Multi-temperature Synchrotron Powder X-ray Diffraction Study and Hirshfeld Surface Analysis of Chemical Bonding in the Thermoelectric Zintl Phase Yb14MnSb11

High quality synchrotron powder X-ray diffraction (PXRD) data measured from 90 to 900 K were used to carry out crystal structure refinements of the thermoelectric Zintl phase, Yb14MnSb11, made up of Yb cations and polyanions along with Sb anions. The crystal structure exhibits near linear thermal expansion with high-temperature expansion coefficients of 2.20(3) x 10(-4) K-1 and 3.67(3) x 10(-4) K-1 for a and c of Yb14MnSb11. A subtle structural transition is observed between 500 and 600 K, which primarily involves the [MnSb49-] tetrahedron where the Mn-Sb bond length is increased by about 0.015 angstrom. The atomic displacement parameters (ADPs) of the Mn atom were found to be larger than the ADPs of the Sb and Yb atoms reflecting the lower mass of Mn. On the other hand the heavy Yb atoms were found to vibrate significantly more than the lighter Sb atoms, and this presumably reflects the stronger chemical bonding of the covalently bonded anions relative to the isolated Yb cations. Modeling of the ADPs gives a Debye temperature of 168(2) K. The chemical bonding in Yb14MnSb11 was analyzed using Atomic Hirshfeld Surfaces. Overall, the analysis supports the presence of the structural elements of Yb cations, [MnSb49-] tetrahedra, linear [Sb-3(7-)] trimers and isolated Sb3-. There are, however, indications of a complex network of directional interactions between the Sb anions and the Yb cations.