ICT2014 Abstracts

Intermetallic clathrates and oxide compounds have become recent object of study as thermoelectric materials, important because of the environmental preservation and energy conservation issues. Efficient thermoelectric materials must have low electrical resistivity, low thermal conductivity and a large Seebeck coefficient. Oxide materials have better stability in oxidizing environments, so their use enables the fabrication of more durable devices, although the thermoelectric properties of oxides are generally inferior to those of intermetallic clathrates. The purpose of this work is to prepare and study thin films of both classes of materials. Single crystals of type-I clathrate Ba₈Ga₁₆Ge₃₀ (BGG) with p-type and n-type carriers were grown by a self-flux method using excess Ga, and single crystals of type-VIII clathrate Ba₈Ga_16-xCu_xSn₃₀ (x=1) with p- and n-type carriers were grown from Ga flux and Sn flux, respectively. Pellets of the oxide materials Bi₂A₂Co_2-xCu_xO_y (x=0; 0,5; 2; A=Sr; Ba) were synthesized using solid state reaction: the reagents were pressed unixially into pellets and sintered at 900^oC for 10 hours. The clathrate crystals and oxide pellets were then used as targets for deposition of thin films on silicon (1 0 0) substrates by physical vapour deposition (PVD) techniques. The structures of the as-deposited films were confirmed by X-ray diffraction (XRD). Composition analysis and the depth measurements were performed by Rutherford backscattering spectrometry (RBS). The deposited film thickness was evaluated using a profilometer and the microstructures analyzed by scanning electron microscopy (SEM). In addition, the surface morphology and the roughness of the deposited Ba₈Ga₁₆Ge₃₀ thin films were characterized by atomic force microscopy (AFM). The thin films were thermoelectrically characterized with electrical resistivity and thermopower measurements as functions of temperature, which showed strong microstructure-dependent behaviors. The relationship between morphologies and transport properties of the thin films is discussed.