The phase analysis was carried out for the system of(2-y)FeSi
2+yFeAl
2 in the range 0≤y≤0.20 by an X-ray technique. The solid solution FeSi
2-yAl
y was identified in the composition range 0≤y≤0.12. Electrical resistivity ρ and Hall coefficient were measured as a function of temperature over the range from 80 to 1100K. The measurement of thermal conductivity was also carried out by a comparative method at 300K. The pure FeSi
2 was p-type semiconductor with the hole concentration n
p of 1.70×10
23/m
3 at 300K. ρ was independent of y in the range 0≤y≤0.02 and rapidly decreased above y=0.03. Below y=0.03, the hole mobility μ
H indicated the relationship of exp[-E
h/(kT)] in the temperature range from 200 to 300K, where Eh and k are the hopping energy and Boltzman constant, respectively. Eh was determined to be 0.110eV from the hopping mobility μ
pol=μ
0 exp[-E
h/(kT)]. In the range 0.04≤y≤0.12, it was shown that the changes in μ
pol have relationships of T
-3/2 and T
3/2 above and below 250K, respectively, and the band conduction was predominant. The maximum figure of merit was found to be 9.6×10
-5K
-1 for y=0.08.
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