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,結構與物性分析

Abstract

五種新的四元 MnPb4In8Se17( M=Mn, Fe )與 M0.5Pb4In8.5S17( M=Cu, Ag, Au )化合物可以利用固態反應法在溫度750℃與900℃下被合成出來。它們的晶系都屬於 monoclinic，空間群同為 P21/m，若從 b 軸垂直投影，可以發現晶體結構是由一層 CdI2-type， [InX2] 與一層 NaCl [100]-type， [(MxIn1-x)PbInX3] 的單元構造沿著c軸堆疊排列而成。對於 Se 的系統，過渡元素 Mn 與 Fe 填在 M12和 M13( M:原子位置)，S 系統的 Cu, Ag 則變換成 M10與 M11，而 Au 更只填在 M10的位置。透過能帶計算得知 Mn 與 Fe 的 d 軌域似獨立存在，與周圍 Se 原子軌域形成弱的反鍵結作用力，而且接近未鍵結狀態，造成電子不易傳導。在電導係數與 Thermopower 係數測量方面，則顯出上述五種化合物都屬於半導體行為，而且同樣都是具有較大的電阻。藉由 UV 吸收光譜實驗，可以估算出 Cu, Ag, Au 的系統其能隙都在1.4 eV 左右。關於含 Mn 化合物的磁化率測量結果則表現出是典型的順磁性行為( Mn2+: t2g3eg2，S=5/2 )，至於 Fe 的系統則會在溫度約 125K 時發生相變化。

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.