新型半导体材料BaSi2的结构及其热电性能的研究

正交相的BaSi2是一种新型半导体材料,具有较小的热传导系数、较大的光学吸收系数和适合的带隙值,是一种潜在的热电材料和理想太阳能电池材料,有着广阔的应用前号。文章介绍了正交相BaSi2晶体结构、电学特性,综述了近年来对其热电性质的研究状况,并就当前BaSi2究中存在的问题和研究动向做了简要讨论。     

温差发电用BiCuSeO基热电材料的研究进展

BiCuSeO基热电材料由于具有较低的热导率和较高的Seebeck系数,热电性能优异,且原料储藏丰富、价格低廉、安全无毒,被认为是一种具有潜在应用前景的新型热电转换材料。首先介绍了BiCuSeO基材料的晶体结构、电子结构、热电性能等基本特征,随后综述了近年来国内外关于BiCuSeO基热电材料的研究进展,评述了提高其热电性能的手段,包括Na、Ag、Mg、Ca、Sr、Ba等低价元素掺杂,铜空位,双空位,带隙调整,晶粒细化,织构化和调制掺杂等。通过电热输运特性的协同调控,可使其ZT值从未掺杂样品的0.4左右提高到1.5。最后从实际应用的角度出发提出了今后BiCuSeO基热电材料的研究方向及研究重点。     

氧化物热电材料研究进展

氧化物基热电材料具有高温稳定性、抗氧化性和安全长效等优点而受到人们的广泛关注, 但其应用受到了热电性能的限制。本文详细介绍了几种典型氧化物热电体系, 如层状钴基氧化物、钙钛矿结构化合物、透明导电氧化物和一些新型氧化物热电材料的研究进展。从能带结构和微观形貌两方面入手进行调节, 以达到热电材料热学性能和电学性能的协调统一。分析了氧化物热电材料研究中的主要问题, 并对未来的发展提出了一些新的思路。     

变价稀土元素Eu掺杂BiCuSeO热电性能的研究

作为一种适于中温下使用的极具发展前景的新型热电材料,BiCuSeO由于本征热导率低且Seebeck系数较高而广受关注。本研究探索了变价稀土元素Eu替换Bi位对BiCuSeO热电材料微观组织和热电性能的影响。实验结果显示,样品中同时存在Eu²⁺和Eu³⁺两种价态的离子,掺杂Eu元素不仅可以增加样品的载流子浓度,还可以调整样品的能带结构,进而改善样品的电输运性能, Bi_0.85Eu_0.15CuSeO电导率显著提升,在823K时达到了98S·cm^–1,相比于未掺杂样品提升了将近6倍。在温度为823K时,Bi_0.975Eu_0.025CuSeO的功率因子可达0.32mW·m^–1·K–2,ZT值为0.49。本研究表明,掺杂变价稀土元素可以有效改善BiCuSeO热电材料的性能。     

锑化物二类超晶格热电材料:能带结构、热电性能、制备与测试

热电器件由于结构简单、可靠性好、无污染等优点,在微电子、能源等领域具有广泛的应用。探索具有高热电优值(ZT)的新材料是近些年来的研究热点。超晶格材料由于独特的量子限制效应和声子界面散射,ZT值比块体材料大幅度提高。而锑化物二类超晶格与传统超晶格不同,其禁带呈错开状,由此又可以带来热电性能新的变化。阐述了锑化物二类超晶格的能带结构以及能够获得高ZT值的优势,介绍了其热电机理和研究进展,以及当前该类超晶格的制备工艺和测试方法。     

无钴p型方钴矿热电材料的制备及热电性能研究

采用熔体旋甩结合热压烧结技术,制备了无钴p型方钴矿热电材料。利用X射线衍射仪以及扫描电子显微镜对其组织结构进行分析,并对烧结后的样品进行热电性能研究。结果表明,Fe和Ni可有效地取代Co,获得纯的方钴矿相。另外,即使无钴样品的高温ZT值略低于参比样品,但功率因子及低温ZT值基本相当,这对节约Co这一战略资源以及实现产业化应用具有重要的意义。     

基于分步式双重调控n型(PbTe)1-x-y(PbS)x(Sb2Se3)y体系的热电传输特性

PbTe在中温区热电材料中广受关注, 然而, n型PbTe因其较低的载流子浓度和复杂的能带结构, 其热电性能难以大幅提升。本研究通过分步式添加PbS、Sb₂Se₃组元以调控n型PbTe基体的热、电传输性能。研究发现, PbS与Sb₂Se₃组元可分别提升功率因子和降低热导率。通过扩大带隙、增加点缺陷、第二相弥散等途径可改善能带, 加剧散射, 从而有效提升热电优值ZT。其中(PbTe)_0.94(PbS)_0.05(Sb₂Se₃)_0.01表现出最佳的热电性能, 700 K时ZT最大值为1.7, 且ZT平均值较PbTe基体显著提高, 这表明分步式双组元调控可为改善其它材料体系的热电性能提供技术途径。     

梯度结构热电材料的研究动态

为了获得高的热电能量转换效率,可以把不同单体联接制成多段热电装置形成梯度结构(FGM),能有效扩大工作温度区间;同时又可以使每段材料工作在其最佳温度范围内,获得最佳的热电优值,有效提高热电转换效率.概述了梯度结构热电材料的设计与研究现状,并简要介绍了梯度结构中的界面稳定性和性能表征.     

Manipulating the Ge Vacancies and Ge Precipitates through Cr Doping for Realizing the High‐Performance GeTe Thermoelectric Material

GeTe alloy is a promising medium‐temperature thermoelectric material but with highly intrinsic hole carrier concentration by thermodynamics, making this system to be intrinsically off‐stoichiometric with Ge vacancies and Ge precipitations. Generally, an intentional increase of formation energy of Ge vacancy by element substitution will lead to an effective dissolution of Ge precipitates for reduction in hole concentration. Here, an opposite direction of decreasing the formation energy of Ge vacancies is demonstrated by substituting Cr at Ge site. This strategy produces more but nearly homogenously distributed Ge precipitations and Ge vacancies, which provides enhanced phonon scattering and effectively reduces the lattice thermal conductivity. Furthermore, Cr atom carries one more electron than Ge and serves as an electron donor for decreasing the hole carrier concentrations. Further optimization incorporates the effect of Bi substitution for facilitating band convergence. A maximum figure of merit (ZT) of 2.0 at 600 K with average ZT of over 1.2 is achieved in the sample of Ge_0.92Cr_0.03Bi_0.05Te, making it one of the best thermoelectric materials for medium‐temperature application.     

(Ag2Se)1-x(Bi2Se3)x的热电性能研究

具有本征低晶格热导率的I-V-VI₂族三元硫属化合物在热电领域引起了广泛关注。AgBiSe₂作为这类化合物中少有的n型半导体, 成为一种有潜力的热电材料。本工作系统研究了AgBiSe₂的热电性能。基于Ag₂Se-Bi₂Se二元相图, 单相的(Ag₂Se)_1-x(Bi₂Se₃)_x的成分在x=0.4~0.62范围可调, 使得该材料载流子浓度具有可调性。结果表明, 通过组分调控获得了较宽范围的载体浓度1.0×10¹⁹~5.7×10¹⁹ cm^-3, 并基于声学声子散射的单一抛物带模型对其电传输性能进行了综合评估。本研究获得的最高载流子浓度接近理论最优值, 在700 K实现了最高ZT值0.5。本研究有助于深入理解AgBiSe₂的传输特性和决定热电性能的基本物理参数。     

便携式热电制冷器制冷性能优化的试验分析

设计、组装一台便携式热电制冷器并对其性能进行试验研究,结果显示,200 mL的水在33 min内降温17.0℃,折合制冷量7.3 W,制冷器容器的高度方向上存在较大温差,且水温降低后密度增大而下沉,使水的自然对流换热过程受到抑制,这2个因素的综合作用使制冷片冷热端温差增大,制冷量减小,工况恶化。为优化该制冷器的制冷性能,在制冷片冷端增设重力式热管(充注R134a)并进行试验研究,结果表明,1 L的水在75 min内温度降低12℃,折合制冷量9.3 W,比优化前增大了27.4%。表明重力式热管的加入能够改善制冷器内水的对流换热情况,增大换热面积,减小竖直方向上的传热温差。     

半导体降温服交盖效应的实验研究

近年来,频繁的高温天气已经严重影响作业人员的身心健康,因此有必要研制降温服以改善工人工作条件。通过对半导体降温服的部分制冷性能进行实验研究,结果表明:当最大制冷量为68.9 W的单个制冷片工作时,以P_0为中心,半径相同处,温度也基本相同,且随着距离的增加,各测点温差降低率先加快后减慢;当三个制冷片工作时,温度变化呈现一定的差异性,且随着距离的增加,P_5~P_8和P_9~P_(12)测点的温差先降低后上升,在距离制冷中心3 cm处有明显的转折点;半导体降温服交盖效应的范围为以制冷中心为圆心、半径4 cm左右的圆域,且在相邻两个制冷片距离相同的情况下,当制冷中心位于同一水平线时,交盖效应更明显。研究为半导体降温服的应用提供了一定的指导意义。     

水冷式半导体冰箱制冷性能的研究

研究了水冷式散热方法对半导体冰箱制冷性能的提高.以常用的半导体小冰箱为实例,分别测试了在风冷、循环水和恒温水条件下小冰箱的制冷性能.结果表明,水冷制冷效果明显优于传统风冷式,且其制冷性能与冷却水的温度有关.水温越低,半导体制冷器的制冷效率越高,制冷温度越低.当冷却水温度为171 ℃时,水冷半导体小冰箱很快达到冷冻.建立了水冷式半导体冰箱的制冷模型,计算分析了在不同恒定冷却水温度下半导体制冷器冷端温度随时间的变化关系,并将理论结果与实验测量结果进行了拟合分析,发现理论模型与实验测量结果一致.研究结果为水冷式半导体冰箱制冷性能的提高提供了实验和理论依据.     

Band Modification and Localized Lattice Engineering Leads to High Thermoelectric Performance in Ge and Bi Codoped SnTe–AgBiTe2 Alloys

SnTe, emerging as an environment-friendly alternative to conventional PbTe thermoelectrics, has drawn significant attention for clean energy conversion. Here, a high peak figure of merit (ZT) of 1.45 at 873 K in Ge/Bi codoped SnTe–AgBiTe₂ alloys is reported. It is demonstrated that the existence of Ge, Bi, and Ag facilitate band convergence in SnTe, resulting in remarkable enhancement of Seebeck coefficient and power factor. Simultaneously, localized lattice imperfections including dislocations, point defects, and micro/nanopore structures are caused by incorporation of Ge, Bi, and Ag, which can effectively scatter heat carrying phonons with different wavelengths and contribute to an extremely low κ_L of 0.61 W m⁻¹ K⁻¹ in Sn_0.92Ge_0.04Bi_0.04Te–10%AgBiTe₂. Such high peak ZT is achieved by decouples electron and phonon transport through band modification and localized lattice engineering, highlighting promising solutions for advancing thermoelectrics.     

填充方钴矿类热电材料的研究进展

首先介绍了填充方钴矿类热电材料的电子结构特征,重点评述了方钴矿类热电材料的优化成分设计,并介绍了填充式skutterudite化合物能带结构的模拟计算、制备方法及其应用前景.     

Thermoelectric Power and Thermal Conduction Studies on the Gd Substituted BPSCCO (2234) Superconductors

Measurements of the electrical resistance (R-T), thermoelectric power (S-T) and thermal conductivity (κ-T) have been carried out on the superconductor Bi_1.7Pb_0.3-x Gd _x Sr₂Ca₃Cu₄O_12+y , (0.01 ≤ x ≤ 0.1). According to the XRD patterns the volume fraction of the Bi-2223 phase decreases in favor of Bi-2212. All the samples show normal metallic behavior down to their relevant transition temperature, T _c . T _c -values decrease significantly with increasing Gd concentration in the system. The hole concentration per Cu has been calculated by using the Presland method and found to decrease with increasing Gd content. The thermoelectric power values of the samples are positive and increase in magnitude with increasing the substitution level. The results obtained have been analyzed in terms of “Two band model with linear T-term” and “Xin’ s two band model”. A very good agreement between the first model and our thermoelectric power data was obtained, but the fit to the second model was poor. The substitution has considerable effect on the thermal conductivity, κ. The magnitude of κ is suppressed and a peak appears just below their T _c , values but becomes weaker and broader when the Gd concentration is increased.      

Static Theory of a Self-Driven Photo-Thermoelectrical High-Temperature Superconductor Bolometer

At the present time, radiation detection in the far infrared with millisecond response time requires use of complicated technology to obtain mK-degree operating temperatures and very high quality, critical temperature materials (e.g., W, Al). It is also customary to use films of nanometer thickness in the manufacture of such devices. In this paper, we present theory and computations for the performance a composite high-temperature superconductor (HTSC)–thermolectric materials bolometer, operated at 77 K and with films of thickness around 1 . A practical device with performance comparable to available photoelectrical bolometers is investigated. The simplicity of the technology involved makes it an attractive proposition. A semimetal film leg (SML; e.g., BiSb) is connected in parallel with a HTSC leg (HTSCL; e.g., YBCO). The bolometer is operated in a photovoltaic mode with no external source of bias power. The thermoelectric voltage developed across the SML leg due to radiation absorbed on the sensitive area of the bolometer remains shorted till there is a sufficient temperature rise of the HTSCL so that its resistance becomes comparable to that of the SML. The voltage thus developed across the bolometer would drive an external electronic readout circuit.     

High-Temperature Thermoelectric Power of The Metal Oxides: La2?xSrxCuO4 and Bi1?xSrxMnO3

We have investigated the high-temperature thermoelectric power (TEP) of La_{2− x} Sr _x CuO₄ (0.05 ≤ x ≤ 0.35) and Bi_{1− x} Sr _x MnO₃ (0.5 ≤ x ≤ 0.8) up to 700 K. Based on the TEP results we have discussed the phase transitions on each case. In the case of high-T _C cuprates, La_{2− x} Sr _x CuO₄ (0.05 ≤ x ≤ 0.35), the TEP shows different temperature dependences in three temperature regions. At low temperature, the positive TEP rises showing a broad peak at temperature T _P, which shifts to lower temperature upon Sr doping. Right above T _P, the TEP decreases linearly as temperature increases. At high temperature, TEP deviates from the linear-T dependence at a certain temperature, T _H, showing a saturation behavior. The systematic change of the TEP behavior is discussed in terms of the two-fluids model, which is an intrinsically inhomogeneous state, consisted of bound pairs and independent carriers in the normal state of the high-T _C superconductors. For Bi_{1− x} Sr _x MnO₃ (0.5 ≤ x ≤ 0.8), the negative TEP is almost temperature-independent in the high temperature regime (T _CO < T < 700 K). Near the charge ordering temperature (T _CO), however, TEP suddenly decreases with decrease of temperature, indicating the suppression of carrier mobility with charge ordering transition. As Bi concentration decreases, T _CO shifts to lower temperature from T _CO ∼ 520 K for x = 0.5 to T _CO ∼ 435 K for x = 0.8, which suggests that charge ordering is related to the local lattice distortion due to highly polarizable 6s² character of Bi³⁺ ion. In comparison with the resistivity data, the TEP results have been discussed in terms of the carrier localization accompanied by local lattice distortion.     

Soft x-ray photoelectron spectroscopy study of type-I clathrates

Abstract

Extensive soft x-ray photoelectron spectroscopy studies are performed on Ba₈ Ga₁₆ Ge₃₀ (BGG) and Sr₈Ga₁₆Ge₃₀ (SGG) single crystals ranging from Fermi to core levels, at a high-energy facility. Valence band x-ray photoelectron spectroscopy (XPS) experiments with theoretical calculations revealed that the valence band is mainly constructed by the Ge/Ga 4s and 4p wave functions with little contribution of the Ba/Sr atomic orbitals. Surprisingly, unexpected features evidencing the different shift for the 2a- and 6d- sites between Ba 4d and Sr 3d are observed. The detailed analyses including theoretical support by first-principles band-structure calculations lead to the conclusion that the component distributions of the larger tetrakaidecahedral cage are different depending on the endohedral atoms, which contrasts with the past consensus that BGG and SGG have the same framework structure. This may give thorough reconsiderations on earlier interpretations of experimental data.     

半导体致冷表面温度的动态特性

全面考虑半导体致冷器件冷热端的瞬时温度特性,对研究半导体致冷的精确控制有重要意义.根据半导体致冷器件的工作原理,结合实际工作情况,推导出了半导体致冷器件任意时刻的表面温度计算公式,从而可以得到任意时刻的致冷量,所用方法和结果可用以指导对半导体致冷实时温度控制系统的设计.