Pressure-induced disordering of site occupation in iron–nickel nitrides

Binbin Wu,Shan Liu,Meifang Pu,Hiroaki Ohfuji,Qiqi Tang,Leiming Fang,Yuanhua Xia,Li Lei,Feng Zhang,Tetsuo Irifune,Duanwei He

doi:10.1063/5.0040041

Abstract

Controlled disordering of substitutional and interstitial site occupation at high pressure can lead to important changes in the structural and physical properties of iron–nickel nitrides. Despite important progress that has been achieved, structural characterization of ternary Fe–Ni–N compounds remains an open problem owing to the considerable technical challenges faced by current synthetic and structural approaches for fabrication of bulk ternary nitrides. Here, iron–nickel nitride samples are synthesized as spherical-like bulk materials through a novel high-pressure solid-state metathesis reaction. By employing a wide array of techniques, namely, neutron powder diffraction, Rietveld refinement methods combined with synchrotron radiation angle-dispersive x-ray diffraction, scanning electron microscopy/energy dispersive x-ray spectroscopy, and transmission electron microscopy, we demonstrate that high-temperature and high-pressure confinement conditions favor substitutional and interstitial site disordering in ternary iron–nickel nitrides. In addition, the effects of interstitial nitrogen atoms and disorderly substituted nickel atoms on the elastic properties of the materials are discussed.

Highlights

By employing a wide array of techniques, namely, neutron powder diffraction, Rietveld refinement methods combined with synchrotron radiation angle-dispersive x-ray diffraction, scanning electron microscopy/energy dispersive x-ray spectroscopy, and transmission electron microscopy, we demonstrate that high-temperature and high-pressure confinement conditions favor substitutional and interstitial site disordering in ternary iron–nickel nitrides
Iron–nickel nitrides were synthesized using an High-pressure solid-state metathesis (HPSSM) reaction in which Fe2O3, NiO, and hBN were used as reaction precursors
The homogeneity of the iron–nickel nitrides was measured by scanning electron microscopy (JSM-7000F field emission SEM, JEOL), and the elemental composition was determined using energy dispersive x-ray spectroscopy (EDX)

Summary

INTRODUCTION

Iron and nickel are the most important components of the inner core of the Earth, with recent reports indicating that at 364 GPa and 5000–6000 K, the maximum nitrogen content in the inner core can vary from 2.0 to 3.2 wt. %.1–5 The study of iron–nickel alloys and iron–nickel nitrides has been an important focus of experimental and computational research over the past few decades. Iron–nickel alloys have considerable potential for materials applications, owing to their high magnetoconductivities and low coefficients of thermal expansion. Iron-based nitrides have been considered important candidates for use as corrosion-proof layers on steel and for magnetic data storage systems, thanks to their significant thermal stability and suitable magnetic properties. The ordering of substitutional and interstitial site occupation at high pressures can lead to fundamental changes in structural phase relationships and in the properties of iron–nickel nitrides. The ordering of substitutional and interstitial site occupation at high pressures can lead to fundamental changes in structural phase relationships and in the properties of iron–nickel nitrides. High-pressure solid-state metathesis (HPSSM) reactions provide a useful synthetic method for fabrication of metal-based nitrides.20,23 Metal oxides, such as Fe2O3, Co2O3, NiO, LiNiO2, LiGaO2, KGaO2, NaReO4, Na2MoO4, and K2OsO4, are used as precursors in HPSSM reaction routes for the production of spherical bulk iron-based nitride samples, such as ε-Fe3N1+x and γ-Fe4Nx.. The principal motivation for this study is the synthesis of bulk ternary iron–nickel nitrides under HTHP conditions and further investigation and explanation of the disordering of substitutional and interstitial site occupancy, with the aim of obtaining better understanding of the structural properties of iron–nickel nitrides at high pressure

High-pressure synthesis

Structural Characterization

RESULTS AND DISCUSSION

CONCLUSION