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The defective structure of the PrFe0.4Sn2 and ThFe0.2Sn2 compounds has been studied by 57 Fe and 119 Sn Mossbauer spectro- scopy, first-principle and binomial distribution calculations. It is shown that the iron and tin sites display different local interactions of atoms located in the same structural position of the defective structure. The analysis of the obtained data together with the theoretical calculations show that defect formation in the samples has a thermal origin. The experimental and theoretical data show that the studied defective structure is locally ordered. # 2002 Elsevier Science Ltd. All rights reserved.

The phase diagram of the Ca-Si system has been investigated across almost the whole composition range (0 to 70 at% Si) using differential thermal analysis, metallographic analysis, X-ray diffraction and electron microscopy. Six intermediate phases have been found: CaSi2 (CaSi2-type), Ca14Si19 (Ca14Si19-type), Ca3Si4 (Ca3Si4-type), CaSi (CrB-type), Ca5Si3 (Cr5B3-type) and Ca2Si (anti-PbCl2-type). Ca3Si4, not previously known, is a Zintl phase representative of a new structural type: hexagonal hP42, a=854.1, c=1490.6 pm, space group P6 3 /m. Three eutectics occur in this system: at about 3.5 at% Si and 795°C, 42.5 at% Si and 1230°C, 72.0 at% Si and 1020°C.

Thermodynamic, magnetic and electrical properties of the Nd 7 Co 6 Al 7 intermetallic phase have been extensively studied. The compound crystallises in the tetragonal Pr 7 Co 6 Al 7 type structure (space group P4/mbm) and undergoes a ferromagnetic transition at 15.5 K. From the hysteresis loop the values of the remanence and of the coercive field were obtained. Magnetic heat capacity measurements allow to obtain the magnetocaloric effect related to the magnetic transition. An estimate of refrigerant capacity of the compound is obtained.

We report the synthesis and some physical properties of four Th-based compounds ThCoGe, ThNiGe, ThCuAl3 and ThNiAl3. These compounds, are to our knowledge, being reported here for the first time. We observe Pauli paramagnetic behaviour in all the four compounds (with possible exception of ThCoGe), which shows that the 3d-derived electronic bands are filled by charge transfer. No signature of superconductivity is observed down to 1.4 K in these materials.