歐敏男

Abstract:

Understanding lattice dynamics is essential for investigating fundamental physical properties in solid-state materials, particularly the interactions between electrons and phonons. A prominent example is thermoelectric (TE) materials, where strategies to enhance energy conversion efficiency include optimizing the power factor (PF) and reducing the total thermal conductivity (κₜ). The total thermal conductivity comprises contributions from both charge carriers (κₑ) and phonons (κₚ), with κₑ also influenced by the behavior of the power factor. This interdependence provides valuable insights for optimizing TE properties and achieving high-performance materials.

In our study of GeTe-based compounds, we found that κₜ can be further reduced by suppressing phonon propagation in samples with optimized power factors. However, robust methodologies and quantitative metrics for evaluating phonon transport behavior remain to be established. To this end, probing thermal transport through measurements of phonon dispersion relations can facilitate the reduction of thermal conductivity and the enhancement of TE efficiency. In this work, GeTe-based crystals with optimized dopants were synthesized using the Bridgman method. Their lattice structures and crystallographic textures were characterized by powder X-ray diffraction (XRD) and X-ray Laue diffraction.

As a second example, Bi₂SeₓTe₃₋ₓ crystals exhibit an electronic topological transition (ETT) under high pressure, which induces anomalies in mechanical, electrical, thermodynamic, and vibrational properties. To investigate the phonon excitations associated with ETT in the low-energy regime, inelastic neutron scattering (INS) measurements under ambient pressure are employed as an initial step to assess the effects of doping on lattice dynamics. The cold neutron spectrometer SIKA, located at the Taiwan neutron beamline at ANSTO, Australia, offers an ideal energy range for such investigations. Energy scans at constant momentum transfer using SIKA reveal the impact of chemical substitutions on phonon behavior.

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