Crystal Growth and Characterization of the Narrow-Band-Gap Semiconductors OsPn2 (Pn = P, As, Sb)

• Published in: Inorganic chemistry Vol. 53; no. 18; pp. 9959 - 9968
• Main Authors: Bugaris, Daniel E, Malliakas, Christos D, Shoemaker, Daniel P, Do, Dat T, Chung, Duck Young, Mahanti, Subhendra D, Kanatzidis, Mercouri G
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 15.09.2014
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic501733z

Using metal fluxes, crystals of the binary osmium dipnictides OsPn2 (Pn = P, As, Sb) have been grown for the first time. Single-crystal X-ray diffraction confirms that these compounds crystallize in the marcasite structure type with orthorhombic space group Pnnm. The structure is a three-dimensional framework of corner- and edge-sharing OsPn6 octahedra, as well as [Pn2 4–] anions. Raman spectroscopy shows the presence of P–P single bonds, consistent with the presence of [Pn2 –4] anions and formally Os4+ cations. Optical-band-gap and high-temperature electrical resistivity measurements indicate that these materials are narrow-band-gap semiconductors. The experimentally determined Seebeck coefficients reveal that nominally undoped OsP2 and OsSb2 are n-type semiconductors, whereas OsAs2 is p-type. Electronic band structure using density functional theory calculations shows that these compounds are indirect narrow-band-gap semiconductors. The bonding p orbitals associated with the Pn2 dimer are below the Fermi energy, and the corresponding antibonding states are above, consistent with a Pn–Pn single bond. Thermopower calculations using Boltzmann transport theory and constant relaxation time approximation show that these materials are potentially good thermoelectrics, in agreement with experiment.