Synthesis, characterization, and structure determination of the orthorhombic U2(PO4)(P3O10)

β-UP₂O₇ has been synthesized under hydrothermal conditions (θ=500°C, P=200 MPa), using UO₂ and H₃PO₄. β-UP₂O₇ crystallizes in the orthorhombic space group Pn2₁a, with a=11.526 (2) Å, b=7.048 (2) Å, c=12.807 (2) Å and Z=4. Its structure has been determined through direct methods and difference Fourier synthesis and has been refined to R=0.0396. The structure is built on UO₈ polyhedral chains along the b-axis. PO₄³⁻ and P₃O₁₀⁵⁻ groups coexist in the structure and the latter groups form non-linear chains. Cohesion of the structure is made through the linkage of UO₈ chains by PO₄ and P₃O₁₀ groups leading to the formula U₂(PO₄)(P₃O₁₀) instead of β-UP₂O₇. Vibrational and optical spectra confirm the results obtained by X-ray diffraction. DTA-TGA measurements show that the transformation of U₂(PO₄)(P₃O₁₀) to the cubic α-UP₂O₇ occurs at θ=870°C.     

Synthesis, structure and magnetic properties of new phosphates K2Mn0.5Ti1.5(PO4)3 and K2Co0.5Ti1.5(PO4)3 with the langbeinite structure

New complex phosphates of the general formula K₂M_0.5Ti_1.5(PO₄)₃ (M=Mn, Co) have been obtained from the melting mixture of KPO₃, K₄P₂O₇, TiO₂ and CoCO₃·mCo(OH)₂ or Mn(H₂PO₄)₂ by means of a flux technique. The synthesized phosphates have been characterized by the single-crystal X-ray diffraction and the FTIR-spectroscopy. The compounds crystallize in the cubic system with the space group P2₁3 and cell parameters a=9.9030(14) Å for K₂Mn_0.5Ti_1.5(PO₄)₃ and a=9.8445(12) Å for K₂Co_0.5Ti_1.5(PO₄)₃. Both phosphates are isostructural with the langbeinite mineral and contain four formula unit K₂M_0.5Ti_1.5(PO₄)₃ per unit cell. The structure can be described using [M₂(PO₄)₃] framework composed of two [MO₆] octahedra interlinked via three [PO₄] tetrahedra. The Curie-Weiss-type behavior is observed in the magnetic susceptibility.     

Synthesis, crystal structure and electrical characterization of two new potassium uranyl molybdates K2(UO2)2(MoO4)O2 and K8(UO2)8(MoO5)3O6

Two new potassium uranyl molybdates K₂(UO₂)₂(MoO₄)O₂ and K₈(UO₂)₈(MoO₅)₃O₆ have been obtained by solid state chemistry . The crystal structures were determined by single crystal X-ray diffraction data, collected with MoKα radiation and a charge coupled device (CCD) detector. Their structures were solved using direct methods and Fourier difference techniques and refined by a least square method on the basis of F² for all unique reflections, with R₁=0.046 for 136 parameters and 1412 reflections with I?2σ(I) for K₂(UO₂)₂(MoO₄)O₂ and R₁=0.055 for 257 parameters and 2585 reflections with I?2σ(I) for K₈(UO₂)₈(MoO₅)₃O₆. The first compound crystallizes in the monoclinic symmetry, space group P2₁/c with a=8.250(1) Å, b=15.337(2) Å, c=8.351(1) Å, β=104.75(1)°, ρ_mes=5.22(2) g/cm³, ρ_cal=5.27(2) g/cm³ and Z=4. The second material adopts a tetragonal unit cell with a=b=23.488(3) Å, c=6.7857(11) Å, ρ_mes=5.44(3) g/cm³, ρ_cal=5.49(2) g/cm³, Z=4 and space group P4/n.In both structures, the uranium atoms adopt a UO₇ pentagonal bipyramid environment, molybdenum atoms are in a MoO₄ tetrahedral environment for K₂(UO₂)₂(MoO₄)O₂ and MoO₅ square pyramid coordination in K₈(UO₂)₈(MoO₅)₃O₆. These compounds are characterized by layered structures. The association of uranyl ions (UO₇) and molybdate oxoanions MoO₄ or MoO₅, give infinite layers [(UO₂)₂(MoO₄)O₂]²⁻ and [(UO₂)₈(MoO₅)₃O₆]⁸⁻ in K₂(UO₂)₂(MoO₄)O₂ and K₈(UO₂)₈(MoO₅)₃O₆, respectively. Conductivity properties of alkali metal within the interlayer spaces have been measured and show an Arrhenius type evolution.     

Crystal structure and vibrational properies of Rb2MgWO2(PO4)2—A new framework phosphate

The new compound Rb₂MgWO₂(PO₄)₂ has been synthesized and characterized by a single-crystal X-structure determination, and IR and Raman spectroscopic studies. The crystal structure is orthorhombic, space group Pbca, with the unit cell dimensions a=9.891(2), b=12.641(2), , Z=8. Compared to the K₂M^IIWO₂(PO₄)₂ series, where M^II=Mg, Mn, Fe, Co, Ni, and Cd, the volume of the unit cell in the present compound is nearly doubled. The MgO₆ and WO₆ octahedra are arranged into polyhedral groups consisting of two edge sharing MgO₆ joined by corners with two WO₆ octahedra. These groups are interconnected through the PO₄ tetrahedra into layers in a×b plane. The Rb⁺ ions perform thermally activated displacements within the cavities formed between the polyhedral layers. The origin of various Raman and IR modes is discussed. These results indicate that a clear energy gap exists between the stretching and remaining modes. The most intense modes are shown to be due to vibrations of the W-O bonds.     

Topotactic insertion of lithium in the layered structure Li4VO(PO4)2: The tunnel structure Li5VO(PO4)2

A new V(III) lithium phosphate Li₅VO(PO₄)₂ has been synthesized by electrochemical insertion of lithium into Li₄VO(PO₄)₂. This phase, which crystallizes in the space group I4/mcm, exhibits a tunnel structure closely related to the layered structure of Li₄VO(PO₄)₂ and to the tunnel structure of VO(H₂PO₄)₂. The topotactic reactions that take place during lithium exchange and intercalation, starting from VO(H₂PO₄)₂ and going to the final phase Li₅VO(PO₄)₂ are explained on the basis of the flexible coordinations of V⁴⁺ and V³⁺ species. The electrochemical and magnetic properties of this new phase are also presented and explained on the basis of the structure dimensionality.     

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.     

K3Na(FeO4)2的电合成及其晶体结构

本文采用间接法电合成出较高纯度的复盐K₃Na(FeO₄)₂晶体，用粉末XRD结构分析法对其晶体结构作了详细研究。用EDX和AAS确认了其化学式。结构分析表明，K₃Na(FeO₄)₂晶体属三方晶系，具有六方晶胞，空间群为P3m1(No.164)，Z=1,晶胞中有6个O位于6(i)位，O,Fe和K各自有2个位于2(d)位，1个K和Na分别位于1(b)位和1(a)位，晶胞参数a=0.583 3(1) nm,c=0.755 9(1) nm，D=2.824 g·cm^-3。同时晶胞中各原子间化学键键长得到确定。     

Pressure induced phase transformation in U2O(PO4)2

The high pressure behavior of U₂O(PO₄)₂ has been investigated with the help of Raman scattering and X-ray diffraction measurements up to ∼14 and 6.5 GPa, respectively. The observed changes in the Raman spectra as well as the X-ray diffraction patterns suggest that U₂O(PO₄)₂ undergoes a phase transition at ∼6 GPa to a mixture of a disordered ambient pressure phase and a new high pressure phase. The new phase resembles the triclinic mixed-valence phase of uranium orthophosphate (U(UO₂)(PO₄)₂). On release of pressure the initial phase is not retrieved.     

可见光响应的Co3(PO4)2/Ag3PO4纳米复合光催化剂的制备及表征

采用简单的化学偏聚法合成出Ag₃PO₄纳米颗粒、磷酸钴（Co₃（PO₄）₂,CoP）纳米片以及它们两者的纳米复合结构（CoP/Ag₃PO₄）,同时还比较了它们的可见光催化活性. 采用场发射扫描电镜（FESEM）、X 射线衍射（XRD）、紫外-可见（UV-Vis）吸收光谱以及光致发光谱等手段对其形貌、结构、光学以及可见光催化性能等进行表征. 结果表明,CoP/Ag₃PO₄复合纳米结构的可见光降解甲基橙（MO）的速率和循环稳定性均明显优于其它两种物质. 这表明CoP应该起着共催化剂的作用,它能够抑制光生电子与空穴之间的复合,并且提供大量高活性的光生空穴. 此外,我们还发现CoP/Ag₃PO₄降解另一种阳离子型染料——罗丹明B（RhB）的能力则远不如纯Ag₃PO₄,这可能是与光催化剂的表面性质发生改变有关,造成更低的RhB吸附能力. 本文提供了一种廉价制备高效可见光催化剂的新方法.     

LnSrScO4 (Ln=La, Ce, Pr, Nd and Sm) systems and structure correlations for A2BO4 (K2NiF4) structure types

The compounds LnSrScO₄, where Ln=La, Ce, Pr, Nd and Sm, have been synthesized. Rietveld profile analysis of powder X-ray diffraction data collected at room temperature reveal that the compounds possess a modified K₂NiF₄-type structure with orthorhombic cell symmetry formed by tilting of the ScO₆ octahedra. Variable temperature (25-1200 °C) powder X-ray diffraction data show that at the highest temperatures the structures of LaSrScO₄ and PrSrScO₄ transform to the regular tetragonal K₂NiF₄-structure type but the degree of orthorhombicity (c/a) in the unit cells initially increases on heating for all materials, reaching a maximum near 300 °C. This structural behavior is analyzed in terms of relative ionic radii of the various lanthanides and scandium. A general structural model based on tolerance factors has been developed for the family of materials A₂BO₄ with various A and B cation sizes.     

Raman spectroscopic study of K3H(SO4)2 (phases I and II) single crystals

A Raman study of K₃H(SO₄)₂ as a function of temperature reveals that this compound undergoes a phase transition at T_c = 483 K prior to the decomposition at 508 K.     

Cr2(WO4)3和Cr2(MoO4)3的负热膨胀特性研究

用液相反应-前驱物烧结法制备了Cr₂(WO₄)₃和Cr₂(MoO₄)₃粉体。298～1 073 K的原位粉末X射线衍射数据表明Cr₂(WO₄)₃和Cr₂(MoO₄)₃的晶胞体积随温度的升高而增大, 本征线热膨胀系数分别为(1.274±0.003)×10^-6 K^-1和(1.612±0.003)×10^-6 K^-1。用热膨胀仪研究了Cr₂(WO₄)₃和Cr₂(MoO₄)₃在静态空气中298～1 073 K范围内热膨胀行为，即开始表现为正热膨胀，随后在相转变点达到最大值，最后表现为负热膨胀，其负热膨胀系数分别为(-7.033±0.014)×10^-6 K^-1和(-9.282±0.019)×10^-6 K^-1。     

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.     

Li3V2(PO4)3的溶胶-凝胶合成及其性能研究

以LiOH·H₂O(LiF、Li₂CO₃、LiCH₃COO·2H₂O)、NH₄VO₃、H₃PO₄和柠檬酸为原料,采用Sol-gel法合成锂离子电池正极材料Li₃V₂(PO₄)₃。优化了锂源、溶胶的pH值、预烧条件、煅烧温度等合成条件,并采用XRD、SEM、恒电流充放电及循环伏安试验等方法,研究了所合成的Li₃V₂(PO₄)₃的结构形貌和电化学性能。结果表明,以LiOH·H₂O为锂源,溶胶的pH值等于3,于氩气氢气(体积比9∶1)混合气中300 ℃预烧 4 h,并在氩气氢气(体积比9∶1)混合气中600 ℃煅烧8 h合成的Li₃V₂(PO₄)₃正极材料为标准的单斜结构,具有较高的放电比容量和较好的循环稳定性,0.1C和1C倍率下首次放电比容量分别为130 mAh·g^-1和129 mAh·g^-1;1C倍率下循环40次后,容量仍为127 mAh·g^-1,容量保持率为98.4%;随后又进行10C倍率放电,10次循环后容量为105 mAh·g^-1,容量保有率达98.1%。循环伏安测试表明,该正极材料具有较好的电化学可逆性。     

三维花状Fe_2(MoO_4)_3微米球的水热制备及电化学性能

以Fe Cl3·7H2O和Na2Mo O4为原料,采用水热合成法制备三维花状Fe2(Mo O4)3微米球。探讨不同合成温度对样品形貌的影响,利用XRD、SEM和EDS等分析技术对样品的结构、形貌进行了表征,对该材料的电化学性能进行了测试。结果表明:Fe2(Mo O4)3微米球是由二维纳米片自组装而成的花状结构,合成温度为160℃时,制备的样品具有良好的电化学性能,当电流密度为100 m A·g-1,首次放电比容量为1 431 m Ah·g-1;并具有较好的循环性能和倍率性能。并对160℃合成样品表现较好电化学性能的原因进行了探讨。     

Vibrational spectra of the peroxotantalates (NH4)3[Ta(O2)4], K3[Ta(O2)4], Rb3[Ta(O2)4] and Cs3[Ta(O2)4] and the crystal structure of Rb3[Ta(O2)4]

The compounds (NH₄)₃[Ta(O₂)₄], K₃[Ta(O₂)₄], Rb₃[Ta(O₂)₄] and Cs₃[Ta(O₂)₄] have been prepared and investigated by X-ray powder methods as well as Raman- and IR-spectroscopy. In the case of Rb₃[Ta(O₂)₄] the structure has been solved from single crystal data. It is shown that all these compounds are isotypic and crystallize in the K₃[Cr(O₂)₄] type (SG , No. 121). The infrared- and Raman spectra (recorded on powdered samples) are discussed with respect to the internal vibrations of the peroxo-group and the dodecahedral [Ta(O₂)₄]³⁻ ion. Symmetry coordinates for the [Ta(O₂)₄]³⁻ ion are given from which the vibrational modes of the O-O stretching vibrations of the O₂²⁻ groups, the Ta-O stretching vibrations and the Ta-O bending vibrations are deduced.     

K2Mo4O13 phases prepared by hydrothermal synthesis

Hydrothermal synthesis in the K-Mo oxide system was investigated as a function of the pH of the reaction medium. Four compounds were formed, including two K₂Mo₄O₁₃ phases. One is a new low-temperature polymorph, which crystallizes in the orthorhombic, space group Pbca, with Z=8 and unit cell dimensions a=7.544(1) Å, b=15.394(2) Å, c=18.568(3) Å. The other is the known triclinic K₂Mo₄O₁₃, whose structure was re-determined from single crystal data; its cell parameters were determined as a=7.976(2) Å, b=8.345(2) Å, c=10.017(2) Å, α=107.104(3)°, β=102.885(3)°, γ=109.760(3)°, which are the standard settings of the crystal lattice. The orthorhombic phase converts endothermically into triclinic phase at ca. 730 K with a heat of transition of 8.31 kJ/mol.     

Synthesis, crystal structure, spectrum properties, and electronic structure of a novel non-centrosymmetric borate, BiCd3(AlO)3(BO3)4

A novel non-centrosymmetric borate, BiCd₃(AlO)₃(BO₃)₄, has been prepared by solid state reaction methods below 750 °C. Single-crystal XRD analysis showed that it crystallizes in the hexagonal group P6₃ with a=10.3919(15) Å, c=5.7215(11) Å, Z=2. In its structure, AlO₆ octahedra share edges to form 1D chains that are bridged by BO₃ groups through sharing O atoms to form the 3D framework. The 3D framework affords two kinds of channels that are occupied by Bi³⁺/Cd²⁺ atoms only or by Bi³⁺/Cd²⁺ atoms together with BO₃ groups. The IR spectrum further confirmed the presence of BO₃ groups. Second-harmonic-generation measurements displayed a response of about 0.5×KDP (KH₂PO₄). UV-vis diffuse reflectance spectrum showed a band gap of about 3.19 eV. Solid-state fluorescence spectrum exhibited the maximum emission peak at around 390.6 nm. Band structure calculations indicated that it is an indirect semiconductor.     

Syntheses and characterization of two oxoborates, (Pb3O)2(BO3)2MO4 (M=Cr, Mo)

Two oxoborates, (Pb₃O)₂(BO₃)₂MO₄ (M=Cr, Mo), have been prepared by solid-state reactions below 700 °C. Single-crystal XRD analyses showed that the Cr compound crystallizes in the orthorhombic group Pnma with a=6.4160(13) Å, b=11.635(2) Å, c=18.164(4) Å, Z=4 and the Mo analog in the group Cmcm with a=18.446(4) Å, b=6.3557(13) Å, c=11.657(2) Å, Z=4. Both compounds are characterized by one-dimensional chains formed by corner-sharing OPb₄ tetrahedra. BO₃ and CrO₄ (MoO₄) groups are located around the chains to hold them together via Pb–O bonds. The IR spectra further confirmed the presence of BO₃ groups in both structures and UV–vis diffuse reflectance spectra showed band gaps of about 1.8 and 2.9 eV for the Cr and Mo compounds, respectively. Band structure calculations indicated that (Pb₃O)₂(BO₃)₂MoO₄ is a direct semiconductor with the calculated energy gap of about 2.4 eV.     

真空辅助法合成Fe_3(PO_4)_2·8H_2O及对LiFePO_4/C结构、形貌和电化学性能的影响(英文)

采用了一种真空辅助沉淀法制备Fe3(PO4)2·8H2O,并以此进一步合成粒径尺寸在400 nm左右LiFePO4颗粒.研究了Fe3(PO4)2·8H2O对于磷酸铁锂的形貌、结构、电化学性能的影响.X射线衍射(XRD)结果表明,真空辅助制备的Fe3(PO4)2·8H2O具有高纯度,以此制备的LiFePO4具有高结晶度和纯度.扫描电子显微镜(SEM)结果表明,真空辅助制备的Fe3(PO4)2·8H2O具有未完全发育的颗粒,以此制备的LiFePO4均匀无硬团聚.透射电子显微镜(TEM)结果显示真空辅助制备的LiFePO4包覆一层均匀的碳.真空制备的LiFePO4显示了优异的电化学性能,在1C、10C、20C倍率下的容量分别为140、113、100 mAh·g-1.真空制备的LiFePO4的循环伏安曲线显示了小的极化电压和尖锐的氧化峰.充放电平台曲线表明真空对LiFePO4高倍率性能起到重要作用.电化学阻抗谱(EIS)计算结果显示,真空和非真空制备的LiFePO4的锂离子扩散系数分别为1.42×10-13和4.22×10-14cm2·s-1,说明真空辅助能够提高LiFePO4的扩散系数.