High-pressure synthesis of intermetallic compounds and investigations of the high-pressure properties of thermoelectric materials

Under conditions of high pressure, the heavy alkali metals (potassium, rubidium, and cesium) undergo a s to d electronic transition, adopting a d 1 electron configuration. The enhanced d character of these metals makes them more "transition metal-like" and allows reactions that do not occur at ambient pressure with transition metals.; This thesis reports research that continues our laboratory's systematic study of the high-pressure behavior of alkali metals, focusing on experiments performed on the potassium-copper system. Results obtained from powder x-ray diffraction experiments conducted inside a Mao-Bell diamond anvil cell indicate that compound formation occurs at elevated pressure.; A species of stoichiometry KCu forms at a pressure of 47 GPa on heating for 21 hours at ∼108°C. The KCu structure possesses a tetragonal unit cell, with a ∼6.0 A and c ∼ 12.8 A. This structure is stable upon quenching to a pressure of 6 GPa. Although this structure has not been unambiguously solved, these results serve as a "proof of principle" that the potassium-copper system warrants further investigation. Additionally, these experiments successfully expand our knowledge of the K-Cu phase diagram and provide an excellent example of the interesting chemistry that can be shown for both alkali metals and transition metals at high pressure.; A second study discussed in this thesis concerns the high-pressure chemistry of iridium antimonide (IrSb3), an unfilled skutterudite.; Compression of IrSb3 to pressures up to 42 GPa shows that the structure is surprisingly stable given the presence of large cavities, one in the center of each unit cell. The stability of skutterudite structure has implications for both the implantation of atomic or molecular species within the cavities by means of pressure and the stability of IrSb3 under hot isostatic pressing conditions. From a fit to the universal pressure-volume equation of state, values were obtained for the bulk modulus and pressure derivative of the bulk modulus of 136 +/- 5 GPa and 4.8 +/- 0.5, respectively. Rietveld refinement of the crystal structure at high pressure further demonstrates the stability of the cavities under compression. (Abstract shortened by UMI.)...