Experimental search for high ZT semiconductors: A survey of the preparation and properties of several alloy systems

摘要

A survey was conducted of several alloy systems identified as having certain properties thought to be desirable in high figure-of-merit thermoelectric materials. The systems examined include the cerium and lanthanum borocarbides, yttrium nitrides, osmium silicides, and titanium sulfides. Various approaches to the preparation of these alloy systems were explored including vapor transport, arc melting, and mechanical alloying. Among these systems, the borocarbides were found to exhibit p-type conductivity but generally suffered from relatively high carrier concentrations (on the order of 10(sup 21)/cm(sup 3)) and low mobilities ((le)10 cm(sup 2)/V-s). Both carbon and sulfur dopants produced the highest figure of merit (0.13 (times) lO(sup (minus)3)/(degree)C) in the yttrium nitride system at room temperature. Excess silicon was observed to increase carrier concentration and Hall mobility in osmium disilicide while additions of chromium were observed to stabilize the OsSi(sub 2) crystal structure. Electrical power factors comparable to state of the art silicon-germanium alloys were achieved in titanium disulfide, however, the electrical transport properties were found to be critically dependent upon the amount of excess Ti in Ti(sub 1+x)S(sub 2).