Probing lattice dynamics of Cd2Re2O7 pyrochlore: Thermal transport and thermodynamics study

Cd2Re2O7 single crystals exhibit an amorphouslike lattice thermal conductivity, kappa(latt). At temperatures about twice the Debye temperature, the phonon mean-free path approaches the value of the average Cd-Cd spacing while the specific heat is at values notably lower than the classical Dulong-Petit limit. We show that a model that treats Cd ions as Einstein oscillators embedded in a Debye host with strong optical-acoustic phonon coupling and some very high-frequency optical phonon modes in the system, can account for these features. Despite no structural change, kappa(latt) undergoes a smooth slope change at similar to 340 K, above which the resistivity adopts a weak power-law behavior. The combined results of resistivity, thermopower, specific-heat, thermalconductivity, and Hall coefficient measurements corroborate that a phonon-mediated electron-hole scattering mechanism sets in above room temperature.