Apparatus for Seebeck coefficient and electrical resistivity measurements of bulk thermoelectric materials at high temperature

A high temperature Seebeck coefficient and electrical resistivity measurement apparatus has been designed and built for measuring advanced thermoelectric materials. The apparatus covers the range of temperatures from 300 to 1300 K300to1300K. Different sources of errors involved in the two measurements are discussed. The accuracy of the electrical resistivity measurement is estimated to be better than ±1%±1% by measuring standard graphite sample from NIST.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87891/2/023901_1.pd

Pressure enhancement of the electrical conductivity of graphite intercalation compounds

A novel approach to achieve high electrical conductivity in graphite intercalation compounds is suggested. It is based on a recently observed pressure-induced staging transition in GICs which leads to a higher areal density of the intercalant while the quasi-2D character of the structure, believed to exhibit lower carrier scattering, is still preserved.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/48996/2/jcv14i30pL911.pd

Thermal conductivity of several exfoliated graphites from 2 k to 300 k

The thermal conductivity of several exfoliated graphites (Grafoil, Foam, and UCAR-ZYX graphite) has been measured in the range 2 to 300 K. The temperature dependence of the thermal conductivity is similar to that of near-single-crystal pyrolytic graphite, but the value is two orders of magnitude lower.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23188/1/0000115.pd

Growth of high purity single crystals of arsenic

Large, high quality, single crystals of arsenic have been grown from the melt in a high pressure bomb made from synthetic quartz. The crystals have residual resistance ratios (RRR) of up to 5500, the largest reported to date.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/25199/1/0000638.pd

Correlating optical absorption and thermal conductivity in diamond

The presence of defects in diamond induces one‐phonon infrared absorption which is not allowed in the perfect crystal due to symmetry. Concomitantly the thermal conductivity is reduced by additional phonon‐defect scattering. For single crystal diamonds irradiated with fast neutrons, we find a correlation between the one‐phonon absorption and the room‐temperature thermal conductivity valid over three orders of magnitude in defect concentration. This relation holds for both unannealed and annealed crystals for which the detailed configuration of defects is different, as well as for a synthetic diamond film containing a similar type of disorder. Infrared absorption can thus be used to determine the thermal conductivity of diamonds containing vacancy‐related defect centers.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70107/2/APPLAB-63-2-165-1.pd

Influence of neutron irradiation on the thermal conductivity of vapor‐deposited diamond

The influence of neutron irradiation on the thermal conductivity κ of diamond films fabricated by hot filament (HF) and microwave plasma assisted (MPA) deposition has been studied. The additional thermal resistivity induced by irradiation is similar to that found in single crystal diamond and is due mainly to the formation of clusters of disordered carbon material. Despite a significant difference in κ prior to irradiation, the thermal conductivity of the HF and MPA films is almost the same after a cumulative dose of 2.7×1017 neutrons cm−2.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69811/2/JAPIAU-76-3-1515-1.pd

Thermoelectric performance of films in the bismuth-tellurium and antimony-tellurium systems

Coevaporated bismuth-tellurium and antimony-tellurium films were fabricated under various deposition conditions (controlled evaporation rates of individual species, substrate temperature, and substrate material), and their thermoelectric (TE) properties (Seebeck coefficient, electrical resistivity, and carrier concentration) were measured in search of optimal TE performance. The tellurium atomic concentration was varied from 48% to 74%, the substrate temperature ranged from 130 to 300 °C, and glass, mica, magnesium oxide, and sapphire substrates were used. The chemical composition and crystal structure of the films were recorded (using microprobe and x-ray diffractometer, respectively), analyzed, and compared with available standard Bi2Te3Bi2Te3 and Sb2Te3Sb2Te3 single-crystal samples. High-performance TE films had tellurium atomic concentration around 60% and were deposited at a substrate temperature between 260 and 270 °C.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87588/2/114903_1.pd

Smoothening of Cu films grown on Si(001)

We report an in situ study of the molecular-beam epitaxy growth and annealing of Cu(001) films grown on hydrogen-terminated Si(001) substrates, resulting in a promising approach to achieve smooth epitaxial morphology. Using correlated reflection high-energy electron diffraction and scanning tunneling microscopy data, we find a temperature interval below the onset of silicide formation where a dramatic smoothening of the epitaxial Cu surfaces occurs. Our measurements indicate that a reduction in roughness is possible in this regime because the annealing is controlled by lateral diffusion kinetics. © 2000 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71331/2/APPLAB-76-6-724-1.pd

Thermal transport properties of SbCl5-graphite and of HOPG in the c-direction

We report measurements of the c-axis thermal conductivity and thermoelectric power of SbCl5-GIC's. Thermal conduction is dominated by the lattice, with defects being the dominant scatterers. The thermopower is in good agreement with theoretical predictions for GICs. Finally, results for the very low temperature thermal conductivity of pure graphite in the c-direction are presented and discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/25507/1/0000048.pd

Experimental evidence for multi-band conduction in highly-doped La-Sr-Cu-O superconductors

We have measured the Hall coefficient in highly-doped La2-xSrxCuO4 superconductors (x=0.2 and 0.25), finding a large decrease with temperature. A good fit to the data is obtained using the two-band model involving both holes and electrons (as suggested by our earlier thermopower measurements), with the carrier-phonon interaction being relatively stronger for the holes.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26501/1/0000037.pd