Prof. Zhi Feng Ren

(Department of Physics and Texas Center for Superconductivity at the University of Houston (TcSUH), University of Houston, Houston, TX 77204, USA; zren@uh.edu)

Title

Progress on Thermoelectric Materials, Devices, and Measurements

Abstract

Modules based on thermoelectric materials can either generate cooling/heating using electrical power or electrical power from heat, which is very much needed for some applications. However, the thermoelectric properties of the traditional materials are not good enough to make efficient modules to compete with the traditional coolers using compressors or steam engines. However, in the past fifteen years, we have been able to not only achieve some good progress in improving the thermoelectric properties of traditional materials but also discover new materials with better properties and lower costs. At the same time, thermoelectric modules have also been extensively studied resulting in record-breaking cooling and power generation devices. In this talk, I will present the advances in both materials and devices.

Prof. Chih Wei Chang

(Associate Research Fellow, CCMS National Taiwan University;cwchang137@ntu.edu.tw)

Title

Quantifying vacancy concentration at the nanoscale

Abstract

Thermodynamic principles dictate the omnipresence of vacancy defects within all materials. However, very few experimental tools are capable of measuring vacancy concentrations in materials, let alone detecting them at the nanoscale. Here we introduce atomic number electron microscopy (ZEM), a technique that establishes quantitative correlations between the thermal absorbance of investigated materials under an incident electron beam and their effective atomic number (Z). The ZEM has advantages in detecting light elements and compounds, and recently we further demonstrate its capabilities in unraveling vacancy concentrations in SiC nanoparticles and SnS micrograins, etc. The ZEM would emerge to bridge the technological gap that was previously unattainable using the most advanced tools available today.

Dr. Cheng Rong Hsing

(Postdoctoral Fellow, IAMS Academia Sinica)

Title

Exploring the thermoelectric properties using first-principles approaches and machine-learning interatomic potentials

Abstract

Thermoelectric materials play a crucial role in energy conversion applications. To design and optimize these materials, accurate and efficient simulations are necessary. First-principles simulations, based on density functional theory (DFT), have emerged as powerful tools for understanding and predicting the thermoelectric properties of materials. However, predicting the crystal structure, especially superionic materials and defect-containing systems, has been one of the core issues in materials research. In this talk, I will first present our recent study using molecular dynamics (MD) simulations. We add up all the positions of diffusing atoms in each time step to form a 3-dimensional atomic density distribution function (3D-ADDF). This 3D-ADDF will automatically reveal or hint the crystal symmetry, partial-occupancy positions, and the mobile atoms’ diffusing or hopping pathways and regions. However, the computational cost of first-principles approaches to large-scale systems (such as superionic materials and defect-containing thermoelectric systems) still limits their applicability. Machine-learning interatomic potentials offer an alternative approach by combining the accuracy of first-principles calculations with the computational efficiency of classical force fields, thereby providing a more clear and reliable insights into the dynamic behavior of superionic materials. I will take Ag₈SiTe₆ as an example to demonstrate the capability of machine-learning interatomic potentials, which makes the calculation feasible and applicable to large-scale systems and extended time scales.

Dr. Peramiyan Ganesan

(Postdoctoral Fellow, IOP Academia Sinica)

Title

High thermoelectric performance in Tin chalcogenide thermoelectric materials

Abstract

Massive consumption, scarcity, and environmental impacts of fossil fuels trigger the research and development efforts towards sustainable and green energy resources. In this context, converting thermoelectric energy (TE) waste heat into electricity becomes an inevitable alternative for a clean and green energy source. For the past few decades, considerable efforts have been made in developing mid- and high-temperature thermoelectric materials. However, progress on near-room-temperature candidates with substantial conversion efficiency, which would benefit cooling and waste-heat power generation near room temperature, has been sluggish. Tin sulfide (SnS), an analogous crystal structure to SnSe, with a distinct layered lattice structure and a low-cost semiconductor, attracts particular interest due to its impressive electronic band structure and its evolution upon alloying. We realized the remarkable thermoelectric response in hole-doped SnS single crystals, attributing to band sharpening, band divergence and carrier optimization. Heavier satellite valence bands near the valence band maximum at the Γ-Z direction were pushed down by the alloying effect. They made inaccessible by decreasing the carrier concentration to the optimal level, i.e. moving the Fermi level away from these bands. Carrier tuning and band sharpening result in record-high hole mobility of about ~1579 cm ²V^-1s^-1. Surprisingly, alloying in single-crystalline hole-doped SnS leads to a synergistic optimization between effective mass, mobility, and thermal conductivity, enhancing the record high power factor of about ~177.7 μWcm s^-1K^-2 and 58.8 μWcm^-1K^-2 at 300 K and 512 K, respectively along the c-axis direction. Moreover, polycrystalline hole-doped SnS samples show a remarkable TE performance in the mid-temperature range.

Dr. Suneesh M. Vailyaveettil

(Postdoctoral Fellow, IAMS Academia Sinica)

Title

Ge-Sb-Te bases thermoelectric thin films: dopants and nano architecture

Abstract

Thermoelectric (TE) modules heavily rely on the availability of compatible p-type and n-type TE materials. This study focuses on the development of suitable p- and n-type materials based on Ge-Sb-Te (GST) to enhance the overall TE performance. Previous research has explored various strategies, with an emphasis on the rhombohedral phase (R3m) of GeTe, resulting in improved TE performance. Moreover, GeTe-rich GST stabilized in a metastable cubic phase (Fm-3m) at room temperature exhibited a unique electronic transition and a remarkably high-power factor. In this ongoing pursuit to further comprehend p-type GST, this study delves deeper into the potential of the cubic phase. A specific post-annealing treatment was employed to obtain the cubic phase in thin films at room temperature. Additionally, indium was introduced as a resonant dopant to enhance TE performance. The introduction of indium distorted the density of states, increased the effective mass, optimized carrier concentration, and significantly improved the Seebeck coefficient and power factor. This substantial improvement led to a zT of 1.9 at 575 K. Furthermore, by incorporating cobalt into GST thin films, a distinct crystal structure known as the skutterudite was formed, exhibiting n-type conduction behavior. The unique crystal structure and electronic properties of skutterudites open avenues for exploring the Co-Ge-Sb-Te-based ternary skutterudite structure. This exploration highlights the potential of Co-Ge-Sb-Te-based thin films, demonstrating a high zT of 1.3 at 673 K, as a promising alternative for efficient n-type TE materials.