三元硒化物La4In4.66Se13之合成及陽離子填佔在Na-La-M-In-Se系統中之研究

Abstract

在本論文中，所有化合物都是以該比例的元素態反應物在825˚C的溫度下合成。單晶解析的結果顯示，此些化合物的空間群皆為Pbam，斜方晶系，並與兩種已知物La4In5S13及Pb4In2Bi4S13為相同之結構。 La4In4.66Se13的晶格常數為a = 12.434(4) Å, b = 22.168(7) Å and c = 4.1946(12) Å, R1/wR2 = 0.0432/0.1107。結構上主要是由InSe6以鄰邊共享的方式連結，並在端點的地方與InSe4相接形成二維的層狀結構後，再以La-Se的離子鍵將層與層串連起來。單晶數據的結果顯示，其中一八面體的中心位置是僅被三分之二的In填佔。我們分別建構三種不同的分子模型去瞭解此化合物的電子結構，結果顯示La4In4.66Se13應為一電子傳導效率不佳的半導體。 一系列的四元硒化物在以NaCl為助熔劑的反應中得到，如Na2La4In4Se13，晶格常數為a = 21.36(1) Å,b = 26.39(1) Å,c =4.151(2) Å , R1/wR2 = 0.0320 /0.0650。而摻雜金屬的化合物，包含Mg、Ca、Sr、Mn、Pb亦是在類似的反應中製備而成。此系統中的化合物都是相同的結構，藉由六個InSe6八面體及兩個MSe6八面體所形成的單元M2In6Se26，以兩個不同的方向堆疊所組成。比較金屬位置上的電子密度，我們可以了解金屬離子是根據其環境的喜好及鍵結類型與Na、La混合填佔在所有的金屬位置上。

In this dissertation, the title compounds were synthesized at 825˚C by stoichiometric ratios of elements. Single crystal study revels two structure types of known compound La4In5S13 and Pb4In2Bi4S13 are obtained and all crystallizes in the space group Pbam of the orthorhombic system. La4In4.66Se13 with cell dimension a = 12.434(4) Å, b = 22.168(7) Å and c = 4.1946(12) Å, R1/wR2 = 0.0432/0.1107, which is mainly structured by edge shared InSe6 octahedra with InSe4 tetrahedra connected at the corners, forming 2-D layers linked by La-Se ionic bonding. Single crystal analysis revels that one of the metal octahedra sites is occupied by 2/3 of In. Three molecule models were constructed to understand the electronic structure. The result indicates that the La4In4.66Se13 should be a semiconductor with low electron transference efficiency. A series of quaternary chalcogenides, such as Na2La4In4Se13 with cell dimension a = 21.36(1) Å, b = 26.39(1) Å, c =4.151(2) Å , R1/wR2 = 0.0320 /0.0650, were found in the reaction using NaCl as flux and doped by Mg、Ca、Sr、Mn、Pb in similar process. The structure of these compounds are the same, which is composed by two directional M2In6Se26 units that formed by six InSe6 octahedra and two MSe6 octahedra. From the comparison of electron density on metal sites, the result indicates that doped metal ions are mix-occupied with Na and La in all metal sites depending on environmental preference and types of bonding.