Ca6.3Mn3Ga4.4Al1.3O18—A novel complex oxide with 3D tetrahedral framework

A new Ca_6.3Mn₃Ga_4.4Al_1.3O₁₈ compound has been prepared by solid state reaction in a dynamic vacuum of 5×10⁻⁶ mbar at 1200 °C. The crystal structure of Ca_6.3Mn₃Ga_4.4Al_1.3O₁₈ was studied using X-ray powder diffraction (, SG F432, Z=8, R_I=0.031, R_P=0.068), electron diffraction and high resolution electron microscopy. The Ca_6.3Mn₃Ga_4.4Al_1.3O₁₈ structure can be described as a tetrahedral [(Ga_0.59Mn_0.24Al_0.17)₁₅O₃₀]^18.24− framework stabilized with embedded [(Ca_0.9Mn_0.1)₁₄MnO₆]^18.24+ polycations, which consists of an isolated MnO₆ octahedron surrounded by a capped cube of (Ca_0.9Mn_0.1) atoms. The Ca_6.3Mn₃Ga_4.4Al_1.3O₁₈ structure is related to the structure of Ca₇Zn₃Al₅O_17.5, but appears to be significantly disordered due to the presence of two orientations of oxygen tetrahedra around the cationic 0,0,0 and x,x,x () positions in a random way according to the F432 space symmetry. The analogy between the Ca_6.3Mn₃Ga_4.4Al_1.3O₁₈ crystal structure and the structure of the “fullerenoid” Sr₃₃Bi_24+δAl₄₈O_141+3δ/2 oxide is discussed. Ca_6.3Mn₃Ga_4.4Al_1.3O₁₈ adopts a Curie-Weiss behavior of χ(T) above with a Weiss temperature and per formula unit. At lower temperatures, the χ(T) deviates from the Curie-Weiss law indicating a strengthening of the ferromagnetic component of the exchange interaction.     

Synthesis, crystal and magnetic structure of a novel brownmillerite-type compound Ca2Co1.6Ga0.4O5

The novel compound Ca₂Co_1.6Ga_0.4O₅ with brownmillerite (BM) structure has been prepared from citrates at 950 °C. The crystal structure of Ca₂Co_1.6Ga_0.4O₅ was refined, from neutron powder diffraction (NPD) data, in space group Pnma, , , , χ²=1.798, , R_wp=0.0378 and R_p=0.0292. On the basis of the NPD refinement the compound was found to be a G-type antiferromagnet (space group Pn^′m^′a) at room temperature, with the magnetic moments of cobalt atoms directed along chains of tetrahedra in the BM structure. Electron diffraction and electron microscopy studies revealed disorder in the crystallites, which can be interpreted as the presence of slabs with BM-type structure of Pnma and I2mb symmetry.     

The disordered cubic structure of Ca7Co3Ga5O18

The new mixed oxide having composition close to Ca₇Co₃Ga₅O₁₈ was synthesized from CaCO₃, Co₃O₄ and Ga₂O₃ at 1150 °C in air and studied by neutron and synchrotron X-ray powder diffraction, selected-area electron diffraction and high-resolution electron microscopy. The structure was refined, using time-of-flight (TOF) neutron powder diffraction data, in space group F432, with and Z=8, to R_F=0.7%. It is considerably disordered, with four different tetrahedral sites randomly occupied by Co and Ga atoms at a ratio of 1:2. The tetrahedra form a disordered (Co_1/3Ga_2/3)O₂ 3D-framework inside which isolated CoO₆ octahedra, surrounded by 8 Ca atoms, are located. The structure is related to the ordered structure of Ca₁₄Al₁₀Zn₆O₃₅. Electron diffraction patterns confirmed the symmetry and unit cell and revealed no diffuse scattering. High-resolution electron microscopy images showed the absence of extended structural defects.     

The mercury chromates Hg6Cr2O9 and Hg6Cr2O10—Preparation and crystal structures, and thermal behaviour of Hg6Cr2O9

The basic mercury(I) chromate(VI), Hg₆Cr₂O₉ (=2Hg₂CrO₄·Hg₂O), has been obtained under hydrothermal conditions (200 °C, 5 days) in the form of orange needles as a by-product from reacting elemental mercury and K₂Cr₂O₇. Hydrothermal treatment of microcrystalline Hg₆Cr₂O₉ in demineralised water at 200 °C for 3 days led to crystal growth of red crystals of the basic mercury(I, II) chromate(VI), Hg₆Cr₂O₁₀ (=2Hg₂CrO₄·2HgO). The crystal structures were solved and refined from single crystal X-ray data sets. Hg₆Cr₂O₉: space group P2₁2₁2₁, Z=4, a=7.3573(12), b=8.0336(13), , 3492 structure factors, 109 parameters, R[F²>2σ(F²)]=0.0371, wR(F² all)=0.0517; Hg₆Cr₂O₁₀: space group Pca2₁, Z=4, a=11.4745(15), b=9.4359(12), , 3249 structure factors, 114 parameters, R[F²>2σ(F²)]=0.0398, wR(F² all)=0.0625. Both crystal structures are made up of an intricate mercury-oxygen network, subdivided into single building blocks [O-Hg-Hg-O] for the mercurous compound, and [O-Hg-Hg-O] and [O-Hg-O] for the mixed-valent compound. Hg₆Cr₂O₉ contains three different Hg₂²⁺ dumbbells, whereas Hg₆Cr₂O₁₀ contains two different Hg₂²⁺ dumbbells and two Hg²⁺ cations. The Hg^I-Hg^I distances are characteristic and range between 2.5031(15) and 2.5286(9) Å. All Hg₂²⁺ groups exhibit an unsymmetrical oxygen environment. The oxygen coordination of the Hg²⁺ cations is nearly linear with two tightly bonded O atoms at distances around 2.07 Å. For both structures, the chromate(VI) anions reside in the vacancies of the Hg-O network and deviate only slightly from the ideal tetrahedral geometry with average Cr-O distances of ca. 1.66 Å. Upon heating at temperatures above 385 °C, Hg₆Cr₂O₉ decomposes in a four-step mechanism with Cr₂O₃ as the end-product at temperatures above 620 °C.     

Crystal structure of Ca12Al14O32Cl2 and luminescence properties of Ca12Al14O32Cl2:Eu

The crystal structure of Ca₁₂Al₁₄O₃₂Cl₂ was determined from laboratory X-ray powder diffraction data (CuKα₁) using the Rietveld method, with the anisotropic displacement parameters being assigned for all atoms. The crystal structure is cubic (space group , Z=2) with lattice dimensions a=1.200950(5) nm and V=1.73211(1) nm³. The reliability indices calculated from the Rietveld method were R_wp=8.48% (S=1.21), R_p=6.05%, R_B=1.27% and R_F=1.01%. The validity of the structural model was verified by the three-dimensional electron density distribution, the structural bias of which was reduced as much as possible using the maximum-entropy methods-based pattern fitting (MPF). The reliability indices calculated from the MPF were R_B=0.75% and R_F=0.56%. In the structural model there are one Ca site, two Al sites, two O sites and one Cl site. This compound is isomorphous with Ca₁₂Al_10.6Si_3.4O₃₂Cl_5.4. Europium-doped sample Ca₁₂Al₁₄O₃₂Cl₂:Eu²⁺ was prepared and the photoluminescence properties were presented. The excitation spectrum consisted of two wide bands, which were located at about 268 and 324 nm. The emission spectrum, when excited at 324 nm, resulted in indigo light with a peak at about 442 nm.     

Synthesis, structure and physical properties of the new Zintl phases Eu11Zn6Sb12 and Eu11Cd6Sb12

Reported are the syntheses, crystal structure determinations from single-crystal X-ray diffraction, and magnetic properties of two new ternary compounds, Eu₁₁Cd₆Sb₁₂ and Eu₁₁Zn₆Sb₁₂. Both crystallize with the complex Sr₁₁Cd₆Sb₁₂ structure type—monoclinic, space group C2/m (no. 12), Z=2, with unit cell parameters a=31.979(4) Å, b=4.5981(5) Å, c=12.3499(14) Å, β=109.675(1)° for Eu₁₁Zn₆Sb₁₂, and a=32.507(2) Å, b=4.7294(3) Å, c=12.4158(8) Å, β=109.972(1)° for Eu₁₁Cd₆Sb₁₂. Their crystal structures are best described as made up of polyanionic and ribbons of corner-shared ZnSb₄ and CdSb₄ tetrahedra and Eu²⁺ cations. A notable characteristic of these structures is the presence of Sb-Sb interactions, which exist between two tetrahedra from adjacent layers, giving rise to unique channels. Detailed structure analyses shows that similar bonding arrangements are seen in much simpler structure types, such as Ca₃AlAs₃ and Ca₅Ga₂As₆ and the structure can be rationalized as their intergrowth. Temperature-dependent magnetization measurements indicate that Eu₁₁Cd₆Sb₁₂ orders anti-ferromagnetically below 7.5 K, while Eu₁₁Zn₆Sb₁₂ does not order down to 5 K. Resistivity measurements confirm that Eu₁₁Cd₆Sb₁₂ is poorly metallic, as expected for a Zintl phase.     

The crystal structure of the new ternary antimonide Dy3Cu20+xSb11−x (x≈2)

New ternary antimonide Dy₃Cu_20+xSb_11−x (x≈2) was synthesized and its crystal structure was determined by direct methods from X-ray powder diffraction data (diffractometer DRON-3M, CuKα-radiation, R_I=6.99%,R_p=12.27%,R_wp=11.55%). The compound crystallizes with the own cubic structure type: space group , Pearson code cF272, . The structure of the Dy₃Cu₂₀Sb_11−x (x≈2) can be obtained from the structure type BaHg₁₁ by doubling of the lattice parameter and subtraction of 16 atoms. The studied structure was compared with the structures of known compounds, which crystallize in the same space group with similar cell parameters.     

Superstructure of a phosphor material Ba3MgSi2O8 determined by neutron diffraction data

Ba₃MgSi₂O₈, a phosphor host examined for use in white-light devices and plant-growth lamps, was synthesized at 1225 °C in air. Its crystal structure has been determined and refined by a combined powder X-ray and neutron Rietveld method (, Z=3, a=9.72411(3) Å, c=7.27647(3) Å, V=595.870(5) Å³; R_p/R_wp=3.79%/5.03%, χ²=4.20). Superstructure reflections, observed only in the neutron diffraction data, provided the means to establish the true unit cell and a chemically reasonable structure. The structure contains three crystallographically distinct Ba atoms—Ba1 resides in a distorted octahedral site with S₆ () symmetry, Ba2 in a nine-coordinate site with C₃ (3) symmetry, and Ba3 in a ten-coordinate site with C₁ (1) symmetry. The Mg atoms occupy distorted octahedral sites, and the Si atom occupies a distorted tetrahedral site.     

Preferential occupation of alkaline-earth metal sites in a seemingly disordered solid solution of Ca11−xSrxSb10: Single crystal structures of Ca8.63(5)Sr2.37Sb10 and Ca3.66(7)Sr7.34Sb10

Two new antimony based intermetallic phases, Ca_8.63(5)Sr_2.37Sb₁₀(1) and Ca_3.66(7)Sr_7.34Sb₁₀(2), crystallizing in Ho₁₁Ge₁₀ structure type (tetragonal, I4/mmm) have been synthesized and characterized. Although both Ca₁₁Sb₁₀ and Sr₁₁Sb₁₀ are known to be isostructural (Ho₁₁Ge₁₀ structure type) and hence all Ca sites should be accessible to Sr as well, it appears that certain sites are preferentially ordered by Ca in the mixed (Ca/Sr)₁₁Sb₁₀ compounds reported here. The crystal structure of Ca_8.63(5)Sr_2.37Sb₁₀ and Ca_3.66(7)Sr_7.34Sb₁₀ has been solved from single crystal X-ray data using direct methods and refined using full-matrix least-squares method. The structure can be described as bonded network of A-Sb (A=Ca, Sr) with Sb existing as isolated Sb³⁻, diantimony and square units. Simple valence electron count reveals these compounds to be Zintl phases. It is found that the larger Sr or Sr/Ca ions preferentially occupy sites that are closer to the diantimony anions as compared to the smaller Ca ions.     

The crystal chemistry of Bi6TP2O15+x, T=Fe, Ni, Zn: Isomorphism and polymorphism, structural relationship to Bi6TiP2O16

The crystal structures of compounds with nominal compositions Bi₆FeP₂O_15+x (I), Bi₆NiP₂O_15+x (II) and Bi₆ZnP₂O_15+x (III) were determined from single-crystal X-ray diffraction data. They are monoclinic, space group I2, Z=2. The lattice parameters for (I) are a=11.2644(7), b=5.4380(3), c=11.1440(5) Å, β=96.154(4)°; for (II) a=11.259(7), b=5.461(4), c=11.109(7) Å, β=96.65(1)°; for (III) a=19.7271(5), b=5.4376(2), c=16.9730(6) Å, β=131.932(1)°. Least squares refinements on F² converged for (I) to R1=0.0554, wR₂=0.1408; for (II) R₁=0.0647, wR₂=0.1697; for (III) R₁=0.0385, wR₂=0.1023. The crystals are complexly twinned by 2-fold rotation about , by inversion and by mirror reflection. The structures consist of edge-sharing articulations of OBi₄ tetrahedra forming layers in the a-c plane that then continue by edge-sharing parallel to the b-axis. The three-dimensional networks are bridged by Fe and Ni octahedra in (I) and (II) and by Zn trigonal bipyramids in (III) as well as by oxygen atoms of the PO₄ moieties. Bi also randomly occupies the octahedral sites. Oxygen vacancies exist in the structures of the three compounds due to required charge balances and they occur in the octahedral coordination polyhedron of the transition metal. In compound (III), no positional disorder in atomic sites is present. The Bi-O coordination polyhedra are trigonal prisms with one, two or three faces capped. Magnetic susceptibility data for compound (I) were obtained between 4.2 and 350 K. Between 4.2 and 250 K it is paramagnetic, μ_eff=6.1 μ_B; a magnetic transition occurs above 250 K.     

The crystal structure determinations and refinements of K2S2O7, KNaS2O7 and Na2S2O7 from X-ray powder and single crystal diffraction data

The crystal structures of K₂S₂O₇, KNaS₂O₇ and Na₂S₂O₇ have been solved and/or refined from X-ray synchrotron powder diffraction data and conventional single-crystal data. K₂S₂O₇: From powder diffraction data, monoclinic C2/c, Z=4, a=12.3653(2), b=7.3122(1), , β=93.0792(7)°, R_Bragg=0.096. KNaS₂O₇: From powder diffraction data; triclinic , Z=2, a=5.90476(9), b=7.2008(1), , α=101.7074(9), β=90.6960(7), γ=94.2403(9)°, R_Bragg=0.075. Na₂S₂O₇: From single-crystal data; triclinic , Z=2, a=6.7702(9), b=6.7975(10), , α=116.779(2), β=96.089(3), γ=84.000(3)°, R_F=0.033. The disulphate anions are essentially eclipsed. All three structures can be described as dichromate-like, where the alkali cations coordinate oxygens of the isolated disulphate groups in three-dimensional networks. The K-O and Na-O coordinations were determined from electron density topology and coordination geometry. The three structures have a cation-disulphate chain in common. In K₂S₂O₇ and Na₂S₂O₇ the neighbouring chains are antiparallel, while in KNaS₂O₇ the chains are parallel. The differences between the K₂S₂O₇ and Na₂S₂O₇ structures, with double-, respectively single-sided chain connections and straight, respectively, corrugated structural layers can be understood in terms of the differences in size and coordinating ability of the cations.     

Crystal structure of lanthanum bismuth silicate Bi2−xLaxSiO5 (x∼0.1)

A melting and glass recrystallization route was carried out to stabilize a new tetragonal form of Bi₂SiO₅ with bismuth partially substituted by lanthanum. The crystal structure of Bi_2−xLa_xSiO₅ (x∼0.1) was determined from powder X-ray and neutron diffraction data (space group I4/mmm, , c=15.227(1) Å, V=224.18 Å³, Z=2; reliability factors: R_Bragg=5.65%, R_p=14.6%, R_wp=16.8%, R_exp=8.3%, χ²=8.3 (X-ray) and R_Bragg=2.40%, R_p=8.1%, R_wp=7.5%, R_exp=4.2%, χ²=3.3 (neutrons); 11 structural parameters refined).The main effect of lanthanum substitution is to introduce, by removing randomly some bismuth 6s² lone pairs, a structural disorder in the surroundings of (Bi₂O₂)²⁺ layers, that is in the (SiO₃)²⁻ pyroxene files arrangement. It results in a symmetry increase relatively to the parent compound Bi₂SiO₅, which is orthorhombic. The two structures are compared.     

Multianvil high-pressure/high-temperature preparation, crystal structure, and properties of the new oxoborates Dy4B6O14(OH)2 and Ho4B6O14(OH)2

This paper reports about two new hydrogen-containing rare-earth oxoborates RE₄B₆O₁₄(OH)₂ (RE=Dy, Ho) synthesized under high-pressure/high-temperature conditions from the corresponding rare-earth oxides, boron oxide, and water using a Walker-type multianvil equipment at 8 GPa and 880 °C. The single crystal structure determination of Dy₄B₆O₁₄(OH)₂ showed: Pbcn, a=1292.7(2), b=437.1(2), , Z=2, R1=0.0190, and wR2=0.0349 (all data). The isotypic holmium species revealed: Pbcn, a=1292.8(2), b=436.2(2), , Z=2, R1=0.0206, and wR2=0.0406 (all data). The compounds exhibit a new type of structure, which is built up from layers of condensed BO₄-tetrahedra. Between the layers, the rare-earth cations are coordinated by 7+2 oxygen atoms. Furthermore, we report about temperature-resolved in situ powder diffraction measurements, DTA/TG, and IR-spectroscopic investigations into RE₄B₆O₁₄(OH)₂ (RE=Dy, Ho).     

Sr4PbPt4O11, the first platinum oxide containing Pt2 ions

We report the synthesis and crystal structure of the new compound Sr₄PbPt₄O₁₁, containing platinum in highly unusual square pyramidal coordination. The crystals were obtained in molten lead oxide. The structure was solved by X-ray single crystal diffraction techniques on a twinned sample, the final R factors are R=0.0260 and wR=0.0262. The symmetry is triclinic, space group P1¯, with , , , α=90.421(3)°, β=89.773(8)°, γ=90.140(9)° and Z=2. The structure is built from dumbell-shaped Pt₂O₉ entities formed by a dinuclear metal-metal bonded Pt₂⁶⁺ ion with asymmetric environments of the two Pt atoms, classical PtO₄ square plane and unusual PtO₅ square pyramid. Successive Pt₂O₉ entities deduced from 90° rotations are connected through the oxygens of the PtO₄ basal squares to form [Pt₄O₁₀⁸⁻]_∞ columns further connected through Pb²⁺ and Sr²⁺ ions. Raman spectroscopy confirmed the peculiar platinum coordination environment.     

High resolution and in situ neutron powder diffraction study of the crystal structure and the stability of Ba4CaCu3O8+δ

The crystal structure and stability of Ba₄CaCu₃O_8+δ have been investigated by neutron powder diffraction, differential thermal analysis and thermogravimetry. It is found that the phase is not stable below 1065 K in p(O₂)=1 bar and decomposes according to the eutectoid reaction Ba₄CaCu₃O_8+δ+x O₂⇒Ba₂CuO_3.4+CaO+2BaCuO₂. However, the equilibrium with the outer gas is not reached for sintered ceramics so that Ba₄CaCu₃O_8+δ can be obtained in a metastable state after normal cooling conditions. In this case, the crystal structure is cubic (Im-3m, , δ=0.68, Z=2, R_wp=2.5%, R_Bragg=5.4%) as reported in the literature. In reduced oxygen partial pressure (p(O₂)<10⁻⁶ bar), Ba₄CaCu₃O_8+δ is stable down to room temperature and has a tetragonal structure with a significant lower oxygen content (P4/mmm, , , δ=-0.81, Z=2, R_wp=2.8%, R_Bragg=5.1%). The difference between the two crystal structures is discussed in terms of oxygen content, copper formal valence and cation coordination. The influence of the oxygen pressure on the stability of Ba₄CaCu₃O_8+δ is also discussed.     

V2Cu3Ga8, Mo2Cu3Ga8 and W2Cu3Ga8—New compounds with a novel order variant of a bcc packing and motifs of self-similarity

Single crystals of the new compounds TM₂Cu₃Ga₈ (TM=V, Mo, W) were synthesised from the elements. Structure determinations of the isotypic compounds (cI104, space group , Z=8; Mo₂Cu₃Ga₈: a=11.9171(10) Å, 613 refl., 23 param., R₁(F)=0.022, wR₂(F²)=0.047; W₂Cu₃Ga₈: 11.9248(8) Å, 346 refl., 23 param., R₁(F)=0.048, wR₂(F²)=0.086; V₂Cu₃Ga₈: 11.7861(14) Å, 374 refl., 24 param., R₁(F)=0.033, wR₂(F²)=0.081) showed a new cubic structure type which can be classified as an ordered defect variant of a bcc packing with a^′=4a: [(TM)₂(Cu)₃(□)₃][Ga₈]. The coordination polyhedra of the transition metals consist of Ga₈-cubes with 3 sides capped by Cu leading to coordination number 11. The arrangement of the TMGa₈Cu₃-polyhedra is in a way they form itself a 3-fold capped cube. All compositions were confirmed by EDX measurements.     

X-ray powder diffraction studies and thermal behaviour of NaK2B9O15, Na(Na.17K.83)2B9O15, and (Na.80K.20)K2B9O15

The crystal structures of NaK₂B₉O₁₅ (, , , β=94.080(1)°, R_p=0.047, R_wp=0.059, R_B=0.026), Na(Na_.17K_.83)₂B₉O₁₅ (, , , β=94.228(2)°, R_p=0.053, R_wp=0.068, R_B=0.026), and (Na_.80K_.20)K₂B₉O₁₅ (, , , β=94.071(1)°, Z=4, R_p=0.041, R_wp=0.052, R_B=0.023) were refined in the monoclinic space groups P2₁/c(Z=4) using X-ray powder diffraction data and the Rietveld method. These nonaborates are isostructural to K₃B₉O₁₅. Their crystal structure consists of a three-dimensional open framework built up from three crystallographically independent triborate groups. The alkali metal cations are located on three different sites in the voids of the framework. High-temperature X-ray diffraction studies show that NaK₂B₉O₁₅ decomposes at about 700 °C in accordance with the peritectic reaction NaK₂B₉O₁₅↔K₅B₁₉O₃₁+liquid. The thermal expansion of NaK₂B₉O₁₅ and Na(Na_.17K_.83)₂B₉O₁₅ is highly anisotropic. A similarity of the thermal and compositional (Na-K substitution) deformations of NaK₂B₉O₁₅ is revealed: heating of NaK₂B₉O₁₅ by 1 °C leads to the same deformations of the crystal structure as increasing the amount of K atoms in (Na_1−xK_x)₃B₉O₁₅ by 0.04 at% K.     

Neutron diffraction study of the crystal structure and structural phase transition of La0.7Ca0.3−xSrxCrO3 (0≤x≤0.3): The relationship between thermodynamic behavior and crystal structure changes at the phase transition

The crystal structure of the La_0.7Ca_0.3−xSr_xCrO₃ series, including the compositional and temperature dependence of the structural parameters, has been studied by variable temperature neutron diffraction measurements. The extent of the distortions from the ideal cubic perovskite structure has been evaluated quantitatively using the average bond lengths and the mean volumes of the [CrO₆] octahedron and [(La/Ca/Sr)O₁₂] polyhedron, and has been shown to decrease with increase of Sr content or temperature. At the structural phase transition from the orthorhombic (Pnma) structure to the rhombohedral one, the volume of the [CrO₆] octahedron decreases whereas that of the [(La/Ca/Sr)O₁₂] polyhedron shows little difference, resulting in an overall decrease in the level of distortion. The change in the degree of distortion at the phase transition decreases with increase of Sr content, in agreement with the smaller variation of the enthalpy and volume for the specimens with higher Sr content.     

The crystal structure of CuSb2O3Br: Slabs from cubic Sb2O3 interspersed between puckered hexagonal CuBr-type layers

The new compound CuSb₂O₃Br crystallize in the monoclinic space group Cc. The unit cell parameters are , , , β=90°, Z=16. The crystal structure is solved from single crystal data, R=0.0490. The compound show a layered structure with slabs from cubic Sb₂O₃ interspersed in between puckered layers of CuBr. The Sb(III) atoms have tetrahedral [SbO₃E] coordination where E is the 5s² lone pair, these units build up Sb₄O₄E₆ cages. The CuBr layers resemble those in hexagonal CuBr but the Cu(I) ions have actually tetrahedral [CuBr₃O] coordination. The Cu-O bonds link the Sb₄O₆ cages with the CuBr layers.