Computational Search for Novel Hard Chromium-Based Materials

Abstract

Nitrides, carbides, and borides of transition metals are an attractive class of hard materials. Our recent preliminary explorations of the binary chemical compounds indicated that chromium-based materials are among the hardest transition metal compounds. Motivated by this, here we explore in detail the binary Cr-B, Cr-C, and Cr-N systems using global optimization techniques. Calculated enthalpy of formation and hardness of predicted materials were used for Pareto optimization to define the hardest materials with the lowest energy. Our calculations recover all numerous known stable compounds (except CrC with its large unit cell) and discover a novel stable phase Pmn2-CrC. We resolve the structure of CrN and find it to be of anti-CaCl type (space group Pnnm). Many of these phases possess remarkable hardness, but only CrB is superhard (Vickers hardness 48 GPa). Among chromium compounds, borides generally possess the highest hardnesses and greatest stability. Under pressure, we predict stabilization of a layered TMDC-like phase of CrN, a WC-type phase of CrN, and a new compound CrN. Nitrogen-rich chromium nitride CrN is a high-energy-density material featuring polymeric nitrogen chains. In the presence of metal atoms (e.g., Cr), polymerization of nitrogen takes place at much lower pressures; CrN becomes stable at ∼15 GPa (cf. 110 GPa for synthesis of pure polymeric nitrogen).

Evolutionary Algorithm‐based Crystal Structure Prediction for Gold(I) Fluoride

“…The use of structure prediction algorithms enables the evaluation of potential structures which may adopt an unexpected or unique structure type . Evolutionary algorithms have so far been used successfully in many structural prediction studies of transition metal compounds and prospective materials based on them, both at ambient and higher pressures . The valence states of gold in Au−F compounds under high pressure have very recently been studied by Liu et al .…”

Single-crystal diffractometer coupled with double-sided laser heating system at the Extreme Conditions Beamline P02.2 at PETRAIII

“…The thermal parameters acquired during laser heating are about twice as large as those at room temperature (Table I and fundamental role in the steel hardening process 29 and is often used as a component in advanced coating systems. 30 Theoretically predicted nitrogen-rich chromium nitrides CrN 2 and CrN 4 were suggested to become thermodynamically stable at pressures above 7 and 15 GPa, respectively, 31,32 and are expected to be superhard compounds. 31,32 The high-pressure reaction between chromium and nitrogen, studied by Hasegawa and Yagi at 10 GPa and 1800 K in a laser-heated DAC, yielded CrN as the only product.…”

“…30 Theoretically predicted nitrogen-rich chromium nitrides CrN 2 and CrN 4 were suggested to become thermodynamically stable at pressures above 7 and 15 GPa, respectively, 31,32 and are expected to be superhard compounds. 31,32 The high-pressure reaction between chromium and nitrogen, studied by Hasegawa and Yagi at 10 GPa and 1800 K in a laser-heated DAC, yielded CrN as the only product. 33 Here, we studied the same reaction but at a pressure of 47 GPa in order to search for predicted nitrogen-rich chromium nitrides.…”

The Hardness and Corrosion Properties of Trivalent Chromium Hard Chromium

“…[1] [2]. Hexavalent chromium has been used as the main solution composition of hard chromium plating as hexavalent chromium plating process stability and plating quality are reliable up to now [3].…”