La-filled skutterudites (La z Fe4-x Co x Sb12) were prepared by encapsulated melting and hot pressing, and filling and doping (charge compensation) effects on the transport and thermoelectric properties were examined. The signs of the Hall and Seebeck coefficients were positive and it means that the majority carriers are holes (p-type). The electrical and thermal conductivities were reduced by substitution of Co for Fe, which was responsible for the decrease in carrier concentration. La0.9Fe3CoSb12 shows the maximum dimensionless thermoelectric figure of merit: Z T max = 0.65 at 823 K.

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The surface properties (water sorption and repellency, adhesion) are closely related to the surface tension of polymer solid. Critical surface tension c C and surface tension c S of a polymer solid have been estimated by the contact angle method by our quantitative imaging system. BPDA (3,3 0 ,4,4 0 -biphenyl tetracarboxylic dianhydride) -EDA (4,4 0 -ethylenedianiline) polyimide was successfully synthesized. The critical surface tensions c C were analyzed by a Zisman plot, a Young-Dupre´-Good-Girifalco plot, and a log (1 þ cos h) vs log c L plot. The surface tension c S of BPDA-EDA polyimide was evaluated using the geometric mean equation and our multiple regression analysis. The calculated values of c d S (a dispersion component), c p S (a polar component), c h S (a hydrogen bonding component), and c S are 30.49, 4.52, 0.08, and 35.09 mN Á m À1 , respectively. The c S of BPDA-EDA polyimide containing two methylene groups is smaller than those of the polyimides containing both methylene group and ether group.