Anomalous barium filling fraction and n-type thermoelectric performance ofBayCo4Sb12

Barium-filled skutterudites BayCo4Sb12 with an anomalously large filling fr action of up to y=0.44 have been synthesized. The lattice parameters increa se linearly with Ba content. Magnetic susceptibility data show that Ba0.44C o4Sb12 is paramagnetic, which implies that some of the Co atoms in BayCo4Sb 12 have acquired a magnetic moment. The presence of the two different valen ce states of Co (Co3+ and Co2+) leads to the anomalously large barium filli ng fraction even without extra charge compensation. All samples show n-type conduction. The electrical conductivity increases with increasing the Ba f illing fraction. The lattice thermal conductivity of BayCo4Sb12 is signific antly depressed as compared to unfilled Co4Sb12. The dimensionless thermoel ectric figure of merit, ZT, increases with increasing temperature reaching a maximum value of 1.1 for Ba0.24Co4Sb12 at 850 K. (C) 2001 American Instit ute of Physics.