Structural, transport, magnetic, and thermal properties of Eu8Ga16Ge30 -: art. no. 214404
Structural, transport, magnetic, and thermal properties of Eu8Ga16Ge30 -: art. no. 214404
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DOI：
10.1103/physrevb.64.214404
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发表时间：
2001-12-01
影响因子：
3.7
通讯作者：
Steglich, F
中科院分区：
文献类型：
--
作者：
Paschen, S;Carrillo-Cabrera, W;Steglich, F
Eu 8 Ga 16 Ge 30是迄今为止已知的唯一一种客体位置完全被稀土元素占据的笼形物。我们的研究表明，除了先前合成的Eu 8 Ga 16 Ge 30具有笼形物-I结构的修改。存在具有笼形物-VIII结构的第二种变体。这两个阶段的多晶样品表现为局部矩铁磁体与相对较低的居里温度（10.5和36 K）。电荷载流子浓度相当小（在2 K时为3.8和12.5 x 10（20）cm（-3）），加上居里温度低，表明具有半金属特性。比热和热导率都与客体原子在超大的主体笼中“嘎嘎作响”的概念一致，导致低热导率（“声子玻璃”）。然而，电子迁移率非常低，如果是固有的，这将质疑“电子晶体”的性质，通常假设在“填充笼”材料中。在100 K时，无量纲热电优值达到0.01.
Eu8Ga16Ge30 is the only clathrate known so far where the guest positions are fully occupied by a rare-earth element. Our investigations show that, in addition to the previously synthesized Eu8Ga16Ge30 modification with clathrate-I structure. there exists a second modification with clathrate-VIII structure. Polycrystalline samples of both phases behave as local-moment ferromagnets with relatively low Curie temperatures (10.5 and 36 K). The charge-carrier concentrations are rather small (3.8 and 12.5 x 10(20) cm(-3) at 2 K) and, together with the low Curie temperatures, point to a semimetallic behavior. Both the specific heat and the thermal conductivity are consistent with the concept of guest atoms "rattling" in oversized host cages, leading to low thermal conductivities ("phonon glasses"). However, the electron mobilities are quite low, which, if intrinsic, would question the properties of an "electron crystal", commonly presumed in "filled-cage" materials. The dimensionless thermoelectric figure of merit reaches values of 0.01 at 100 K.