# Investigation of the La–Al–H and La–Si–H Systems at High Pressures

## TL;DR

This study explores the stability and properties of lanthanum-based hydrides under high pressure, revealing new compounds and potential superconducting behaviors.

## Contribution

The paper identifies new stable hydrides in the La–Si–H system and provides insights into their structural and superconducting properties under high pressure.

## Key findings

- LaAlH6 is the only stable compound in the La–Al–H system at high pressure.
- LaSiH2 and LaSiH7 are predicted to be stable in the La–Si–H system at 20 GPa.
- LaSiH2 shows superconductivity with a critical temperature of approximately 10 K.

## Abstract

Hydrogenation at
gigapascal pressures can produce hydrides
with
potential superconducting, ionic, and hydrogen-storage properties.
We studied the La–Al–H and La–Si–H systems
up to 20 GPa using structure prediction and in situ synchrotron diffraction. In La–Al–H, only rhombohedral
LaAlH6 is stable. The La–Si–H system forms
an orthorhombic monohydride, LaSiH, at low pressure, while LaSiH2 and LaSiH7 are predicted to be stable at 20 GPa,
and LaSiH6 is slightly unstable. LaSiH2 is structurally
related to the monohydride, whereas LaSiH6 and LaSiH7 feature SiH6
2– units characteristic
of hydridosilicates. Calculations predict superconductivity in LaSiH2 and LaSiH6 with T
c ≈ 10 and 6 K. Experimentally, LaSiH2 formation
is indicated at 20 GPa, but higher hydrides were not observed due
to decomposition into LaH3 and Si, suggesting that pressures
above 20 GPa are required to stabilize these phases at synthesis temperatures.