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The high-pressure transport properties have been determined for nickel and PbTe. Nickel shows a reduction in electrical resistivity, an increase in thermal conductivity, and a variable effect on the Seebeck coefficient with pressure. In PbTe, a dramatic decrease in resistivity and a slow increase in thermal conductivity have been observed with increasing pressure. The three transport properties in PbTe are affected by a pressure-induced structural phase transition. The measurements show that the high-pressure phase is likely a more effective thermoelectric material than the ambient-pressure phase.

The high-figure-of-merit thermoelectric material AgPb18SbTe20 has been investigated by in situ angular-dispersive x-ray diffraction (XRD) and x-ray absorption fine-structure (XAFS) measurements up to 30 GPa. Resistivity and thermopower were measured with Bridgman-type opposed metal anvil cells. The results show that the ambient cubic \( \left( {Fm\overline{3} m} \right) \) structure transforms to orthorhombic (Pnma) at 6.4 GPa and then to the CsCl-type \( \left( {Pm\overline{3} m} \right) \) structure at 15 GPa. The ambient cubic \( \left( {Fm\overline{3} m} \right) \) phase is found to be recoverable on releasing the pressure. The thermoelectric power is found to increase with pressure for the cubic phase. The XAFS studies performed at the Pb L3-edge and Ag K-edge along with resistivity studies complement the XRD findings.

Correlated-electron systems are so named due to strong interactions between electrons unlike traditional metals (e.g. copper) that have “free electrons” that interact very weakly. Knowledge of the Fermi surface, density of electron states and band structure are the starting points for a first-principles understanding of the electronic and electronically related macroscopic properties, e.g. equation of state. The use of high pressure and high magnetic fields to alter the electron-electron (hybridization) and electron-lattice interactions give us powerful tools to understand complicated rare earth and actinide correlated-electron systems and allows precise testing of experiment to theory. Correlated-electron systems yield a wide variety of ground states that are a direct result of the hybridization strength including: short and long range magnetic order, spin fluctuating, enhanced Pauli paramagnetism, heavy fermion behavior and superconductivity. We will review some results on U compounds in high magnetic fields and high pressures. By comparing the results to Ce compounds that have significantly more localized f electrons, the effect of direct 5f electron wavefunction overlap in U compounds can be discerned. Consequences on the search for U based heavy fermion superconductors will be discussed.