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This study investigates the facile hydride synthesis method guided by theoretical predictions to explore the K–T–Bi (T = Zn, Cd) phase spaces. Using an adaptive genetic algorithm (AGA) and density functional theory (DFT), candidate compositions are identified for experimental validation via a facile hydrides route, permitting experimental screening of K–Zn–Bi and “empty” K–Cd–Bi systems. The previously reported KZnBi and KZn₂Bi₂are synthesized alongside newly discovered KCdBi and KCd₂Bi₂. While the AGA and DFT predict the stability of these compounds, structural predictions align with the experiment only for KZnBi and KZn₂Bi₂. Single‐crystal X‐ray structure refinements confirm that KZnBi and KZn₂Bi₂adopt the hexagonal ZrBeSi‐ and tetragonal ThCr₂Si₂‐structure types, respectively. KCdBi has tetragonal PbClF‐structure type and KCd₂Bi₂belongs to the ThCr₂Si₂‐structure type. A trend based on the ratio of the metal ionic radii allows to rationalize variation in the structure types within theATBi family (A = Li–Cs), correctly identifying KCdBi as isostructural to NaZnBi. Thermal stability studied by high‐temperature powder X‐ray diffraction reveals that Zn‐containing compounds melt at higher temperatures (821 K for KZn₂Bi₂) than Cd‐containing KCd₂Bi₂(635 K). This study highlights the efficacy of combining rapid synthesis techniques with predictive modeling, though structural predictions show some limitations in accuracy. 

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 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 groupwas 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‐gapp‐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.