In this work, a global
search for crystal structures of ternary
Mg–Sc–H hydrides (Mg
x
Sc
y
H
z
) under high
pressure (100 ≤ P ≤ 200 GPa) was performed
using the evolutionary algorithm and first-principles calculations.
On their basis, we computed the thermodynamic convex hull and pressure-dependent
phase diagram of Mg
x
Sc
y
H
z
for a wide range of compositions
(x + y = 2, 3, 4 and z = 2–12, 14, 16, 18). Our crystal structure search and convex
hull analysis revealed no thermodynamically stable compounds in the
hydrogen-rich range (z/(x + y) ⩾ 4). On the other hand, we identified the crystal
structures of four thermodynamically stable compounds in the hydrogen-middle
range (3 ≤ z/(x + y) < 4), that is, R3̅m-MgScH6, C2/m-Mg2ScH10, Immm-MgSc2H9, and Pm3̅m-Mg(ScH4)3. Their superconducting transition temperatures
were computationally predicted by the McMillan formula combined with
first-principles phonon calculations. They were found to exhibit superconductivity;
among them, R3̅m-MgScH6 was predicted to have the highest T
c (i.e., 41 K) at 100 GPa.