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

Abstract

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 an ovel clathrate type XI K 58 Zn 122 Sb 207. This clathrate consists of a3 DZ n-Sb framework hosting K + ions inside polyhedral cages,some of which are reminiscent of knownclathrate types while others are unique to this structure type.T he complex non-centrosymmetric structure in the tetragonal space group I " 42mw as solved by means of single crystal X-ray diffraction as a6-component twin due to pseudocubic symmetry and further confirmed by high-resolution synchrotron powder X-ray diffraction and state-of-theart scanning transmission electron microscopy. The electronprecise composition of this clathrate yields narrow-gap p-type semiconductor with extraordinarily low thermal conductivity due to displacement or "rattling" of Kcations inside oversized cages and as well as to twinning,stacking faults and antiphase boundary defects.

Ternary antimonide NaCd4Sb3: hydride synthesis, crystal structure and transport properties

“…The hydride reaction method was utilized to synthesize the NaCdSb phase as a proof of concept, and to further explore the phase space for additional novel phases. By lowering the synthesis temperature and shortening the annealing time, the hydride method is an effective technique for the rapid synthesis of phase‐pure samples and has been used previously in similar systems [15–17,20,22] . Initially, Na‐poor compositions in the Na−Cd−Sb system were synthesized in an attempt to explore the phase space.…”

“…This procedure is similar to what was used previously [15–17,20,22] . All manipulations were completed in an argon‐filled glovebox.…”

“…One of the alternatives to traditional solid‐state synthesis methods is the hydride synthesis [7,15–22] . The hydride method has the advantages of a single‐step synthesis and improved precursor incorporation due to the salt‐like nature of the alkali metal hydrides (LiH, NaH, etc.).…”

“…Accounting for all the advantages, the hydride method allows for an overall quicker synthesis time. Recent examples of new antimonides synthesized using the hydride method are: NaZnSb, NaZn 4 Sb 3 , HT ‐Na 1‐x Zn 4‐y Sb 3 , K 8‐x Zn 18+3x Sb 16 , NaZn 3 Sb 3 , Na 4 Zn 9 Sb 9 and clathrate type‐XI K 58 Zn 122 Sb 207 [15–17,20,22] . Now, new antimonides that are more complex or difficult‐to‐synthesize have the opportunity to be discovered, their structure and thermoelectric properties to be studied [8,16–18,20,22] …”

Strong Scattering from Low-Frequency Rattling Modes Results in Low Thermal Conductivity in Antimonide Clathrate Compounds

“…Lattice thermal conductivity of Sbbased clathrates can be as low as 0.35 W m −1 K −1 , whose values were obtained for type-XI clathrate. 7 The known antimonide clathrates are narrow-band-gap semiconductors, E g = 25−340 meV. 7,26,27 Last, but not least, some of the representatives of this family of compounds are also known for excellent hole mobility, reaching 880 cm 2 V −1 s −1 at room temperature.…”