Crystal chemistry of M[PO2(OH)2]2·2H2O compounds (M=Mg, Mn, Fe, Co, Ni, Zn, Cd): Structural investigation of the Ni, Zn and Cd salts

The compounds M[PO₂(OH)₂]₂·2H₂O (M=Mg, Mn, Fe, Co, Ni, Zn, Cd) were prepared from super-saturated aqueous solutions at room temperature. Single-crystal X-ray structure investigations of members with M=Ni, Zn, Cd were performed at 295 and 120 K. The space-group symmetry is P2₁/n, Z=2. The unit-cell parameters are at 295/120 K for M=Ni: a=7.240(2)/7.202(2), b=9.794(2)/9.799(2), c=5.313(1)/5.285(1) Å, β=94.81(1)/94.38(1)°, V=375.4/371.9 Å³; M=Zn: a=7.263(2)/7.221(2), b=9.893(2)/9.899(3), c=5.328(1)/5.296(2) Å, β=94.79(1)/94.31(2)°, V=381.5/377.5 Å³; M=Cd: a=7.356(2)/7.319(2), b=10.416(2)/10.423(3), c=5.407(1)/5.371(2) Å, β=93.85(1)/93.30(2)°, V=413.4/409.1 Å³. Layers of corner-shared MO₆ octahedra and phosphate tetrahedra are linked by three of the four crystallographically different hydrogen bonds. The fourth hydrogen bond (located within the layer) is worth mentioning because of the short O_h?O bond distance of 2.57-2.61 Å at room temperature (2.56-2.57 Å at 120 K); only for M=Mg it is increased to 2.65 Å. Any marked temperature-dependent variation of the unit-cell dimension is observed only vertical to the layers. The analysis of the infrared (IR) spectroscopy data evidences that the internal PO₄ vibrations are insensitive to the size and the electronic configuration of the M²⁺ ions. The slight strengthening of the intra-molecular P-O bonds in the Mg salt is caused by the more ionic character of the Mg-O bonds. All IR spectra exhibit the characteristic “ABC trio” for acidic salts: 2900-3180 cm⁻¹ (A band), 2000-2450 cm⁻¹ (B band) and 1550-1750 cm⁻¹ (C band). Both the frequency and the intensity of the A band provide an evidence that the PO₂(OH)₂ groups in M[PO₂(OH)₂]₂·2H₂O compounds form weaker hydrogen bonds as compared with other acidic salts with comparable O?O bond distances of about 2.60 Å. The observed shift of the O-H stretching vibrations of the water molecule in the order M=Mg>Mn≈Fe≈Co>Ni>Zn≈Cd has been discussed with respect to the influence of both the character and the strength of M↔H₂O interactions.     

Crystal Growth and Structure Determination of LaMIn5 (M=Co, Rh, Ir)

The compounds CeMIn₅ (M=Co, Rh, Ir) have been shown to exhibit heavy fermion behavior. In order to better understand this effect and the nature of the observed superconductivity, we have synthesized and characterized the non-magnetic analogs, LaMIn₅ (M=Co, Rh, Ir). The structures of LaCoIn₅, LaRhIn₅, and LaIrIn₅ were determined by single-crystal X-ray diffraction. CeMIn₅ and LaMIn₅ compounds are isostructural and adopt a tetragonal structure with space group P4/mmm, Z=1. Lattice parameters are a=4.6399(4) and c=7.6151(6) Å for LaCoIn₅, a=4.6768(3) and c=7.5988(7) Å for LaRhIn₅, and a=4.6897(6) and c=7.5788(12) Å for LaIrIn₅. We compare these experimental data with band structure computations and examine structural trends that affect the magnetic and transport properties of these compounds.     

Subsolidus phase relations in Na2O-CuO-Sb2On system and crystal structure of new sodium copper antimonate Na3Cu2SbO6

Subsolidus phase relation studies in the NaSb₃O₇-Na₃SbO₄-CuO-CuSb₂O₆ quadrangle of Na₂O-CuO-Sb₂O_n system at 1123-1173 K revealed the formation of one new compound Na₃Cu₂SbO₆. It is a superstructure derived from α-NaFeO₂ type, space group C2/m, lattice constants: a=5.6759(1) Å, b=8.8659(1) Å, c=5.8379(1) Å, β=113.289(1)°. All ions are in octahedral environment, but CuO₆ polyhedron exhibits strong elongation due to Jahn-Teller effect (Cu-O: 2.000(2) Å×2, 2.021(2) Å×2, 2.494(3) Å×2), whereas SbO₆ octahedron is almost regular. The relationship to other similar superlattices is discussed.     

Transition metal tetramolybdate dihydrates MMo4O13·2H2O (M=Co,Ni) having a novel pillared layer structure

Hydrothermal synthesis in the M/Mo/O (M=Co,Ni) system was investigated. Novel transition metal tetramolybdate dihydrates MMo₄O₁₃·2H₂O (M=Co,Ni), having an interesting pillared layer structure, were found. The molybdates crystallize in the triclinic system with space group P−1, Z=1 with unit cell parameters of a=5.525(3) Å, b=7.058(4) Å, c=7.551(5) Å, α=90.019(10)°, β=105.230(10)°, γ=90.286(10)° for CoMo₄O₁₃·2H₂O, and a=5.508(2) Å, b=7.017(3) Å, c=7.533(3) Å, α=90.152(6)°, β=105.216(6)°, γ=90.161(6)° for NiMo₄O₁₃·2H₂O The structure is composed of two-dimensional molybdenum-oxide (2D Mo-O) sheets pillared with CoO₆ octahedra. The 2D Mo-O sheet is made up of infinite straight ribbons built up by corner-sharing of four molybdenum octahedra (two MoO₆ and two MoO₅OH₂) sharing edges. These infinite ribbons are similar to the straight ones in triclinic-K₂Mo₄O₁₃ having 1D chain structure, but are linked one after another by corner-sharing to form a 2D sheet structure, like the twisted ribbons in BaMo₄O₁₃·2H₂O (or in orthorhombic-K₂Mo₄O₁₃) are.     

Crystal Structure of Pseudorhombohedral InFe1−xTixO3+x/2 (x=2/3)

The structure of pseudorhombohedral-type InFe_1−xTi_xO_3−x/2 (x=2/3) was refined by Rietveld profile fitting. The crystal is a commensurate member of a series in a solution range on InFeO₃-In₂Ti₂O₇ including incommensurate structures. The structure with the unit cell of a=5.9188(1), b=10.1112(2), and c=6.3896(1) Å, β=108.018(2)°, and a space group P2₁/a is the alternate stacking of an edge-shared InO₆ octahedral layer and an Fe/Ti-O plane along c^*. Metal sites on the Fe/Ti-O plane are surrounded by four oxygen atoms on the Fe/Ti-O plane and two axial ones. Electric conductivities of the order 10⁻⁴ S/cm were observed for the samples at 1000 K, while the oxide ion transport number is almost zero as no electromotive force was detected by an oxygen concentration cell.     

Preparation, crystal structures and rapid hydration of P2- and P3-type sodium chromium antimony oxides

Two new Na_x[Cr_(1+x)/2Sb_(1−x)/2]O₂ compounds have been prepared by solid-state reactions in argon. Their structures have been determined by the X-ray Rietveld method. Both new phases together with NaCrO₂-based solid solution comprise brucite-like layers of edge-shared (Cr,Sb)O₆ octahedra but differ by packing mode of the layers and coordination of the interlayer Na⁺ ions. A P3 phase exists at x≈0.5-0.58. It is rhombohedral (R3?m), a=2.966, c=16.937 Å at x≈0.58, with 29% Na⁺ occupancy of trigonal prisms. A P2 phase exists at x≈0.6-0.7. It is hexagonal (P6₃/mmc), a=2.960, c=11.190 Å at x≈0.7, with 37% and 33% Na⁺ occupancy of two non-equivalent trigonal prisms. Both P2 and P3 phases rapidly absorb moisture in air; packing mode is preserved, the a parameter changes slightly but c increases by 24-25%. Very high sodium ion conductivity is predicted for both P2 and P3 anhydrous phases.     

Crystal structure, thermal expansion and conductivity of anisotropic La1−xSrxGa1−2xMg2xO3−y (x=0.05, 0.1) single crystals

Crystal structure and anisotropy of the thermal expansion of single crystals of La_1−xSr_xGa_1−2xMg_2xO_3−y (x=0.05 and 0.1) were measured in the temperature range 300-1270 K. High-resolution X-ray powder diffraction data obtained by synchrotron experiments have been used to determine the crystal structure and thermal expansion. The room temperature structure of the crystal with x=0.05 was found to be orthorhombic (Imma, Z=4, a=7.79423(3) Å, b=5.49896(2) Å, c=5.53806(2) Å), whereas the symmetry of the x=0.1 crystal is monoclinic (I2/a, Z=4, a=7.82129(5) Å, b=5.54361(3) Å, c=5.51654(4) Å, β=90.040(1)°). The conductivity in two orthogonal directions of the crystals has been studied. Both, the conductivity and the structural data indicate three phase transitions in La_0.95Sr_0.05Ga_0.9Mg_0.1O_2.92 at 520-570 K (Imma-I2/a), 770 K (I2/a-R3c) and at 870 K (R3c-R-3c), respectively. Two transitions at 770 K (I2/a-R3c) and in the range 870-970 K (R3c-R-3c) occur in La_0.9Sr_0.1Ga_0.8Mg_0.2O_2.85.     

Phase relations in a barium-rich high-temperature region (25-45 mol% CuO, 900-1100 °C) of the BaO-CuOx system

The phase relations have been studied in the BaO-CuO_x system in the range of 25.0-45.0 mol% CuO at 900-1100 °C at P(O₂)=21 kPa (air) by visual polythermal analysis (VPA), powder X-ray diffraction (XRD), electron diffraction (ED) with simultaneous energy-dispersive X-ray (EDX) elemental analysis in a transmission electron microscope (TEM), and iodometric chemical analysis. The discrete deviations 2.02 (101:50), 2.04 (102:50), 2.10 (105:50) of Ba/Cu (Ba:Cu) composition from the stoichiometric ratio 2:1 have been found for the known Ba₂CuO_3+δ oxides in the subsolidus region 900-970 °C. Unit cell parameters of the 101:50 orthorhombic oxide, 102:50 tetragonal one, 105:50 orthorhombic one are, respectively, a=4.049, b=3.899, c=13.034 Å; a=3.985, c=12.968 Å; a=4.087, b=3.897 and c=12.950 Å. ED patterns of the 101:50, 102:50, 105:50 oxides show characteristic supercell reflections with the respective vector 1/60[5 4 0], ≈2/11〈1 1 0〉 and 1/6[2 0 0]. Oxides of the 2:1, 7:4, 5:3 and 23:20 compositions have been found in the crystallization region 970-1050 °C. Unit cell parameters of the 2:1 orthorhombic oxide are a=4.095, b=3.795, c=13.165 Å. Interplanar spacings and X-ray characteristic peak intensities of the 7:4, 5:3 and 23:20 oxides are given. Oxides 2:1 and 7:4 melt pseudocongruently at 1020 and 1005 °C, oxides 5:3 and 23:20 melt incongruently at 995 and 980 °C, respectively. A diagram of the phase relations in the studied region of the BaO-CuO_x system has been constructed, whose structure is considered as the total projection of phase states of the system existing for different x.     

The Crystal Chemistry of Lithium in the Alluaudite Structure: A Study of the (Na1−xLix)CdIn2(PO4)3 Solid Solution (x=0 to 1)

Several compounds of the (Na_1−xLi_x)CdIn₂(PO₄)₃ solid solution were synthesized by a solid-state reaction in air, and pure alluaudite-like compounds were obtained for x=0.00, 0.25, and 0.50. X-ray Rietveld refinements indicate the occurrence of Cd²⁺ in the M(1) site, and of In³⁺ in the M(2) site of the alluaudite structure. This non-disordered cationic distribution is confirmed by the sharpness of the infrared absorption bands. The distribution of Na⁺ and Li⁺ on the A(1) and A(2)′ crystallographic sites cannot be accurately assessed by the Rietvled method, probably because the electronic densities involved in the Na⁺→Li⁺ substitution are very small. A comparison with the synthetic alluaudite-like compounds, (Na_1−xLi_x)MnFe₂(PO₄)₃, indicates the influence of the cations occupying the M(1) and M(2) sites on the coordination polyhedra morphologies of the A(1) and A(2)′ crystallographic sites.     

Crystal growth and structural investigation of A2BReO6 (A=Sr, Ba; B=Li, Na)

Single crystals of the double perovskite rhenates A₂BReO₆ (A=Sr, Ba; B=Li, Na) were grown out of molten hydroxide fluxes. Single crystals of orange/yellow Ba₂LiReO₆, Ba₂NaReO₆ and Sr₂LiReO₆ were solved in the cubic, Fm-3m space group with a=8.1214(11) Å, 8.2975(3) Å, and 7.9071(15) Å, respectively, while Sr₂NaReO₆ was determined to be monoclinic P2₁/n with a=5.6737(6) Å, b=5.7988(6) Å, c=8.0431(8) Å, and β=90.02(6) °. The cubic structure consists of a rock salt lattice of corner-shared ReO₆ and MO₆ (M=Li, Na) octahedra which, in the monoclinic structure, are both tilted and rotated. A discrepancy exists between the symmetry of Sr₂LiReO₆ indicated by the single-crystal refinement of flux-grown crystals (cubic, Fm-3m) and the symmetry indicated by the powder diffraction data collected on polycrystalline samples prepared by the ceramic method (tetragonal, I4/m). It is possible that the cubic crystals are a kinetic product that forms in small quantities at low temperatures, while the powder represents the more stable polymorph that forms at higher reaction temperature.     

Structure Study of Bi2.5Na0.5Ta2O9 and Bi2.5Nam−1.5NbmO3m+3 (m=2-4) by Neutron Powder Diffraction and Electron Microscopy

The crystal structures of Bi_2.5Na_0.5Ta₂O₉ and Bi_2.5Na_m-1.5Nb_mO_3m+3 (m=3,4) have been investigated by the Rietveld analysis of their neutron powder diffraction patterns (λ=1.470 Å). These compounds belong to the Aurivillius phase family and are built up by (Bi₂O₂)²⁺ fluorite layers and (A_m-1B_mO_3m+1)^2- (m=2-4) pseudo-perovskite slabs. Bi_2.5Na_0.5Ta₂O₉ (m=2) and Bi_2.5Na_2.5Nb₄O₁₅ (m=4) crystallize in the orthorhombic space group A2₁am, Z=4, with lattice constants of a=5.4763(4), b=5.4478(4), c=24.9710 (15) and a=5.5095(5), b=5.4783(5), c=40.553(3) Å, respectively. Bi_2.5Na_1.5Nb₃O₁₂ (m=3) has been refined in the orthorhombic space group B2cb, Z=4, with the unit-cell parameters a=5.5024(7), b=5.4622(7), and c=32.735(4) Å. In comparison with its isostructural Nb analogue, the structure of Bi_2.5Na_0.5Ta₂O₉ is less distorted and bond valence sum calculations indicate that the Ta-O bonds are somewhat stronger than the Nb-O bonds. The cell parameters a and b increase with increasing m for the compounds Bi_2.5Na_m-1.5Nb_mO_3m+3 (m=2-4), causing a greater strain in the structure. Electron microscopy studies verify that the intergrowth of mixed perovskite layers, caused by stacking faults, also increases with increasing m.     

The non-centrosymmetric borate oxides, MBi2B2O7 (M=Ca, Sr)

Two novel noncentrosymmetric borates oxides, MBi₂B₂O₇ or MBi₂O(BO₃)₂ (MCa, Sr), have been synthesized by solid-state reactions in air at temperatures in the 600-700 °C range. Their crystal structures have been determined ab initio and refined using powder neutron diffraction data. CaBi₂B₂O₇ crystallizes in the orthorhombic Pna2₁ space group with a=8.9371(5) Å, b=5.4771(3) Å, c=12.5912(7) Å, Z=4, R_wp=0.118, χ²=2.30. SrBi₂B₂O₇ crystallizes in the hexagonal P6₃ space group with a=9.1404(4) Å, c=13.0808(6) Å, Z=6, R_wp=0.115, χ²=4.15. Large displacement parameters suggest the presence of disorder in SrBi₂B₂O₇ as also revealed by diffuse 2×a superstructure reflections in electron diffraction patterns. Both structures are built of identical (001) neutral layers of corner-sharing BO₃ triangles and MO₆ trigonal prisms forming six-membered rings in which Bi₂O groups are located. Adjacent layers are stacked in a staggered configuration and connected through weak Bi-O bonds. A moderate efficiency for second harmonic generation (SHG) has been measured for a powder sample of CaBi₂B₂O₇ (d_eff=2d_eff(KDP)).     

Preparation of ternary metal chalcogenide (M1-xFexS, M = Cd and Zn) nanocrystallites using single source precursors

M_1−xFe_xS (M = Cd, Zn) nanocrystallites were prepared by pyrolysis and solvothermal decomposition methods using [M(Aftscz)₂] and [M(AftsczH)₂Cl₂] (M = Cd, Zn and AftsczH = monoacetylferrocene thiosemicarbazone) as single source precursors. The M_1−xFe_xS nanocrystallites were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray analysis and UV-Visible spectroscopy. XRD patterns show that the Cd_1−xFe_xS and Zn_1−xFe_xS nanocrystallites prepared by pyrolysis and solvothermal decomposition routes have hexagonal phase. TEM images show presence of spherical and spherical plate-like morphology of M_1−xFe_xS nanoparticles. M_1−xFe_xS nanoparticles obtained by solvothermal decomposition in ethylene glycol are found to be capped with ethylene glycol as evident from IR spectra.     

Subsolidus phase relations and crystal structures of R-Ca-Cu-O (R=Nd, Sm, Gd, Tm) systems

The subsolidus phase relations of R₂O₃-CaO-CuO ternary systems (R=Nd, Sm, Gd, Tm) have been investigated by X-ray powder diffraction. All samples were synthesized at about 950° in air. There exists a ternary compound Ca_14−xR_xCu₂₄O₄₁ (x = 4 for R=Nd, Gd and x = 5 for R = Sm) and a ternary solid solution Ca_2+xR_2−xCu₅O₁₀ (R=Nd, Sm, Gd, Tm) with a wide composition range Δx of about 0.6. The compound Ca_14−xR_xCu₂₄O₄₁ possesses a layered orthorhombic structure and is isostructural to Sr_14−xCa_xCu₂₄O₄₁. The lattice parameters a and c of the compound are basically independent of the ionic radius of R, while the lattice parameter b and unit-cell volume V decrease substantially with the decrease of the ionic radii of R. The Ca_2+xR_2−xCu₅O₁₀ solid solution is isostructural to Ca_2+xY_2−xCu₅O₁₀, the structure of which is based on an orthorhombic “NaCuO₂-type” subcell containing infinite one-dimensional chains of edge-shared square planar cuprate groups crosslinked by the layered cations Ca and R that locate in the inter-chain tunnels.     

The first quaternary lanthanide(III) nitride iodides: NaM4N2I7 (M=La-Nd)

In attempts to synthesize lanthanide(III) nitride iodides with the formula M₂NI₃ (M=La-Nd), moisture-sensitive single crystals of the first quaternary sodium lanthanide(III) nitride iodides NaM₄N₂I₇ (orthorhombic, Pna2₁; Z=4; a=1391-1401, b=1086-1094, c=1186-1211 pm) could be obtained. The dominating structural features are chains of trans-edge linked [NM₄]⁹⁺ tetrahedra, which run parallel to the polar 2₁-axis [001]. Between the chains, direct bonding via special iodide anions generates cages, in which isolated [NaI₆]^5- octahedra are embedded. The IR spectrum of NaLa₄N₂I₇ recorded from 100 to 1000 cm^-1 shows main bands at υ=337, 373 and 489 cm^-1. With decreasing radii of the lanthanide trications these bands, which can be assigned as an influence of the vibrations of the condensed [NM₄]⁹⁺ tetrahedra, are shifted toward higher frequencies for the NaM₄N₂I₇ series (M=La-Nd), following the lanthanide contraction.     

Structural studies of five layer Aurivillius oxides: A2Bi4Ti5O18 (A=Ca, Sr, Ba and Pb)

The room temperature structures of the five layer Aurivillius phases A₂Bi₄Ti₅O₁₈ (A=Ca, Sr, Ba and Pb) have been refined from powder neutron diffraction data using the Rietveld method. The structures consist of [Bi₂O₂]²⁺ layers interleaved with perovskite-like [A₂Bi₂Ti₅O₁₆]²⁻ blocks. The structures were refined in the orthorhombic space group B2eb (SG. No. 41), Z=4, and the unit cell parameters of the oxides are a=5.4251(2), b=5.4034(1), c=48.486(1); a=5.4650(2), b=5.4625(3), c=48.852(1); a=5.4988(3), b=5.4980(4), c=50.352(1); a=5.4701(2), b=5.4577(2), c=49.643(1) for A=Ca, Sr, Ba and Pb, respectively. The structural features of the compounds were found similar to n=2-4 layers bismuth oxides. The strain caused by mismatch of cell parameter requirements for the [Bi₂O₂]²⁺ layers and perovskite-like [A₂Bi₂Ti₅O₁₆]²⁻ blocks were relieved by tilting of the TiO₆ octahedra. Variable temperature synchrotron X-ray studies for Ca and Pb compounds showed that the orthorhombic structure persisted up to 675 and 475 K, respectively. Raman spectra of the compounds are also presented.     

Crystal growth, structure determination, and optical properties of new potassium-rare-earth silicates K3RESi2O7 (RE=Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu)

Single crystals of K₃RESi₂O₇ (RE=Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) were grown from a potassium fluoride flux. Two different structure types were found for this series. Silicates containing the larger rare earths, RE=Gd, Tb, Dy, Ho, Er, Tm, Yb crystallize in a structure K₃RESi₂O₇ that contains the rare-earth cation in both a slightly distorted octahedral and an ideal trigonal prismatic coordination environment, while in K₃LuSi₂O₇, containing the smallest of the rare earths, lutetium is found solely in an octahedral coordination environment. The structure of K₃LuSi₂O₇ crystallizes in space group P6₃/mmc with a=5.71160(10) Å and c=13.8883(6) Å. The structures containing the remaining rare earths crystallize in the space group P6₃/mcm with the lattice parameters of a=9.9359(2) Å, c=14.4295(4) Å, (K₃GdSi₂O₇); a=9.88730(10) Å, c=14.3856(3) Å, (K₃TbSi₂O₇); a=9.8673(2) Å, c=14.3572(4) Å, (K₃DySi₂O₇); a=9.8408(3) Å, c=14.3206(6) Å, (K₃HoSi₂O₇); a=9.82120(10) Å, c=14.2986(2) Å, (K₃ErSi₂O₇); a=9.80200(10) Å, c=14.2863(4) Å, (K₃TmSi₂O₇); a=9.78190(10) Å, c=14.2401(3) Å, (K₃YbSi₂O₇). The optical properties of the silicates were investigated and K₃TbSi₂O₇ was found to fluoresce in the visible.     

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.     

Synthesis, structure and physical properties of Ru ferrites: BaMRu5O11 (M=Li and Cu) and BaM′2Ru4O11 (M′=Mn, Fe and Co)

The synthesis, structure, and physical properties of five R-type Ru ferrites with chemical formula BaMRu₅O₁₁ (M=Li and Cu) and BaM′₂Ru₄O₁₁ (M′=Mn, Fe and Co) are reported. All the ferrites crystallize in space group P6₃/mmc and consist of layers of edge sharing octahedra interconnected by pairs of face sharing octahedra and isolated trigonal bipyramids. For M=Li and Cu, the ferrites are paramagnetic metals with the M atoms found on the trigonal bipyramid sites exclusively. For M′=Mn, Fe and Co, the ferrites are soft ferromagnetic metals. For M′=Mn, the Mn atoms are mixed randomly with Ru atoms on different sites. The magnetic structure for BaMn₂Ru₄O₁₁ is reported.     

Phase relations in NaxCrxTi8−xO16 at 1350 °C and crystal structure of hollandite-like Na2Cr2Ti6O16

Phase relations of rutile, freudenbergite, and hollandite structures were examined in the pseudobinary system NaCrO₂-TiO₂ (i.e., Na_xCr_xTi_8−xO₁₆) at 1350 °C. The hollandite structure was obtained in the composition range 1.7?x?2.0. The symmetry of the samples at room temperature was tetragonal for x=1.7 and 1.75, and monoclinic for x=1.8 and above. Single crystals of monoclinic hollandite Na₂Cr₂Ti₆O₁₆ were grown and the structure refinement has been carried out using an X-ray diffraction technique. The space group was I2/m and cell parameters were a=10.2385(11), b=2.9559(9), c=9.9097(11)Å, and β=90.545(9)° with Z=1. The Na ion distribution in the tunnel was markedly deformed from that in the tetragonal form. It was suggested that Cr/Ti ratios were different between the two framework metal sites.