Elastic constants and high-pressure structural transitions in lanthanum monochalcogenides from experiment and theory

TL;DR

This study combines experimental and theoretical approaches to investigate the high-pressure structural transitions and elastic properties of lanthanum monochalcogenides, revealing phase changes and providing accurate property predictions.

Contribution

It provides the first combined experimental and density functional theory analysis of high-pressure behavior in lanthanum monochalcogenides, including elastic constants.

Findings

Structural phase transition from NaCl to CsCl occurs at specific pressures.

Calculated transition pressures closely match experimental values.

Elastic constants and ground state properties are accurately predicted.

Abstract

The high-pressure structural behavior of lanthanum monochalcogenides is investigated by theory and experiment. Theory comprises density functional calculations of LaS, LaSe and LaTe with the general gradient approximation for exchange and correlation effects, as implemented within the full-potential linear muffin-tin orbital method. The experimental studies consist of high-pressure angle dispersive x-ray diffraction investigations of LaS and LaSe up to a maximum pressure of 41 GPa. A structural phase transition from the NaCl type to CsCl type crystal structure is found to occur in all cases. The experimental transition pressures are 27-28 GPa and 19 GPa, for LaS and LaSe, respectively, while the calculated transition pressures are 29 GPa, 21 GPa and 10 GPa for LaS, LaSe and LaTe, respectively. The calculated ground state properties such as equilibrium lattice constant, bulk modulus and its pressure derivative, and Debye temperatures are in good agreement with experimental results. Elastic constants are predicted from the calculations.