Improvement of thermoelectric properties of chimney-ladder compounds by controlling compositional/structural grade

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Phase relationships of manganese-substituted ruthenium sesquisilicide alloys have been investigated by using x-ray powder diffraction, scanning and transmission electron microscopy. A series of chimney-ladder phases Ru_<1-x>Mn_xSi_y are formed over a wide compositional range between Ru_2Si_3 and Mn_4Si_7. Directionally solidified chimney-ladder compounds in the Ru-Mn-Si system exhibit a microstructure containing columnar domains of different chimney-ladder phases with compositional interfaces between adjacent phases. Despite a compositional variation, the transition-metal (Ru/Mn) sublattice is continuous over the interface while the Si sublattice is discontinuous. The lattice thermal conductivity of the directionally solidified alloys along the transverse direction decreases by increasing the density of the compositional interfaces while the electrical properties are preserved.