Thermoelectrics (TE) have received a lot of attention for their ability to directly convert heat into electricity. This capability provides a promising solution for waste heat recovery and clean energy utilization. Strontium titanate (SrTiO 3 ) is a promising N-type oxide TE material. However, its practical application is limited by low electrical conductivity and high thermal conductivity. Here, we present a high-pressure synthesis technique aimed at simultaneously introducing defects as well as enhancing phonon scattering. Enhancing the thermoelectric properties of strontium titanate thermoelectric materials. SrTiO 3 samples doped with different concentrations of La were synthesized by high-pressure high-temperature (HPHT) synthesis, which effectively promotes the solid-phase reaction and thus allows for a more homogeneous and efficient doping of La atoms into the SrTiO 3 lattice as compared to the conventional synthesis method. The introduction of La 3+ creates a charge imbalance, which is compensated by the formation of oxygen vacancies. These oxygen vacancies act as donor defects, which in turn increase the carrier concentration and significantly improve the electrical conductivity of the samples. At the same time, the HPHT synthesis conditions induced severe lattice distortions, leading to grain refinement and the formation of dislocation networks and nanopores. By modulating the density and distribution of multiscale defects, La doping significantly improves the interfacial phonon scattering efficiency. This condition reduces the thermal conductivity and improves the thermoelectric properties. By combining defect engineering and interfacial phonon scattering, we achieved the decoupling of electrical and thermal transport properties in La-doped SrTiO 3 . Consequently, the thermoelectric figure of merit ( zT ) was significantly enhanced, reaching 0.18 at 973 K. This study introduces a new methodology and theoretical foundation for the development of high-performance oxide TE materials.
Li Lijia,Chen Jiajun,Hu Laigui,Qiu Zhijun,Zou Zhuo,Liu Ran,Zheng Lirong,Cong Chunxiao
Collective vibration is pivotal for materials’ thermal, electrical, phase transition and topological properties. Lately, the rising of moiré superlattices, characterized by overarching periodicity of moiré pattern, generates highly tunable interfacial structures that manipulate collective excitations in material at the atomic scale. Here, we experimentally demonstrate moiré collective vibrations, the mechanical counterparts of moiré excitons, at heterointerfaces of twisted tungsten diselenide/tungsten disulfide heterobilayers. Using helicity-resolved inelastic Raman scattering, we find chiral interfacial phonons carrying angular momentum analogous to that of chiral bulk phonons in quartz, enabling unprecedented spectral resolution of rich vibrational modes at heterointerface in a few atomic layers. Upon mutual torsion of heterobilayers, we observe terahertz interlayer vibrations proportional to moiré periodicity as a periodic function of rotation angles, demonstrating moiré-tuned interlayer modes which couple to Coulomb-bound electron-hole pairs in interlayer moiré excitons. In low-angle strong coupling regime, interlayer dynamics exhibit a distinct long-lived breathing mode with zero angular momentum and pronounced high energy, highlighting phonon-hybridization character wherein intralayer breathing vibrations are folded into moiré mini-Brillouin zone by spatial periodicity and hybridize with interlayer vibrations. Our findings establish moiré collective vibrations as candidates for exploitation in energy-efficient thermal management, strongly correlated electrical engineering, and new emergent topological phononics.
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