Clathrate XI K58Zn122Sb207: A New Branch on the Clathrate Family Tree

The compositional screening of K-Zn-Sb ternary system aided by machine learning, rapid exploratory synthesis using KH salt-like precursor and in situ powder X-ray diffraction yielded a novel clathrate type XI K58Zn122Sb207. This clathrate consists of a 3D Zn-Sb framework hosting K+ ions inside polyhedral cages, some of which are reminiscent of known clathrate types while others are unique to this structure type. The complex non-centrosymmetric structure in the tetragonal space group I4?2m was solved by means of single crystal X-ray diffraction as a 6-component twin due to pseudocubic symmetry and further confirmed by high-resolution synchrotron powder X-ray diffraction and state-of-the-art scanning transmission electron microscopy. The electron-precise composition of this clathrate yields narrow-gap p-type semiconductor with extraordinarily low thermal conductivity due to displacement or rattling of K cations inside oversized cages and as well as to twinning, stacking faults and antiphase boundary defects.

Automated summary

The study utilized machine learning for compositional screening of the K-Zn-Sb ternary system, resulting in the synthesis of a novel clathrate type XI K58Zn122Sb207 with a complex non-centrosymmetric structure. This clathrate exhibits a narrow-gap p-type semiconductor behavior with extremely low thermal conductivity, attributed to the displacement of K cations inside oversized cages and structural defects.