Die Reaktion von Tellurhexafluorid mit Trimethylamin,Strukturen der TeF5−- und SeF5−-Anionen

Reaction of Telluriumhexafluoride and Trimethylamine, Structures of the TeF₅^? and SeF₅^? Anions The reaction of TeF₆ and (CH₃)₃N is of the redox kind, resulting in reduction of tellurium: X-ray single crystal analysis reveals the compounds (CH₃)₂N? CH₂? N(CH₃)₂⁺TeF₅^? and [(CH₃)₃NH⁺]₅(TeF₅^?)₃(HF₂^?)₂. By comparison with published data it can be shown that this mixture is identical to previously published [(CH₃)₃N]₂TeF₆. The latter was supposed to be one of the few examples of tellurium in a coordination state of eight. (CH₃)₄N⁺TeF₅^? and (CH₃)₄N⁴SeF₅^? are obtained and their structure is investigated by single crystal x-ray methods also. The anions SF₅^?, SeF₅^? and TeF₅^? are discussed in terms of weak interactions.     

Activation Energy for Electroconduction of Aqueous Solutions of Sulfuric and Selenic Acids and Potassium Tellurate

The temperature and concentration dependences of the electroconductivity of aqueous solutions of sulfuric and selenic acids and potassium tellurate are studied. Coefficients of empirical equations that describe these dependences are determined. Activation energies for electroconduction of these solutions as a function of concentration are calculated and it is assumed that these are linked with the hydration degree of ions and the destruction of the quasi-crystalline tetrahedral water cage.     

Raman spectroscopic study of the metatellurate mineral: xocomecatlite Cu3TeO4(OH)4

The mineral xocomecatlite is a hydroxy metatellurate mineral with Te⁶⁺ O₄ units. Tellurates may be subdivided according to their formula into three types of tellurate minerals: type (a) (AB)_m (TeO₄)_pZ_q, type (b) (AB)_m(TeO₆)^·xH₂O and (c) compound tellurates in which a second anion including the tellurite anion, is involved. The mineral xocomecatlite is an example of the first type. Raman bands for xocomecatlite at 710, 763 and 796 cm⁻¹, and 600 and 680 cm⁻¹ are attributed to the ν₁(TeO₄)²⁻ symmetric and ν₃ antisymmetric stretching mode. Raman bands observed at 2867 and 2926 cm⁻¹ are assigned to TeOH stretching vibrations and enable estimation of the hydrogen bond distances of 2.622 Å (2867 cm⁻¹), 2.634 Å (2926 cm⁻¹) involving these OH units. The hydrogen bond distances are very short implying that they are necessary for the stability of the mineral. Copyright © 2008 John Wiley & Sons, Ltd.     

Structural and conductivity studies of CsKSO4Te(OH)6 and Rb1.25K0.75SO4Te(OH)6 materials

The crystal structures of the title compounds were solved using the single-crystal X-ray diffraction technique. At room temperature CsKSO₄Te(OH)₆ was found to crystallize in the monoclinic system with Pn space group and lattice parameters: ; ; ; β=106.53(2)°; ; Z=4 and . The structural refinement has led to a reliability factor of R₁=0.0284 (wR₂=0.064) for 7577 independent reflections. Rb_1.25K_0.75SO₄Te(OH)₆ material possesses a monoclinic structure with space group P2₁/a and cell parameters: ; ; ; β=106.860(10)°; ; Z=4 and . The residuals are R₁=0.0297 and wR₂=0.0776 for 3336 independent reflections. The main interest of these structures is the presence of two different and independent anionic groups (TeO₆⁶⁻ and SO₄²⁻) in the same crystal.Complex impedance measurements (Z^*=Z^′—iZ^″) have been undertaken in the frequency and temperature ranges 20-10⁶ Hz and 400-600 K, respectively. The dielectric relaxation is studied in the complex modulus formalism M^*.     

Phase transitions and vibrational study of Rb2SeO4·Te(OH)6 and Rb1.12(NH4)0.88SO4·Te(OH)6

Calorimetry, conductivity, IR and Raman studies of the two ionic-protonic conductors Rb₂SeO₄·Te(OH)₆ (RbSeTe) and Rb_1.12(NH₄)_0.88SO₄·Te(OH)₆ (RNST) have been recorded and analyzed. These compounds crystallize in the monoclinic system, the space groups being, respectively, P2₁/c and P2₁/a for (RbSeTe) and (RNST) with four formula units in their unit cells.

The main feature of these atomic arrangements is the coexistence of two independent and different types of anions in the unit cell, connected by hydrogen bonds, which insure the cohesion of the crystalline edifice. Differential scanning calorimetry traces show three peaks for both the materials, corresponding to three phase transitions, at 430, 470 and 493 K for RbSeTe and at 418, 458 and 483?K for RNST.

A sudden surge in the temperature dependence of conductivity confirms the presence of the third transition, which is characterized by a high conductivity. The Raman spectra of these two materials were investigated in the range 295–600?K and IR spectra achieved at room temperature between 10 and 4000?cm^?1, confirm the presence of the phase transitions and show that anionic groups coexist independently in the same crystal.     

Raman spectroscopic study of the mixed anion mineral yecoraite Bi5Fe3O9(Te4+O3)(Te6+O4)2·9H2O

Tellurates are rare minerals as the tellurate anion is readily reduced to the tellurite ion. Often minerals with both tellurate and tellurite anions are found. An example of such a mineral containing tellurate and tellurite is yecoraite. Raman spectroscopy has been used to study this mineral, the exact structure of which is unknown. Two Raman bands at 796 and 808 cm⁻¹ are assigned to the ν₁(TeO₄)²⁻ symmetric and ν₃(TeO₃)²⁻ antisymmetric stretching modes and Raman bands at 699 cm⁻¹ are attributed to the ν₃(TeO₄)²⁻ antisymmetric stretching mode and the band at 690 cm⁻¹ to the ν₁(TeO₃)²⁻ symmetric stretching mode. The intense band at 465 cm⁻¹ with a shoulder at 470 cm⁻¹ is assigned the (TeO₄)²⁻ and (TeO₃)²⁻ bending modes. Prominent Raman bands are observed at 2878, 2936, 3180 and 3400 cm⁻¹. The band at 3936 cm⁻¹ appears quite distinct and the observation of multiple bands indicates the water molecules in the yecoraite structure are not equivalent. The values for the OH stretching vibrations listed provide hydrogen bond distances of 2.625 Å (2878 cm⁻¹), 2.636 Å (2936 cm⁻¹), 2.697 Å (3180 cm⁻¹) and 2.798 Å (3400 cm⁻¹). This range of hydrogen bonding contributes to the stability of the mineral. A comparison of the Raman spectra of yecoraite with that of tellurate containing minerals kuranakhite, tlapallite and xocomecatlite is made. Copyright © 2009 John Wiley & Sons, Ltd.     

2018年9期电子期刊

采用高温固相法在1 150℃下经二次煅烧合成了双钙钛矿型的红色荧光粉Sr₂ZnTeO₆∶xEu³⁺（x=0.05-0.40）,并进行了相组成、发光性质和热稳定性的研究。结果表明,所合成的Sr₂ZnTeO₆与Sr₂ZnWO₆具有相同的结构,掺杂离子的加入没有改变相结构。样品的激发光谱由电荷迁移带和Eu³⁺离子的特征激发峰组成,主激发峰位于464 nm（⁷F₀→⁵L₆）。样品的发射光谱位于614 nm（⁵D₀→⁷F₂）。Sr₂ZnTeO₆∶xEu³⁺荧光粉的发光强度随着Eu³⁺离子的掺杂,先增大后减小,在x≥0.25时,发生浓度猝灭现象。通过变温荧光发现它具有非常好的热稳定性。由于荧光粉的最佳激发位于464 nm,因而可以用于蓝光激发下的白光LED的红色荧光粉。     

Temperature and Concentration Dependence of the Electrical Conductance,Diffusion, and Kinetics Parameters of the Ions in Aqueous Solutions of Sulfuric Acid,Selenic Acid,and Potassium Tellurate

The temperature and concentration dependences of the electrical conductance of aqueous solutions of sulfuric acid, selenic acid, and potassium tellurate were studied. The coefficients of the corresponding empirical equations were determined, and the values of equivalent conductances of the anions were evaluated at infinite dilution at the experimental temperatures. The values of the coefficients in the Fuoss and Onsager equation were evaluated for the three electrolytes at 298 K. The values of the molecular and ionic coefficients of self-diffusion at infinite dilution were calculated in the temperature range 288–318 K. The change of the translational energy Δ E∘_tr. of water molecules in the ionic hydration sphere was determined. The number of water molecules participating in the ionic hydration sphere at 298 K and the changes of Gibbs free energy, enthalpy, and entropy of activation of ionic conductance were calculated. The results obtained were interpreted according to the Samoylov’s theory of positive and negative hydration of ions. The differences observed in the temperature dependences of the mentioned parameters were explained in terms of the different radii and hydration numbers of the ions.     

The local structure of gadolinium vanadate–tellurate glasses and glass ceramics: Te2V2O9 crystalline phase

Glasses in the system xGd₂O₃ · (100 − x)[0.7TeO₂ · 0.3V₂O₅] with 0 ≤ x ≤20 mol% have been prepared from melt quenching method. Influence of gadolinium ions on structural behavior in vanadate–tellurate glasses has been investigated using FTIR spectroscopy, X-ray diffraction (XRD), and magnetic susceptibility measurements. The structural changes have been analyzed with increasing rare earth concentration. The structural changes, as recognized by analyzing band shapes of XRD and FTIR spectra, revealed that Gd₂O₃ causes a higher extent of network polymerization as far as 20 mol%. The structure of the heat-treated glasses was found to consist mainly of the Te₂V₂O₉ crystalline phase. These vitreous systems were investigated by magnetic susceptibility measurements. From the paramagnetic susceptibility χ was calculated at different temperature and from the 1/χ(T) graph, the Curie temperature of the glass has been evaluated. Magnetic susceptibility data show the presence of small antiferromagnetic interactions between the Gd⁺³ ions.     

近紫外宽带激发LED用红色荧光粉(Gd_(1-x)Eu_x)6(Te_(1-y)Mo_y)O_(12)的制备与性能

利用高温固相法制备了一种新型红色荧光粉(Gd_(1-x)Eu_x)_6(Te_(1-y)Mo_y)O_(12),研究了Eu~(3+)单掺和Eu~(3+),Mo~(6+)共掺Gd_6TeO_(12)荧光粉的结构、形貌和荧光性能.实验结果表明,所合成的粉体为纯相.在393 nm近紫外光激发下,(Gd_(1-x)Eu_x)_6(Te_(1-y)Mo_y)O_(12)荧光粉发出特征红光,位于632 nm处的发射主峰属于Eu~(3+)的~5D_0→~7F_2跃迁.当Eu~(3+)掺杂浓度超过20%(物质的量分数)时发光出现浓度淬灭,经证实这是由电偶极-电偶极相互作用造成的.随着工作温度升高,荧光粉发光强度减小,计算得到Eu~(3+)热淬灭过程中的激活能为0.1796 eV.当(Gd_(0.8)Eu_(0.2))_6TeO_(12)中共掺Mo~(6+_(取代Te~(6+)),该荧光粉发射光谱的峰位、强度变化不大,但是Mo~(6+)-O~(2-)电荷迁移态显著增大了近紫外波段的激发带宽度,可以有效提高激发效率.具有近紫外宽带激发特征的(Gd_(0.8)Eu_(0.2))_6(Te_(0.6)Mo_(0.4))O_(12)是一种潜在的白光LED用荧光粉材料.