Pressure-induced phase transitions in Al2(WO4)3

The high pressure behavior of aluminum tungstate [Al₂(WO₄)₃] has been investigated up to ∼18 GPa with the help of Raman scattering studies. Our results confirm the recent observations of two reversible phase transitions below 3 GPa. In addition, we find that this compound undergoes two more phase transitions at ∼5.3 and ∼6 GPa before transforming irreversibly to an amorphous phase at ∼14 GPa.     

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.     

Pressure-induced amorphization in Y2(WO4)3: in situ X-ray diffraction and Raman studies

The high-pressure behavior of Y₂(WO₄)₃ has been investigated at room temperature by in situ X-ray diffraction and Raman scattering measurements. Both the studies show that beyond ∼3 GPa, this compound smoothly transforms from the ambient orthorhombic phase to a disordered phase. The structural modifications are found to be reversible up to ∼4 GPa but become irreversible at higher pressures. Low pressures of transformation imply that these changes are intrinsic and not due to non-hydrostatic stresses. In addition, the correlation between the stability range of orthorhombic phase and counter cation size supports that this compound has a large field of negative thermal expansion in this family of compounds.     

Synthesis, crystal structure, infrared and Raman spectra of Sr4Cu3(AsO4)2(AsO3OH)4·3H2O and Ba2Cu4(AsO4)2(AsO3OH)3

The two new compounds, Sr₄Cu₃(AsO₄)₂(AsO₃OH)₄·3H₂O (1) and Ba₂Cu₄(AsO₄)₂(AsO₃OH)₃(2), were synthesized under hydrothermal conditions. They represent previously unknown structure types and are the first compounds synthesized in the systems SrO/BaO-CuO-As₂O₅-H₂O. Their crystal structures were determined by single-crystal X-ray diffraction [space group C2/c, a=18.536(4) Å, b=5.179(1) Å, c=24.898(5) Å, β=93.67(3)°, V=2344.0(8) Å³, Z=4 for 1; space group P4₂/n, a=7.775(1) Å, c=13.698(3) Å, V=828.1(2) Å³, Z=2 for 2]. The crystal structure of 1 is related to a group of compounds formed by Cu²⁺-(XO₄)³⁻ layers (X=P⁵⁺, As⁵⁺) linked by M cations (M=alkali, alkaline earth, Pb²⁺, or Ag⁺) and partly by hydrogen bonds. In 1, worth mentioning is the very short hydrogen bond length, D···A=2.477(3) Å. It is one of the examples of extremely short hydrogen bonds, where the donor and acceptor are crystallographically different. Compound 2 represents a layered structure consisting of Cu₂O₈ centrosymmetric dimers crosslinked by As1φ₄ tetrahedra, where φ is O or OH, which are interconnected by Ba, As2 and hydrogen bonds to form a three-dimensional network. The layers are formed by Cu₂O₈ centrosymmetric dimers of CuO₅ edge-sharing polyhedra, crosslinked by As1O₄ tetrahedra. Vibrational spectra (FTIR and Raman) of both compounds are described. The spectroscopic manifestation of the very short hydrogen bond in 1, and ABC-like spectra in 2 were discussed.     

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。     

Ti(NMe2)4-catalyzed Markovnikov hydroamination of alkynes in the presence of N-heterocyclic carbenes and LiN(SiMe3)2

Intermolecular hydroamination of alkynes catalyzed by Ti(NMe₂)₄ was much improved with N-heterocyclic carbenes and LiN(SiMe₃)₂, by which high Markovnikov selectivity was attained for the coupling of nearly all alkynes and amines.     

Spectroscopic properties of guanidinium zinc sulphate [C(NH2)3]2Zn(SO4)2 and ab initio calculations of [C(NH2)3]2 and HC(NH2)3

Raman and FTIR spectra of guanidinium zinc sulphate [C(NH₂)₃]₂Zn(SO₄)₂ are recorded and the spectral bands assignment is carried out in terms of the fundamental modes of vibration of the guanidinium cations and sulphate anions. The analysis of the spectrum reveals distorted SO₄²⁻ tetrahedra with distinct S–O bonds. The distortion of the sulphate tetrahedra is attributed to Zn–O–S–O–Zn bridging in the structure as well as hydrogen bonding. The CN₃ group is planar which is expressed in the twofold symmetry along the C–N (1) vector. Spectral studies also reveal the presence of hydrogen bonds in the sample. The vibrational frequencies of [C(NH₂)₃]₂ and HC(NH₂)₃ are computed using Gaussian 03 with HF/6-31G* as basis set.     

Synthesis and nonlinear optical properties of BaTi(BO3)2 and Ba3Ti3O6(BO3)2 crystals in glasses with high TiO2 contents

The ternary BaO-TiO₂-B₂O₃ glasses containing a large amount of TiO₂ (20-40 mol%) are prepared, and their optical basicities (Λ), the formation, structural features and second-order optical nonlinearities of BaTi(BO₃)₂ and Ba₃Ti₃O₆(BO₃)₂ crystals are examined to develop new nonlinear optical materials. It is found that the glasses with high TiO₂ contents of 30-40 mol% show large optical basicities of Λ=0.81-0.87, suggesting the high polarizabity of TiO_n polyhedra (n=4-6) in the glasses. BaTi(BO₃)₂ and Ba₃Ti₃O₆(BO₃)₂ crystals are found to be formed as main crystalline phases in the glasses. It is found that BaTi(BO₃)₂ crystals tend to orient at the surface of crystallized glasses. The new XRD pattern for the Ba₃Ti₃O₆(BO₃)₂ phase is proposed through Rietvelt analysis. The second harmonic intensities of crystallized glasses were found to be 0.8 times as large as α-quartz powders, i.e., I^2ω(sample)/I^2ω(α-quartz)=0.8, for the sample with BaTi(BO₃)₂ crystals and to be I^2ω(sample)/I^2ω(α-quartz)=68 for the sample with Ba₃Ti₃O₆(BO₃)₂ crystals. The Raman scattering spectra for these two crystalline phases are measured for the first time and their structural features are discussed.     

Preparation of a highly active nanocrystalline TiO2 photocatalyst from titanium oxo cluster precursor

Nanocrystalline TiO₂ (sample S1) was prepared from a titanium oxo cluster (Ti₇O₄(OEt)₂₀) precursor via a sol-gel route. This photocatalyst showed a higher photocatalytic activity than the TiO₂ (sample S2) obtained from titanium tetraisopropoxide. The samples were characterized by thermal analysis (TGA/DSC), X-ray diffraction, micro-Raman spectroscopy, transmission electron microscopy, N₂ adsorption (BET surface area), infrared absorption spectroscopy (FT-IR) and X-ray photoelectron spectroscopy. The characterization results show that both samples are anatase nanocrystals with particle sizes of about 12 nm, but the more photocatalytically active sample S1 has more surface hydroxyl groups and larger surface area and pore volume than sample S2.     

Non-centrosymmetric Ba3Ti3O6(BO3)2

The compound previously reported as Ba₂Ti₂B₂O₉ has been reformulated as Ba₃Ti₃B₂O₁₂, or Ba₃Ti₃O₆(BO₃)₂, a new barium titanium oxoborate. Small single crystals have been recovered from a melt with a composition of BaTiO₃:BaTiB₂O₆ (molar ratio) cooled between 1100°C and 850°C. The crystal structure has been determined by X-ray diffraction: hexagonal system, non-centrosymmetric space group, a=8.7377(11) Å, c=3.9147(8) Å, Z=1, wR(F²)=0.039 for 504 unique reflections. Ba₃Ti₃O₆(BO₃)₂ is isostructural with K₃Ta₃O₆(BO₃)₂. Preliminary measurements of nonlinear optical properties on microcrystalline samples show that the second harmonic generation efficiency of Ba₃Ti₃O₆(BO₃)₂ is equal to 95% of that of LiNbO₃.     

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.     

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.     

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.     

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.     

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.     

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.     

Ni-P-Zn3(PO4)2(ZnSnO3、ZnSiO3)纳米复合化学镀层性质和组成的研究

研究了温度、时间、浓度等对Ａ３钢片上Ｎi-P-Zn3(PO4)2、Ni-P-ZnSnO3和Ｎi-P-ZiSiO3纳米复合合化学镀层外貌的影响,用扫描电子显微镜（ＳＥＭ）观察外貌、称重法测定厚度;通过１０％ＮaCl溶液、１％Ｈ２Ｓ气体加速腐蚀试验,１０％ＣuSO4溶液点滴试验等多种手段测定其耐腐蚀性能,用Ｘ－射线光电子谱（ＸＰＳ）及俄歇电子能谱（ＳＥＳ）测定其价态组成,结果表明：在最佳施镀条件下,可得光亮、致密、耐腐蚀性强于Ａ３钢、磷化膜及Ｎi-P镀层的纳米复合化学镀层,镀层的原子百分组成约为（％）：Ｎi-P-Zn3(PO4)2:Ni70.00,P12.47,Zn3(PO4)213.93,C3.6;Ni-P-ZnSnO3;Ni77.56,P10.00,ZnSnO39.84,C2.6;Ni-P-NiSiO3,Ni83.00,P10.96,ZnSi5.15,C0.89.     

Calorimetric study and thermal analysis of [Gd4/3Y2/3(Gly)6(H2O)4](ClO4)6·5H2O and [ErY(Gly)6(H2O)4](ClO4)6·5H2O (Gly: glycin)

Two solid-state coordination compounds of rare earth metals with glycin, [Gd_4/3Y_2/3(Gly)₆(H₂O)₄](ClO₄)₆·5H₂O and [ErY(Gly)₆(H₂O)₄](ClO₄)₆·5H₂O were synthesized. The low-temperature heat capacities of the two coordination compounds were measured with an adiabatic calorimeter over the temperature range from 78 to 376 K. [Gd_4/3Y_2/3(Gly)₆(H₂O)₄](ClO₄)₆·5H₂O melted at 342.90 K, while [ErY(Gly)₆(H₂O)₄](ClO₄)₆·5H₂O melted at 328.79 K. The molar enthalpy and entropy of fusion for the two coordination compounds were determined to be 18.48 kJ mol⁻¹ and 53.9 J K⁻¹ mol⁻¹ for [Gd_4/3Y_2/3(Gly)₆(H₂O)₄](ClO₄)₆·5H₂O, 1.82 kJ mol⁻¹ and 5.5 J K⁻¹ mol⁻¹ for [ErY(Gly)₆(H₂O)₄](ClO₄)₆·5H₂O, respectively. Thermal decompositions of the two coordination compounds were studied through the thermogravimetry (TG). Possible mechanisms of the decompositions are discussed.     

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.     

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。