Topological phase transition and selective charge Anderson localization as a route to enhance thermoelectric performance
일 시 : 2021년 05월 04일 화요일 16:00
연 사 : 이 종 수 교수 (경희대학교 응용물리학과)
장 소 : 온라인 진행 ( https://us02web.zoom.us/j/89235295426 , 줌회의 ID: 892 3529 5426 )
HOST : 문 순 재 교수님
Topologically protected materials system generally share commonalities with good thermoelectric materials because of their narrow band gaps and heavy constituent elements. Here we propose that a topological crystalline insulator (TCI) and Dirac semimetal could exhibit a high thermoelectric performance by breaking its crystalline symmetry and tuning chemical potential by elemental doping. As a candidate material, we demonstrate that a weak disordering in the topological crystalline state can enhance thermoelectric performance significantly due to highly dispersive band dispersion and high band degeneracy which guarantee high electrical mobility and a high Seebeck coefficient, respectively. In addition, we demonstrate selective charge Anderson localization as a route to maximize the Seebeck coefficient while simultaneously preserving high electrical conductivity and lowering the lattice thermal conductivity. We confirm the viability of interface potential modification in an n-type Bi-doped PbTe/Ag2Te nanocomposite, and the resulting enhancement in thermoelectric figure-of-merit ZT. The introduction of random potentials via Ag2Te nanoparticle distribution using extrinsic phase mixing was determined using scanning tunneling spectroscopy measurements. When the Ag2Te undergoes a structural phase transition (T > 420 K) from monoclinic β-Ag2Te to cubic α-Ag2Te, the band gap in the α-Ag2Te increases due to the p-d hybridization. This results in a decrease in the potential barrier height, which gives rise to partial delocalization of the electrons, while wave packets of the holes are still in a localized state. Using this strategic approach, we achieved an exceptionally high thermoelectric figure-of-merit in n-type PbTe materials, a ZT greater than 2.0, suitable for waste heat power generation.