新穎含鉿之金屬間化合物的合成與分析

Abstract

在本論文中，我們利用電弧反應合成含鉿之金屬間化合物，藉由單晶繞射解析其結構，並透過理論計算研究這些化合物的電子結構。首先，在Hf–Cu–Al 的三元系統中，我們得到三個Laves phase 結構化合物HfAl2–xCux (x = 0.49, 0.88, 1.04)。實驗顯示，隨著鋁逐漸被銅取代，化合物的結構會依序呈現MgCu2，MgNi2，MgZn2 三種不同類型的變化。電性測量顯示在室溫下，其電阻率分別為4.35 ( x = 0.5)，5.85 ( x = 0.7)，6.50 ( x = 0.9)。透過理論計算，我們可以得到化合物在穩定態時，銅原子與鋁原子在結構中的分布傾向，同時此結果亦可印證我們在實驗中實際觀察到的現象。接著，同樣是在Hf–Cu–Al 的三元系統中，我們得到一化合物Hf6Cu16Al7.58。此化合物的結構可視為一組成單體以立方最密推積的方式所構成，而此組成單體則是由四個多面體層所組合。儘管由結構上來看，Al2 原子處於一個在鍵結環境上較不適宜的位置，但是電子結構的計算顯示Al2 與鄰近的Hf 原子仍有很強烈的鍵結。然後，在Hf–Al–Sb 的三元系統中，我們得到三個化合物Hf5Al3–xSbx (x = 0.70, 1.44, 2.14)。此系統在0 ≤ x ≤ 1.0 以及2.0 ≤ x ≤ 2.5 的範圍內，分別呈現Mn5Si3 與W5Si3 兩種結構類型的相寬。這兩種結構各為兩種不同的多面體沿著c 軸所構成。理論計算的結果說明該化合物的電子結構主要是來自於Hf–Sb 鍵結的貢獻，而系統的穩定度則同時受到異鍵結Hf–Al 與Hf–Sb 的影響。最後，在Hf–Ni–Ga 的三元系統中，我們得到兩個金屬間化合物Hf13.0Ni40.8Ga30.9 與Zr13.0Ni40.6Ga31.0，其結構是由鍵結數不等的多面體所組成(鉿：12–15，鎳與鎵：6–12)。進一步的結構分析顯示，此化合物可視為CaCu5 的結構延伸，即透過取代與移除原子位置所得的層狀架構。

The main topic for this dissertation focuses on the synthesis, structures, and physical properties of ternary hafnium aluminides that contains four parts as listed below: 1) A series of new ternary intermetallic phases HfAl2–xCux (x = 0.49, 0.88, 1.04) and characterized them as Laves phase structures. X-ray diffraction revealed homogeneity within the ranges 0.2 ≤ x ≤ 0.5 and 0.7 ≤ x ≤ 0.9 for the MgCu2 and MgNi2 structure types, respectively. When Cu atoms gradually replaced the Al atoms, the structure type altered in the sequence MgCu2, MgNi2, MgZn2, and distortion of Kagomé nets occurred with varying bond lengths. Measurements of physical properties revealed these phases were metallic, with resistances of 4.35(x = 0.5), 5.85 (x = 0.7), and 6.50 (x = 0.9)mΩ·cm, respectively, at temperatures 300 K. The coloring schemes revealed that, upon increasing the Cu atom content, the stability of these phases correlated with the arrangements of the Al and Cu atoms. Calculated electronic structures indicated that the bonding character was consistent with experimentally observed phase width. 2) Hafnium copper aluminide Hf6Cu16Al7.58 was synthesized from the pure elements in an arc- melting reaction; its structure was solved from X-ray diffraction data of a single crystal. The structure contains building unit as four successive polyhedral shells adopting cubic close packing. Calculations of the band structure indicate an intense interaction in Hf-Al contacts despite the unfavorable coordination environment, and a strong contribution from Cu–Al interactions. 3) Three new hafnium aluminium antimonides Hf5Al3–xSbx (x = 0.70, 1.44, 2.14) were synthesized from the pure elements in an arc-melting reaction; their structures were solved from X-ray diffraction data of single crystals. Two ranges of homogeneity were observed through Al/Sb mixing, which appeared within ranges 0 ≤ x ≤ 1.0 for Mn5Si3 structure type and 2.0 ≤ x ≤ 2.5 for W5Si3 type. Both structures are regarded as condensations of two polyhedra stacking along the c axis. Calculations of their electronic structures revealed substantial contributions from Hf-Sb interactions; the heteroatomic bonding (Hf-Al and Hf-Sb contacts) affected the stability of these two phases. Measurements of resistivity on polycrystalline samples showed dependence on temperature, indicating a metallic behavior consistent with the results from calculations. 4) Ternary compounds Hf13.0Ni40.8Ga30.9 and Zr13.0Ni40.6Ga31.0 that were synthesized from the pure elements in an arc-melting reaction, and characterized their structures through X-ray diffraction of single crystals. Each compound adopted a hexagonal structure of Y13Pd40Sn31 type and crystallized in the space group P6/mmm (no. 191). The cell parameters of Hf13.0Ni40.8Ga30.9 were a = 17.895(3) Å; c = 8.2434(16) Å; V = 2286.0(6) Å3; and R1/wR2 = 0.0299/0.0598. The cell parameters of Zr13.0Ni40.6Ga31.0 were a = 17.964(3) Å; c = 8.2757(17) Å; V = 2312.7(7) Å3; and R1/wR2 = 0.0348/0.0686. These structures comprise polyhedra with diverse coordination numbers (Hf 12–15, Ni and Ga 6–12) and the analysis of structures revealed the layer frameworks based on the CaCu5-type structures. Calculated electronic structures revealed a strong contribution from Ni-Ga interaction and the characteristics of a polar intermetallics phase.