Crystal Structure and Transport Properties of Nickel Containing Germanium Clathrates.

• Four Ba8Ni6-xGe40+x clathrate samples with x = 0-0.6 were synthesized and characterized using conventional and synchrotron x-ray powder diffraction. Thermopower, resistivity, thermal cond., Hall effect, and magnetic susceptibility were measured between 2 and 400 K. To support the interpretation of the phys. property data, d. functional theory calcns. were used to obtain band structures and theor. transport properties for a wide range of transition metal substituted clathrate systems having a fully ordered Ba8TM6Ge40 structure. A systematic dependence on x was found for both the structural and the electronic properties, and the latter varies from p- to n-type properties. Despite relatively low mobilities (H) of the charge carriers in all the samples, the thermoelec. properties of p-type Ba8Ni6-xGe40+x are promising. The p-type samples, with the best thermoelec. properties, have ZT = 0.13 at 400 K, where ZT is the dimensionless thermoelec. figure of merit. It is estd. that p-type samples with lower charge carrier concns. will have improved thermoelec. properties. The effect of transition metal substitution on the thermopower and mobility in clathrates is discussed.

Publication and Content Type

ref (subject category)

art (subject category)