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The Hall effect and electrical resistivity of iron disilicide, Fe1−xCoxSi2(0.01≦x≦0.03) and Fe1−yNiySi2 (0.01≦y≦0.03) have been measured in the temperature range between 80 and 300 K. The solid solution Fe1−xCoxSi2 is n type over the measured temperature range, while the solid solution Fe1−yNiySi2 is p type below 160 K and n type above 160 K. The carrier concentration of Fe1−xCoxSi2 at 300 K, which is in good agreement with the Co atom concentration, is one order of magnitude higher than that of Fe1−yNiySi2. The electron conduction at high temperatures for these solid solutions is explained by the small polaron mechanism.

In order to clarify the mechanism of electrical conduction of Mn-doped β-FeSi2 (Fe1−xMnxSi2), the Hall effect and electrical resistivity of Fe1−xMnxSi2 (0.01≦x≦0.10) have been measured in the temperature range between 80 and 300 K. The hole concentration of Fe1−xMnxSi2 at 300 K ranges from 8.9×1017 cm−3 for x=0.01 to 1.1×1019 cm−3 for x=0.10, which is almost proportional to the Mn doping concentration (x). The temperature dependence of electrical resistivity of Fe1−xMnxSi2 shows an S-like decay curve at high temperatures. It is concluded that this shape results from the drastic decrease of the mobility with increasing temperature. We present experimental evidence that explains the electrical conduction of Fe1−xMnxSi2 at high temperatures by the impurity scattering mechanism.

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Phenolic resin/ZrW 2 O 8 composites were successfully fabricated and their coefficient of thermal expansion (CTE) as well as mechanical properties was investigated. The CTE of the composites decreases from 46 3 10 -6 to 14 3 10 -6 K 21 when the ZrW 2 O 8 volume fraction increases from 0 to 52 vol %. The CTE of the composites is analyzed by some theoretical models; Schapery's upper bound provides the best estimate of the reduction in CTE. The Barcol hardness of the composites increases with an increase in the ZrW 2 O 8 volume fraction. The bending strength of the composites with 19-25 vol % of ZrW 2 O 8 fillers shows a maximum value of 130 MPa, which is 45% larger than that of phenolic resin without fillers.

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