标题: | 四元新化合物, (MxIn1-x)Pb4In8X17( M=Mn, Fe, Cu, Ag, Au; X=S, Se; x=0.5, 1 )的合成,结构与物性分析 Synthesis and Characterization of New Quaternary Chalcogenides, (MxIn1-x)Pb4In8X17( M=Mn, Fe, Cu, Ag, Au; X=S, Se; x=0.5, 1 ) |
作者: | 王冠程 Kuan-Chen Wang 李积琛 Chi-Shen Lee 应用化学系硕博士班 |
关键字: | 半导体;电子结构;铅;晶体结构;热电材料;磁性;semiconductor;electronic structure;chalcogenides;solid state structure;thermoelectric;magnetic |
公开日期: | 2004 |
摘要: | 五种新的四元 MnPb4In8Se17( M=Mn, Fe )与 M0.5Pb4In8.5S17( M=Cu, Ag, Au )化合物可以利用固态反应法在温度750℃与900℃下被合成出来。它们的晶系都属于 monoclinic,空间群同为 P21/m,若从 b 轴垂直投影,可以发现晶体结构是由一层 CdI2-type, [InX2] 与一层 NaCl [100]-type, [(MxIn1-x)PbInX3] 的单元构造沿着c轴堆叠排列而成。对于 Se 的系统,过渡元素 Mn 与 Fe 填在 M12和 M13( M:原子位置),S 系统的 Cu, Ag 则变换成 M10与 M11,而 Au 更只填在 M10的位置。透过能带计算得知 Mn 与 Fe 的 d 轨域似独立存在,与周围 Se 原子轨域形成弱的反键结作用力,而且接近未键结状态,造成电子不易传导。在电导系数与 Thermopower 系数测量方面,则显出上述五种化合物都属于半导体行为,而且同样都是具有较大的电阻。藉由 UV 吸收光谱实验,可以估算出 Cu, Ag, Au 的系统其能隙都在1.4 eV 左右。关于含 Mn 化合物的磁化率测量结果则表现出是典型的顺磁性行为( Mn2+: t2g3eg2,S=5/2 ),至于 Fe 的系统则会在温度约 125K 时发生相变化。 In this report, five new chalcogenides, MPb4In8Se17 ( M=Mn, Fe ) and M0.5Pb4In8.5S17 ( M=Cu, Ag, Au ) were synthesized at 1023K and 1123K by solid-state reactions. These compounds crystallized in the space group P21/m, monoclinic system. The crystal structure features the combinations of CdI2-type layer of [InX2] and NaCl [100]-type layer of [(MxIn1-x)PbInX3] units along c-axis. For selenide phases, Mn and Fe atoms prefer to occupy on M12 and M13 sites. On the other hand, for the sulfide phases, the late transition metals ( Cu, Ag, Au ) favor to occupy on M10 and M11 sites. The results of LMTO band calculations indicate that Mn d and Fe d orbitals dominate the electronic states near the Fermi level and the interactions to surrounding Se atoms are essentially weak antibonding, which suggest bad mobility of electrons from Mn d and Fe d orbitals. These compounds show semiconducting behavior and possess large resistance in the electrical conductivity and thermopower measurements. UV absorption experiments for the sulfide phases suggest the band gap are close to 1.4eV. The magnetic susceptibility measurements for the Mn-phase show typical paramagnetic behavior of spin only Mn2+ ( t2g3eg2, S=5/2 ). However, the molar susceptibility of Fe-phase indicates a phase transition occurred at 125K. |
URI: | http://140.113.39.130/cdrfb3/record/nctu/#GT009225559 http://hdl.handle.net/11536/76848 |
显示于类别: | Thesis |
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