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A high efficiency thermoelectric material requires being a "phonon glass -electron crystal". Zintl phase compounds can be engineered to combine a "phonon glass" with an "electron crystal" by selectively doping the system to optimize the electronic properties. Current research on thermoelectrics is concentrated on (I) chemical or physical changes to improve the existing materials such as doping and reducing particle size to nano-size and (II) new materials with superior thermoelectric properties. Chapters 2 and 3 have been focused on tuning the transport properties of existing materials to improve the thermoelectric performance. In chapters 4 and 5, new Zintl phases have been synthesized and investigated with respect to their thermoelectric properties. In chapter 2, silicon nanoparticles embedded Mg2Si/xSi nanocomposites have been synthesized at 623 K from MgH2 and Bi containing Si nanoparticle powders. This synthetic route avoids the production of oxides and lowers the formation temperature of Mg2Si. It also provides a route to homogeneously mixed Si nanoparitcles within a Mg2Si matrix. Powder X-ray diffraction (XRD), thermogravimetry/differential scanning calorimetry (TG/DSC), electron microprobe analysis (EMPA), and scanning transmission electron microscopy (STEM) are applied to characterize the phase and micro-structure. Thermoelectric properties measurements indicate that the thermal conductivity is reduced by a small amount of Si nano-inclusions, which is in agreement of our theoretical calculations. A dimensionless figure of merit zT ~ 0.7 is obtained at 775 K for 1% Bi doped Mg2Si/x Si with x = 0 and 2.5 mol.%. In chapter 3, magnetic and transport properties of a series of Te doped Yb14MnSb11 samples prepared by Sn flux method have been studied. Increasing amounts of Te increases the saturation moment of Yb14MnSb11−(x)Te(x) and magnetoresistence effect. Both Seebeck coefficient and electrical resistivity increase with increasing amount of Te as a result of decreasing carrier concentration. Approximately 12% improvement of zT has achieved for x = 0.07 at 1240 K. Thermoelectric properties of the compounds Yb11MSb9 (M = Ga, In) via self-flux synthesis, closely structure related to Yb14MnSb11, have been investigated in chapter 4. Particularly low lattice thermal conductivity values, less than 0.6 W/m*K, are obtained for both compounds. The low lattice thermal conductivity suggests that Yb11MSb9 (M = Ga, In) has the potential for high thermoelectric efficiency at high temperature if charge carrier doping can be optimized. A two-step solid-state method is developed to fabricate two rare-earth containing ternary phosphides, Eu3Ga2P4 and Eu3In2P4, and their thermoelectric properties are investigated in chapter 5. The powder XRD and TG-DSC are employed to characterize the phase purity and thermal stability. Electronic structures of both compounds are calculated and provide band-gaps of 0.60 and 0.29 eV for Eu3Ga2P4 and Eu3In2P4, respectively. Transport properties measurements suggest that these Zintl phosphides have the potential to be good high temperature thermoelectric materials with optimization of the charge carrier concentration by appropriate extrinsic dopants.
III-V semiconductors have attracted considerable attention due to their applications in the fabrication of electronic and optoelectronic devices as light-emitting diodes and solar cells. Because of their wide applications in a variety of devices, the search for new semiconductor materials and the improvement of existing materials is an important field of study. This new book covers all known information about phase relations in ternary systems based on III-V semiconductors. This book will be of interest to undergraduate and graduate students studying materials science, solid state chemistry, and engineering. It will also be relevant for researchers at industrial and national laboratories, in addition to phase diagram researchers, inorganic chemists, and solid state physicists.
Handbook on the Physics and Chemistry of Rare Earths: Including Actinides, Volume 60 presents the latest release in this continuous series that covers all aspects of rare earth science, including chemistry, life sciences, materials science and physics. Presents up-to-date overviews and new developments in the field of rare earths, covering both their physics and chemistry Contains individual chapters that are comprehensive and broad, along with critical reviews Provides contributions from highly experienced, invited experts
The thesis focuses on the syntheses, structural characterizations and chemical bonding analyses for several ternary R–M–Ge (R = rare earth metal; M = another metal) intermetallics. The challenges in understanding the main interactions governing the chemistry of these compounds, which lead to our inability to predict their formation, structure and properties, are what provided the motivation for this study. In particular, the R2MGe6 (M = Li, Mg, Al, Cu, Zn, Pd, Ag), R4MGe10-x (M = Li, Mg), R2Pd3Ge5, Lu5Pd4Ge8, Lu3Pd4Ge4 and Yb2PdGe3 phases were synthesized and structurally characterized. Much effort was put into the stabilization of metastable phases, employing the innovative metal flux method, and into the accurate structure solution of twinned crystals. Cutting-edge position-space chemical bonding techniques were combined with new methodologies conceived to correctly describe the Ge–M, Ge–La and also La–M polar-covalent interactions for the La2MGe6 (M = Li, Mg, Al, Cu, Zn, Pd, Ag) series. The present results constitute a step forward in our comprehension of ternary germanide chemistry as well as providing a good playground for further investigations.
Seven chapters report current research into the phases and ions of a class of compounds that are electronically positioned between the intermetallic compounds and insulating valence compounds. They cover structure and bonding at the Zintl border, structural patterns of homo- and hetero-nuclear anions and related intermetallic compounds and concepts for interpreting them, the early p-block elements, polyanions in liquid ionic alloys, molecular transition metal complexes, transition metal compounds, and synthesizing and characterizing intermetallic materials using Zintl phases as precursors. An introduction surveys the life and work of German chemist Eduard Zintl (1898-1941). Annotation copyright by Book News, Inc., Portland, OR
Wie kann man heute in seinem Fachgebiet den Überblick behalten, obwohl die Spezialisierung in der Wissenschaft mehr und mehr zunimmt? Die "Highlights in Inorganic Chemistry" wollen dabei helfen. Die Anorganische Chemie gliedert sich in Molekülchemie, Festkörperchemie, Hauptgruppenchemie, Materialwissenschaften und viele weitere Teilbereiche auf. Viel tut sich Jahr für Jahr in jedem dieser Forschungsschwerpunkte! Zu jedem dieser Disziplinen präsentieren Wissenschaftler aus aller Welt in diesem Buch interessante und aktuelle Beiträge. Jeder, der einen Blick über den eigenen Tellerrand hinaus riskieren will, sollte dieses Buch sein Eigen nennen.