The crystal structure of magnesium arsenate,Mg8.5As3O16

Single crystals of magnesium arsenate have been grown from a PbOAs₂O₅ eutectic by flux crystallization of a ceramic preparation having an initial composition of 6MgO·As₂O₅. The crystals are rhombohedral, space group $\text{R}\text{3}\text{m}$, with hexagonal unit cell parameters a = 6.0278(6) and c = 27.600(3) Å. A three-dimensional structural analysis using automatic diffractometer data has been completed and refined by full-matrix least-squares procedures to a residual R = 0.049 (R_w = 0.059) with a data-parameter ratio of 36 in the final anisotropic refinement. The structure analysis indicated that magnesium arsenate has the composition Mg_8.5As₃O₁₆ and is isostructural with the previously reported Co₈As₃O₁₆. The structure is based upon a cubic close-packed oxygen array with charge balance achieved in magnesium arsenate through partial occupancy of a unique magnesium site occurring in an arsenic-substituted MgO-type layer.     

Investigation of crystal structure and associated electronic structure of Sr6BP5O20

Strontium borophosphate phosphate (Sr₆BP₅O₂₀, SrBP), activated by divalent europium ions is a bluish-green phosphor emitting in a broad band with the emission peak near 480 nm. In this paper, we report the crystal structure of SrBP determined from an analysis of the X-ray diffraction pattern of a prismatic single crystal (size 60 μm×50 μm×40 μm). This crystal was chosen from undoped phosphor powder samples prepared for this purpose by solid-state reaction. SrBP is observed to crystallize in a body-centered tetragonal lattice with the lattice parameters and , the associated space group being (space group 120). Using the structural data from this study, we have also calculated its electronic structure using the augmented spherical wave method and the local density approximation (LDA). We show the ordering of the electronic states by the density of states (DOS) and the partial DOS plots. The LDA gives a direct optical band gap at the Γ point of about 5 eV. The significance of the crystal structure and associated electronic structure is discussed with respect to maintenance of this phosphor in Hg-discharge lamps.     

The crystal structure of α-SrMnO3

α-SrMnO₃ crystallizes in the hexagonal system with unit-cell dimensions a = 5.454(1) Å, c = 9.092(2)Å, space group $\text{P6}{}_3\text{mmc}\text{, Z = 4}$. The structure was solved by the heavy-atom method; of 404 unique reflections measured by counter method, 203 that obeyed the condition |F₀| ≥ 3σ (|F₀|) were used in the refinement to a conventional R value of 0.043. The structure consists of four close-packed SrO₃ layers in an ABAC stacking sequence along the hexagonal c axis. Oxygen octahedra containing Mn⁴⁺ are grouped into face-sharing pairs linked by corner sharing within the cubically stacked “A” layer.     

Networks of icosahedra in the sodium-zinc-stannides Na16Zn13.54Sn13.46(5), Na22Zn20Sn19(1), and Na34Zn66Sn38(1)

The three new ternary phases Na₁₆Zn_13.54Sn_13.46(5) (I), Na₂₂Zn₂₀Sn₁₉₍₁₎ (II), and Na₃₄Zn₆₆Sn₃₈₍₁₎ (III) were obtained by direct fusion of the pure elements and characterized by single crystal X-ray diffraction experiments: I, Ibam, Z=8, a=27.401(1), b=16.100(1), c=18.431(1) Å, R₁/wR₂ (all data)=0.051/0.088; II, Pnma, Z=4, a=16.403(1), b=15.598(1), c=22.655(6) Å, R₁/wR₂ (all data)=0.038/0.071; III, R3¯m, Z=3, a=16.956(1), c=36.861(1) Å, R₁/wR₂ (all data)=0.045/0.092. The structures consist of complex 3D cluster networks made of Zn and Sn atoms with the common motif of Kagomé nets of icosahedra. Additionally to the new heteroatomic {Zn_12−xSn_x} icosahedra that are omnipresent, triangular units, cages, and pairs of triply fused icosahedra fill the cavities of the Kagomé nets in compounds I, II, and III, respectively. Whereas I crystallizes in a new structure type, II and III have structural analogs in trielide chemistry. All three compounds closely approach the electron numbers expected for valence compounds according to the extended 8-N rule. The concept of achieving an isovalent situation to triel elements by combination of electron poorer and richer elements and the readily mixing of Zn and Sn allow the formation of icosahedral and triangular clusters without the participation of a group 13 element.     

The crystal structure of β-Ga2Se3

From new X-ray powder diffraction data reported in this paper, the structure of the ordered, superstructural phase of Ga₂Se₃ is found to be different from the structures stated in the literature up to now. The difference relates essentially to the structure distortion involved in the formation of the superstructure. This distortion is clarified in a way which, in general, is suitable for investigations of small distortions of cubic structures. The superstructure cell turns out to be monoclinic, with a = 6.6608(3), b = 11.6516(4), c = 6.6491(3) Å, β = 108.840(5)°, and Z = 4. Furthermore, the coordinates of the Ga and Se positions in this cell are deduced. The space group is shown to be C⁴_s-Cc (No. 9).     

A new structure type of phosphate: Crystal structure of Na2Zn5(PO4)4

A new compound, Na₂Zn₅(PO₄)₄, was identified in the system ZnONa₂OP₂O₅ and high-quality crystal was obtained by the melt method. The crystal structure of this compound was solved by direct method from single crystal X-ray diffraction data. The structure was then refined anisotropically using a full-matrix least square refinement on F² and the refinement converged to R₁=0.0233 and wR₂=0.0544. This compound crystallizes in the orthorhombic system with space group Pbcn, lattice parameters a=10.381(2) Å, b=8.507(1) Å, c=16.568(3) Å and Z=4. The structure is made up of 3D [Zn₅P₄O₁₆]_n²ⁿ⁻ covalent framework consisting of [Zn₄P₄O₁₆]_n⁴ⁿ⁻ layers. The powder diffraction pattern of Na₉Zn₂₁(PO₄)₁₇ is explained by simulating a theoretical pattern with NaZnPO₄ and Na₂Zn₅(PO₄)₄ in the molar ratio of 1:4 and then by Rietveld refinement of experimental pattern. Na₂Zn₅(PO₄)₄ melts congruently at 855 °C and its conductivity is 5.63×10⁻⁹ S/cm.     

The crystal structure of triclinic β-BiNbO4

The crystal structure of β-BiNbO₄ has been determined from three-dimensional X-ray data. The crystals are triclinic with a = 7.61₁ Å, b = 5.53₆ Å, c= 7.91₉ Å, α = 89.88°, β = 77.43°, γ = 87.15°, Z = 4, space group $\text{P}\text{1}$. Full-matrix least-squares refinement using isotropic temperature factors has reached R = 0.122 for 642 visually estimated reflections.The structure contains unusual sheets of formula [NbO₄]_∞ in which the NbO octahedra are joined at four vertices such that the two free ones are cis. NbO distances range from 1.80 to 2.31 Å. The bismuth atoms hold these sheets together and are coordinated to eight oxygens in the form of a very distorted square antiprism.Structurally, β-BiNbO may be considered an antiferroelectric, ferroelastic member of the BaMF₄ prototype family.     

The crystal structure of Ba2V2O7

Ba₂V₂O₇ is triclinic with a = 13.571(3), b = 7.320(2), c = 7.306(2) Å, α = 90.09(1), β = 99.48(1), β = 99.48(1), γ = 87.32(1)°, V = 7.15.1 ų, Z = 4, and space group $\text{P}\text{1}$. The crystal structure was solved by Patterson and Fourier methods and refined by full-matrix least-squares analysis to a R_w of 0.034 (R = 0.034) using 2484 reflections measured on a Syntex $\text{P}\text{1}$ automatic four-circle diffractometer. The structure has two unique divanadate groups that are repeated by the b and c lattice translations to form sheets of divanadate groups parallel to (100). These sheets are linked by four unique Ba atoms that lie between these sheets. Ba(1) and Ba(3) are coordinated by eight oxygens arranged in a distorted biaugmented triangular prism and a distorted cubic antiprism, respectively. Ba(2) is coordinated by 10 oxygens arranged in a distorted gyroelongated square dipyramid and Ba(4) is coordinated by nine oxygens arranged in a distorted triaugmented triangular prism. These coordination numbers are substantiated by a bond strength analysis of the structure, and the variation in 〈BaO〉 distances is compatible with the assigned cation and anion coordination numbers. Both divanadate groups are in the eclipsed configuraton with 〈VO(br)〉 bond lengths of 1.821(4) and 1.824(4) Å and VO(br)V angles of 125.6(3) and 123.7(3)°, respectively. Examination of the divanadate groups in a series of structures allows certain generalizations to be made. Longer 〈VO(br)〉 bond lengths are generally associated with smaller VO(br)V angles. When VO(br)V < 140°, the divanadate group is generally in an eclipsed configuration; when VO(br)V > 140°, the divanadate group is generally in a staggered configuration. Nontetrahedral cations with large coordination numbers require more oxygens with which to bond, and hence O(br) is more likely to be three coordinate, with the divanadate group in the eclipsed configuration. In the eclipsed configuration, decrease in VO(br)V promotes bonding between O(br) and nontetrahedral cations, and hence smaller nontetrahedral cations are generally associated with smaller VO(br)V angles.     

The crystal structure of Nb2Zr6O17

Nb₂Zr₆O₁₇ is orthorhombic, space group Ima2, with a = 40.91, b = 4.93, c = 5.27 Å. The asymmetric structural unit contains one octahedron, three sevenfold coordinated ions, and one square antiprism, and its relations to the fluorite and ZrO₂ structures are discussed. Variations in compositions can be accounted for by increasing or decreasing the number of sevenfold coordinated ions in the structure.     

Comparative analysis of some thermo-physical properties of Se90Zn10 and Te90Zn10 alloys

The present paper reports a comparative study of some thermo-physical properties (thermal conductivity, diffusivity and specific heat per unit volume) of Se₉₀Zn₁₀ and Te₉₀Zn₁₀ alloys. Simultaneous measurements of effective thermal conductivity (λ_e) and effective thermal diffusivity (χ_e) of twin pellets of Se₉₀Zn₁₀ and Te₉₀Zn₁₀ alloys using transient plane source (TPS) technique have been made at room temperature. From the measured values of λ_e and χ_e, the specific heat per unit volume (C_v) has been calculated. The results indicate that the measured values of these parameters are higher for Te₉₀Zn₁₀ alloy as compared to Se₉₀Zn₁₀ alloy. This is explained in terms of thermal conductivity of chalcogen elements Se and Te.     

The crystal structure of Sc2Ru5B4

The crystal structure of Sc₂Ru₅B₄ has been determined by single-crystal X-ray analysis. Sc₂Ru₅B₄ crystallizes in the primitive monoclinic space group $\text{P2}\text{m}$ with a = 9.983(6), b = 8.486(4), c = 3.0001(3)Å, γ = 90.01(7)°, Z = 2. Deviations from the orthorhombic space group Pbam-D⁹_2h are small but significant. Intensity measurements were obtained from a four-circle diffractometer. The structure was solved by Patterson methods and refined by full matrix least-squares calculation. $\text{R =}\text{∑|ΔF|}\text{∑|F}{}_0\text{|}\text{= 0.036}$ for an asymmetric set of 863 independent reflections (|F₀|>2σ(F₀)). The crystal structure is characterized by two different types of boron atoms: (a) isolated borons B(1) and B(3) in distorted trigonal Ru-prisms with tetrakaidekahedral metal coordination: 6Ru + 3Sc, and (b) boron atoms B(2) and B(4) with a pronounced tendency to form boron pairs (B(2)-B(2) = 1.86 Å, B(4)-B(4) = 1.89 Å); the metal coordination of these boron atoms is 6Ru + 2Sc. Sc atoms have a coordination number of 17 consisting of 10Ru + 2Sc + 5B. The crystal structure of Sc₂Ru₅B₄ is a pentagon layer structure (Ru, B atoms) with a 4.3.4.3²-secondary layer of Sc atoms. The structure is furthermore related to the structure types of Ti₃Co₅B₂ and CeCo₃B₂. From powder photographs Sc₂Os₅B₄ is isotypic. No superconductivity was observed for Sc₂(Ru, Os)₅B₄ down to 1.5 K.     

Synthesis, crystal structures and photoluminescence properties of new oxyborates, Mg5NbO3(BO3)3 and Mg5TaO3(BO3)3, with novel warwickite-type superstructures

Single crystals of new oxyborates, Mg₅NbO₃(BO₃)₃ and Mg₅TaO₃(BO₃)₃, were prepared at 1370 °C in air using B₂O₃ as a flux. They were colorless and transparent with block shapes. X-ray diffraction analysis of the single crystals revealed Mg₅NbO₃(BO₃)₃ and Mg₅TaO₃(BO₃)₃ to be isostructural. The X-ray diffraction reflections were indexed to the orthorhombic Pnma (No. 62) system with a=9.3682(3) Å, b=9.4344(2) Å, c=9.3379(3) Å and Z=4 for Mg₅NbO₃(BO₃)₃ and a=9.3702(3) Å, b=9.4415(3) Å, c=9.3301(2) Å and Z=4 for Mg₅TaO₃(BO₃)₃. The crystal structures of Mg₅NbO₃(BO₃)₃ and Mg₅TaO₃(BO₃)₃ are novel warwickite-type superstructures having ordered arrangements of Mg and Nb/Ta atoms. Polycrystals of Mg₅NbO₃(BO₃)₃ prepared by solid state reaction at 1200 °C in air showed broad blue-to-green emission with a peak wavelength of 470 nm under 270 nm ultraviolet excitation at room temperature.     

The crystal structure of Ca3Cu3(PO4)4

Single crystals of Ca₃Cu₃(PO₄)₄ synthesized hydrothermally at 420°C and 55 kpsi (3.8 kbar) were found to occur in the space group $\text{P2}{}_1\text{a}$ (No. 14) with a = = 17.619(2), b = 4.8995(4), c = 8.917(1)Å, β = 124.08(1)°, and Z = 2. Full-matrix least-squares refinement of the structure using diffractometer data converged to a final anisotropic R = 0.037 (R_w = 0.046). The two calcium atoms are in six- and nine-coordination and the two copper-containing polyhedra (four- and five-coordinated) are similar to those previously found in Cu₃(PO₄)₂.     

The hollandite-related structure of Ba2Ti9O20

The crystal structure of Ba₂Ti₉O₂₀ has been determined by comparison of experimental high-resolution electron micrographs with images simulated using structural models deduced from the micrographs in conjunction with crystallochemical principles. The structure consists of lamellae of hollandite-type structure alternating with BaTiO₃-like units, which effectively immobilize the Ba ions. This material should be relatively more leach resistant to attack by aqueous sodium chloride solutions. The structure determination clarifies the observation that this material has unique properties as a microwave resonator, compared with other barium and alkali titanate structures.     

The crystal structure of cobalt orthophosphate Co3(PO4)2

The crystal structure of cobalt orthophosphate has been refined by full-matrix least-squares procedures using automatic diffractometer data to a residual R = 0.039 (R_w = 0.058). The space group is $\text{P2}{}_{\mathrm{l}}\text{c}$, with a = 5.063(1), b = 8.361(2), c = 8.788(2) Å, and β = 121.00(2)°. Co₃(PO₄)₂ is isotypic with the previously reported γ-Zn₃(PO₄)₂ and Mg₃(PO₄)₂. Cobalt ions occupy two distinct coordination polyhedra, one five and one six-coordinated, in a ratio of two to one. The structure is described in detail.     

The crystal structure of Cu4(PO4)2O

Cu₄(PO₄)₂O crystallizes in the space group $\text{P}\text{1}$ with a = 7.5393(8) Å, b = 8.1021(9) Å, c = 6.2764(8) Å, α = 113.65(1)°, β = 98.42(1)° and γ = 74.19(1)°. The structure was refined by full-matrix least-squares techniques using automatic diffractometer data to R = 0.046 (R_w = 0.056). Four unique copper atoms are in six, five-, and four-coordinated polyhedra which are linked together to form a three-dimensional network. The structure is best described in terms of a cubic close-packed array of oxygen atoms with one-tenth of the possible anion sites vacant.     

La3Pd4Zn4 and La3Pt4Zn4 with a different coloring of the Gd3Cu4Ge4-type structure

Abstract  

The intermetallic zinc compounds La₃Pd₄Zn₄ and La₃Pt₄Zn₄ were synthesized by induction melting of the elements in sealed tantalum tubes. The structures were refined from X-ray single-crystal diffractometer data: Gd₃Cu₄Ge₄ type, Immm, a = 1,440.7(5), b = 743.6(2), c = 419.5(2) pm, wR ₂ = 0.0511, 353 F ² for La₃Pd₄Zn₄; and a = 1,439.9(2), b = 748.1(1), c = 415.66(6) pm, wR ₂ = 0.0558, 471 F ² for La₃Pt₄Zn₄ with 23 variables per refinement. The palladium (platinum) and zinc atoms build up a three-dimensional polyanionic [Pd₄Zn₄] (260–281 pm Pd–Zn) and [Pt₄Zn₄] (260–279 pm Pt–Zn) network in which the lanthanum atoms fill cavities of CN 14 (6 Pd/Pt + 8 Zn for La1) and CN 12 (6 Pd/Pt + 6 Zn for La2), respectively. The copper position of the Gd₃Cu₄Ge₄ type is occupied by zinc and the two crystallographically independent germanium sites by palladium (platinum), a new coloring pattern for this structure type. Within the [Pd₄Zn₄] and [Pt₄Zn₄] the Pd2 and Pt2 atoms form Pd2–Pd2 (291 pm) and Pt2–Pt2 (296 pm) dumbbells. The structures of La₃Pd₄Zn₄ and La₃Pt₄Zn₄ are discussed with respect to the prototype Gd₃Cu₄Ge₄ and the Zintl phase Sr₃Li₄Sb₄. Temperature-dependent magnetic susceptibility measurements indicate diamagnetism for La₃Pt₄Zn₄ and Pauli paramagnetism for La₃Pd₄Zn₄.     

Crystal structure of a barium-zinc decametaphosphate Ba2Zn3P10O30

Barium-zinc decametaphosphate, Ba₂Zn₃P₁₀O₃₀, is monoclinic, $\text{P2}\text{n}$, with the unit cell parameters a = 21.738(15), b = 5.356(5), c = 10.748(8) Å, β = 99.65(3)° and Z = 2. The crystal structure was solved with a final R value of 0.041. This salt provides the first structural evidence for the existence of a 10-phosphorus ring anion.     

The crystal structure of niobium trisulfide,NbS3

The crystal structure of NbS₃ was determined from single-crystal diffractometer data obtained with MoKα radiation. The compound is triclinic, space group $\text{P}\text{1}$, with: a 4.963(2) Å; b = 6.730(2) Å; c = 9.144(4)Å; α = 90°; β = 97.17(1)°; γ = 90°. The structure is closely related to the ZrSe₃ structure type; it shows that the compound can be formulated as Nb⁴⁺(S₂)^2?S^2?, in agreement with XPS spectra. The main difference with ZrSe₃ is that the Nb atoms are shifted from the mirror planes of the surrounding bicapped trigonal prisms of sulfur atoms to form NbNb pairs (NbNb = 3.04 Å); this causes a doubling of the b axis relative to ZrSe₃ and a decrease of the symmetry to triclinic.     

The crystal structure of Na7Mg4.5(P2O7)4

The crystal structure of Na₇Mg_4.5(P₂O₇)₄ has been solved by direct methods from the three-dimensional X-ray data. The space group is $\text{P}\text{1}$. The crystal structure consists of Mg²⁺, Na⁺, and P₂O^4?₇ ions. One magnesium atom at symmetry center (0,0,0) and two sodium atoms at ±(?0.0421, ?0.0596, 0.2230) display occupation factors 0.5 each. A short interatomic distance between these Na⁺ and Mg²⁺ ions (1.80 ± 0.01 Å) excludes the occupation of both sites in the same unit cell. The crystal structure of Na₇Mg_4.5(P₂O₇)₄ consists of unit cells containing Na₈Mg₄(P₂O₇)₄ or Na₆Mg₅(P₂O₇)₄ with a statistical occurrence 1:1.Each Mg²⁺ ion is octahedrally coordinated by six O^2? ions at distances 1.979 – 2.270 Å. The coordination polyhedra around the Na⁺ ions are ill-defined. The bond angles POP in the P₂O^4?₇ groups are 126.6 and 133.6° (±0.3°). The final reliability factor R is 7.1%.