Zintl Chemistry for Designing High Efficiency Thermoelectric Materials

Zintl phases and related compounds are promising thermoelectric materials; for instance, high zT has been found in Yb_(14)MnSb_(11), clathrates, and the filled skutterudites. The rich solid-state chemistry of Zintl phases enables numerous possibilities for chemical substitutions and structural modifications that allow the fundamental transport parameters (carrier concentration, mobility, effective mass, and lattice thermal conductivity) to be modified for improved thermoelectric performance. For example, free carrier concentration is determined by the valence imbalance using Zintl chemistry, thereby enabling the rational optimization of zT. The low thermal conductivity values obtained in Zintl thermoelectrics arise from a diverse range of sources, including point defect scattering and the low velocity of optical phonon modes. Despite their complex structures and chemistry, the transport properties of many modern thermoelectrics can be understood using traditional models for heavily doped semiconductors

Optimizing Thermoelectric Efficiency in La_(3−x)Te_4 via Yb Substitution

A low temperature, solid state synthesis technique has enabled the production of homogeneous samples of La_(3−x−y)Yb_yTe_4. This allows the substitution of divalent Yb to be utilized to optimize the thermoelectric performance in lanthanum telluride. The addition of Yb^(2+) changes the electrical transport properties in a manner that can be well understood using valence counting rules and a corresponding change in the Fermi energy. The substitution of Yb^(2+) for La^(3+) results in a threefold finer control over the carrier density n, thus allowing the optimum n ~ 0.3 × 10^(21) cm^(−3) to be both predicted and prepared. The net result is an improvement in thermoelectric efficiency, with zT reaching ~ 1.2 at 1273 K

Transport properties of the layered Zintl compound SrZnSb_2

Transport properties of the layered Zintl compound SrZnSb_2 have been characterized from room temperature to 725 K on polycrystalline samples. SrZnSb_2 samples were found to be p-type with a Hall carrier concentration of 5×10^(20) cm^(−3) at room temperature, and a small Seebeck coefficient and electrical resistivity are observed. A single band model predicts that, even with optimal doping, significant thermoelectric performance will not be achieved in SrZnSb_2. A relatively low lattice thermal conductivity is observed, κ_L~1.2 W m^(−1) K^(−1), at room temperature. The thermal transport of SrZnSb_2 is compared to that of the layered Zintl compounds AZn2Sb_2 (A=Ca,Yb,Sr,Eu), which have smaller unit cells and larger lattice thermal conductivity, κ_L~2 W m^(−1) K^(−1), at 300K. Ultrasonic measurements, in combination with kinetic theory and the estimated κ_L values, suggest that the lower κ_L of SrZnSb_2 is primarily the result of a reduction in the volumetric specific heat of the acoustic phonons due to the increased number of atoms per unit cell. Therefore, this work recommends that unit cell size should be considered when selecting Zintl compounds for potential thermoelectric application

Thermoelectric properties of p-type LiZnSb: Assessment of ab initio calculations

In response to theoretical calculations on the thermoelectric performance of LiZnSb, we report the pertinent transport properties between room temperature and 523 K. Nominal LiZnSb samples are found to be p-type, with a carrier concentration in the range (4–7)×10^(20) cm^(−3). The thermoelectric figure of merit (zT) is found to be 0.02–0.08 at 523 K. Analysis of material transport parameters and previously reported ab initio calculations demonstrates that even with optimal doping, p-type LiZnSb is unlikely to achieve zT>0.2 at 523 K. The accuracy of the high zT estimate (zT>2) for n-type compositions from ab initio calculations is discussed within the current synthetic limits

Hybrid carcinoma of the salivary gland: salivary duct adenocarcinoma adenoid cystic carcinoma

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73933/1/j.1365-2559.1999.00761.x.pd

Conceptual design of single turbofan engine powered light aircraft

The conceptual design of a four place single turbofan engine powered light aircraft was accomplished utilizing contemporary light aircraft conventional design techniques as a means of evaluating the NASA-Ames General Aviation Synthesis Program (GASP) as a preliminary design tool. In certain areas, disagreement or exclusion were found to exist between the results of the conventional design and GASP processes. Detail discussion of these points along with the associated contemporary design methodology are presented

Some comments on the universal constant in DSR

Deformed Special Relativity is usually presented as a deformation of Special Relativity accommodating a new universal constant, the Planck mass, while respecting the relativity principle. In order to avoid some fundamental problems (e.g. soccer ball problem), we argue that we should switch point of view and consider instead the Newton constant $G$ as the universal constant.Comment: 12 pages, Proceedings of DICE2006 (Piombino, Italy