Thermoelectrics carbides

Doping has been investigated extensively for compounds like /3-boron and boron carbide to try to modify their thermoelectric properties (e.g., Werheit et al., 1981 Slack et al., 1987 Aselage and Emin, 2003). There have not been as many attempts to dope the rare earth higher borides, we are only aware of transition metal doping into YB66 (Tanaka et al., 2000,2006 Mori and Tanaka, 2006). 

From Eq. (11), an obviously desirable characteristic for thermoelectric materials is to have low thermal conductivity k. The thermal diffusivity constant, Dt, of ErB44Si2 has been found to have small values of Dt < 1.1 x 10 2 cm 2/s (Mori, 2006c). These values are significantly smaller than what has been observed for boron carbide samples (Wood et ah, 1985). Although no data exists for the sound velocities of ErB44Si2, the velocities are probably high since borides are typically hard materials. Therefore, the small values of Dt indicate extremely short phonon... 

Although the presently obtained absolute values of power factors still need to be improved, these compounds may offer a n-type boride counterpart to the well known p-type boron carbide which is one of the few thermoelectric material viable for extremely high temperature use (1500 K), and further research on the R-B-C(N) compounds is merited. 

Interesting problems remain to be solved. Although the figure of merit is still quite low due to the poor density, can the homologous R-B-C(N) borides be den-sified and/or doped to become a viable n-type counterpart to boron carbide which is an exemplar p-type high temperature thermoelectric compound ... 

Boron carbide is very hard, refi-actory solids (m.p.>2400 °C). And its thermoelectric properties are unconventional in high temperature range above... 

Carbides, Silicides, and Related Compounds. Niobium carbide has been obtained by deposition from a NbCl4-H2-CH4 mixture. There has been a review of the electrical, thermoelectrical, and magnetic properties of MC-TaC systems (M = Hf or... 

Abzianidze, T., G. Karumidze, L. Kekelidze, E. Tabatadze, L. Shengelia, G. Bokuchava, and B. Shirokov. 2004. Possibilities of rising in the radiation stability and thermoelectric efficiency of boron carbide. In Proceedings of the 16th International Conference on Physics Radiation Phenomena and Radiative Materials Science, Kharkov, Ukraine, p. 88. 

In addition to the magnetic susceptibility, the electrical resistivity and the thermoelectric power at low temperatures for the RC,- and R2C-type carbides have been measured (Lallement 1968). The resultant magnetic and electrical data are shown in table 22. 

Boron carbide (B4C) is also surprisingly oxidation-resistant. Its weight decrease after 100 h in air at 1200°C is llmg/cm. It is an abrasive used in sandblasting nozzles, chemical vessels, ignitrons (semiconductor sparkers), thermoelectric energy converters, and nonlinear electronics. It is considered one of the most suitable... 

Boron carbide is characterized by a relatively wide gap in its forbidden band, a low thermal conductivity, and a high thermoelectric power. These properties make it a potentially useful material for high-temperature thermoelectric energy conversion. Electrical conductivity and Seebeck coefficient as a function of temperature and composition are shown in Figs. 8.5 and 8.6. 

This chapter briefly reviews what is known of the rare earth borides, carbides, and nitrides. This review wonld particularly like to showcase interesting features of the crystal structure and intriguing physical properties ranging ft-om the fundamental to the very applicable, with an emphasis on recent emerging results in important functionalities such as magnetism, thermoelectricity, and superconductivity. 

Boron carbide is a lightweight refractory material with high hardness and Young s modulus, aud excellent thermoelectric properties. The material is a water-resistant ceramic and has very high... 

Recently, photoluminescence properties of boron carbide nanowires were being studied and reported. Photoluminescence spectrum of a thin film made out of B4C nanowires exhibited a broad band at 638 nm, which strongly suggests the potential application of boron nanowires in visible optical devices. Nonetheless, nanowire and nanorod structures based on boron carbide find their application in different areas, including field emission devices and thermoelectric energy converters, neutron adsorbent in nuclear industries, and especially in composite materials as reinforcing agents. ... 

Boron carbides are of interest for their thermal stability, neutron capture capability, and high temperature thermoelectric properties. Appended to norbornenes, the monomers 6-(norbornenyl)decaborane and 6-(cyclooctenyl)decaborane underwent ROMP to afford their respective homopolymers with low polydispersity index (PDI) values (Figure 5). The applications of these materials in boron carbide/carbon... 

DT Morelli. Thermal conductivity and thermoelectric power of titanium carbide single crystals. Phys Rev B 44 5453, 1991. 

The thermal conductivity is important for many applications in semiconductor technology, e.g., for thermoelectric devices. In Fig. 41 the thermal conductivity of boron carbide is plotted versus chemical composition (163-165). The strong decrease from B4.3C at the carbon-rich limit of the homogeneity range toward more boron-rich compositions can easily be explained by the change of the most homogeneous structure at 64,30 to the most distorted one at about B6.5C shown in Fig. 26. For temperature dependence, see Ref. 166. 

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