Study in Micro and Nano-Structured Thermoelectric Materials

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Project title

Code/計畫編號

MOST109-2221-E019-013

Translated Name/計畫中文名

探討具微奈米結構之熱電材料在能源上的應用

Project Coordinator/計畫主持人

Chun-I Wu

Funding Organization/主管機關

National Science and Technology Council

Department/Unit

Department of Mechanical and Mechatronic Engineering

Website

https://www.grb.gov.tw/search/planDetail?id=13535180

Year

2020

Start date/計畫起

01-08-2020

Expected Completion/計畫迄

31-07-2021

Bugetid/研究經費

1376千元

ResearchField/研究領域

能源工程

熱電材料可以直接將溫差轉為電能，而具有奈米結構的熱電材料藉由聲子散射，將熱傳導係數更為降低，並藉此提高熱電因子。本研究計畫的主題是”探討具微奈米結構之熱電材料在能源上的應用”，從理論方面研究在奈米結構對於聲子散射的影響開始，並以實驗製備具奈米結構的熱電材料，藉由電子顯微鏡與性質量測，驗證理論值與實驗值的異同。並在此一基礎上，以火花放電燒結法(SPS)製備同時包含微、奈米結構之熱電材料。並以理論探討微奈米結構並存對不同波長之聲子的影響。藉由理論引導實驗，目標是熱傳導係數降為更低。本計畫預計達成下列三個目標:第一，從理論計算開始，以微觀的角度去探討熱電材料的結構，使用量子力學理論預測材料性質利用第一原理的材料計算方法，從材料組成的元素從解其對應的薛丁格方程，求出其物性。本計畫將選擇使用量子物理模擬計算軟體VASP，了解並設計微米結構對聲子的影響，以預測熱傳導係數。並藉由加入參雜物質，以形成奈米結構，實際製作具奈米結構之熱電材料以驗證VASP推導值。第二，使用第一原理的材料計算方式，探討微米尺度晶界對聲子的影響，以VASP模擬計算軟體，探討不同尺度晶界對不同波長之聲子影響。以往材料晶界較不易控制，本計畫將以火花放電燒結法快速成形之特性，控制熱電材料晶界的生長，以火花放電法製備不同尺度晶界的熱電材料，以電子顯微鏡觀察晶界並量測熱電性質，以驗證晶界對聲子散射的理論推算。第三，計算微奈米結構同時並存於材料內對聲子的影響，預期將同時對不同波長的聲子進行散射，此現象預期將使熱傳導係數更為降低。為了驗證此一理論，首先將熱電材料加入參雜物質，藉以製備具奈米結構之熱電材料，經由粉末工程，準備不同尺度之熱電粉末，利用火花放電法改變熱壓參數，藉此對熱電材料的晶界取得一定程度的控制，以製造微米尺度之晶界，並藉由電子顯微鏡與熱電性質測量，對不同波長的聲子進行散射，此現象預期將使熱傳導係數更為降低。為了驗證此一理論，首先將熱電材料加入參雜物質，藉以製備具奈米結構之熱電材料，經由粉末工程，準備不同尺度之熱電粉末，利用火花放電法改變熱壓參數，藉此對熱電材料的晶界取得一定程度的控制，以製造微米尺度之晶界，並藉由電子顯微鏡與熱電性質測量，對比理論數值與實驗結果。藉由上述三個目標，這個計畫將對熱電材料研究在微奈米結構方面，將有所貢獻，藉由這個實驗結論，希能提升熱電因子效率超過2.7。 Thermoelectricity attracted a lot of attention in recent years. Thermoelectric materials, which can generate electricity from waste heat or be used as solid-state coolers, are an ideal solution to the search for sustainable energy. The efficiency of thermoelectric generators is related to material thermoelectric figure of merit (zT). For the temperature range of 500–900K, PbTe-based thermoelectrics are the top performing materials, thanks to a two-valence-band structure: a primary light hole band at the L point and a second heavy hole band at the Σ point with an energy separation of about 0.15eV at 300K between them. Nanostructured thermoelectric materials with complex crystal structures where the defects would act as phonon scattering centers and reduce the thermal conductivity greatly. We will use first principles to calculate the phonon properties. Frequency-dependent simulation of thermal transport in nanostructured thermoelectric materials will be performed by solving phonon Boltzmann transport equation. Nanostructured thermal electrical samples will also be prepared. Transmission electron microscopy characterizations and transport measurements will apply on these nanostructured thermoelectric samples. We will compare the measurement results with theoretical values. We will use Spark Plasma Sintering (SPS) to prepare thermoelectric materials with various grain boundaries. Defects with different dimensions should be able to scatter phonon of different wavelength. And this should further reduce thermal conductivity. The project is expected to achieve the following four objectives: 1) from the theoretical calculations to estimate thermoelectric properties. We will use quantum mechanics based computational software to study the thermal transport in nanocrystalline PbTe–based materials. The Vienna Ab initio Simulation Package (VASP) will be used for the calculations. We will also add dopants into the PbTe matrix to form nanostructure thermoelectric samples which will be used to verify VASP value. 2) using the first principle of material calculation, the samples with microscale grain boundaries will be discussed. The VASP simulation software is used to investigate the effect of different grain boundaries on the phonon with different wavelengths. In this project, SPS method will be used due to its fast process time for controlling the grain boundaries. Transport measurements and transmission electron microscopy characterizations will apply on these nanostructured thermoelectric samples. 3) we will study materials have both micro- and nanostructures in the solid solution. The combination of different size defects is expected to further reduce the thermal conductivity. We will first prepare nanostructured thermoelectric materials. We will adjust SPS pressing conditions to create samples with various grain boundaries. Several samples with different sintering temperature, sintering pressure, and particle sizes will be prepared. 4) The mechanical properties of cast and SPS sampleswill be measured. This study will focus on the relationship between the sintering conditions, grain size and mechanical properties. With these four goals in mind, this project will contribute to the study of thermoelectric materials in the area of micro- and nanostructures. Based on the results of this experiment, it is hoped that we can make thermoelectric materials with ZT over 2.7.

Keyword(s)

熱電材料
微奈米結構
第一原理
Thermoelectric materials
micro- nano-structured materials
First principles approach
VASP

DSpace CRIS

Study in Micro and Nano-Structured Thermoelectric Materials

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