Germanides and silicides


Another complex is the advanced investigation of superconducting Pt-Ge compounds with filled skutterudite structure and with the general formula MPt4Ge12 (M = Sr, Ba, La, Pr). While the basic superconducting parameters are well known, the superconducting order parameters are still under debate for the most prominent members LaPt4Ge12 and PrPt4Ge12. (cf. Scientific Report MPI-CPFS 2009-2010, p.59-62). For the high-quality single crystals of the Pr compound (synthesized by R. Gumeniuk) high-resolution data of the penetration depth (obtained in co-operation with the MPI partner group at Zhejiang University, China) as well as specific heat data can be consistently described by a multi-gap model [10].


The superconducting properties of several new metastable silicide and germanide phases – CaGe3, CaSi3, YSi3 and LuSi3 – which were obtained by high-pressure high-temperatures syntheses, were investigated [11,12]. Also, the superconducting parameters of the new cage compound Ba3Ge13Ir4 and of isostructural Ba3Ge13Rh4 were determined [13]. For the type-I clathrate compound Ba8-xSi46 the major attention was on the preparation of samples with enhanced thermoelectric properties. However, also the superconducting properties (cf. Fig. 2 for the specific heat anomaly) could be improved and were re-investigated [14].

Fig. 1: Specific heat anomaly of the type-II superconducting clathrate Ba8-xSi46 in various magnetic fields. The inset shows the upper critical field Bc2(T) determined from the midpoint temperatures of the transition steps in the measured magnetic fields.
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