a severe contraction) with an overall decreasing in length. Interestingly, the latter one is likely due to the so-favored AFM interactions between Co2+-Co2+ couples along edge-shared TBPs. The temperature-dependent magnetic susceptibility confirms the very strong AFM interactions, however no magnetic order can be established above 5 ​K.

Ambiguity in indexing electron diffraction patterns of R 3 crystals

The R3 space group inherently lacks 2110, m001 and m_{{\bar 1}10} symmetry operations. However, in crystals with R3 symmetry, these transformations produce `pseudoplanes' with the same interplanar spacing and angles as the original crystallographic planes, causing a lack of uniqueness in the electron diffraction (ED) pattern. The difference in atomic arrangements of pseudoplanes and original planes is reflected in the intensities of diffraction spots; it is hard to differentiate in standard ED patterns, frequently causing wrong assignment of the zone axes. The implications of this ambiguity in analysis of crystal orientations are discussed in detail and a suitable routine to follow while indexing R3 ED patterns is proposed.

Synthesis, structure, characterization, and electronic structure calculation of a new molecule-inclusion strontium gallate Sr6(Ga12O24)·Bi2O3

Inorganic oxide crystalline materials have been attractive owing to unusual structural and physical properties including superconductivity, nonlinear optics, photocatalytic degradation, molecular sieve and solar cells. Herein, a new molecule-inclusion strontium gallate, Sr6(Ga12O24)·Bi2O3, has been obtained by solid-state method. The compound crystallizes in the centrosymmetric space group R3¯(no. 148), and exhibits a three-dimensional network structure composed by corner-sharing connected GaO4 tetrahedra and edge-sharing connected SrO9 polyhedra with Bi atoms located in hexagonal tunnels. Spectral analysis shows that the compound exhibits strong Raman peak. Synthesis, crystal structure, versatile characterizations as well as theory calculations of Sr6(Ga12O24)·Bi2O3 are presented in this work.

Theoretical study of the M7X6 type of vacancy ordered phases in nonstoichiometric hafnium and tantalum carbides

Carbides of IV and V group transitional metals with B1 structure contain large amounts of vacancies in the carbon sublattice. Ordering of the vacancies leads to formation of new phases with various stoichiometry. Ordered structures were discovered and studied for all the IV and V group transitional metal carbides except carbides of hafnium and tantalum. Nevertheless, recent theoretical works have predicted large variety of ordered structures in non-stoichiometric HfCy and TaCy including unusual Hf7C6 and Ta7C6. Such a stoichiometry is not typical for the ordered carbides. In this work, we study in detail the new M7X6 type of vacancy ordered structures using ab initio methods. For both compounds Hf7C6 and Ta7C6, we have found two B1-derived vacancy-ordered phases: trigonal (space group R3¯) and monoclinic (space group C2/m). The comparison of their formation enthalpies with the disordered B1 structure has showed that the only ordered phase Hf7C6 can be trigonal phase while in Ta7C6 both trigonal and monoclinic structures are possible. Using the predicted monoclinic superstructure, we explain some peculiarities of the neutron diffraction pattern of the annealed partially ordered samples of TaC0.83–0.85. The theoretical and experimental data on the short range structural order in superstructures is discussed. We also study the influence of the M7X6 type of ordered structure on mechanical properties. The highest Vickers hardness ∼27.1 GPa is expected for the trigonal ordered Hf7C6 phase.