Thermoelectric Properties of the As/P-Based Zintl Compounds EuIn₂As_2–xP_x (x = 0–2) and SrSn₂As₂

Abstract

Zintl compounds containing Sb have been studied extensively because of their promising thermoelectric properties. In this study, we prepared As/P-based Zintl compounds, EuIn2As2−xPx (x = 0 to 2) and SrSn2As2, and examined their potential for use as thermoelectric materials. These compounds show p-type polarity with Hall carrier concentrations of ~10 19 cm −3 for EuIn2As2−xPx and ~10 21 cm −3 for SrSn2As2 at 300 K. The high carrier concentration of SrSn2As2 is likely owing to self-doping by hole-donating Sn vacancies. The electrical power factor reaches ~1 mW m 1 K 2 at ~600 K for EuIn2As2−xPx with x = 0.1 and 0.2, which is almost twice that of the end-member compounds (x = 0 and 2). The lattice thermal conductivity l is determined to be 1.6-2.0 W m 1 K 1 for EuIn2As2 and SrSn2As2 and 2.8 W m 1 K 1 for EuIn2P2 at 673 K. The dimensionless figure of merit reaches ZT = 0.29 at 773 K for EuIn2As2−xPx with x = 0.2 owing to the optimized carrier concentration and/or electronic structure, as well as a reduced lattice thermal conductivity in the solid solution. First-principles calculations show that EuIn2As2 and SrSn2As2 are topologically nontrivial materials with band inversion, while EuIn2P2 is a conventional semiconductor with a bandgap. The present study demonstrates that As/P-based Zintl compounds can also show promising thermoelectric properties, thus expanding the frontier for efficient thermoelectric materials.

Band Anisotropy Generates Axis-Dependent Conduction Polarity of Mg3Sb2 and Mg3Bi2

“…Let us stress that there are many 122-type Zintl phases that crystallize in several different structure types, including the CaAl 2 Si 2 -type structure (space group P 3̅ m 1), α-BaCu 2 S 2 -type structure (space group Pnma ), ThCr 2 Si 2 -type structure (space group I 4/ mmm ), etc. However, if we focus on pnictides, these compounds have a similar character that VBM mainly consists of pnictogen p orbitals. ,,− Therefore, we can expect that band anisotropy engineering to induce axis-dependent conduction polarity is also possible in these compounds, although the crystal structure is different. The single crystal growth of some of these compounds using a flux method has already been reported. , Hence, the 122-type Zintl phase could represent a new family of materials possessing axis-dependent conduction polarity, and so the anisotropic thermoelectric transport properties of these materials should be further studied.…”

Recent progress in phosphide materials for thermoelectric conversion

“…7d). 61 Focussing on the P-rich compositions, the samples are degenerate semiconductors, with a largely temperature independent S 2 σ ~ 0.5 mW.m -1 .K -2 between 300-800 K. Alloying leads to a substantial reduction in κ L , consistent with mass and strain disorder, with a reduction from κ L 300 K = 6.7 W.m -1 .K -1 in EuIn 2 P 2 to ~3 W.m -1 .K -1 in alloyed EuIn 2 PAs. With this beneficial alloying contribution, zT 773 K ~ 0.25 is achieved.…”

Stereochemical Rearrangement of Functional Units in Pressurized Sn4As3 Superconductor

“…The charge transfer from the intercalation layer to the lone-pair electrons of Sn dictates their properties, and the conductivity in these materials can change from insulators to metals and superconductors. For instance, SrSn 2 As 2 and EuSn 2 As 2 with fully occupied lone-pair electrons are topological insulators. − Reducing the electron counts, as observed in Li 1– x Sn 2+ x As 2 (0.2 < x < 0.4), results in a metallic ground state with high anisotropic resistivity . Further reduction of electrons from the SnAs 3 layer results in superconductivity of Li 0.6 Sn 2 As 2 and NaSnAs with similar T c = 1.6 K. − Thus, the conductivity of SnAs-based compounds can be effectively modulated through carrier doping, although enhancing their T c remains a challenging task with this approach.…”