Realizing Cd and Ag codoping in p-type Mg_(3)Sb_(2)toward high thermoelectric performance

Mg_(3)Sb_(2)has attracted intensive attention as a typical Zintl-type thermoelectric material.Despite the exceptional thermoelectric performance in n-type Mg_(3)Sb_(2),the dimensionless figure of merit(zT)of p-type Mg_(3)Sb_(2)remains lower than 1,which is mainly attributed to its inferior electrical properties.Herein,we synergistically optimize the thermoelectric properties of p-type Mg_(3)Sb_(2)materials via codoping of Cd and Ag,which were synthesized by high-energy ball milling combined with hot pressing.It is found that Cd doping not only increases the carrier mobility of p-type Mg_(3)Sb_(2),but also diminishes its thermal conductivity(κ_(tot)),with Mg_(2.85)Cd_(0.5)Sb_(2)achieving a lowκtot value of∼0.67 W m^(−1)K^(−1)at room temperature.Further Ag doping elevates the carrier concentration,so that the power factor is optimized over the entire temperature range.Eventually,a peak zT of∼0.75 at 773 K and an excellent average zT of∼0.41 over 300−773 K are obtained in Mg_(2.82)Ag_(0.03)Cd_(0.5)Sb_(2),which are∼240%and∼490%higher than those of pristine Mg_(3.4)Sb_(2),respectively.This study provides an effective pathway to synergistically improve the thermoelectric performance of p-type Mg_(3)Sb_(2)by codoping Cd and Ag,which is beneficial to the future applications of Mg_(3)Sb_(2)-based thermoelectric materials.

Magnetic interactions in a proposed diluted magnetic semiconductor(Ba_(1-x)K_x)(Zn_(1-y)Mn_y)_2P_2

By using first-principles electronic structure calculations, we have studied the magnetic interactions in a proposed BaZn2P2-based diluted magnetic semiconductor（DMS）. For a typical compound Ba（Zn（0.944）Mn（0.056））2P2 with only spin doping, due to the superexchange interaction between Mn atoms and the lack of itinerant carriers, the short-range antiferromagnetic coupling dominates. Partially substituting K atoms for Ba atoms, which introduces itinerant hole carriers into the p orbitals of P atoms so as to link distant Mn moments with the spin-polarized hole carriers via the p–d hybridization between P and Mn atoms, is very crucial for the appearance of ferromagnetism in the compound. Furthermore, applying hydrostatic pressure first enhances and then decreases the ferromagnetic coupling in（Ba0.75 K0.25）（Zn（0.944）Mn（0.056））2P2 at a turning point around 15 GPa, which results from the combined effects of the pressure-induced variations of electron delocalization and p–d hybridization. Compared with the BaZn2 As2-based DMS, the substitution of P for As can modulate the magnetic coupling effectively. Both the results for BaZn2 P2-based and BaZn2As2-based DMSs demonstrate that the robust antiferromagnetic（AFM） coupling between the nearest Mn–Mn pairs bridged by anions is harmful to improving the performance of these Ⅱ–Ⅱ–Ⅴ based DMS materials.

Super deformability and thermoelectricity of bulkγ-InSe single crystals

Indium selenide,aⅢ–Ⅴgroup semiconductor with layered structure,attracts intense attention in various photoelectric applications,due to its outstanding properties.Here,we report super deformability and thermoelectricity ofγ-In Se single crystals grown by modified Bridgeman method.The crystal structure of In Se is studied systematically by transmission electron microscopy methods combined with x-ray diffraction and Raman spectroscopy.The predominate phase ofγ-In Se with dense stacking faults and local multiphases is directly demonstrated at atomic scale.The bulkγ-In Se crystals demonstrate surprisingly high intrinsic super deformative ability which is highly pliable with bending strains exceeding12.5%and 264%extension by rolling.At the meantime,In Se also possesses graphite-like features which is printable,writable,and erasable.Finally,the thermoelectric properties ofγ-In Se bulk single crystals are preliminary studied and thermal conductivity can be further reduced via bending-induced defects.These findings will enrich the knowledge of structural and mechanical properties'flexibility of In Se and shed lights on the intrinsic and unique mechanical properties of In Se polytypes.

Complex alloying effect on thermoelectric transport properties of Cu2Ge(Se(1-x)Tex)3

To enhance the thermoelectric performance of Cu2GeSe3, a series of Te-alloyed samples Cu2Ge（Se（1-x）Tex）3 are synthesized and investigated in this work. It is found that the lattice thermal conductivity is reduced drastically for x = 0.1 sample, which may be attributed to the point defects introduced by alloying. However, for samples with x ≥ 0.2, the lattice thermal conductivity increases with increasing x, which is related to a less distorted structure. The structure evolution,together with the change in carrier concentration, also leads to a systemically change in electrical properties. Finally, a z T of 0.55@750 K is obtained for the sample with x = 0.3, about 62% higher than that for the pristine sample.

Band modification towards high thermoelectric performance of SnSb_(2)Te_(4) with strong anharmonicity driven by cation disorder

As a typical (IV–VI)_(x)(V_(2)VI_(3))_(y) compound, the tetradymite-like layered SnSb_(2)Te_(4) -based compounds have attracted increasing attention in the thermoelectric community owing to the intrinsically low lattice thermal conductivity. Nevertheless, the effect of cations disorder on the inherent physical characteristics remains puzzling, and its inferior Seebeck coefficient is the bottleneck to achieving high thermoelectric performance. In this work, the thermoelectric properties of polycrystalline In_(x)Sn_(1−x)Sb_(2)(Te_(1−y)Se_(y))_(4) (0≤x≤0.1,0≤y≤0.15) samples are comprehensively investigated. In conjunction with the calculated band structure and experimental results, the Seebeck coefficient and power factor are markedly improved after the introduction of indium and selenium, which originates from the combined effects of the emergent resonant states and converged valence bands along with optimal carrier concentration. Additionally, compared with the ordered lattice structure, the disordered cations occupancy in SnSb_(2)Te_(4) further strengthens lattice anharmonicity and reduces phonon group velocity verified by first-principles calculations, securing intrinsically low lattice thermal conductivity. Finally, a record zT value of ∼0.6 at 670 K and an average zT of ∼0.4 between 320 and 720 K are obtained in the In0.1 Sn0.9 Sb2 Te3.4 Se0.6 sample, being one of the highest zT values among SnSb2 Te4 -based materials. This work not only demonstrates that SnSb2 Te4 -based compounds are promising thermoelectric candidates, but also provides guidance for the promotion of thermoelectric performance in a broad temperature range.

Planar Zintl-phase high-temperature thermoelectric materials XCuSb(X=Ca,Sr,Ba)with low lattice thermal conductivity

A recent discovery of high-performance Mg_(3)Sb_(2) has ignited tremendous research activities in searching for novel Zintl-phase compounds as promising thermoelectric materials.Herein,a series of planar Zintl-phase XCuSb(X=Ca,Sr,Ba)thermoelectric materials are developed by vacuum induction melting.All these compounds exhibit high carrier mobilities and intrinsic low lattice thermal conductivities(below 1 W·m^(−1)·K^(−1) at 1010 K),resulting in peak p-type zT values of 0.14,0.30,and 0.48 for CaCuSb,SrCuSb,and BaCuSb,respectively.By using BaCuSb as a prototypical example,the origins of low lattice thermal conductivity are attributed to the strong interlayer vibrational anharmonicity of Cu–Sb honeycomb sublattice.Moreover,the first-principles calculations reveal that n-type BaCuSb can achieve superior thermoelectric performance with the peak zT beyond 1.1 because of larger conducting band degeneracy.This work sheds light on the high-temperature thermoelectric potential of planar Zintl compounds,thereby stimulating intense interest in the investigation of this unexplored material family for higher zT values.

拉曼光谱定义SbCrSe_(3)单晶的振动模式对称性和声子非谐性

本文报道了SbCrSe_(3)单晶的合成方法及其在2–300 K温度范围内的热输运性能.通过角分辨偏振拉曼光谱技术、群论和理论计算分析,我们首次定义了该晶体沿(00l)解理面的拉曼振动模式对称性,并可利用其某些模式确定晶体轴向.另外,通过原位变温拉曼光谱和理论计算相结合的方式,分析得出三声子散射过程即可准确地描述晶格热导率对温度的依赖关系.本文从一个全新的角度揭示了SbCrSe_(3)的热输运性质,为研究其他低维材料热性能提供了有力借鉴.

一种新的过渡金属层状材料Na4Cu3TaAs4的结构和物理性质(英文)

我们报道了一种新的过渡金属层状砷化物Na4Cu3TaAs4的合成、结构和物理性质.这种材料采用Ⅰ√2 m空间群,晶胞参数为a=5.9101(3)?,c=13.8867(12)?.这个材料的结构中包含两层Na,而Na夹在反氧化铅型(Cu/Ta)As层之间,类似于"111"型铁基超导体NaFeAs.过渡金属位由75%的Cu和25%的Ta占据,Ta形成了明确的√2超结构.Cu和Ta分别为+1和+5价.角分辨光电子能谱测得的Na4Cu3TaAs4能带结构能够和DFT计算结果良好地吻合.角分辨光电子能谱和输运测量均表明该材料表现为金属行为,具有p型载流子.磁化率测量表明该材料表现为几乎不依赖温度的抗磁性.这种新材料扩展了含有反氧化铅型层的材料系统,并为进一步研究该材料系统提供了一个很好的平台.