A new antimonide K8–x Zn18+3x Sb16 was synthesized using reactive potassium hydride KH as a precursor. Owing to intimate mixing of starting materials, the hydride route allows rapid phase “screening” of ternary systems and is particularly suitable for the search of new antimonides. The crystal structure of K8–x Zn18+3x Sb16 (x = 1.12(8); P42/nmc (no. 137), a = 12.3042(5) Å, c = 7.3031(3) Å, V = 1105.6(1) Å3, R 1 = 0.029) has a [Zn18Sb16] framework with large channels alternately filled by K cations and Zn3 triangular units. The Zn3 triangles break the channels into finite cages by forming covalent bonds to the framework, preventing K migration along the channel. This structural feature is responsible for its stability in air, uncommon for this class of compounds, as well as for its low thermal conductivity. Transport property measurement and computational analysis of the electronic structure indicate that the title compound is a semimetal with properties highly dependent on the precise composition, i.e., the K/Zn3 ratio in the channels. The hydride preparative route provides accurate control over the composition of the target phase, thereby facilitating transport properties tuning. This synthetic method will allow for the synthesis of novel alkali metal antimonides as well as for the development of functional materials via precise compositional control.

Two new sodium zinc antimonides NaZn4Sb3 and HT-Na1-xZn4-ySb3 were synthesized by using reactive sodium hydride, NaH, as a precursor. The hydride route provides uniform mixing and comprehensive control over the composition, facilitating fast reactions and high-purity samples, whereas traditional synthesis using sodium metal results in inhomogeneous samples with a significant fraction of the more stable NaZnSb compound. NaZn4Sb3 crystalizes in the hexagonal P63/mmc space group (No. 194, Z = 2, a = 4.43579(4) Å, c = 23.41553(9) Å), and is stable upon heating in vacuum up to 736 K. The layered crystal structure of NaZn4Sb3 is related to the structure of the well-studied thermoelectric antimonides AeZn2Sb2 (Ae = Ca, Sr, Eu). Upon heating in vacuum NaZn4Sb3 transforms to HT-Na1-xZn4-ySb3 (x = 0.047(3), y = 0.135(1)) due to partial Na/Zn evaporation/elimination, as was determined from hightemperature in-situ synchrotron powder X-ray diffraction. HT-Na1-xZn4-ySb3 has a complex monoclinic structure with considerable degrees of structural disorder (P21/c (No. 14, Z = 32), a = 19.5366(7) Å, b = 14.7410(5) Å, c = 20.7808(7) Å, β = 90.317(2)°) and is stable exclusively in a narrow temperature range of 736 − 885 K. Further heating of HT-Na1-xZn4-ySb3 leads to a reversible transformation to NaZnSb above 883 K. Both compounds exhibit similarly low thermal conductivity at room temperature (0.9 W•m −1 K −1 ) and positive Seebeck coefficients (38-52 µV/K) indicative of holes as the main charge carriers. However, resistivities of the two phases differ by two orders of magnitude.Here, we have explored the ternary Na-Zn-Sb system and discovered two new compositionally similar, but structurally different ternary antimonides, both are featuring new structure types. Using the fast hydride route coupled with in-situ high-temperature powder X-ray diffraction experiments, compositional and temperature screening allowed for synthesis of two new ternary phases: NaZn4Sb3 phase and what at first appeared to be its polymorph, but in fact it is a different compound with slightly Na/Zn depleted composition HT-Na1-xZn4-ySb3, stable in narrow temperature range. The hydride route yields single phase samples of both antimonides, allowing for the experimental access to their transport properties. The crystal structures, synthesis, structural transformations, and transport properties of the NaZn4Sb3 and HT-Na1-xZn4-ySb3 are discussed herein.

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.

were synthesized utilizing sodium hydride NaH as a reactive sodium source. In comparison to the synthesis using sodium metal, salt-like NaH can be ball-milled, leading to the easy and uniform mixing of precursors in the desired stoichiometric ratios. Such comprehensive compositional control enables a fast screening of the Na− Zn−Sb system and identification of new compounds, followed by their preparation in bulk with high purity. Na 11 Zn 2 Sb 5 crystallizes in the triclinic P1 space group (No. 2, Z = 2, a = 8.8739( 6) Å, b = 10.6407(7) Å, c = 11.4282(8) Å, α = 103.453(2)°, β = 96.997(2)°, γ = 107.517(2)°) and features polyanionic [Zn 2 Sb 5 ] 11clusters with unusual 3-coordinated Zn atoms. Both Na 4 Zn 9 Sb 9 (Z = 4, a = 28.4794(4) Å, b = 4.47189(5) Å, c = 17.2704(2) Å, β = 98.3363(6)°) and NaZn 3 Sb 3 (Z = 8, a = 32.1790(1) Å, b = 4.51549(1) Å, c = 9.64569(2) Å, β = 98.4618( 1)°) crystallize in the monoclinic C2/m space group (No. 12) and have complex new structure types. For both compounds, their frameworks are built from ZnSb 4 distorted tetrahedra, which are linked via edge-, vertex-sharing, or both, while Na cations fill in the framework channels. Due to the complex structures, Na 4 Zn 9 Sb 9 and NaZn 3 Sb 3 compounds exhibit low thermal conductivities (0.97−1.26 W•m −1 K −1 ) at room temperature, positive Seebeck coefficients (19−32 μV/K) suggestive of holes as charge carriers, and semimetallic electrical resistivities (∼1.0−2.3 × 10 −4 Ω•m). Na 4 Zn 9 Sb 9 and NaZn 3 Sb 3 decompose into the equiatomic NaZnSb above ∼800 K, as determined by in situ synchrotron powder Xray diffraction. The discovery of multiple ternary compounds highlights the importance of judicious choice of the synthetic method.

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.