Assessing structure of Mg3Bi2−xSbx (0 ≤ x ≤ 2) at pressures below 40 GPa

Abstract

Mg3Bi2–xSbx (0 ≤ x ≤ 2) have gained significant attention due to their potential in thermoelectric (TE) applications. However, there has been much debating regarding their structural properties and phase diagram as a function of pressure, which is crucial for understanding of their TE properties. Here, we investigate a unified phase diagram of Mg3(Bi,Sb)2 materials up to 40 GPa at room temperature using high-pressure X-ray diffraction. Two high-pressure phases with the structural transition succession of P3¯m1 → C2/m → P21/n are observed, which is valid for all Mg3Bi2–xSbx (0 ≤ x ≤ 2) compounds. We further explore the low-pressure phase P3¯m1 and report that alloying does not change the quasi-isotropic compression of the unit lattice parameters nor has effect on the anisotropic bond compressibility, as recently reported for the end-members. Our study presents a comprehensive picture of Mg3Bi2–xSbx as a function of pressure and chemical composition providing a solid foundation for the future experimental and theoretical studies searching for the most efficient TE compound in Mg3(Bi,Sb)2.