Structure, heat capacity, and high-temperature thermal properties of Yb ₁₄Mn _1-xAl _xSb ₁₁

A series of compounds, Yb ₁₄Mn _1-xAl _xSb ₁₁ with (0 < x < 1), was prepared via Sn flux and the structures investigated. Single-crystal X-ray diffraction reveals that the volume of the unit cell increases with increasing Al content. Bond-distance changes are less than 2% and the increase in volume of the unit cell is associated with the decreasing distortion of the tetrahedron with increasing Al content. The specific heat, C _p, was measured from 300 to 1100 K. The measured C _p for these compounds is 19% higher than the Dulong-Petit value at the peak zT temperature (1223 K). These measured values permit a recalculation of thermal conductivity, revealing an extremely low lattice thermal conductivity of approximately 0.3-0.4 W/(m K) at 1223 K. The maximum zT of Yb ₁₄Mn1-;Al _xSb ₁₁ is approximately 0.8 and 1.1 for the x = 0 and x = 0.6 compositions, respectively.