Rapid Phase Screening via Hydride Route: A Discovery of K_8–xZn_18+3xSb₁₆

Abstract

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.

Thermal Stability and Thermoelectric Properties of NaZnSb

“…Synthesis from elements led to a single-phase sample; however, mass scale-up proved to be difficult, as increased Na resulted in side reactions and impurity phases. We have shown that by using alkali metal hydrides, homogeneous mixing and control over the local concentration of alkali metal can be achieved, leading to substantially shorter reaction times and higher yields of the target phase [9,10,11]; while for the traditional synthesis with elemental alkali metals as the starting materials, long reactions at high temperatures, prereactions, and subsequent grindings of the samples are required to facilitate diffusion and achieve impurity-free samples. The ductility of the elemental alkali metals prevents their thorough mixing with other starting materials, often leading to alkali-metal-rich phases.…”

“…For instance, Cs 8 Zn 18 Sb 28 clathrate type-I [22], in which Cs + cations are trapped inside large polyhedral cages of Zn and Sb, is air- and water-stable. Recently discovered, K 8−x Zn 18+3x Sb 16 [11] has open channels in the Zn–Sb framework filled by alternating K + cations and Zn 3 triangles. The alternating Zn 3 triangles block the “diffusion” of the K + from the structure and are believed to be a reason for the observed stability of K 8−x Zn 18+3x Sb 16 in air.…”

“…We are interested in ternary antimonides containing alkali metals. Using the unconventional hydride synthetic route [9,10], K 8−x Zn 18+3x Sb 16 was recently discovered [11]. Here, we report the thermoelectric properties and thermal stability of NaZnSb, studied using a comprehensive set of methods including high-temperature powder X-ray diffraction and differential scanning calorimetry.…”

Lithium nickel borides: evolution of [NiB] layers driven by Li pressure

“…To further shed light on the evolution of Li and B coordination environment upon incorporation of extra-Li in the structures of RT-Li 1+x NiB and HT-Li 1+y NiB compounds, 7 Li and 11 B solid-state magic angle spinning (MAS) NMR spectra were collected (Fig. 11, a).…”

“…The hydride synthesis route, where salt-like alkali metal hydrides are used as a source of alkali metals, has been successfully utilized for the preparation of alkali/alkali-earth antimonides, arsenides, germanides, and silicides. [4][5][6][7][8][9][10] Application of this method for the Li-Ni-B system significantly shortened the synthesis time of ternary phases. For instance, LiNi 3 B 1.8 can be synthesized in a span of ~24 hours compared with the previously reported 3-month annealing for the reaction of elements.…”