# Novel magnesium borides and their superconductivity

## TL;DR

This study uses ab initio methods to discover new stable magnesium borides and analyze their potential superconducting properties under high pressure conditions.

## Contribution

It identifies previously unknown stable Mg-B compounds and predicts their stability ranges and superconducting transition temperatures.

## Key findings

- Discovery of new stable Mg-B compounds MgB3 and Mg3B10.
- MgB2 remains stable across 0-200 GPa.
- Most magnesium borides have low T_c below 3 K.

## Abstract

With the motivation of searching for new superconductors in the Mg-B system, we performed ab initio evolutionary searches for all the stable compounds in this binary system in the pressure range of 0-200 GPa. We found previously unknown, yet thermodynamically stable, compositions MgB$_3$ and Mg$_3$B$_{10}$. Experimentally known MgB$_2$ is stable in the entire pressure range 0-200 GPa, while MgB$_7$ and MgB$_{12}$ are stable at pressures below 90 GPa and 35 GPa, respectively. We predict a reentrant behavior for MgB$_4$, which becomes unstable against decomposition into MgB$_2$ and MgB$_7$ at 4 GPa and then becomes stable above 61 GPa. We find ubiquity of phases with boron sandwich structures analogous to the AlB$_2$-type structure. However, with the exception of MgB$_2$, all other magnesium borides have low electron-phonon coupling constants $\lambda$ of 0.32 to 0.39 and are predicted to have T$_c$ below 3 K.