几种含Sn（Si）层状化合物的结构与物性研究

发布时间：2018-05-03 08:21

本文选题：层状化合物 + 热导率　；参考：《中国科学院大学(中国科学院物理研究所)》2017年博士论文

【摘要】：层状化合物具有易于调控的结构和丰富的物性,通常在热、电、光、磁等方面表现出优良的性能,具有广泛的应用前景。探索新的层状化合物将有助于不断提高这类材料的性能,以及揭示决定和影响材料性能的物理机制。本论文以SnAs层作为材料的物性决定层,设计出新型低晶格热导化合物并揭示了它们低晶格热导率的物理起源,为寻找和设计新型低晶格热导材料提供了新思路;此外,以AlSi层作为材料的物性决定层,对层状SrAlSi超导体进行掺杂调控研究,加深了对层状超导体的认识。本论文的主要研究结果如下:第一,首次报道了含双孤对电子的低晶格热导新材料NaSnAs,揭示了其低晶格热导率的起因。实验发现窄带隙半导体材料NaSnAs和NaSnP的最小晶格热导率分别为0.62 W/m/K和0.58 W/m/K,很接近理论预言的最小晶格热导率。这两个化合物的晶格热导率只有与它们有相似SnAs层和Na原子层的NaSn_2As_2化合物晶格热导率的60%。这种明显的晶格热导率的差别主要是由于NaSnAs和NaSnP化合物比NaSn_2As_2化合物含有更多的孤对电子。双孤对电子导致材料的晶格产生更强的非简谐作用,即格林内森值((?))更大,从而降低了材料的晶格热导率。本结果为探索和发现新的本征低晶格热导材料提供了新思路。第二,设计出不同晶型的新化合物Li_(1.67)Sn_(0.33)As,研究了它们的结构与低晶格热导率性质的关系。设计出两种不同晶体结构的Li_(1.67)Sn_(0.33)As化合物,分别是高温相和低温相,其空间群为Fm3(?)m和Ia3(?)。这两种晶型的材料均呈现出半导体行为,载流子激活能分别为0.93 eV和1.04 eV。在500 K时,高温相和低温相的晶格热导率分别为0.91 W/m/K和1.00 W/m/K。它们的本征低晶格热导率主要是由于轻原子(Li原子)和重原子(Sn原子)的混合占位。通过高低温相的对比实验表明Li原子和Sn原子的无序程度越高,声子散射和非简谐振动越强,对应的晶格热导率越低。另外,通过调控Li和Sn的含量,发现了新化合物Li1.76Sn0.24As,空间群为Pa3(?),500 K温度下的晶格热导率为0.78 W/m/K。第三,研究了对NaSn_2As_2的物性决定层和载流子库层的掺杂调控以及掺杂对其物性的影响。首先,对NaSn_2As_2的As位进行了P掺杂,EDX的结果表明实际P的最大掺杂量为6%。电学方面,调控前后的样品均表现出金属行为,且电阻率随掺杂量的增加而变大。磁性方面表现出顺磁性,并没有看到超导转变信号。其次,对NaSn_2As_2的Na位进行了Sr掺杂,掺杂样品可以形成连续固溶体,都是顺磁金属材料。随着掺杂量的增加,载流子类型从空穴型向电子型转变,这是因为它费米能级处的多带结构和Sr掺杂向体系中引入更多的电子。化学压力和载流子浓度的调控都未能在NaSn_2As_2材料中诱导出超导电性。第四,研究了V和Cr原子在SrAlSi超导体中的掺杂效应。V和Cr能够部分替代SrAlSi中的Al原子,最大掺杂量分别是16 at.%和13 at.%。V的掺杂使得其载流子浓度降低了三个数量级并且快速地降低了其超导转变温度;当掺杂量为0.2时,超导淬灭。这可能是由V的掺杂降低了费米面的位置和态密度导致的。不同的是,Cr的掺杂基本不改变载流子浓度,对应的费米面位置和态密度均保持不变,Tc~(onset)也只变化了0.6 K。这些结果表明过渡族金属原子的价电子对材料的超导电性具有重要的影响,也为更好地理解超导材料的掺杂效应提供了线索。
[Abstract]:Layered compounds have an easy to regulate structure and rich physical properties. They usually exhibit excellent properties in heat, electricity, light and magnetism, and have wide application prospects. Exploring new layered compounds will help to improve the properties of these materials and reveal the physical mechanisms that determine and influence the properties of the materials. This paper is based on the SnAs layer. A new type of low lattice thermal conductivity compound is designed for the material property determination layer and the physical origin of their low lattice thermal conductivity is revealed. A new idea is provided for the search and design of a new type of low lattice thermal conductivity material. In addition, the AlSi layer is used as the material determination layer to study the doping control of layered SrAlSi superconductors. The main results of this paper are as follows: first, a new thermal conductivity new material NaSnAs with double soliton pair electrons is reported for the first time. The cause of the thermal conductivity of low lattice is revealed. It is found that the minimum lattice thermal conductivity of the narrow band gap semiconductor material NaSnAs and NaSnP is divided into 0.62 W/m/K and 0.58 W/m/K, which is very close to the theoretical prediction. The thermal conductivity of the lattice of the two compounds is only the difference between the lattice thermal conductivity of the lattice thermal conductivity of the NaSn_2As_2 compounds with similar SnAs and Na atomic layers. The difference in the thermal conductivity of the lattice is mainly because the NaSnAs and NaSnP compounds contain more isolated electrons than the NaSn_2As_2 compounds. The lattice of the material has a stronger non harmonic action, that is, the Green Nathan value ((?)) is larger, thus reducing the thermal conductivity of the lattice. The results provide a new idea for exploring and discovering new intrinsic low lattice thermal conductivity materials. Second, new compounds of different crystalline forms Li_ (1.67) Sn_ (0.33) As are designed and their structure and low lattice heat are studied. Li_ (1.67) Sn_ (0.33) As compounds with different crystal structures are designed to be Fm3 (?) m and Ia3 (?). These two crystalline materials show semiconductor behavior, carrier activation energy is 0.93 eV and 1.04 eV. at 500 K, and the thermal conductivity of high temperature phase and low temperature phase The intrinsic low lattice thermal conductivities of 0.91 W/m/K and 1 W/m/K. are mainly due to the mixed occupancy of light atoms (Li atoms) and heavy atoms (Sn atoms). The higher the degree of disorder of the Li and Sn atoms, the higher the Li and the Sn atoms, the stronger the phonon scattering and the non harmonic oscillating, the lower the corresponding lattice thermal conductivity. The content of Li and Sn was regulated, the new compound Li1.76Sn0.24As was found, the space group was Pa3 (?), the thermal conductivity of the lattice at 500 K was 0.78 W/m/K. third. The doping control of the physical determination layer and the carrier reservoir of NaSn_2As_2 and the effect of doping on its properties were studied. First, P doping on As bit of NaSn_2As_2, EDX result table The maximum doping amount of the actual P is 6%. electrical field. The samples before and after the regulation show the metal behavior, and the resistivity becomes larger with the increase of the doping amount. The magnetic aspect shows paramagnetic, and the superconducting transition signal is not seen. Secondly, Sr doping is carried out on the Na position of NaSn_2As_2, and the doped samples can form continuous solid solution, all of which are paramagnetic. Metal materials. With the increase of the amount of doping, the carrier type changes from the cavity type to the electron type. This is due to its multi band structure at the Fermi level and the introduction of more electrons in the Sr doping system. The regulation of the chemical pressure and carrier concentration can not induce superconductivity in the NaSn_2As_2 material. Fourth, the V and Cr atoms are studied in Sr The doping effect.V and Cr in AlSi superconductors can partially replace Al atoms in SrAlSi, the doping of the maximum amount of 16 at.% and 13 at.%.V makes the carrier concentration reduced by three orders of magnitude and rapidly reduces the superconducting transition temperature. When the doping amount is 0.2, the superconductivity quenching. This may be caused by the doping of V to reduce Fermi. The position and density of the surface are different. The doping of Cr does not change the carrier concentration, the corresponding Fermi position and the density of states remain unchanged, and the Tc~ (onset) also only changes 0.6 K.. These results show that the valence electrons of the transition metal atoms have an important influence on the superconductivity of the material, and the better solution of the superconductivity. The dopant effect of the material provides a clue.

【学位授予单位】：中国科学院大学(中国科学院物理研究所)
【学位级别】：博士
【学位授予年份】：2017
【分类号】：O511.3

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