New [K2NiF4] compounds with mixed B-ions

The synthesis and characterization of new [K₂NiF₄]-type compounds is described. New tolerance factors for this structure are given, and the lack of ordering is discussed.     

Plane,zu ketten verknüpfte [Te5]6−-anionen im K2SnTe5

The new compound K₂SnTe₅ crystallizes in the tetragonal system (space group: 14cm, Nr. 108) with a = 848.1(3) pm, c = 1536.9(7) pm, $\text{c}\text{a}\text{= 1.812}$, z = 4. In the structure there are plane [Te₅]^6?-anions, which are connected to chains by tetrahedrally coordinated Sn-atoms.     

Preparation and some properties of K2NiF4 type Eu(II) vanadites

Europium vanadites, containing bi-valent europium, were synthesized by reacting Eu₂O₃, V₂O₃ and V. The vanadites obtained were EuO·EuVO₃ and EuO·2EuVO₃. The crystal structures and some physical properties of these compounds were studied.     

[H(4,4''''-bpy)]2[K2Mo8O26]的水热合成和结构研究

采用水热法合成了[H(4,4'-bpy)]2[K2Mo8O26],X-ray单晶结构解析表明该化合物属三斜晶系,空间群P-1,晶胞参数a=0.78029(8)nm,b=0.98715(8)nm,c=1.32438(6)nm,α=99.383(3),β=102.0600(19),γ=108.090(2),β-[Mo8O26]单元通过部分端氧原子与K原子相连成层状,4,4'-联吡啶中质子化的N原子与非质子化的N原子通过氢键联成链状,链与链之间通过π-π堆垛成层状结构.     

Preparation, characterization and luminescence of La2TeO6 phosphor doped with Eu

Phosphors of La₂TeO₆ doped with Eu³⁺ ions have been synthesized by the oxidation of the corresponding rare-earths oxytellurides of formula La_2−xEu_xO₂Te (x = 0.02, 0.06, and 0.1) at 1050 K. Powder X-ray diffraction confirms that the as prepared materials consist of the orthorhombic La₂TeO₆ as main phase. The photoluminescence (PL) of red-emitting La_2−xEu_xTeO₆ powder phosphors is reported. The emission spectrum, exhibits an intense emission peak due to ⁵D₀ → ⁷F₂ transition at 616 nm, which indicates that the Eu³⁺ ion occupies a non-centrosymmetric site in the host lattice. These materials could find application for use as lamp phosphors in the red region.     

Crystal structure of K4[H2J2O10].8H20

Crystals of K₄ [H₂J₂O₁₀] 8H₂O belong to the triclinic system, space group P 1 with a = 7.161 (2) $\text{A}\text{?}\text{, b}\text{= 10,553}$ (5) $\text{A}\text{?}\text{, c}\text{= 7,081}$ (2) $\text{A}\text{?}\text{, α = 98°1′}$, β = 117°8′, γ = 90°6′ and Z = 1. The crystal structure has been determined on the basis of photographic data from 877 independent reflections, with the final R value of 6,6%. The iodine atoms are surrounded by a distorted octahedra consisting of five oxygen atoms and one OH group. The average J-O distance is 2.03 Å. There are 2 independent K atoms in the structure. K(1) has a coordination number of eight, while K(2) is surrounded by 6 (5 water molecules + one OH group) nearest neighbours.     

Syntheses of hollandite type Rb2Cr8O16, K2Cr2V6O16 and K2V8O16

Hollandite-type compounds, Rb₂Cr₈O₁₆, K₂Cr₂V₆O₁₆ and K₂V₈O₁₆, were synthesized under high P-T conditions up to 1200°C and 7GPa. The structural refinement using a single crystal of Rb₂Cr₈O₁₆ confirms that the structure is similar to that of K₂Cr₈O₁₆. Magnetic measurements indicate that Rb₂Cr₈O₁₆ is ferromagnetic below 295K, K₂Cr₂V₆O₁₆ paramagnetic down to 77K and K₂V₈O₁₆ has susceptibility anomaly at 175K. These compounds are all semiconductive and show discontinuities in temperature-resistivity curves at points corresponding to magnetic anomalies.     

New arsenates (V) NaKAl2O[AsO4]2 and Na2KAl3[AsO4]4

The title compounds have been synthesized by a solid state reaction route using a salt flux. Their crystal structures were determined from single crystal X-ray data. NaKAl₂O[AsO₄]₂ crystallizes with the orthorhombic K₂Fe₂O[AsO₄]₂-type, Pnma, a = 8.2368(6) Å, b = 5.5228(3) Å, c = 17.0160(13) Å and Z = 4, whereas Na₂KAl₃[AsO₄]₄ crystallizes with the orthorhombic K₃Fe₃[AsO₄]₄-type, Cmce, a = 10.5049(9), b = 20.482(2), c = 6.3574(6) Å and Z = 4. The NaKAl₂O[AsO₄]₂ structure is built up of [Al₂As₂O₉]²⁻ layers perpendicular to the c-axis which are separated by A⁺ alkali layers. The [Al₂As₂O₉]²⁻ layers consist of ribbons of edge-sharing AlO₆ octahedra, running along the a direction and which are connected through AsO₄ tetrahedra by sharing corners. The Na₂KAl₃[AsO₄]₄ structure contains [Al₃As₄O₁₆]³⁻ layers perpendicular to the b-axis separated by A⁺ alkali layers. The [Al₃As₄O₁₆]³⁻ layer consists of a layer of corner-sharing AlO₆ octahedra which are also connected to the AsO₄ tetrahedra by sharing corners.     

Nd2[MoC2] and RE2[WC2], RE=Ce, Pr, Nd: New carbometalates with Pr2[MoC2] structure type

Four new ternary rare-earth-metal carbometalates, Nd₂[MoC₂] and RE₂[WC₂] with RE=Ce, Pr, Nd, have been synthesized by argon arc melting and subsequent heat treatment at 1170 K for 30 days. They crystallize with the Pr₂[MoC₂] structure type with isolated C⁴⁻ species and are typical carbometalates with (i) low metal-to-carbon ratio, (ii) tetrahedral coordination of the transition metals (T) by carbon, and (iii) a polyanionic network . According to resistivity measurements the compounds are bad metals. Volume chemistry and magnetic susceptibility measurements indicate Pr³⁺, Nd³⁺, and Ce⁴⁺ species, respectively. In the latter case, the additional electron is not transferred to the polyanionic network, instead it mainly populates the Ce partial structure.     

Seebeck coefficient of K2SO4

The thermopotential of the cell (SO₂+O₂), Pt/K₂SO₄/Pt, (SO₂+O₂)′ was measured, and a Seebeck coefficient of 1.6 mV/°C was obtained. This value is higher than that of most salts that have been measured to date. The high Seebeck coefficient has implications in the use of the cell in SO₂ gas measurements.     

K2(Rb2,Cs2,Tl2)TeBr6(I6) and Rb3(Cs3)Sb2(Bi2)Br9(I9) perovskite compounds

We systematize available experimental data on the crystal structure of the ternary halides K₂(Rb₂,Cs₂,Tl₂)TeBr₆(I₆) and Rb₃(Cs₃)Sb₂(Bi₂)Br₉(I₉), analyze the general trends in the properties of their single crystals, and examine the key features of the physicochemical interaction in related systems.     

Crystal structure of KCP (K2[Pt (CN)4]Br0.3 · 3 H2O) at 90 K

We have investigated the crystal structure of KCP at 90 K using single crystal methods. The Pt-Pt distances within a chain are equal only within the limits of three standard deviations, but show a strongly anisotropic thermal vibration with a preferred motion parallel to the c-axis. The center of the KCP structure is fully occupied, either by Br or by water.     

Ionic conductivities of Na2Ti3O7, K2Ti4O9 and their related materials

Ionic conductivities were measured on the polycrystalline samples of layered titanates, Na₂Ti₃O₇ and K₂Ti₄O₉, and their derivatives. The activation energies and the prefactors of the conductions were 0.70 eV and 7.9 × 10 (Ωcm)^?1K for Na₂Ti₃O₇ and 0.81 eB and 1.1 × 10³ (Ωcm)^?1K for K₂Ti₄O₉. A small amount of Nb₂O₅ was doped to these titanates substituting TiO₂. Remarkable enhancements of ionic conductivities were observed with the doping. A new metastable phase, Li₂Ti₃O₇, was prepared by ion-exchange of Na₂Ti₃O₇ and its ionic conductivity was measured.     

A TSC investigation of K2ZnF4 and KZnF3

Thermal stimulated polarization (TSP) and depolarization (TSD) currents with two specific peaks were obtained in insulated undoped and trivalent cation doped K₂ZnF₄ and undoped KZnF₃. It is shown that the high temperature peaks are caused by a surface polarization by point defects, the low temperature peaks in doped samples by defect-impurity complex reorientation. Basing on the data, the parameters of the charge transport and the defect order are discussed.     

Crystal growth and structure determinations of potassium hafnates: K2Hf2O5 and K4Hf5O12

Crystals of K₂Hf₂O₅ and K₄Hf₅O₁₂ were grown from molten potassium hydroxide flux. The crystal structures were determined by single-crystal X-ray diffraction. K₂Hf₂O₅ crystallizes in the space group Pnna of the orthorhombic system, with unit cell dimensions of a = 5.780(1) Å, b = 10.640(2) Å, and c = 8.666(2) Å. This compound contains infinite chains of HfO₆ octahedra that form a channel structure. K₄Hf₅O₁₂ crystallizes in the space group of the trigonal system, with unit cell dimensions of a = 5.7877(2) Å and c = 10.3693(7) Å. This compound possesses a layered structure with six-coordinate Hf in three different coordination environments (trigonal prismatic, distorted octahedral, and regular octahedral).     

TiO2/Bi2WO6复合光催化剂的制备及光催化性能研究

TiO₂/Bi₂WO₆异质结是当前最具潜力的一种可见光响应半导体光催化剂。以富含缺陷的TiO2纳米带为基体,采用水热法,诱导Bi2WO6在基体缺陷位点进行异质生长,从而合成具有异质结构的TiO₂/Bi₂WO₆复合材料。利用XRD、SEM、UV-Vis等技术,分析了基体表面缺陷、Bi2WO6负载量对TiO₂/Bi₂WO₆复合材料微观结构和性能的影响。结果表明,在基体表面引入缺陷,可以使TiO₂/Bi₂WO₆复合材料在可见光下对有机污染物Rh B的降解速率提高约50%。Bi2WO6负载量为0.12时的TiO₂/Bi₂WO₆复合材料,在可见光下,辐照6 min后对Rh B的降解率达99.3%,辐照30 min后对MB的降解率达99.7%,辐照15 min后对TC-HCl的降解率达87.7%。     

SiO2 / 杉木粉复合材料的制备和表征

以人工林杉木粉为原料和正硅酸乙酯( TEOS) 为无机前驱体, 依据溶剂热法反应原理, 采用溶胶凝胶的方法制备了SiO₂ / 木材复合材料。通过红外光谱分析( FTIR) 、X射线衍射分析(XRD) 、热失重分析( TGA) 、扫描电子显微镜分析(SEM) 等方法, 研究了该复合材料的结构和性能。研究结果表明, 使用这种方法, 木材的增重率显著提高。木材中的羟基与正硅酸乙酯水解后的羟基发生了缩合反应, 体系中存在Si —O —C 交联网络, 微观上形成了纳米网络结构。木质纤维素的结晶被破坏, 结晶度从75. 37 %(纯木粉) 下降到37. 42 %(木材增重率为78 %的复合体系) 。交联网络的形成显著提高了该材料的耐热性能, 使失重10 %时的热分解温度从270 ℃(纯木粉) 提高到409 ℃。      

New palladium phosphate complexes: K2PdP2O7 and K3.5Pd2.25(P2O7)2 synthesis, single crystal structure and conductivity

Two new diphosphate complexes containing potassium and palladium, K₂PdP₂O₇ and K_3.5Pd_2.25(P₂O₇)₂, have been synthesized and characterized by single crystal X-ray diffraction. K₂PdP₂O₇ exists with layers formed of linked PdP₂O₇ polyhedra, between which are found the potassium ions. K_3.5Pd_2.25(P₂O₇)₂ with a Pd/P₂O₇ ratio of 1.125:1 crystallizes with tunnels of various sizes in which are found the potassium ions. Conductivity measurements reveal the material to be conducting.     

Superstructure of potassium selenate K2SeO4

Structural phase changes in K₂SeO₄ are studied by using a low-temperature X-ray diffraction technique. As shown by Aiki et al. the phase changes occur at 129.5 K (T_M) from the room-temperature phase to the M phase and at 93 K (T_C) from the M to the Ferro phases. A superstructure along the a axis is observed both in the M and Ferro phases with a period three times as long as that at room temperature. The space group is determined to be Pnam or Pna2₁ in the M phase, while in the Ferro phase non-centrosymmetric Pna2₁ is unique. The superstructure is attributed to rather small, atomic displacements parallel to the a plane. The following lattice constants at room temperature (302±1 K) are determined from back-reflection Weissenberg photographs: a₀ = 7.6479±2, b₀ = 10.4656±4 and $\text{c}{}_0\text{= 5.9963±2}\text{A}\text{?}$.     

Preparation, characterization and luminescence of a new green-emitting phosphor: Gd2TeO6 doped with Tb

Novel green-emitting Gd_2 − xTb_xTeO₆ powder phosphor has been prepared by the oxidation of corresponding rare-earth oxytellurides. The photoluminescence (PL) properties were reported. Five dominant bands centered at 302 nm, 318 nm, 339 nm, 353 nm and 378 nm characterize the excitation spectrum. Under the excitation of 378 nm UV light, the emission spectrum exhibits an intense peak centered at 543-548 nm corresponding to the ⁵D₄ → ⁷F₅ transition of Tb³⁺. This phosphor can be excited by light with wavelengths of 350-400 nm and therefore can be used as a green phosphor for white lighting devices utilizing near-UV LED as a light source.