반도체 재료의 격자열전도도 분석

임종찬,양희선,김현식,Lim, Jong-Chan,Yang, Heesun,Kim, Hyun-Sik 한국마이크로전자및패키징학회 2020 마이크로전자 및 패키징학회지 Vol.27 No.4

열전소재의 격자열전도도 저감은 열전성능 증대를 위해 가장 빈번하게 사용되는 방법이다. 하지만 전체 열전도도에서 다른 열전도도 기여분을 제외하는 방법으로만 격자열전도도를 구할 수 있기 때문에 격자열전도도를 정확하게 분석하는 것을 간단한 작업이 아니다. 본 연구에서는 먼저 전자/홀에 의한 열전도도 기여분 (모든 소재 적용)과 쌍극 전도에 의한 기여분 (작은 밴드 갭 소재 적용)을 정확하게 계산해야만 격자열전도도를 정확하게 분석할 수 있음을 설명한다. 전자/홀에 의한 기여분을 계산하기 위해 필수적인 로렌츠 숫자 계산법 (싱글 파라볼릭 모델링 및 간단한 식 이용)과 쌍극 전도에 의한 기여분 계산법 (투 밴드 모델링) 또한 소개한다. 격자열전도도의 정확한 분석은 격자열전도도 저감을 위한 여러 결함 제어 전략의 효과를 객관적으로 평가할 수 있는 강력한 분석 도구로 사용될 수 있다. Suppressing lattice thermal conductivity of thermoelectric materials is one of the most popular approach to improve their thermoelectric performance. However, accurate characterization of suppressed lattice thermal conductivity is challenging as it can only be acquired by subtracting other contributions to thermal conductivity from the total thermal conductivity. Here we explain that electronic thermal conductivity (for all materials) and bipolar thermal conductivity (for narrow band gap materials) need to be determined accurately first to characterize the lattice thermal conductivity accurately. Methods to calculate Lorenz number for electronic thermal conductivity (via single parabolic model and using a simple equation) and bipolar thermal conductivity (via two-band model) are introduced. Accurate characterization of the lattice thermal conductivity provides a powerful tool to accurately evaluate effect of different defect engineering strategies.

Quantitative analysis on the influence of Nb substitutional doping on electronic and thermal properties of <i>n</i>-type Cu_0.008Bi₂Te_2.7Se_0.3 alloys

Choo, Sung-sil,Cho, Hyun-jun,Kim, Ji-il,Kim, Sang-il Elsevier 2019 PHYSICA B-CONDENSED MATTER - Vol.552 No.-

<P><B>Abstract</B></P> <P>Cation substitutional doping has been shown to be an effective method to modify both the electronic and thermal transport in <I>p</I>-type (Bi,Sb)<SUB>2</SUB>Te<SUB>3</SUB>-based thermoelectric alloys. However, there are not many studies that have attempted a quantitative analysis on the influence of cation substitution on the electronic and thermal properties of <I>n</I>-type Bi<SUB>2</SUB>(Te,Se)<SUB>3</SUB>-based alloys. In this work, we report a comprehensive analysis of the influence of substitutional Nb doping on the electrical and thermal conductivity in <I>n</I>-type Cu<SUB>0.008</SUB>Bi<SUB>2</SUB>Te<SUB>2.7</SUB>Se<SUB>0.3</SUB> alloys. First, we found that Nb doping increases the carrier concentration of both the electrons and holes, whereas the weighted mobility of the electrons and holes is only slightly modified based on a single parabolic band model. As a result, the bipolar thermal conductivity was increased as the Nb was doped. Next, the contribution of point defect scattering by the Nb substitution on the thermal conductivity of the lattice was quantitatively analyzed using a Debye-Callaway model, and it was concluded that the influence of cation substitutional doping in <I>n</I>-type Bi<SUB>2</SUB>(Te,Se)<SUB>3</SUB> is as effective as that in <I>p</I>-type (Bi,Sb)<SUB>2</SUB>Te<SUB>3</SUB>.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Electronic properties of Nb-doped <I>n</I>-type Cu<SUB>0.008</SUB>Bi<SUB>2</SUB>Te<SUB>2.7</SUB>Se<SUB>0.3</SUB> alloys was analyzed. </LI> <LI> Carrier concentrations of electrons and holes were increased by the Nb doping. </LI> <LI> Reduction of lattice thermal conductivities was analyzed based on Callaway model. </LI> <LI> Doping in <I>n</I>-type Cu-Bi<SUB>2</SUB>Te<SUB>2.7</SUB>Se<SUB>0.3</SUB> is effective in reducing thermal conductivity. </LI> </UL> </P>

Advances in Heat Conduction Models and Approaches for the Prediction of Lattice Thermal Conductivity of Dielectric Materials

Banashree Saikia 한국물리학회 2017 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.70 No.5

An overview of predominant theoretical models used for predicting the thermal conductivities of dielectric materials is given. The criteria used for different theoretical models are explained. This overview highlights a unified theory based on temperature-dependent thermal-conductivity theories, and a drifting of the equilibrium phonon distribution function due to normal three-phonon scattering processes causes transfer of phonon momentum to (a) the same phonon modes (KK-S model) and (b) across the phonon modes (KK-H model). Estimates of the lattice thermal conductivities of LiF and Mg2Sn for the KK-H model are presented graphically.

Toward high-accuracy and high-applicability of a practical model to predict effective thermal conductivity of particle-reinforced composites

Kim, Jeonggeon,Goo, Yong-Rack,Choi, Indae,Kim, Songkil,Lee, Donggeun Elsevier 2019 INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER - Vol.131 No.-

<P><B>Abstract</B></P> <P>A particle-reinforced composite material is a matrix with thermally conductive particles that has a diverse range of applications from electronics to energy harvesting/storage systems. In the engineering design of a particle-reinforced composite material for application, it is crucial to accurately and practically predict its effective thermal conductivity. Here, we report the development of a simple analytical model for predictions with improved accuracy and applicability. Comprehensive evaluation of existing models was first conducted to clarify their limitations in prediction accuracy and applicability to various experimental conditions. To overcome the challenges of the existing models, our new model was derived to consider the effect of shape, particle aggregation, and mutual interaction of particles on effective thermal conductivity. Lattice Boltzmann simulations were conducted to obtain a quasi-universal coefficient representing interactions of particles, whereas a shape coefficient characterizing microstructures of aggregated particles was obtained from experimental data available from literature. As a result, our model prediction outperformed the existing models in its prediction accuracy, and it could be applicable to any experimental circumstances where previous model predictions are inappropriate to use.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Comprehensive evaluation showed that existing models had their conditional limitations. </LI> <LI> The models were unacceptably degraded under conditions for electronics applications. </LI> <LI> We developed a new model to accurately predict effective thermal conductivity. </LI> <LI> The new model was self-consistent and described asymptotic behaviors of existing models. </LI> <LI> With an additional correlation, the new model was reasonably applicable to any conditions. </LI> </UL> </P>

Mo(Se1-xTex)2 열전합금의 점 결함에 의한 포논 산란 효과 분석

이유종,김상일,황성미,김정연,서원선,김현식 대한금속·재료학회 2023 대한금속·재료학회지 Vol.61 No.1

One of the most popular routes used to improve the thermoelectric performance of materials is tosuppress their lattice thermal conductivities. Thermoelectric performance is characterized by a figure-of-meritzT, which is defined as σS2T/(κe + κl), where the σ, S, T, κe, and κl are the electrical conductivity, Seebeckcoefficient, temperature (in Kelvin), electronic thermal conductivity, and the lattice thermal conductivity,respectively. Among the variables in zT, the κl is the only variable that is independent of all other variables. In other words, reduction in κl guarantees zT improvement. Therefore, several different strategies to decreaseκl have been introduced and implemented. Among the many κl reduction strategies, introducing point defectsin the material by forming an alloy is particularly effective. Here, phonon scattering due to point defects inMo(Se1-xTex)2 (x = 0.0, 0.25, 0.50, 0.75, 1.0) was studied using both the Debye-Callaway (DC) model andCallaway-von Baeyer (CvB) model. The advantages and disadvantages of using DC or CvB models arethoroughly discussed. When analyzing the effect of phonon scattering due to point defects, the CvB model issimpler and gives more information about the details of phonon scattering.

Acoustic phonon lifetimes limit thermal transport in methylammonium lead iodide

Gold-Parker, Aryeh,Gehring, Peter M.,Skelton, Jonathan M.,Smith, Ian C.,Parshall, Dan,Frost, Jarvist M.,Karunadasa, Hemamala I.,Walsh, Aron,Toney, Michael F. National Academy of Sciences 2018 PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF Vol.115 No.47

<▼1><P><B>Significance</B></P><P>Hybrid organic–inorganic perovskites are a promising class of materials for efficient and low-cost solar cells. Unlike conventional inorganic semiconductors such as silicon and gallium arsenide, hybrid perovskites feature significant dynamic disorder in their crystal structure. This dynamic disorder can be broadly classified into lattice vibrations (phonons) and molecular rotations. Phonons interact with charge carriers through electron–phonon coupling, which has substantial impacts on the operation of solar cells. Our study shows that acoustic phonons, the type responsible for transmitting heat in conventional semiconductors, have extraordinarily short lifetimes in the archetypal hybrid perovskite methylammonium lead iodide. These short lifetimes have direct implications on the cooling and transport of electrons and reflect a key difference between hybrid perovskites and conventional photovoltaic semiconductors.</P></▼1><▼2><P>Hybrid organic–inorganic perovskites (HOIPs) have become an important class of semiconductors for solar cells and other optoelectronic applications. Electron–phonon coupling plays a critical role in all optoelectronic devices, and although the lattice dynamics and phonon frequencies of HOIPs have been well studied, little attention has been given to phonon lifetimes. We report high-precision momentum-resolved measurements of acoustic phonon lifetimes in the hybrid perovskite methylammonium lead iodide (MAPI), using inelastic neutron spectroscopy to provide high-energy resolution and fully deuterated single crystals to reduce incoherent scattering from hydrogen. Our measurements reveal extremely short lifetimes on the order of picoseconds, corresponding to nanometer mean free paths and demonstrating that acoustic phonons are unable to dissipate heat efficiently. Lattice-dynamics calculations using ab initio third-order perturbation theory indicate that the short lifetimes stem from strong three-phonon interactions and a high density of low-energy optical phonon modes related to the degrees of freedom of the organic cation. Such short lifetimes have significant implications for electron–phonon coupling in MAPI and other HOIPs, with direct impacts on optoelectronic devices both in the cooling of hot carriers and in the transport and recombination of band edge carriers. These findings illustrate a fundamental difference between HOIPs and conventional photovoltaic semiconductors and demonstrate the importance of understanding lattice dynamics in the effort to develop metal halide perovskite optoelectronic devices.</P></▼2>

Chemically synthesized Cu₂Te incorporated Bi-Sb-Te <i>p</i>-type thermoelectric materials for low temperature energy harvesting

Song, Jae Min,Rahman, Jamil Ur,Cho, Jung Young,Lee, Soonil,Seo, Won Seon,Kim, Seyun,Kim, Sang-il,Lee, Kyu Hyoung,Roh, Dongkyu,Shin, Weon Ho Pergamon 2019 Scripta materialia Vol.165 No.-

<P><B>Abstract</B></P> <P>We report a facile and efficient way to enhance and modulate thermoelectric performance by incorporating chemically synthesized Cu<SUB>2</SUB>Te nanoparticles on p-type Bi<SUB>0.5</SUB>Sb<SUB>1.5</SUB>Te<SUB>3</SUB> matrix. By varying the amount of Cu<SUB>2</SUB>Te nanoparticles, the temperature of maximum thermoelectric performance shifted systematically from room temperature to 425 K. The highest figure-of-merit value, 1.1, was achieved at 377 K by incorporating 0.1 wt% Cu<SUB>2</SUB>Te nanoparticles in Bi<SUB>0.5</SUB>Sb<SUB>1.5</SUB>Te<SUB>3</SUB> matrix, which is due to enhancement in power factor and reduction in lattice thermal conductivity. The results demonstrate that Cu<SUB>2</SUB>Te incorporation could be an effective strategy for Bi-Te based thermoelectric power generation.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Effect of Si content on the thermoelectric transport properties of Ge-doped higher manganese silicides

Lee, Hwijong,Kim, Gwansik,Lee, Byunghun,Kim, Jeongmin,Choi, Soon-Mok,Lee, Kyu Hyoung,Lee, Wooyoung Elsevier 2017 Scripta materialia Vol.135 No.-

<P><B>Abstract</B></P> <P>Polycrystalline bulks of Si-content tuned Ge-doped higher manganese silicides (HMSs) were fabricated to elucidate the effects of Si content on the phase formation behavior and thermoelectric properties. The phase formation and electronic transport characteristics of HMSs were significantly dependent on Si content. Improved power factor was obtained at higher Si contents because of an enhanced Seebeck coefficient due to the increase in density of states effective mass, maintaining electrical conductivity. Furthermore, the lattice thermal conductivity was reduced through Si-content tuning, which suppressed the formation of secondary phases. Thus, a maximum <I>ZT</I> of 0.61 at 823K was obtained in MnSi<SUB>1.77</SUB>Ge<SUB>0.027</SUB>.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Study of optoelectronic, thermoelectric, mechanical, and thermodynamic properties of Cs2NaTlX6 (X = Cl, Br, I) for energy harvesting

Hedhili Fekhra,Hassan Belqees,Rashid M.S.,Bakr Mohammed,Mahmood Q.,M. Al-Shomar Shereen,Alahmad Waed,Alimi Fathi,Mechi Lassaad 한국물리학회 2023 Current Applied Physics Vol.53 No.-

The inorganic double perovskites are remarkable materials for renewable energy which can be realized through solar cells and thermoelectric generators. Here, we have comprehensively elaborated the stability, mechanical, thermodynamic, optical and transport characteristics. The formation energy is computed to ensure thermodynamic validity and the tolerance factor is assessed for structural existence. The elastic constants satisfied the Born criteria and mechanical stability. Naviera’s velocities have been used to study the Debye temperature and directional lattice conductivity. Modifying the band gap from 3.1 to 0.58 eV by halide ions (Cl to I) probes the distinct optoelectronic characteristics. Absorption bands, dispersion of light energy, refraction, and optical loss explain the optical characteristics. In addition, the above thermoelectric factors like conductivities, Seebeck effect, and performance are studied in the temperature range of 100–600 K. Large figure of merit and extremely low lattice vibration at room temperature indicate their significance for thermoelectric devices.

Enhanced TE performance of FeVSb1-xSnx half-heusler matrices using zirconia vial

Rahidul Hasan,KyuHyoungLee,Soon-Chul Ur 한양대학교 세라믹연구소 2020 Journal of Ceramic Processing Research Vol.21 No.3

Thermoelectric and transport properties of FeVSb1-xSnx (0.015<x<0.055) alloys were studied with respect to types of vials(zirconia and stainless steel), Sn contents and temperature. The results were compared with the previously studied samplessynthesized by using stainless-vial. All the designated compositions in current work were prepared via a mechanical alloyingprocess using a zirconia vial. Vacuum hot pressing was conducted to consolidate the mechanically alloyed powders. F43msymmetry was being confirmed from the Rietveld refinement pattern. The phase transitions during the milling process andvacuum hot processing were investigated and the results exhibited near single half-Heusler phases with a minor portion of thesecond phase within the matrix. The Second phase might play a role to reduce thermal conductivity. Electrical conductivityexhibited semi-metallic behavior in all the temperature range. Carrier concentrations are found to be decreased with theincreasing Sn contents and the FeVSb0.955Sn0.045 specimen showed the ZTmax of 0.23 at 757 K.