Thermoelectric Properties of (Bi2Te3)1 ? x ? y(Sb2Te3)x(Sb2Se3)y Single Crystals

Homogeneous and graded n- and p-type (Bi₂Te₃)_{1 − x − y} (Sb₂Te₃) _x (Sb₂Se₃) _y crystals are grown by the Czochralski technique with melt supply through a floating crucible. The dimensionless thermoelectric figure of merit of the n- and p-type crystals is ZT = 1.1 (350 K) and 1.0 (375 K), respectively. It is shown that (Bi₂Te₃)_{1 − x − y} (Sb₂Te₃) _x (Sb₂Se₃) _y pseudoternary solid solutions can be used to produce monolithic n- and p- type graded and segmented thermoelectric materials by Czochralski growth. The thermoelectric power distribution across the seed-crystal interface is studied using scanning hot microprobe measurements. __________ Translated from Neorganicheskie Materialy, Vol. 41, No. 10, 2005, pp. 1186–1193. Original Russian Text Copyright ? 2005 by Svechnikova, Shelimova, Konstantinov, Kretova, Avilov, Zemskov, Stiewe, Zuber, Muller.     

Cs2Si2Te6, ein polypertelluridosilikat (IV)

The new compound Cs₂Si₂Te₆ crystallizes in the monoclinic system (space group: Cc, No. 9) with the lattice constants a = 828.5(4) pm, b = 1393.5(6) pm, c = 1340.4(6) pm, ß = 100.35(12)°.Fivefold Si₂Te₃-rings, each formed by two SiTe₄ tetrahedra, connected by common Te atoms and Te-Te groups, are linked by Te bridges to infinite strings.     

(K0.44,Na0.52,Li0.04) (Nb0.84,Ta0.10,Sb0.06)O3 Ferroelectric Ceramics

Recent progress in (K_0.44,Na_0.52,Li_0.043-based ceramics (KNN) with special emphasis on (K_0.44,Na_0.52,Li_0.040.84,Ta_0.10,Sb_0.06))O₃ (KNN-LT-LS) is reviewed concisely. The base KNN and its compositional derivatives are analyzed in terms of dopant-property relationships, which are then extended to the ternary derivatives. The effects of processing conditions such as humidity, precursor purity, and oxygen partial pressure during sintering are elaborated on from a phenomenological perspective. It is also shown that the spontaneous polarization is sensitive to the processing route chosen for synthesis (mixed oxide versus perovskite routes). Special attention is devoted to the discussion of the morphotropic phase boundary (MPB) dilemma in the KNN-LT-LS system, where it is shown that the origin of high piezoelectric activity is actually due to a polymorphic transition at room temperature. It is shown that prototype transducers based on pure and 1 mol% Ba²⁺ doped KNN-LT-LS exhibit performance metrics comparable to those fabricated using PZT-5H. Overall, KNNLT- LS ceramics show great promise for lead-free applications, although issues such as temperature dependence of properties and strong sensitivity to processing conditions remain as the 2 major challenges.     

Performance of novel materials for radiation detection: Tl3AsSe3, TlGaSe2, and Tl4HgI6

In this paper we report on the electrical characteristics of three novel ternary compounds, Tl₃AsSe₃ (TAS), TlGaSe₂ (TGS), and Tl₄HgI₆ (THI), pertaining to their use as radiation detectors. The details for growth and material characterization are not presented. A semiconductor based gamma ray detector requires a material with high Z, high density, high resistivity, appropriate bandgap (1.5-2 eV), low energy/electron-hole pair, and a high μτ product. CZT is currently the best semiconductor material for room temperature gamma ray spectroscopy; however, it is extremely difficult to produce large volumes of detector grade material, making it expensive and in limited supply. DNDO/DHS began searching for other materials that might perform as well as CZT but be easier to grow and in the end lower the cost. For this purpose, we investigated the above three materials as possible replacements for CZT as gamma ray detectors. The bulk resistivity, I-V curves, X-ray response, and gamma ray response measurements for doped and undoped crystals are presented and discussed. TAS shows good X-ray and gamma ray response, but has poor resistivity, which results in large dark current and poor spectral response. TGS has good resistivity, but shows poor X-ray and gamma ray response. THI has excellent resistivity, shows some X-ray and gamma ray response, and has great potential as a gamma ray detector.     

Preparation,cristallogenese et caracterisation des bromures mixtes de lanthanide,de sodium et de cesium Cs2 NaLn (III) Br6

Single crystals of the new perovskites Cs₂Na Ln (III) Br₆ (with Ln (III) = Ce, Nd, Gd, Y) have been grown by the Bridgmann-Stockbarger method, using sealed silica-glass ampoules. They have been characterised by analytical and standard X-Ray methods; they crystallised with cubicface centered lattices, the parameters of which are: $\text{a}\text{= 11.508 - 11.421 - 11.370 - 11.304}\text{A}\text{?}$ for Ln = Ce - Nd - Gd - Y.     

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.     

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.     

Bi3(FeO4)(MoO4)2 and Bi3(GaO4)(MoO4)2 - new compounds with scheelite related structures

The title compounds have been prepared for the first time. They have monoclinic structures related to the scheelite (CaWO₄) structure, and they represent the first example of trivalent cations on tetrahedral sites of the scheelite structure. A superstructure is observed due to an ordering of the cations on the tetrahedral sites.     

Hydrothermal Crystallization in the Systems La2(CO3)3 ? 6H2O-CaCO3(BaCO3)-R-H2O (R = Na2CO3, K2CO3, NaHCO3, KHCO3, NaCl, NH4Cl, CO(NH2)2)

Crystallization in the systems La₂(CO₃)₃ ⋅ 6H₂O-CaCO₃(BaCO₃)-R-H₂O (R = Na₂CO₃, K₂CO₃, NaHCO₃, KHCO₃, NaCl, NH₄Cl, CO(NH₂)₂) was studied under hydrothermal conditions (400–450°C). The solid reaction products were found to contain LaOHCO₃ and NaLa(CO₃)₂. Detailed thermal decomposition schemes were proposed for these phases, and their lattice parameters were refined. __________ Translated from Neorganicheskie Materialy, Vol. 41, No. 11, 2005, pp. 1366–1372. Original Russian Text Copyright ? 2005 by Nikol'skaya, Dem'yanets.     

Cs4GeTe6, ein o-Pertelluridogermanat (IV)

The new compound Cs₄GeTe₆ crystallizes in the monoclinic system, space group P2₁/n (No. 14) with the lattice constants a = 1784.5(8) pm, b = 1398.1(6) pm, c = 786.7(4) pm, β = 101.6(1)°. The Ge-atoms are tetrahedrally coordinated by two single Te-atoms and two “end on” bonded Te₂-dumbbells, forming hitherto unknown discrete GeTe₆^4?-anions.     

A modified model for calculating lattice thermal expansion of I2-IV-VI3 and I3-V-VI4 tetrahedral compounds

A general empirical formula was found for calculating lattice thermal expansion for compounds having their properties extended for compound groups having different mean ionicity as well as more than one type of cation atoms with that of different numbers of them such as I₂-IV-VI₃ and I₃-V-VI₄. The difference in the valence electrons for cations and anions in the compound was used to correlate the deviations caused by the compound ionicity. The ionicity effects, which are due to their different numbers for their types, were also added to the correlation equation. In general, the lattice thermal expansion for a compound semiconductor can be calculated from a relation containing melting point, mean atomic distance and number of valence electrons for the atoms forming the compound. The mean ionicity for the group compounds forming I₂-IV-VI₃ was found to be 0.323 and 0.785 for the ternary group compounds of I₃-V-VI₄.     

Crystal structure of (Sr,Ba)Bi2Ta2O9

The crystal structure of (Sr_0.9Ba_0.1)Bi₂Ta₂O₉ has been refined to elucidate the nature of the lower phase transition observed in even-layered members of the bismuth titanate family. Least squares analysis based on x-ray and neutron diffraction intensities led to an R-factor of 0.13 for 1135 reflections. Bismuth strontium barium tantalate is orthorhombic, space group A2₁am, with a = 5.504, b = 5.488, $\text{c}\text{= 25.06}\text{A}\text{?}$, and Z = 4. Near the lower transition, five short Bi-O bonds are retained in the bismuth oxide layer, but distortions in the perovskite are reduced considerably, with the Ta ion displaced just 0.05Å from the center of the octahedron.     

Synthesis and structural characterization of (Bi2O3)1?x (Y2O3)x and (Bi2O3)1?x (Gd2O3)x solid solutions

Solid solution series, (Bi₂O₃)_1−x (Y₂O₃)_x and (Bi₂O₃)_1−x (Gd₂O₃)_x, forx = 0.10, 0.20, 0.30 and 0.40 were synthesized by standard ceramic technique. The structural phase characterization was carried out using X-ray powder diffraction technique. It was found that the solid solution containing 20–40 mole% of Y₂O₃ had face-centred cubic structure. All samples of the solid solution series, (Bi₂O₃)_1−x (Gd₂O₃)_x, had rhombohedral single phase in the concentration range 0.10 ≤x ≤ 0.40. Lattice parameters offcc phase of Y₂O₃ doped samples were calculated from the X-ray diffraction data. The lattice constant ‘a’ gradually decreases with increasing content of dopant concentration (x) for the Y₂O₃ doped system and obeys Vegard’s rule. The unit cell parameters for the (Bi₂O₃)_1−x (Gd₂O₃)_x doped samples showing rhombohedral phase were obtained on hexagonal setting.     

水热合成Sb_2Se_3纳米线及其对Bi_2Te_3纳米粉末热电性能的影响

以SbCl3和Se粉为原料,水合肼(N2H4·H2O)为还原剂,采用水热法在150℃下,分别保温不同的时间合成Sb2Se3纳米粉末.通过X射线衍射(XRD)、场发射电子扫描电镜(FESEM)、透射电镜(TEM)以及高分辨透射电镜(HRTEM)等分析方法对产物的物相成分和微观形貌等进行了表征,实验结果表明保温时间达到24h时,获得产物为单相Sb2Se3纳米线晶体.根据实验结果还研究了水热合成Sb2Se3纳米线晶体可能的反应及生长机理,结果表明一维纳米线沿[001]方向生长,纳米线的形成与其独特的层状晶体结构有关.最后采用放电等离子体快速热压烧结法将水热合成的Bi2Te3纳米粉末与不同含量Sb2Se3纳米线进行复合,分析了Sb2Se3纳米线对Bi2Te3纳米材料热电性能的影响,发现复合约1at%Sb2Se3纳米线可以使Bi2Te3纳米材料热电性能有一定提高.     

NMR study of ionic motions in both Tl2Zr3OF12 and Rb2Zr3OF12 oxyfluorides

The ionic transport properties of two members, namely Tl₂Zr₃OF₁₂ and Rb₂Zr₃OF₁₂ of a new series of oxyfluorides with formula M₂M′₃OF₁₂ (M = Rb, T1, NH₄; M′ = Zr, Hf) have been investigated using pulse NMR techniques and ionic conductivity measurements. The obtained results show that on the low temperature range fluorine is responsible for the conductivity of these materials while at temperatures higher than 450K the thallium ions probably contribute also to the conductivity. The extent of substitution of trivalent ions such as In³⁺ and Y³⁺ for Zr⁴⁺ has been determined as well as the effect of these substitutions on the ionic conductivity.     

Crystal structures of two cesium phosphate-tellurates : Te(OH)6.Cs2HPO4 and Te(OH)6.Cs2HPO4.2CsH2PO4

Te(OH)₆.Cs₂HPO₄ and Te(OH)₆.Cs₂HPO₄.2CsH₂PO₄ are monoclinic, the first one with a = 8.204(5), b = 18.416(9), $\text{c}\text{= 6.995(5)}\text{A}\text{?}$, β = 89.89(5)°, Z = 4, space group P2₁/n, the second one with a = 9.591(6), b = 13.163(9), $\text{c}\text{= 8.367(5)}\text{A}\text{?}$, β = 106.27(5)°, Z = 2, space group P2₁/m. As already observed in previously described phosphate-tellurates the main feature of these atomic arrangements is the coexistence of two independent and different types of anions (PO₄ and TeO₆ groups) in the unit cell.     

Synthesis, structure, and electrical and acoustic properties of Cs2Cd2(MoO4)3

We have studied the physicochemical and physical properties of a langbeinite-structure cesium cadmium molybdate (sp. gr. P2₁3, Z = 4, a = 11.239(1) ?). It has very low thermal expansion and possesses piezoelectric properties. We have constructed the section of the longitudinal piezoelectric surface for Cs₂Cd₂(MoO₄)₃ by a plane containing a threefold axis (body diagonal), along which the piezoelectric modulus has the highest value: 5.8 × 10⁻¹² C/N.     

Structure and ferroelectric properties of Bi(Zn1/2Ti1/2)O3-(Bi1/2K1/2)TiO3 perovskite solid solutions

Lead-free piezoelectric ceramics based on χBi(Zn_1/2Ti_1/2)O₃-(1-χ)(Bi_1/2K_1/2)TiO₃ were obtained via solid state processing techniques. A single perovskite phase with tetragonal symmetry was obtained for Bi(Zn_1/2Ti_1/2)O₃ (BZT) substitutions up to 20 mol%. The maximum density was 97.1% at the composition of χ = 0.1. The dielectric measurement indicated that the transition temperature decreased linearly with increasing BZT content. The P-E loops revealed an increase in remanent polarization (P_r) with the addition of BZT. The maximum planar coupling coefficient, κ_r, for the χ = 0.1 composition was 21.6 and the piezoelectric coefficient, d₃₃, for χ = 0, χ = 0.05, and χ = 0.1 was 108, 185, and 235 pm/V, respectively. Overall, the dielectric and piezoelectric properties showed significant improvement when BZT was added.     

Optimization of Bi2Te3 and Sb2Te3 thin films deposited by co-evaporation on polyimide for thermoelectric applications

The optimization of the deposition process of n-type Bismuth Telluride and p-type Antimony Telluride thin films for thermoelectric applications is reported. The films were deposited on a 25 μm-thick flexible polyimide (kapton) substrate by co-evaporation of Bi and Te, for the n-type element, and Sb and Te, for the p-type element. The evaporation rate of each material was monitorized by an oscillating crystal sensor and the power supplied to each evaporation boat was controlled with a PID algorithm in order to achieve a precise user-defined constant evaporation rate.The influence of substrate temperature (in the range 240-300 °C) and evaporation rates of Bi, Te and Sb on the electronic properties of the films was studied and optimized to obtain the highest Seebeck coefficient. The best n-type Bi₂Te₃ films were deposited at 300 °C with a polycrystalline structure, a composition close to stoichiometry, electrical resistivity ∼20 μΩ m and Seebeck coefficient −195 μV/°C. The best p-type Sb₂Te₃ films were deposited at 240 °C, are slightly Te-rich, have electrical resistivity ∼20 μΩ m and Seebeck coefficient +153 μV/°C. These high Seebeck coefficients and low electrical resistivities make these materials suitable for fabrication of Peltier coolers and thermopile devices.     

Hochdrucksynthesen und transformationen von alkali-oxofluoro-metallaten des typs Cs2NaMOxF6−x und Rb2LiMOxF6−x

Compounds and mixtures of compositions Cs₂NaMO_xF_6?x and Rb₂LiMOF₅ were transformed under high pressure to metastable modifications crystallizing in the hexagonal HT-K₂LiAlF₆ type structure and/or the cubic K₂NaCrF₆ elpasolithe type structure.Mixtures of composition Rb₂LiMO_xF_6?x (M = Nb⁵⁺or Mo⁶⁺) yielded under high pressure besides LiF metastable compounds A₂MO_xF_5?x crystallizing orthorhombic in the K₂VO₂F₃ type structure.