Maximizing the scattering of multiwavelength phonons in novel biphasic high-entropy ZrCoSb-based half-Heusler alloys

The thermoelectric(TE)performance of p-type ZrCoSb-based half-Heusler(HH)alloys has been improved tremendously in recent years;however,it remains challenging to find suitable n-type ZrCoSb-based HH alloys due to their high lattice thermal conductivity(κ_(L)).In this work,n-type Zr_(1−x)Ta_(x)Co_(1−x)Ni_(x)Sb HH alloys were firstly designed by multisite alloying.The evolution of the Raman peak proved that alloy scattering,phonon softening,anharmonicity,entropy-driven disorder,and precipitates had a combined effect on decreasingκ_(L)by 46.7%compared to that of pristine ZrCoSb.Subsequently,Hf_(0.75)Zr_(0.25)NiSn_(0.99)Sb_(0.01)was introduced into Zr_(0.88)Ta_(0.12)Co_(0.88)Ni_(0.12)Sb to further suppressκ_(L).Remarkably,the grain size of the biphasic HH alloys was refined by at least one order of magnitude.A biphasic high-entropy HH alloy with y=0.2 exhibited the minimumκ_(L)of∼2.44 W/(m·K)at 923 K,reducing by 67.7%compared to that of ZrCoSb.Consequently,(Zr_(0.88)Ta_(0.12)Co_(0.88)Ni_(0.12)Sb)_(0.9)(Hf_(0.75)Zr_(0.25)NiSn_(0.99)Sb_(0.01))_(0.1)exhibited the highest TE figure of merit(∼0.38)at 923 K.The cooperation between the entropy and biphasic microstructure resulted in multiscale defects,refined grains,and biphasic interfaces,which maximized the scattering of the multiwavelength phonons in HH alloys.This work provides a new strategy for further reducing the grain size andκ_(L)of medium-and high-entropy HH alloys.

Preparation and Thermoelectric Properties of Zr_(1-x)Ti_xNiSn_(0.975)Sb_(0.025) Half-Heusler Alloys

Zr1-xTixNiSn0.975Sb0.025 （x=0, 0.15, 0.25, 0.5） half-Heusler thermoelectric materials have been prepared by levitation melt, melt spinning and hot pressing. X-ray diffraction analysis and scanning electron microscopy observation showed that nearly single phase half-Heusler compounds were obtained for the levitation-melted ingots. The effects of Ti substitution and grain refinement by melt spinning have been studied. It is found that both the Ti substitution on the Zr site and the grain refinement can reduce the lattice thermal conductivity and total thermal conductivity. The maximum figure of merit ZT value achieved is about 0.47, which is comparable with the previously reported value of ,-0.5 for Zr0.5Ti0.5NiSn.

同构合金化对P型ZrCoSb基高熵half-Heusler合金热电性能的影响

Half-Heusler(HH)合金由于其本身具有较为优异的力学性能和高温热稳定性,已成为目前最具有应用前景的中高温热电材料之一。然而,其本身较高的本征晶格热导率阻碍了热电性能的进一步提升。本文以P型Zr Co Sb0.85Sn0.15合金为研究对象,基于同构合金化具有优异P型热电性能的(Nb0.8Ta0.2)0.8Ti0.2Fe Sb,通过磁悬浮熔炼和放电等离子烧结设计并制备出一种(Zr Co Sb0.85Sn0.15)1-x[(Nb0.8Ta0.2)0.8Ti0.2Fe Sb]x(x=0,0.2,0.3,0.4,0.5)高熵HH合金。微观组织分析表明,同构合金化这一策略引入了大量多尺度多衬度的第二相,这将有效增强对声子的散射。其中,当同构合金化含量为0.3时,晶格热导率在923 K时从Zr Co Sb0.85Sn0.15的4.72 W·m-1·K-1降至3.07 W·m-1·K-1,降低了35%。然而,由于多位点合金化元素间存在较为复杂的掺杂效果,使其电导率和塞贝克系数同时降低,最终导致热电优值存在一定的降低。本研究工作表明,高熵合金设计思想是一种降低HH热电合金晶格热导率的有力措施。

Nb掺杂对微波制备TiCoSb Half-Heusler合金热电性能的提升

TiCoSb Half-Heusler合金固有的高导热性,以及传统制备方法制备周期长、成本高等缺点限制了其商业化应用。采用微波合成与急速热压烧结相结合的方法成功制备了低热导率的Ti_(1-x)Nb_(x)CoSb Half-Heusler合金,大大缩短了制备周期,同时提高了TiCoSb Half-Heusler合金的致密度。研究了Ti位Nb取代对Ti_(1-x)Nb_(x)CoSb Half-Heusler热电材料的相组成、成分分布及热电输运性能的影响。在功率因子增加和晶格热导率降低的共同作用下,Ti_(1-x)Nb_(x)CoSb样品的热电优值(ZT)得到显著优化。在725 K时,Ti 0.93 Nb 0.07 CoSb样品的最大ZT值为0.1,比相同工艺下制备的TiCoSb纯相样品高两个数量级。

Fabrication and thermoelectric properties of Yb-doped ZrNiSn half-Heusler alloys

Half-Heusler(HH)alloys constitute an important class of materials that exhibit promising potential in high-temperature thermoelectric(TE)power generation.In this work,we synthesized Zr_(1−x)Yb_(x)NiSn(x=0,0.01,0.02,0.04,0.06 and 0.10)HH alloys using a time-efficient levitation melting and spark plasma sintering procedure.X-ray diffraction showed that the samples were predominantly single phased,and that the lattice constant increased systematically with increasing Yb doping ratio.The doping effects of Yb on the thermoelectric properties were studied.It was found that Yb doping consistently decreased the electrical and thermal conductivities.On the other hand,the effects of Yb doping on the Seebeck coefficient were found to be non-monotonic.The magnitude of the Seebeck coefficient(n-type)was increased upon Yb doping up to x=0.02,above which Yb doping introduced notable p-type conduction.As a result,the room-temperature Seebeck coefficient of the x=0.10 sample became positive although the magnitude was not high.The thermoelectric figure of merit,ZT,reached a maximum of∼0.38 at 900 K for the x=0.01 sample.Selective doping on the Ni and Sn sites are necessary to further optimize the TE performance of Zr_(1−x)Yb_(x)NiSn alloys.

Theoretical investigations of half-metallic ferromagnetism in new Half-Heusler YCrSb and YMnSb alloys using first-principle calculations

Structural,electronic,and magnetic properties of new predicted half-Heusler YCrSb and YMnSb compounds within the ordered MgAgAs Clb-type structure are investigated by employing first-principal calculations based on density functional theory.Through the calculated total energies of three possible atomic placements,we find the most stable structures regarding YCrSb and YMnSb materials,where Y,Cr(Mn),and Sb atoms occupy the(0.5,0.5,0.5),(0.25,0.25,0.25),and(0,0,0) positions,respectively.Furthermore,structural properties are explored for the non-magnetic and ferromagnetic and anti-ferromagnetic states and it is found that both materials prefer ferromagnetic states.The electronic band structure shows that YCrSb has a direct band gap of 0.78 eV while YMnSb has an indirect band gap of 0.40 eV in the majority spin channel.Our findings show that YCrSb and YMnSb materials exhibit half-metallic characteristics at their optimized lattice constants of 6.67 and 6.56 ,respectively.The half-metallicities associated with YCrSb and YMnSb are found to be robust under large in-plane strains which make them potential contenders for spintronic applications.

Enhanced thermoelectric performance in Ti(Fe, Co, Ni)Sb pseudoternary Half-Heusler alloys

TiFe0.5Ni0.5Sb-based half-Heusler compounds have the intrinsic low lattice thermal conductivity and the adjustable band structure.Inspired by the previously reports to achieve both p-and n-type components by tuning the ratio of Fe and Ni based on the same parent TiFe0.5Ni0.5Sb,we selected Co as the amphoteric dopants to prepare both n-type and p-type pseudo-ternary Ti(Fe,Co,Ni)Sb-based halfHeusler alloys.The carrier concentration,as well as the density of states effective mass was significantly increased by Co doping,contributing to the enhanced power factor of 1.80 mW m^(-1) K^(-2) for n-type TiFe0.3Co_(0.2)Ni_(0.5)Sb and 2.21 mW m^(-1) K^(-2) for p-type TiFe_(0.5)Co_(0.15)Ni_(0.35)Sb at 973 K.Combined with the further decreased lattice thermal conductivity due to the strain field and mass fluctuation scattering induced by alloying Hf on the Ti site,peak ZTs of 0.65 in n-type Ti0.8Hf_(0.2)Fe_(0.3)Co_(0.2)Ni_(0.5)Sb and 0.85 in ptype Ti0.8Hf_(0.2)Fe_(0.5)Co_(0.15)Ni_(0.35)Sb were achieved at 973 K,which is of great significance for the thermoelectric power generation applications.

Half-Heusler合金NiFeSb和NiMnSb的磁性及电子结构的第一性原理研究

用基于密度泛函理论的第一性原理方法,计算了half-Heusler合金NiFeSb和NiMnSb的晶体结构、磁性及电子结构.计算结果表明,磁性原子Fe和Mn在两种合金的总磁矩中贡献最大,在NiFeSb总磁矩中,Ni原子贡献比例接近在NiMnSb中的2倍,而Sb原子的贡献比例是在NiMnSb中的1/5;两种合金的自旋向上能带都具有明显的金属特征,而自旋向下能带有明显的差别;两种合金费米能级以下的总态密度(DOS)主要由Ni—3d和Fe—3d(Mn—3d)态决定,费米能级以上主要由Fe—3d(Mn—3d)自旋向下部分决定.

Half-Heusler合金NiMn_(1-x)Nb_xSb的磁性和半金属稳定性

基于密度泛函理论的第一性原理计算,我们系统地研究了half-Heusler合金NiMn_1-_xNb_xSb的电子结构、磁性和半金属稳定性.结果表明合金的晶格常数和磁性分别很好地符合Vegard定理和S1ater-Pauling规则;当掺杂浓度为25%时,合金的费米面恰好位于其自旋向下带隙的中部.从而呈现最稳定的半金属性.此外,当前的研究也显示Ni-Mn和Ni-Nb之间的d电子杂化依赖于RKKY间接交换机制,共同贡献于合金的总磁矩.

Investigations of the half-metallic behavior and the magnetic and thermodynamic properties of half-Heusler CoMnTe and RuMnTe compounds: A first-principles study

First-principles spin-polarized density functional theory （DFT） investigations of the structural, electronic, magnetic, and thermodynamics characteristics of the half-Heusler, CoMnTe and RuMnTe compounds are carried out. Calculations are accomplished within a state of the art full-potential （FP） linearized （L） augmented plane wave plus a local orbital （APW ＋ lo） computational approach framed within DFT. The generalized gradient approximation （GGA） parameterized by Perdew, Burke, and Ernzerhof （PBE） is implemented as an exchange correlation functional as a part of the total energy calculation. From the analysis of the calculated electronic band structure as well as the density of states for both compounds, a strong hybridization between d states of the higher valent transition metal （TM） atoms （Co, Ru） and lower valent TM atoms of （Mn） is observed. Furthermore, total and partial density of states （PDOS） of the ground state and the results of spin magnetic moments reveal that these compounds are both stable and ideal half-metallic ferromagnetic. The effects of the unit cell volume on the magnetic properties and half-metaliicity are crucial. It is worth noting that our computed results of the total spin magnetic moments, for CoMnTe equal to 4 ~tB and 3 p-B per unit cell for RuMnTe, nicely follow the rule μ2tot = Zt - 18. Using the quasi-harmonic Debye model, which considers the phononic effects, the effecs of pressure P and temperature T on the lattice parameter, bulk modulus, thermal expansion coefficient, Debye temperature, and heat capacity for these compounds are investigated for the first time.

磁控溅射法制备Half-Heusler化合物半导体TiCoSb薄膜

设计一种特别的TiCoSb复合靶材,通过调节各元素在复合靶材上所占面积的大小,可以方便地调节薄膜的成分.采用这种靶材,利用直流磁控溅射和快速退火成功制备单一物相的多晶TiCoSb薄膜;采用X射线衍射(X-raydiffraction,XRD)和原子力显微镜(atomic force microscopy,AFM)分析TiCoSb薄膜的结构和表面形貌;利用Hall测试仪初步研究薄膜的电学性质.结果表明,所制备的TiCoSb薄膜对石英玻璃衬底具有良好的粘附力,薄膜均匀致密.经600℃,5 min退火的TiCoSb薄膜的结晶质量较好,薄膜的室温电导率为13.7 S/cm.

Half-Heusler热电半导体材料

介绍了最近几年在热电半导体材料领域里新出现的half-Heusler化合物的结构和研 究现状,比较了各化合物掺杂及等电子合金化前后的电与热传输参数的变化,并指出了该材料 的进一步研究方向.

悬浮熔炼制备Half-Heusler合金Zr_(1-x)Ti_xNiSn_(0.975)Sb_(0.025)及其热电性能

采用悬浮熔炼法合成了Zr1-xTixNiSn0.975Sb0.025(x=0,0.15,0.25,0.5)基Half-Heusler热电材料,X射线衍射结果表明所制备合金为单相。相对于常规方法,悬浮熔炼显著缩短了制备Half-Heusler合金的时间。同时研究了Ti取代及不同热压条件对材料热电性能的影响。结果表明:ZrNiSn0.975Sb0.025合金进行A位取代可降低材料的热导率,而不会明显影响其热电性能。致密度可以影响材料的热电性能,适当的热压条件可以使合金的ZT值达到最大,约为0.45。

Half-Heusler合金TaCoSb的制备及Sn掺杂对其热电性能的影响

通过粉末烧结、高能球磨和直流快速热压相结合的工艺制备高熔点half-Heusler合金TaCoSb,热电性能测试结果表明TaCoSb是一种n型热电材料,电导率、热导率、塞贝克系数、ZT值在973 K时分别为0.58×105S·m^(-1)、3.8 W·m^(-1)K^(-1)、^(-1)10μV·K^(-1)、0.18。此外,本文还研究了Sb位进行Sn掺杂对TaCoSb热电性能的影响,实验结果发现:Sn掺杂使得样品的热导率和电导率同时下降,塞贝克系数略微增加,功率因子有所降低,最终材料的ZT值未见明显提升;鉴于TaCoSb的室温电导率较低,应该往Sb右侧方向掺杂改性。

Half-Heusler半金属NiMnSb的制备和结构稳定性

本文研究了烧结温度对Half Heusler半金属的结构和物性的影响。结果表明600℃—800℃烧结4h为较佳的烧结条件;磁化强度和电阻率随温度的变化关系符合经典铁磁理论的预言结果,没有发现明显的有序态间的跃迁和原子无序现象。说明用该方法制备的NiMnSb材料具有很好的热稳定性和原子有序稳定性。

Half-Heusler合金Cu_(1-x)Fe_xMnSb的电子结构和反铁磁-铁磁相变

基于密度泛函理论(DFT),使用局域密度近似(LDA)研究了Heusler合金Cu1-xFex MnSb的电子结构和反铁磁-铁磁相变.研究发现,两种磁状态下的合金晶格常数随掺杂浓度x变化很好地满足Vegard定理.当x>0.5时,铁磁态合金的总磁矩很好地符合SP规律,然而当x<0.5时,却发生了明显的偏离.由于整个体系存在RKKY和超交换磁耦合的竞争,因而在x=0.25时,我们观察到了独特的反铁磁—铁磁相变.进一步的态密度分析发现,Cu的掺杂浓度可以有效调整铁磁态合金的费米面位置,并且反铁磁态合金由于不同自旋方向的Mn原子的分波态密度相互补偿,总态密度形成了几乎完全对称的自旋向上带和自旋向下带.

熵调控抑制ZrNiSn基half-Heusler热电材料的晶格热导率

ZrNiSn基half-Heusler热电材料具有较高的热导率,限制了其热电性能进一步提高。为了降低晶格热导率,本研究采用磁悬浮熔炼和放电等离子烧结的方法制备ZrNiSn和Zr_(0.5)Hf_(0.5)Ni_(1-x)Pt_(x)Sn(x=0,0.1,0.15,0.2,0.25,0.3)高熵half-Heusler热电合金。在Zr位进行Hf原子替代,Ni位进行Pt原子替代以调控该合金的构型熵,并研究构型熵对热电性能的影响。本工作优化了Zr_(0.5)Hf_(0.5)Ni_(0.85)Pt_(0.15)Sn在673 K的最小晶格热导率和双极扩散热导率之和为2.1 W·m^(–1)·K^(–1),与ZrNiSn相比降低了约58%。这一发现为降低ZrNiSn基合金的晶格热导率提供了一种有效的策略,有助于改善材料的热电性能。

稀土掺杂对锡基Half-Heusler合金热电特性的影响

采用电弧熔炼法和放电等离子体烧结法,制备了稀土掺杂的金属间化合物Zr1-xLaxNiSn(x=0.05,0.1,0.15,0.2,0.3,0.4)和Zr0.98R0.02NiSn0.98X0.02(R=La,Ce;X=Sb,Bi).用X射线衍射仪分析研究了它们的晶体结构随稀土替代量演化的规律.在室温到700K的范围内,对其热电特性进行了评价.研究结果表明,代换量x小于0.15时,稀土原子可以进入晶格形成单相化合物.代换量x大于0.15的样品中含有非half-Heusler的第二相,且含量随x增大而增加.少量稀土掺杂可以有效地降低材料的热导率而保持良好的电输运特性.在575K,Zr0.98La0.02NiSn0.98Sb0.02的热电优值达到0.5.

Half-Heusler合金CoMn_(1-x)Nb_xSb的电子结构和磁性研究

采用密度泛函理论(DFT)在广义梯度近似(GGA)下的平面波超软赝势方法,研究了Half-Heusler合金CoMn1-xNbxSb(x=0,0.25,0.5,0.75,1)的电子结构和磁性.通过几何优化和能量计算,得到了合金的晶格常数、电子和自旋分布以及自旋磁矩的大小.通过分析得到当掺杂浓度x<0.75时,CoMn1-xNbxSb合金具有半金属铁磁性质,并且自旋磁矩随着Nb掺杂的增加而线性地减小,和Slater-Pauling曲线符合得很好.当掺杂浓度x=1时,体系从铁磁半金属转化成泡利金属.

Half-Heusler热电材料性能优化策略及研究进展

研究废热再利用和太阳能发电在应对能源短缺等方面具有重大现实意义。热电发电装置基于热电效应,以热电材料为核心部件,可直接实现热能与电能间的相互转换。Half-Heusler材料以其良好的电学性能、优异的力学性能等优点在众多热电材料中脱颖而出。本文结合目前Half-Heusler材料的研究现状,从原子尺度下的元素组分、纳米尺度下的微观组织结构两个方面来探讨提升材料热电性能的策略。随后简单介绍了Half-Heusler合金作为热电材料的主要应用。最后对这类材料的研究做一总结和展望。