Temperature behavior of the protonic conductor K4LiH3(SO4)4

The results of the X-ray structural study for the K₄LiH₃(SO₄)₄ single crystal are presented at a wide temperature range. The thermal expansion of the crystal using the X-ray dilatometry and the capacitance dilatometry from 8 to 500 K was carried out. The crystal structures data collection, solution and refinement at 125, 295, 443 and 480 K were performed. The K₄LiH₃(SO₄)₄ crystal has tetragonal symmetry with the P4₁ space group (Z=4) at room temperature as well as at the considered temperature range. The existence of a low-temperature, para-ferroelastic phase transition at about 120 K is excluded. The layered structure of the crystal reflects a cleavage plane parallel to (001) and an anisotropy of the protonic conductivity. The superionic high-temperature phase transition at T_S=425 K is isostructural. Nevertheless, taking into account an increase of the SO₄ tetrahedra libration above T_S, a mechanism of the Grotthus type could be applied for the proton transport explanation.     

Sol-gel synthesis of K3InF6 and structural characterization of K2InC10O10H6F9, K3InC12O14H4F18 and K3InC12O12F18

K₃InF₆ is synthesized by a sol-gel route starting from indium and potassium acetates dissolved in isopropanol in the stoichiometry 1:3, with trifluoroacetic acid as fluorinating agent. The crystal structures of the organic precursors were solved by X-ray diffraction methods on single crystals. Three organic compounds were isolated and identified: K₂InC₁₀O₁₀H₆F₉, K₃InC₁₂O₁₄H₄F₁₈ and K₃InC₁₂O₁₂F₁₈. The first one, deficient in potassium in comparison with the initial stoichiometry, is unstable. In its crystal structure, acetate as well as trifluoroacetate anions are coordinated to the indium atom. The two other precursors are obtained, respectively, by quick and slow evaporation of the solution. They correspond to the final organic compounds, which give K₃InF₆ by decomposition at high temperature. The crystal structure of K₃InC₁₂O₁₄H₄F₁₈ is characterized by complex anions [In(CF₃COO)₄(OH_x)₂]^(5−2x)− and isolated [CF₃COOH_2−x]^(x−1)− molecules with x=2 or 1, surrounded by K⁺ cations. The crystal structure of K₃InC₁₂O₁₂F₁₈ is only constituted by complex anions [In(CF₃COO)₆]³⁻ and K⁺ cations. For all these compounds, potassium cations ensure only the electroneutrality of the structure. IR spectra of K₂InC₁₀O₁₀H₆F₉ and K₃InC₁₂O₁₂F₁₈ were also performed at room temperature on pulverized crystals.     

A structure, conductivity and dielectric properties investigation of A3CoNb2O9 (A=Ca, Sr, Ba) triple perovskites

The room temperature structures as well as the temperature-dependent conductivity and dielectric properties of the A₃CoNb₂O₉ (A=Ca²⁺, Sr²⁺ and Ba²⁺) triple perovskites have been carefully investigated. A constrained modulation wave approach to Rietveld structure refinement is used to determine their room temperature crystal structures. Correlations between these crystal structures and their physical properties are found. All three compounds undergo insulator to semiconductor phase transitions as a function of increasing temperature. The hexagonal Ba₃CoNb₂O₉ compound acts as an insulator at room temperature, while the monoclinic Ca₃CoNb₂O₉ compound is already a semiconductor at room temperature. The measured dielectric frequency characteristics of the A=Ba compound are excellent.     

High temperature crystal structures and superionic properties of SrCl2, SrBr2, BaCl2 and BaBr2

The structural properties of the binary alkaline-earth halides SrCl₂, SrBr₂, BaCl₂ and BaBr₂ have been investigated from ambient temperature up to close to their melting points, using the neutron powder diffraction technique. Fluorite-structured SrCl₂ undergoes a gradual transition to a superionic phase at 900–1100 K, characterised by an increasing concentration of anion Frenkel defects. At a temperature of 920(3) K, the tetragonal phase of SrBr₂ undergoes a first-order transition to a cubic fluorite phase. This high temperature phase shows the presence of extensive disorder within the anion sublattice, which differs from that found in superionic SrCl₂. BaCl₂ and BaBr₂ both adopt the cotunnite crystal structure under ambient conditions. BaCl₂ undergoes a first-order structural transition at 917(5) K to a disordered fluorite-structured phase. The relationship between the (disordered) crystal structures and the ionic conductivity behaviour is discussed and the influence of the size of the mobile anion on the superionic behaviour is explored.     

Single-crystal growth of Tl2Ru2O7 pyrochlore using high-pressure and flux method

Single crystals of the thallium ruthenium pyrochlore have been grown by flux method under high oxygen pressure. The growth conditions were determined by direct observations using in situ powder X-ray diffraction (XRD) method under high pressure and high temperature. The crystals were grown using NaCl-KCl flux at 1350 °C and B₂O₃ flux at 1150 °C. High growth temperature of 1350 °C for the NaCl-KCl flux caused Pt contamination from the crucible and oxygen deficiency for the crystals obtained. The crystal growth using B₂O₃ flux proceeded at lower temperature by grain growth with material transfer through B₂O₃. The crystal obtained was characterized by single-crystal XRD method, and was found to have a stoichiometric composition, Tl₂Ru₂O_7−δ (δ=0), with a structural phase transition around 120 K. The grain growth technique with B₂O₃ is efficient for high-temperature single-crystal growth under high pressure.     

Phase transition in the Ruddlesden-Popper layered perovskite Li2SrTa2O7

The crystal structure of the Ruddlesden-Popper layered perovskite Li₂SrTa₂O₇ has been characterized at various temperatures between −185 and 300 °C by several techniques: X-ray and neutron powder diffraction, single crystal diffraction, transmission electron microscopy and Raman spectroscopy. The low temperature structure has been confirmed to be orthorhombic Cmcm with a small octahedra antiphase tilting (ΦΦ0) (ΦΦ0) inside the perovskite blocks. With temperature, the tilting progressively vanishes leading around 230 °C to a tetragonal symmetry (S.G. I4/mmm). This reversible phase transition, followed by X-ray and neutron thermodiffraction and thermal Raman measurements, is considered as of second order. An attribution of the Raman bands based on normal mode analysis is proposed.     

Low temperature magnetic susceptibility and exchange interaction in Cs3Cr2Cl9

Magnetic susceptibility of Cs₃Cr₂Cl₉ as a single crystal is studied in the temperature range 4.2–77 K. A maximum is obtained at 25 ± 1 K. These experimental data are interpreted by considering the isotropic exchange interaction between two spin quadruplets. The exchange constant J is found to be equal to - 13 cm^?1.     

Structural studies of the disorder and phase transitions in the double perovskite Sr2YTaO6

The evolution of the crystal structure of the double perovskite Sr₂YTaO₆ from room temperature to 1250 °C has been studied using powder neutron and synchrotron X-ray diffraction. At room temperature Sr₂YTaO₆ crystallises in a monoclinic superstructure with the space group P2₁/n. The tilting of the octahedra evident in the room temperature structure is progressively lost on heating, resulting in a sequence of phase transitions that ultimately yields the cubic structure in space group Fm3?m. The high temperature tetragonal and cubic phases are characterised by strongly anisotropic displacements of the anions. The amount of defects in the crystal structure of Sr₂YTaO₆ is found to be sensitive to the preparative method.     

Nucleation and crystal growth in Na2O · 2 CaO · 3 SiO2 glass: a DTA study

The non-isothermal devitrification of Na₂O · 2 CaO · 3 SiO₂ glass has been studied by differential thermal analysis in order to evaluate, from DTA curves, the temperature of maximum nucleation rate, T_m, and the activation energy values, E_c, for crystal growth.The temperature, T_m=580°C, is very close to the glass transition temperature, T_g=570°C, and the value of E_c=78 Kcal mole^?1 for the surface crystal growth is nearly the same as the value E_c=89 kcal mole^?1 for the bulk crystal growth; both are consistent with the activation energy for viscous flow. It is also pointed out that the nucleation rate—temperature curve and the crystallization rate—temperature curve are partially overlapped.     

Synthesis, structure and magnetic properties of new vanadate PbCo2V2O8

A new vanadate PbCo₂V₂O₈ was obtained through the study of PbO-CoO-V₂O₅ ternary system. The crystal structure was determined by Rietveld method, indicating that PbCo₂V₂O₈ has a tetragonal structure of space group I41cd with a spiral chain along the c-axis. Magnetic properties of the titled compound were investigated by means of susceptibility, magnetization, and heat capacity measurements. The results show that PbCo₂V₂O₈ is a quasi-one-dimensional canted antiferromagnet with Neel temperature of ∼4 K, being consistent with its crystal structure.     

Magnetic properties of barium uranate Ba2U2O7

Unique magnetic properties of a ternary uranate Ba₂U₂O₇ are reported. Magnetic susceptibility measurements reveal that this compound undergoes a magnetic transition at 19 K. Below this temperature, magnetic hysteresis was observed. The results of the low-temperature specific heat measurements below 30 K support the existence of the second-order magnetic transition at 19 K. Ba₂U₂O₇ undergoes a canted antiferromagnetic ordering at this temperature. The magnetic anomaly which sets in at 58 K may be due to the onset of one-dimensional magnetic correlations associated with the linear chains formed by U ions. The analysis of the experimental magnetic susceptibility data in the paramagnetic temperature region gives the effective magnetic moment μ_eff=0.73 μ_B, the Weiss constant θ=−10 K, and the temperature-independent paramagnetic susceptibility χ_TIP=0.14×10⁻³ emu/mole.The magnetic susceptibility results and the optical absorption spectrum were analyzed on the basis of an octahedral crystal field model. The energy levels of Ba₂U₂O₇ and the crystal field parameters were determined.     

A comparative study of the Aurivillius phase ferroelectrics CaBi4Ti4O15 and BaBi4Ti4O15

The room temperature structures of the four-layer Aurivillius phase ferroelectrics CaBi₄Ti₄O₁₅ and BaBi₄Ti₄O₁₅ are determined by means of single crystal X-ray diffraction. Regarding the CaBi₄Ti₄O₁₅ phase, in agreement with the tolerance factor, a significant deformation of the perovskite blocks is observed. The rotation system of the octahedra is typical from even layer Aurivillius phases and leads to the use of the space group A2₁am. For the BaBi₄Ti₄O₁₅ phase, only a weak variation with respect to the F2mm space group can be suggested from single crystal X-ray diffraction. A significant presence of Ba atoms in the [M₂O₂] slabs is confirmed in agreement with the previous works but specific Ba²⁺ and Bi³⁺ sites have to be considered due to the large difference in bounding requirement of these cations. Possible origins for the ferroelectric relaxor behavior of the Ba-based compound are discussed in view of the presented structural analyses.     

Crystal structure and magnetic properties of Sr4Mn2NiO9

The crystal structure of Sr₄Mn₂NiO₉ has been refined on single crystal. This phase belongs to the series A_1+x(A^′_xB_1–x)O₃ (x=1/3) related to the 2H-hexagonal perovskite. The structure contains transition metals in chains of oxide polyhedra (trigonal prisms and octahedra); neighboring chains are separated from each other by the Sr atoms. The sequence of the face sharing polyhedra along the chains is two octahedra + one trigonal prism. Mn occupies the octahedra and Ni is disordered in the trigonal prism with ≈80% in the pseudo square faces of the prism and ≈20% at the centre. This result has been confirmed by XANES experiments at Mn K and Ni K edges, respectively. Sr₄Mn₂NiO₉ is antiferromagnetic with a Néel temperature at T=3 K. The Curie constant measured at high temperature is in good agreement with ≈80% of the Ni²⁺ ions in the spin state configuration S=0.     

A room-temperature neutron-diffraction study of NaH2PO4

The monoclinic crystal structure of NaH₂PO₄ at room temperature has been refined from neutron-diffraction measurements on a single-crystal sample and complied with the closely related structure of monoclinic KD₂PO₄. Attention is paid to the information obtained from these two structures about the geometry of hydrogen (deuterium) bonds ?2.6 A.     

K2Fe2B2O7: A transparent nonlinear optical crystal with frustrated magnetism

A new noncentrosymmetric ferroborate crystal, K₂Fe₂B₂O₇, has been grown from high temperature melt. Structure solution from single crystal X-ray diffraction shows that the title compound crystallizes in a trigonal space group P321 with cell dimensions of a=8.7475(12) Å and c=8.5124(17) Å. In the structure, FeO₄ tetrahedron shares its three basal oxygen atoms with BO₃ triangles forming a two-dimensional layer in the ab plane and the layers are connected by the apical Fe-O bonds along the c direction. The crystal is transparent in the visible and near infrared region from 500 to 2000 nm with three pronounced absorption bands ascribed to d-d transitions of tetrahedrally coordinated Fe³⁺ ions. Though, structurally analog to K₂Al₂B₂O₇, the further twisting of the BO₃ groups between adjacent layers reduces its optical nonlinearity to a second-harmonic generation intensity of about 0.4 times that of KDP. Spin-glass behavior is observed at 20 K which is probably due to geometrically magnetic frustration of the triangular Fe net in the ab plane.     

[Bi2Cl10(H2-Norf)4(H2O)8](H-Norf是诺氟沙星)(英)

The crystal structure of [Bi2Cl10(H2-Norf)4(H2O)8] (1) comprises [H2-Norf]^ cations and [Bi2Cl10]4^- anions, that are loosely associated via H-bonding interactions, as well as water molecules that also participate in H-bonding interactions. Strong blue-fluorescent emission of 1 at solid state is observed at the room temperature. CCDC:238237.     

Synthesis and structure of a new uranyl selenate complex with 1-butylamine [CH3(CH2)3NH3](H5O2)[(UO2)2(SeO4)3(H2O)]

Crystals of a new uranyl selenate complex [CH₃(CH₂)₃NH₃](H₅O₂)[(UO₂)₂(SeO₄)₃(H₂O)] were obtained by isothermal evaporation at room temperature of its aqueous solution. The crystal structure was determined by the X-ray diffraction analysis. The observed character of the arrangement of organic molecules in the interlayer space confirms the concept of hydrophilic and hydrophobic zones.     

Magnetic susceptibility of the one-dimensional conductor (H3O)1.6[Pt(C2O4)2]nH2O

The magnetic susceptibility of the dioxalatoplatinate acid (H₃O)_1.6[Pt(C₂O₄)₂]nH₂O, a mixed valency planar (MVP) compound with columnar structure and one-dimensional metallic conduction properties, has been measured in the temperature range 1.5–300°K. The observed paramagnetism, like in other MVP compounds, may be described by a linear $\text{1}\text{T}$ dependence with a break in the slope at a characteristic temperature. The Curie constants as well as the point of discontinuity have been found to depend on the crystal water content. The results are discussed in terms of different theoretical concepts.     

Two novel coordination polymers [Sm2(Pzdc)3(H2O)]x · 2xH2O and [Nd2(Pzdc)3(H2O)]x · 2xH2O: Synthesis, structure, and photoluminescent properties

Coordination polymers, [Sm₂(Pzdc)₃(H₂O)] _x · 2xH₂O (I) and [Nd₂(Pzdc)₃(H₂O)] _x · 2xH₂O (II), were obtained by hydrothermal reactions with 2,3-pyrazinedicarboxylic acid (H₂Pzdc) and the salts nitrates, and characterized by single crystal X-ray structure, thermogravimetric analysis, element analysis and infrared spectroscopy. The X-ray crystal diffraction data indicates that two complexes crystal in a monoclinic system with the space group P2₁/c, of the three dimensional framework. The Pzdc ligand in the complexes I and II adopts tetradentate, hexadentate, and heptadentate bridging modes. The influences of coordination modes of the Pzdc ligand on the superstructural diversity is discussed. The photoluminescent data suggest that the ligands act as efficient “antennas” sensitizing the luminescence of the Sm³⁺ ion. Complex I exhibits strong fluorescent emission bands in the solid state at room temperature.     

Synthesis, crystal structure and magnetic properties of U2Co6Al19

The new compound U₂Co₆Al₁₉ was prepared by reaction of the elemental components in an arc-melting furnace followed by a heat treatment at 1050°C for 500 h. Its chemical composition was checked by energy-dispersive X-ray analyses and its crystal structure was determined by single crystal X-ray diffraction experiments. It crystallizes with four formula units in the monoclinic space group C2/m in a unit cell of dimensions a=17.4617(3)Å, b=12.0474(2)Å, c=8.2003(1)Å, β=103.915(1)°. The crystal structure of U₂Co₆Al₁₉ can be regarded as a superstructure of NdCo_4−xGa₉ structure type. This complex structure consists of a three-dimensional Co-Al framework delimiting tunnels where the U atoms reside. The shortest U-U distances are found in the c direction with alternating values of 3.98(1) and 4.22(1) Å. Temperature-dependent magnetization shows a first peak at 12.5 K and a weak ferromagnetic character below the temperature T_C=8 K. Magnetization at 1.9 K reaches almost saturation in 5 T with the moment of 0.36 μ_B/U atom. The complex magnetic behavior of U₂Co₆Al₁₉ may be ascribed to a canted spin structure resulting from an antiparallel arrangement of the magnetic moments not fully compensated at low temperature. At higher temperature, the compound displays simple paramagnetic behavior.