title: The origin of the n-type behavior in rare earth borocarbide Y1-xB28.5C4.
abstract: Synthesis conditions, morphology, and thermoelectric properties of Y1-xB28.5C4 were investigated. Y1-xB28.5C4 is the compound with the lowest metal content in a series of homologous rare earth borocarbonitrides, which have been attracting interest as high temperature thermoelectric materials because they can embody the long-awaited counterpart to boron carbide, one of the few thermoelectric materials with a history of commercialization. It was revealed that the presence of boron carbide inclusions was the origin of the p-type behavior previously observed for Y1-xB28.5C4 in contrast to Y1-xB15.5CN and Y1-xB22C2N. In comparison with that of previous small flux-grown single crystals, a metal-poor composition of YB40C6 (Y0.71B28.5C4) in the synthesis successfully yielded sintered bulk Y1-xB28.5C4 samples apparently free of boron carbide inclusions. "Pure" Y1-xB28.5C4 was found to exhibit the same attractive n-type behavior as the other rare earth borocarbonitrides even though it is the most metal-poor compound among the series. Calculations of the electronic structure were carried out for Y1-xB28.5C4 as a representative of the series of homologous compounds and reveal a pseudo gap-like electronic density of states near the Fermi level mainly originating from the covalent borocarbonitride network.
authors.affiliation: National Institute for Materials Science (NIMS), International Center for Materials Nanoarchitechtonics (MANA), Namiki 1-1, Tsukuba 305-0044, Japan. MORI.Takao@nims.go.jp.
authors.forename: Takao
authors.initials: T
authors.lastname: Mori
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Nishimura
authors.forename: Walter
authors.initials: W
authors.lastname: Schnelle
authors.forename: Ulrich
authors.initials: U
authors.lastname: Burkhardt
authors.forename: Yuri
authors.initials: Y
authors.lastname: Grin