Improvement of thermoelectric properties of chimney-ladder compounds by introducing high-density interfaces

Phase relationships of Mn-substituted Ru₂Si₃ with the chimney-ladder structure have been investigated by using scanning and transmission electron microscopy. A series of chimney-ladder phases Ru _1-xMn_xSi_y are formed over a wide compositional range between Ru₂Si₃ and Mn₄Si₇. The c-axis dimension of the Si subcell increases with the Mn content accompanied with the increase in the Si/M ratio (y = Si/(Ru + Mn)). A large extent of compositional variation is observed in the directionally solidified chimney-ladder compounds. The interface between adjacent chimney-ladder phases with different Mn contents is considered to have no influence on the electrical properties but have some influence on the lattice thermal conductivity. The dimensionless figure-of-merit increases with the increase in the density of the interfaces.