Crystal structure, magnetic and thermal properties of LaFeTeO6

LaFeTeO₆ was prepared by solid state reaction of La₂O₃, Fe₂O₃ and TeO₂ in 1:1:2 molar ratios and characterized by powder X-ray diffraction, thermogravimetry and magnetometry. The detailed crystal structure analysis was carried out by Rietveld refinement. LaFeTeO₆ crystallizes in a trigonal lattice with unit cell parameters: a = 5.2049(1) Å and c = 10.3457(2) Å, V = 242.73(2) Å³. The crystal structure is built from sheets of the edge shared FeO₆ and TeO₆ octahedra stacked along the c-axis. These sheets are connected together by La³⁺ ions. Thermogravimetric analysis of the compound showed it to be thermally stable up to 1323 K and continuous loss of TeO₂ was observed above 1323 K leading to the formation of LaFeO₃. High temperature XRD studies revealed a normal expansion behavior of the compound. Temperature and field dependent magnetization of LaFeTeO₆ showed paramagnetic behavior in the temperature range of 3-300 K. The effective magnetic moment per Fe³⁺ ion (5.14 μB) indicates the high spin d⁵ state of Fe³⁺ ion.     

Temperature evolution of structure and magnetic properties in the perovskite Sr2MnSbO6

The structural and magnetic properties of the perovskite Sr₂MnSbO₆ have been studied. Combining neutron and X-ray powder diffraction data, the temperature evolution of the structural parameters was investigated with the Rietveld method between 2 and 1000 K. The crystal structure is tetragonal (space group I4/m) within the temperature interval of 2-750 K and cubic (space group Fm-3m) above 750 K. Both octahedral B-site positions were found to be partially occupied by Mn and Sb, but with different Mn/Sb ratios. The magnetic susceptibilities showed irreversibility between field cooled and zero-field cooled (ZFC) conditions and spin glass like magnetic dynamics including aging and memory phenomena at temperatures below 30 K; all appearing well above a broad maximum at 13 K in the ZFC susceptibility curves. This suggests that the material reaches an unconventional spin-glass state at low temperatures, possibly arising from a competitive situation between the double exchange (ferromagnetism) and the super-exchange (antiferromagnetism). Neutron diffraction patterns showed no evidence of a long-range magnetic ordering at 2 K which is consistent with spin glass behavior. The factors governing the observed structural and magnetic properties of Sr₂MnSbO₆ are discussed and compared with those of other quaternary Mn- and Sb-containing perovskites. Graphs of the temperature of magnetic phase transitions as functions of the cation size were constructed and are discussed for the AB³⁺_1/2B⁵⁺_1/2O₃ series with isomorphous substitution of B³⁺ and B⁵⁺ cations. Possible influence of the A-cation sublattice on magnetic properties is also shortly considered.     

Hydrothermal synthesis, characterization and magnetic properties of NaVGe2O6 and LiVGe2O6

Supercritical fluids are shown to be an excellent reaction media for the synthesis of novel solid state phases at intermediate temperatures. LiVGe₂O₆ and NaVGe₂O₆ have the common pyroxene structure composed of VO₆ linear chains. NaVGe₂O₆ crystallizes in the monoclinic space group C2/c with four formula units having cell dimensions a = 9.960(4) Å, b = 8.853(10) Å, c = 5.4861(10) Å, β = 106.403(3)°. The structure was refined until R = 0.0290 and R_w = 0.0370. For LiVGe₂O₆ in space group P2₁/c: a = 9.8508(7) Å, b = 8.754(3) Å, c = 5.3948(13) Å, β = 108(3)°, R = 0.0240 and R_w = 0.0250. The compounds contain edge-shared VO₆ octahedral chains and corner-shared GeO₄ tetrahedral chains. The presence of these VO₆ chains results in spin-Peierls distortion. Structural and physical characterization of the compounds are reported.     

Crystal structure and spectroscopic properties of a new oxyarsenate Li0.5Ni0.25TiOAsO4

The new oxyarsenate Li_0.5Ni_0.25TiOAsO₄ has been synthesized and studied by a combination of X-ray powder diffraction, neutrons powder diffraction and vibrational spectroscopy. Li_0.5Ni_0.25TiOAsO₄ crystallizes in the monoclinic P2₁/c space group with the unit cell parameters: a = 6.5854(3) Å, b = 7.4665(4) Å, c = 7.4969(4) Å, β = 89.884(6)°, V = 368.62(1) Å³ and Z = 4. The structure has been determined at room temperature from neutrons diffraction by the Rietveld method analysis. It is formed by a 3D network of TiO₆ octahedra and AsO₄ tetrahedra sharing corners. Structural refinement shows a partial and a statistical occupancy of 2a and 2b sites by Li⁺ and Ni²⁺ ions. TiO₆ octahedra are linked together by corners and form infinite chains along c-axis. Raman and infrared studies confirm the existence of -TiOTi- chains. Diffuse reflectance spectrum indicates the presence of octahedrally coordinated Ni²⁺ ions.     

Electronic and magnetic properties of triple-layered ruthenate Sr4Ru3O10 single crystals grown by a floating-zone method

We have grown high-quality single crystals of the triple-layered perovskite ruthenate Sr₄Ru₃O₁₀ using a floating-zone (FZ) method and measured their electronic transport and magnetic properties. Our experiments results are consistent with those previously reported for Sr₄Ru₃O₁₀ flux crystals; the magnetic ground state of Sr₄Ru₃O₁₀ is poised between an itinerant metamagnetic and itinerant ferromagnetic state, and its electronic ground state is a Fermi liquid. In addition, we have investigated the effect of disorder on the metallic state of Sr₄Ru₃O₁₀. From resistivity measurements of various Sr₄Ru₃O₁₀ crystals with different levels of disorder, we found that disorder enhances both temperature-independent elastic scattering and also temperature-dependent inelastic scattering. The in-plane metamagnetic transition is also found to be sensitive to disorder. Disorder results in an increase in the metamagnetic transition field and different magnetic behavior above the transition. We discuss the implications of this interesting observation.     

Crystal and magnetic study of the disordered perovskites Ca(Mn0.5Sb0.5)O3 and Ca(Fe0.5Sb0.5)O3

We have investigated the double perovskites Ca₂MSbO₆ (M = Mn, Fe) that have been prepared by solid-state reaction (M = Fe) and wet chemistry procedures (M = Mn). The crystal and magnetic structures have been studied from X-ray (XRD) and neutron powder diffraction (NPD) data. Rietveld refinements show that the crystal structures are orthorhombic (space group Pbnm) with complete disorder of M and Sb cations, so the formula should be rewritten as Ca(M_0.5Sb_0.5)O₃. Due to this disorder no evidences of Jahn-Teller distortion can be observed in the MnO₆ octahedra of Ca(Mn_0.5Sb_0.5)O₃, in contrast with the ordered double perovskite Sr₂MnSbO₆. Ca(Fe_0.5Sb_0.5)O₃ behaves as an antiferromagnet with an ordered magnetic moment for Fe³⁺ of 1.53(4)μ_B and a propagation vector k = 0, as investigated by low-temperature NPD. The antiferromagnetic ordering is a result of the high degree of Fe/Sb anti-site disorder of the sample, which originates the spontaneous formation of Fe-rich islands, characterized by the presence of strong Fe-O-Fe antiferromagnetic couplings with enough long-range coherence to produce a magnetic contribution perceptible by NPD. By contrast, the magnetic structure of Ca(Mn_0.5Sb_0.5)O₃ cannot be observed by low-temperature NPD because the magnitude of the ordered magnetic moments is below the detection threshold for neutrons.     

Neutron powder diffraction and magnetic study of perovskites Pb(Mn1/2Nb1/2)O3 and Pb(Mn1/4Fe1/4Nb1/2)O3

The structural and magnetic properties of the complex metal oxides Pb(Mn_1/2Nb_1/2)O₃ (PMNO) and Pb(Mn_1/4Fe_1/4Nb_1/2)O₃ (PMFNO), which belong to a class of disordered perovskites have been studied. The magnetic susceptibilities of PMNO showed hysteresis between field cooled and zero-field cooled conditions below the transition of 15 K, suggesting that the material has a spin-glass feature. Neutron diffraction patterns of PMNO showed no evidence of a long-range magnetic ordering at 1.5 K, which is consistent with spin-glass behavior. Rietveld refinements of neutron powder diffraction data collected at different temperatures between 1.5 and 700 K have been carried out in order to extract structural information. The crystal structure of this compound is cubic (space group Pmm) within the whole temperature interval. The Mn and Nb ions were found to be disordered over the perovskite B-sites. The main feature of this structure is the positional disorder at the Pb site, the importance of which in connection with the ferroic transitions is briefly discussed. The Pb cations show a positional disorder shifting from their high-symmetry positions along the [1 1 1] direction. The effect of Fe-doping on PMNO has been studied. The substitution of Fe at the Mn site in PMFNO results in a small changes of the magnetic properties without significant differences in the crystal structures. The factors governing the observed structural and magnetic properties of PMNO and PMFNO are discussed and compared with those of other quaternary Mn-containing perovskites. For the PbB³⁺_1/2Nb_1/2O₃ series with the isomorphous substitution B³⁺, graphs of average lattice parameters of the perovskite phase and the temperatures of ferroelectric and magnetic phase transitions as functions of the B³⁺ cation radius were constructed and are discussed. Influence of A-cation sublattice on magnetic properties is also considered.     

Hydrothermal synthesis, crystal structure and spectroscopic and magnetic properties of (C2H10N2)[Mn2.09Co0.91(HPO3)4]

(C₂H₁₀N₂)[Mn_2.09Co_0.91(HPO₃)₄] has been synthesized using mild hydrothermal conditions under autogeneous pressure. The compound crystallizes in the triclinic P-1 space group. The unit-cell parameters are a = 5.4061(8), b = 5.4150(7), c = 14.136(2) Å, α = 80.84(1), β = 85.41(1), γ = 60.00(1) and Z = 1. The compound shows a layered structure constructed from M₃O₁₂ trimer units linked thorough the (HPO₃)²⁻ phosphite oxoanions with the ethylenediammonium cations located between the sheets compensating the anionic charge of the inorganic framework. The IR and Raman spectra confirm the presence of the ethylenediammonium cation and phosphite anion. The diffuse reflectance spectrum is in accordance with the presence of Co(II) and Mn(II) high spin cations in slightly distorted octahedral symmetry. The calculated Dq and Racah parameters for the Co(II) cations are Dq = 710, B = 870 and C = 4100 cm⁻¹. The magnetic measurements indicate the existence of antiferromagnetic interactions as the major interactions. Hysteresis observed at low temperature indicates a weak ferromagnetic component, due to a non-cancellation of spins, with coercitive field of 900 G and magnetization of 700 emu/mol.     

Crystal structure and dynamical properties of a new tellurite: AgTlTeO3

The structure of a newly synthesized AgTlTeO₃ crystalline compound has been solved from single crystal X-ray diffraction data and refined to a final reliability factor R1 = 0.037. It was found having an orthorhombic Iba2 space group symmetry with unit cell parameters a = 14.708(7) Å, b = 10.745(6) Å, c = 5.166(3) Å, Z = 8. Its lattice is divided into separated AgTlTeO₃ sheets parallel to [0 1 0] which are formed by TeO₃ pyramids, TlO₄ disphenoids and AgO₆ octahedra sharing either corners or edges. At the same time, from the crystal chemistry point of view, it can be classified as a typical island-type compound made up from molecular-like [TeO₃]²⁻ ortho-anions weakly connected with Ag⁺ and Tl⁺ cations. The vibrational spectra and their interpretations complemented by the calculated elastic properties confirm this classification. The model-estimated piezoelectric constants allow characterizing AgTlTeO₃ as a strong pyroelectric structure.     

Crystal structure and properties of the new complex vanadium oxide K2SrV3O9

The new complex vanadium oxide K₂SrV₃O₉ has been synthesized and investigated by means of X-ray powder diffraction (XPD), electron microscopy and magnetic susceptibility measurements. The oxide has an orthorhombic unit cell with lattice parameters a = 10.1922(2) Å, b = 5.4171(1) Å, c = 16.1425(3) Å, space group Pnma and Z = 4. The crystal structure of K₂SrV₃O₉ has been refined by Rietveld method using X-ray powder diffraction data. The structure contains infinite chains built by V⁴⁺O₅ square pyramids linked to each other via VO₄ tetrahedra. The chains form layers and potassium and strontium cations orderly occupy structural interstices between these layers. Electron diffraction as well as high resolution electron microscopy confirmed the structure solution. Magnetic susceptibility measurements revealed an antiferromagnetic interaction with J of the order of 100 K inside the chains and no long-range magnetic order above 2 K. The origin of the magnetic exchange is likely a result of super-exchange interaction through the two VO₄ tetrahedra linking the polyhedra with the magnetic V⁴⁺ cations.     

Thermal, spectroscopic and magnetic properties of the CoxNi1−x(SeO3)·2H2O (x = 0, 0.4, 1) phases: Crystal structure of Co0.4Ni0.6(SeO3)·2H2O

The Co_xNi_1−x(SeO₃)·2H₂O (x = 0, 0.4, 1) family of compounds has been hydrothermally synthesized under autogeneous pressure and characterized by elemental analysis, infrared and UV-vis spectroscopies and thermogravimetric and thermodiffractometric techniques. The crystal structure of Co_0.4Ni_0.6(SeO₃)·2H₂O has been solved from single-crystal X-ray diffraction data. This phase is isostructural with the M(SeO₃)·2H₂O (M = Co and Ni) minerals and crystallizes in the P2₁/n space group, with a = 6.4681(7), b = 8.7816(7), c = 7.5668(7) Å, β = 98.927(9)° and Z = 4. The crystal structure of this series of compounds consists of a three-dimensional framework formed by (SeO₃)²⁻ selenite oxoanions and edge-sharing M₂O₁₀ dimeric octahedra in which the metallic cations are coordinated by the oxygens belonging to both the selenite groups and water molecules. The diffuse reflectance spectra show the essential characteristics of Co(II) and Ni(II) cations in slightly distorted octahedral environments. The calculated values of the Dq and Racah (B and C) parameters are those habitually found for the 3d⁷ and 3d⁸ cations in octahedral coordination. The magnetic measurements indicate the existence of antiferromagnetic interactions in all the compounds. The magnetic exchange pathways involve the metal orbitals from edge-sharing dimeric octahedra and the (SeO₃)²⁻ anions which are linked to the M₂O₁₀ polyhedra in three dimensions.     

New type of incommensurate magnetic ordering in Mn3TeO6

The complex metal oxide Mn₃TeO₆ exhibits a corundum related structure and has been prepared both in forms of single crystals by chemical transport reactions and of polycrystalline powders by a solid state reaction route. The crystal structure and magnetic properties have been investigated using a combination of X-ray and neutron powder diffraction, electron microscopy, calorimetric and magnetic measurements. At room temperature this compound adopts a trigonal structure, space group with a = 8.8679(1) Å, c = 10.6727(2) Å. A long-range magnetically ordered state is identified below 23 K. An unexpected feature of this magnetic structure is several types of Mn-chains. Under the action of the incommensurate magnetic propagation vector k = [0, 0, 0.4302(1)] the unique Mn site is split into two magnetically different orbits. One orbit forms a perfect helix with the spiral axis along the c-axis while the other orbit has a sine wave character along the c-axis.     

Hydrothermal synthesis, structural characterization and thermal, spectroscopic and magnetic properties of the inorganic-organic hybrid phosphate, [(C2N2H9)VF(PO4)]

The [(C₂N₂H₉)VF(PO₄)] compound has been synthesized by hydrothermal techniques under autogeneous pressure at 170°C. The compound was characterized from X-ray powder diffraction data with the Rietveld method. Its crystal structure consists of sheets linked by the ethylenediammonium cations and constructed by chains of VO₃F₂N octahedra. The thermal study indicates that the compound is stable up to 290°C. In the IR spectrum the bands of both the ethylenediammonium and phosphate ions are observed. From the reflectance diffuse spectrum the Dq and Racah parameters have been calculated. The magnetic measurements indicate the presence of antiferromagnetic interactions.     

Synthesis, structure and magnetic properties of a new iron phosphonate-oxalate with 3D framework: [Fe(O3PCH3)(C2O4)0.5(H2O)]

A new iron phosphonate-oxalate [Fe(O₃PCH₃)(C₂O₄)_0.5(H₂O)] (1), has been synthesized under hydrothermal condition. The single-crystal X-ray diffraction studies reveal that 1 consists of layers of vertex-linked FeO₆ octahedra and O₃PC tetrahedra, which are further connected by bis-chelate oxalate bridges, giving to a 3D structure with 10-membered channels. Crystal data: monoclinic, P2₁/n (no. 14), a = 4.851(2) Å, b = 16.803(7) Å, c = 7.941(4) Å, β = 107.516(6)°, V = 617.2(5) Å³, Z = 4, R₁ = 0.0337 and wR₂=0.0874 for 1251 reflections [I > 2σ(I)]. Mössbauer spectroscopy measurement confirms the existence of high-spin Fe(III) in 1. Magnetic studies show that 1 exhibits weak ferromagnetism with T_N = 30 K due to a weak spin canting.     

Crystal structures of CdTi2O4(OH)2 and LaTiSbO6

The crystal structures of two PbSb₂O₆-type compounds containing titanium, CdTi₂O₄(OH)₂ and LaTiSbO₆ were refined by X-ray powder diffraction data. For both compounds structure refinements with the space group were successful and the R-factors were R_WP = 6.46% and R_P = 4.90% for CdTi₂O₄(OH)₂ and R_WP = 9.55% and R_P = 7.17% for LaTiSbO₆. These crystal structures were the same as that of the typical PbSb₂O₆-type compound in spite of the existence of protons in the interlayer or two different metal ions in the layer.     

Structural characterization, thermal, spectroscopic and magnetic studies of the (C3H12N2)0.75[Mn1.50Fe1.50(AsO4)F6] and (C3H12N2)0.75[Co1.50Fe1.50(AsO4)F6] compounds

The (C₃H₁₂N₂)_0.94[Mn_1.50Fe_1.50^III(AsO₄)F₆] and (C₃H₁₂N₂)_0.75[Co_1.50Fe_1.50^III(AsO₄)F₆] compounds 1 and 2 have been synthesized using mild hydrothermal conditions. These phases are isostructural with (C₃H₁₂N₂)_0.75[Fe_1.5^IIFe_1.5^III(AsO₄)F₆]. The compounds crystallize in the orthorhombic Imam space group. The unit cell parameters calculated by using the patterns matching routine of the FULPROOF program, starting from the cell parameters of the iron(II),(III) phase, are: a = 7.727(1) Å, b = 11.047(1) Å, c = 13.412(1) Å for 1 and a = 7.560(1) Å, b = 11.012(1) Å, c = 13.206(1) Å for 2, being Z = 8 in both compounds. The crystal structure consists of a three-dimensional framework constructed from edge-sharing [M^II(1)₂O₂F₈] (M = Mn, Co) dimeric octahedra linked to [Fe^III(2)O₂F₄] octahedra through the F(1) anions and to the [AsO₄] tetrahedra by the O(1) vertex. This network gives rise two kinds of chains, which are extended in perpendicular directions. Chain 1 is extended along the a-axis and chain 2 runs along the c-axis. These chains are linked by the F(1) and O(1) atoms and establish cavities delimited by eight or six polyhedra along the [1 0 0] and [0 0 1] directions, respectively. The propanediammonium cations are located inside these cavities. The thermal study indicates that the structures collapse with the calcination of the organic dication at 255 and 285 °C for 1 and 2, respectively. The Mössbauer spectra in the paramagnetic state indicate the existence of two crystallographically independent positions for the iron(III) cations and a small proportion of this cation in the positions of the divalent Mn(II) and Co(II) ones. The IR spectrum shows the protonated bands of the H₂N- groups of the propanediamine molecule and the characteristic bands of the [AsO₄]³⁻ arsenate oxoanions. In the diffuse reflectance spectra, it can be observed the bands characteristic of trivalent iron(III) cation and divalent Mn(II) and Co(II) ones in a distorted octahedral symmetry. The calculated Dq and B-Racah parameters for the cobalt(II) phase are 710 and 925 cm⁻¹, respectively. The ESR spectra of compound 1 maintain isotropic with variation in temperature, being g = 1.99. Magnetic measurements for both compounds indicate that the main magnetic interactions are antiferromagnetic in nature. However, at low temperatures small ferromagnetic components are detected, which are probably due to a spin decompensation of the two different metallic cations. The hysteresis loops give values of the remnant magnetization and coercive field of 84.5, 255 emu/mol and 0.01, 0.225 T for phases 1 and 2, respectively.     

Crystal structure and ionic conductivity of ruthenium diphosphate ARu2(P2O7)2, A=Li, Na, and Ag, with a tunnel structure

Crystal structure and ionic conductivity of ruthenium diphosphates, ARu₂(P₂O₇)₂ A=Li, Na, and Ag, were investigated. The structure of the Ag compound was determined by single crystal X-ray diffraction techniques. It crystallized in the triclinic space group P−1 with a=4.759(2) Å, b=6.843(2) Å, c=8.063(1) Å, α=90.44(2)°, β=92.80(2)°, γ=104.88(2)°, V=253.4(1) Å³. The host structure of it was composed of RuO₆ and P₂O₇ groups and formed tunnels running along the a-axis, in which Ag⁺ ions were situated. The ionic conductivities have been measured on pellets of the polycrystalline powders. The Li and Ag compounds showed the conductivities of 1.0×10⁻⁴ and 3.5×10⁻⁵ S cm⁻¹ at 150 °C, respectively. Magnetic susceptibility measurement of the Ag compound showed that it did not obey the Curie-Weiss law and the effective magnetic moment decreased as temperature decreased due to the large spin-orbital coupling effect of Ru⁴⁺ ions.     

Synthesis, characterization and photocatalytic properties of nanosized Bi2WO6, PbWO4 and ZnWO4 catalysts

Nanosized Bi₂WO₆, PbWO₄ and ZnWO₄ photocatalysts were synthesized by a mild hydrothermal crystallization process. The physical and photophysical properties of the catalysts were characterized by X-ray diffractometry, Brunauer-Emmet-Teller surface area and porosity measurements, transmission electron microscopy, Raman spectra, and diffused reflectance spectroscopy. The rhodamine-B photodegradation in aqueous medium was employed as a probe reaction to test the photoactivities of the as-prepared samples under four irradiation wavelengths. Bi₂WO₆ not only presented the photocatalytic activity in the wide spectral scope, including UV and visible light but also exhibited the strong photosensitized capability to transform RhB under visible light irradiation (λ > 490 nm). ZnWO₄ only displayed relatively high photoactivity under UV irradiation. However, PbWO₄ showed poor photoactivity under any light irradiation. On the basis of the calculated density functional theory (DFT), the photocatalytic mechanisms were discussed.     

Crystal structures and phase transitions in Ba2HoTaO6

The structure of the cation-ordered double perovskite Ba₂HoTaO₆ was examined using synchrotron X-ray powder diffraction at fine temperature intervals over the range of 90-300 K. Ba₂HoTaO₆ has a cubic structure in space group at room temperature. A proper ferroelastic phase transition to I4/m tetragonal symmetry occurs near approximately 260 K. Analysis of the spontaneous tetragonal strain versus temperature indicated that the phase transition is second order in nature.