本文選題：層狀化合物 + 熱導(dǎo)率��； 參考：《中國科學(xué)院大學(xué)(中國科學(xué)院物理研究所)》2017年博士論文

【摘要】：層狀化合物具有易于調(diào)控的結(jié)構(gòu)和豐富的物性,通常在熱、電、光、磁等方面表現(xiàn)出優(yōu)良的性能,具有廣泛的應(yīng)用前景。探索新的層狀化合物將有助于不斷提高這類材料的性能,以及揭示決定和影響材料性能的物理機制。本論文以SnAs層作為材料的物性決定層,設(shè)計出新型低晶格熱導(dǎo)化合物并揭示了它們低晶格熱導(dǎo)率的物理起源,為尋找和設(shè)計新型低晶格熱導(dǎo)材料提供了新思路;此外,以AlSi層作為材料的物性決定層,對層狀SrAlSi超導(dǎo)體進(jìn)行摻雜調(diào)控研究,加深了對層狀超導(dǎo)體的認(rèn)識。本論文的主要研究結(jié)果如下:第一,首次報道了含雙孤對電子的低晶格熱導(dǎo)新材料NaSnAs,揭示了其低晶格熱導(dǎo)率的起因。實驗發(fā)現(xiàn)窄帶隙半導(dǎo)體材料NaSnAs和NaSnP的最小晶格熱導(dǎo)率分別為0.62 W/m/K和0.58 W/m/K,很接近理論預(yù)言的最小晶格熱導(dǎo)率。這兩個化合物的晶格熱導(dǎo)率只有與它們有相似SnAs層和Na原子層的NaSn_2As_2化合物晶格熱導(dǎo)率的60%。這種明顯的晶格熱導(dǎo)率的差別主要是由于NaSnAs和NaSnP化合物比NaSn_2As_2化合物含有更多的孤對電子。雙孤對電子導(dǎo)致材料的晶格產(chǎn)生更強的非簡諧作用,即格林內(nèi)森值((?))更大,從而降低了材料的晶格熱導(dǎo)率。本結(jié)果為探索和發(fā)現(xiàn)新的本征低晶格熱導(dǎo)材料提供了新思路。第二,設(shè)計出不同晶型的新化合物L(fēng)i_(1.67)Sn_(0.33)As,研究了它們的結(jié)構(gòu)與低晶格熱導(dǎo)率性質(zhì)的關(guān)系。設(shè)計出兩種不同晶體結(jié)構(gòu)的Li_(1.67)Sn_(0.33)As化合物,分別是高溫相和低溫相,其空間群為Fm3(?)m和Ia3(?)。這兩種晶型的材料均呈現(xiàn)出半導(dǎo)體行為,載流子激活能分別為0.93 eV和1.04 eV。在500 K時,高溫相和低溫相的晶格熱導(dǎo)率分別為0.91 W/m/K和1.00 W/m/K。它們的本征低晶格熱導(dǎo)率主要是由于輕原子(Li原子)和重原子(Sn原子)的混合占位。通過高低溫相的對比實驗表明Li原子和Sn原子的無序程度越高,聲子散射和非簡諧振動越強,對應(yīng)的晶格熱導(dǎo)率越低。另外,通過調(diào)控Li和Sn的含量,發(fā)現(xiàn)了新化合物L(fēng)i1.76Sn0.24As,空間群為Pa3(?),500 K溫度下的晶格熱導(dǎo)率為0.78 W/m/K。第三,研究了對NaSn_2As_2的物性決定層和載流子庫層的摻雜調(diào)控以及摻雜對其物性的影響。首先,對NaSn_2As_2的As位進(jìn)行了P摻雜,EDX的結(jié)果表明實際P的最大摻雜量為6%。電學(xué)方面,調(diào)控前后的樣品均表現(xiàn)出金屬行為,且電阻率隨摻雜量的增加而變大。磁性方面表現(xiàn)出順磁性,并沒有看到超導(dǎo)轉(zhuǎn)變信號。其次,對NaSn_2As_2的Na位進(jìn)行了Sr摻雜,摻雜樣品可以形成連續(xù)固溶體,都是順磁金屬材料。隨著摻雜量的增加,載流子類型從空穴型向電子型轉(zhuǎn)變,這是因為它費米能級處的多帶結(jié)構(gòu)和Sr摻雜向體系中引入更多的電子�；瘜W(xué)壓力和載流子濃度的調(diào)控都未能在NaSn_2As_2材料中誘導(dǎo)出超導(dǎo)電性。第四,研究了V和Cr原子在SrAlSi超導(dǎo)體中的摻雜效應(yīng)。V和Cr能夠部分替代SrAlSi中的Al原子,最大摻雜量分別是16 at.%和13 at.%。V的摻雜使得其載流子濃度降低了三個數(shù)量級并且快速地降低了其超導(dǎo)轉(zhuǎn)變溫度;當(dāng)摻雜量為0.2時,超導(dǎo)淬滅。這可能是由V的摻雜降低了費米面的位置和態(tài)密度導(dǎo)致的。不同的是,Cr的摻雜基本不改變載流子濃度,對應(yīng)的費米面位置和態(tài)密度均保持不變,Tc~(onset)也只變化了0.6 K。這些結(jié)果表明過渡族金屬原子的價電子對材料的超導(dǎo)電性具有重要的影響,也為更好地理解超導(dǎo)材料的摻雜效應(yīng)提供了線索。
[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.

【學(xué)位授予單位】：中國科學(xué)院大學(xué)(中國科學(xué)院物理研究所)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2017
【分類號】：O511.3

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