Stabilization of tetragonal phase in LaN under high pressure via Peierls distortion

Abstract

First-principles calculations have been carried out using the full potential linearized augmented plane wave method to analyze the structural stability of LaN under hydrostatic compression. Our calculations suggest that the rocksalt-type (B1) phase will transform to a primitive tetragonal structure (HP-LaN) having space group symmetry P4/nmm at a pressure of ∼25.8 GPa as compared to the experimental value of 22.8 GPa [Schneider SB, Baumann D, Salamat A, Schnick W, J Appl Phys. 2012;111:093503-1–6]. Additionally, we predict that the HP-LaN structure will further transform to CsCl type (B2) structure at ∼169 GPa. Analysis of band structures of HP-LaN and B2 phases suggests that the low symmetry HP-LaN phase, which can be viewed as a distortion of the B2 structure also, could be stabilized at lower pressure due to total energy lowering caused by Peierls distortion. The elastic moduli of B1 phase as a function of hydrostatic compression have also been calculated. The examination of behavior of elastic moduli as a function of pressure indicates that though the C₄₄ modulus decreases monotonically with increasing pressure, it softens completely at a pressure much beyond the B1 to HP-LaN transition pressure.

Keywords:

• ab-initio calculation
• structural transformation
• Peierls distortion
• LaN
• high pressure