Solution Synthesis of a New Thermoelectric Zn1-xSb Nanophase and Its Structure Determination Using Automated Electron Diffraction Tomography

Engineering materials with specific physical properties have recently focused on the effect of nanoscopic inhomogeneities at the 10 nm scale. Such features are expected to scatter medium- and long-wavelength phonons thereby lowering the thermal conductivity of the system. Low thermal conductivity is a prerequisite for effective thermoelectric materials, and the challenge is to limit the transport of heat by phonons, without simultaneously decreasing charge transport. A solution-phase technique was devised for synthesis of thermoelectric "Zn4Sb3" nanocrystals as a precursor for phase segregation into ZnSb and a new Zn-Sb intermetallic phase, Zn1+delta Sb, in a peritectoid reaction. Our approach uses activated metal nanoparticles as precursors for the synthesis of this intermetallic compound. The small particle size of the reactants ensures minimum diffusion paths, low activation barriers, and low reaction temperatures, thereby eliminating solid-solid diffusion as the rate-limiting step in conventional bulk-scale solid-state synthesis. Both phases were identified and structurally characterized by automated electron diffraction tomography combined with precession electron diffraction. An ab initio structure solution based on electron diffraction data revealed two different phases. The new pseudo-hexagonal phase, Zn1+delta Sb, was identified and classified within the structural diversity of the Zn-Sb phase diagram. RI Kolb, Ute/A-2642-2011; Birkel, Christina/D-6144-2011; Tremel, Wolfgang/D-8125-2011; Mugnaioli, Enrico/E-6237-201

Solution Synthesis of a New Thermoelectric Zn1-xSb Nanophase and Its Structure Determination Using Automated Electron Diffraction Tomography

Engineering materials with specific physical properties have recently focused on the effect of nanoscopic inhomogeneities at the 10 nm scale. Such features are expected to scatter medium- and long-wavelength phonons thereby lowering the thermal conductivity of the system. Low thermal conductivity is a prerequisite for effective thermoelectric materials, and the challenge is to limit the transport of heat by phonons, without simultaneously decreasing charge transport. A solution-phase technique was devised for synthesis of thermoelectric "Zn(4)Sb(3)" nanocrystals as a precursor for phase segregation into ZnSb and a new Zn-Sb intermetallic phase, Zn(1+delta)Sb, in a peritectoid reaction. Our approach uses activated metal nanoparticles as precursors for the synthesis of this intermetallic compound. The small particle size of the reactants ensures minimum diffusion paths, low activation barriers, and low reaction temperatures, thereby eliminating solid-solid diffusion as the rate-limiting step in conventional bulk-scale solid-state synthesis. Both phases were identified and structurally characterized by automated electron diffraction tomography combined with precession electron diffraction. An ab initio structure solution based on electron diffraction data revealed two different phases. The new pseudo-hexagonal phase, Zn(1+delta)Sb, was identified and classified within the structural diversity of the Zn-Sb phase diagram

Influence of Ni nanoparticle addition and spark plasma sintering on the TiNiSn-Ni system: Structure, microstructure, and thermoelectric properties

The electronic and thermal properties of thermoelectric materials are highly dependent on their microstructure and therefore on the preparation conditions, including the initial synthesis and, if applicable, densification of the obtained powders. Introduction of secondary phases on the nano- and/or microscale is widely used to improve the thermoelectric figure of merit by reduction of the thermal conductivity. In order to understand the effect of the preparation technique on structure and properties, we have studied the thermoelectric properties of the well-known half-Heusler TiNiSn with addition of a small amount of nickel nanoparticles. The different parameters are the initial synthesis (levitation melting and microwave heating), the amount of nickel nanoparticles added and the exact pressing profile using spark plasma sintering. The resulting materials have been characterized by synchrotron X-ray diffraction and microprobe measurements and their thermoelectric properties are investigated. We found the lowest (lattice) thermal conductivity in samples with full-Heusler TiNi2Sn and Ni3Sn4 as secondary phases. © 2013 Elsevier Masson SAS. All rights reserved

Silicon-based thermoelectrics made from a boron-doped silicon dioxide nanocomposite

We report a method for preparing p-type silicon germanium bulk alloys directly from a boron-doped silica germania nanocomposite. This is the first successful attempt to produce and characterize the thermoelectric properties of SiGe-based thermoelectric materials prepared at temperatures below the alloy's melting point through a magnesiothermic reduction of the silica-germania nanocomposite. We observe a thermoelectric power factor that is competitive with the literature record obtained for high energy ball milled nanocomposites. The large grain size in our hot pressed samples limits the thermoelectric figure of merit to 0.5 at 800 C for an optimally doped Si80Ge20 alloy. © 2013 American Chemical Society

Strong law of large numbers for pairwise positive quadrant dependent random variables

Associated random variables, Markov chain, Positive quadrant dependence, Rate of convergence, Stochastic equicontinuity, 60F15,