  We report the thermoelectric properties of polycrystalline samples of
Ca3Pb1-xBixO (x = 0, 0.1, 0.2) and Ca3SnO, both crystallizing in a cubic
antiperovskite-type structure. The Ca3SnO sample shows metallic resistivity and
its thermoelectric power approaches 100 uV K-1 at room temperature, resulting
in the thermoelectric power factor of Ca3SnO being larger than that of
Ca3Pb1-xBixO. On the basis of Hall and Sommerfeld coefficients, the Ca3SnO
sample is found to be a p-type metal with a carrier density of ~1019 cm-3, a
mobility of ~80 cm2 V-1 s-1, both comparable to those in degenerated
semiconductors, and a moderately large hole carrier effective mass. The
coexistence of moderately high mobility and large effective mass observed in
Ca3SnO, as well as possible emergence of a mutivalley electronic structure with
a small band gap at low-symmetry points in k-space, suggests that the
antiperovskite Ca oxides have strong potential as a thermoelectric material.
