First-principles study of phase stability of Ti2N under pressure

Abstract

First-principles study of phase stability of various phases of Ti 2 N under normal conditions and as a function of pressure were carried out. Among the ε-and δ'-phases of Ti 2 N that are observed experimentally, ε-Ti 2 N is the most stable. The δ'-phase can only exist at high temperature due to the soft acoustic modes at the X point. The origin of the tetragonal structure of both the ε-and δ'-phases is supposed to be caused by the tetragonal local lattice distortion around a nitrogen vacancy. Based on the results of the total-energy and phonon-spectrum calculations at zero temperature, the following sequence of phase transformation in Ti 2 N under pressure is predicted: ε-Ti 2 N (space group P4/mnm), P=77.5 GPa → Au 2 Te-type (space group C2/m), P=86.7 GPa → Al 2 Cu-type (space group I4/mcm). The present study shows that, to correctly predict relative phase stability, the peculiarities of the phonon spectra of the materials under investigation have to be properly accounted for.

Phase stability, chemical bonding and mechanical properties of titanium nitrides: a first-principles study

“…Ti 3 N 2 has space group Immm, while Ti 4 N 3 and Ti 6 N 5 belong to space group C2/m. À1 than that of the Au 2 Te-type or Al 2 Cu-type structures proposed by Ivashchenko et al 23 Having investigated the crystal structures and energetics of the various titanium subnitrides Ti n+1 N n and TiN, we now consider their electronic properties. 2.…”

Elastic Properties and Electronic Properties of MxNy (M = Ti, Zr) from First Principles Calculations

“…Wang et al adopted an efficacious strain-stress way to compute the elastic stiffness constants of TiN, and got some related properties by first-principles calculations within the generalized gradient approximation [12]. Ivashchenko et al studied the electromagnetic properties of Ti 2 N with two different structures under pressure [13]. Kim et al obtained the color of TiN and ZrN by first-principles calculations [14].…”

Phase stability, chemical bonding and mechanical properties of titanium nitrides: A first-principles study

“…It is noteworthy that the enthalpy of Cmcm-Ti 2 N is lower by more than 0.24 eV/f.u. than that of the Au 2 Te-type or Al 2 Cu-type structures proposed by Ivashchenko et al [23]. Having investigated the crystal structures and energetics of the various titanium subnitrides Ti n+1 N n and TiN, we now consider their electronic properties.…”

“…ε-Ti 2 N [21] (P4 2 /mnm) is the most stable structure at normal conditions, while the δ' phase (I4 1 /amd) can only exist at high temperatures [22]. Ivashchenko et al [23] predicted phase transformation sequence ε-Ti 2 N → Au 2 Te-type → Al 2 Cu-type with transitions occurred at 77.5 and 86.7 GPa, respectively. For the metastable Ti 3 N 4 , Kroll et al [24] proposed that it adopts the CaTi 2 O 4 -type structure at normal conditions.…”