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Elucidating the impact of point defects on the structural, electronic, and mechanical behaviour of chromium nitride

Barsha Bhattacharjee, Emilia Olsson

TL;DR

This work tackles how intrinsic point defects (vacancies, antisites, interstitials) and extrinsic impurities (H, O) affect the structure, electronics, magnetism, and mechanics of CrN and the nitrogen-rich pernitrides CrN2 using density functional theory. It demonstrates that CrN2, with directional N–N bonding, is highly sensitive to defects, developing localized spin-polarized states and substantial elastic softening, while CrN’s metallic bonding provides robust defect tolerance and efficient screening. Hydrogen generally softens both phases, with CrN showing pronounced directional distortions, whereas oxygen can enhance hardness, especially in CrN2, highlighting defect chemistry and bonding anisotropy as key levers for nanoscale coating design. Collectively, the findings offer mechanistic understanding to guide defect-engineered Cr-N coatings under realistic processing and operating environments.

Abstract

Defect engineering offers an important route to property tuning of nanostructured coatings for advanced applications. Transition metal nitrides, such as CrN, are widely used for their mechanical resilience, but their nitrogen-rich analogue CrN2 remains poorly understood, especially at the atomic scale. This study employs density functional theory to investigate the energetics as well as how intrinsic defects (vacancies, interstitials, and anti-sites) and extrinsic impurities (hydrogen and oxygen) influence the structural, electronic, magnetic, and mechanical response of CrN2, in comparison to the more commonly studied CrN. With directional N-N bonding and semiconducting character, CrN2 shows high sensitivity to defect incorporation, including local spin polarisation, gap states, and mechanical softening. In contrast, CrN's metallic character enables effective screening of similar defects, preserving its structural, magnetic, electronic and mechanical integrity. However, hydrogen induces anisotropic distortions and mechanical degradation in CrN, while oxygen enhances hardness. These findings reveal how defect chemistry and bonding anisotropy govern mechanical performance, with implications for nanoscale control in coatings design.

Elucidating the impact of point defects on the structural, electronic, and mechanical behaviour of chromium nitride

TL;DR

This work tackles how intrinsic point defects (vacancies, antisites, interstitials) and extrinsic impurities (H, O) affect the structure, electronics, magnetism, and mechanics of CrN and the nitrogen-rich pernitrides CrN2 using density functional theory. It demonstrates that CrN2, with directional N–N bonding, is highly sensitive to defects, developing localized spin-polarized states and substantial elastic softening, while CrN’s metallic bonding provides robust defect tolerance and efficient screening. Hydrogen generally softens both phases, with CrN showing pronounced directional distortions, whereas oxygen can enhance hardness, especially in CrN2, highlighting defect chemistry and bonding anisotropy as key levers for nanoscale coating design. Collectively, the findings offer mechanistic understanding to guide defect-engineered Cr-N coatings under realistic processing and operating environments.

Abstract

Defect engineering offers an important route to property tuning of nanostructured coatings for advanced applications. Transition metal nitrides, such as CrN, are widely used for their mechanical resilience, but their nitrogen-rich analogue CrN2 remains poorly understood, especially at the atomic scale. This study employs density functional theory to investigate the energetics as well as how intrinsic defects (vacancies, interstitials, and anti-sites) and extrinsic impurities (hydrogen and oxygen) influence the structural, electronic, magnetic, and mechanical response of CrN2, in comparison to the more commonly studied CrN. With directional N-N bonding and semiconducting character, CrN2 shows high sensitivity to defect incorporation, including local spin polarisation, gap states, and mechanical softening. In contrast, CrN's metallic character enables effective screening of similar defects, preserving its structural, magnetic, electronic and mechanical integrity. However, hydrogen induces anisotropic distortions and mechanical degradation in CrN, while oxygen enhances hardness. These findings reveal how defect chemistry and bonding anisotropy govern mechanical performance, with implications for nanoscale control in coatings design.

Paper Structure

This paper contains 8 sections, 1 equation, 2 figures, 3 tables.

Table of Contents

  1. Introduction
  2. Methodology
  3. Results
  4. Defect Energetics, Structure, and Magnetic Response
  5. Electronic properties
  6. Mechanical properties
  7. Conclusions
  8. Acknowledgements

Figures (2)

  • Figure 1: Overview of structural distortions in presence of defects. 1(a) - (d) show the pristine, $V_{\text{N}}^\times$, $\text{H}_{\text{N}}^\times$, $\text{O}_{\text{N}}^\times$, respectively in CrN2 and (e) - (f) show the pristine, $V_{\text{N}}^\times$, $\text{H}_{i}^\times$ and $\text{O}_{\text{N}}^\times$ in CrN.
  • Figure 2: Projected density of states of (a) pristine (b) $V_{\text{N}}^\times$ (c) $\text{H}_{\text{N}}^\times$ (d) $\text{O}_{\text{N}}^\times$ in CrN2 and (e) pristine (f) $V_{\text{N}}^\times$ (g) $\text{H}_{i}^\times$ (h) $\text{O}_{\text{N}}^\times$ in CrN.