Novel metastable compounds in the Zr-B system: an ab initio evolutionary study

Area of Science:

• Materials Science
• Computational Materials Science
• Solid State Chemistry

Background:

• Zirconium-boron (Zr-B) systems are known for their diverse and often hard crystalline phases.
• Exploration of novel Zr-B stoichiometries is crucial for discovering materials with unique properties.

Purpose of the Study:

• To computationally investigate potential Zr-B crystal structures and identify new stable phases.
• To characterize the mechanical, dynamical, and electronic properties of predicted Zr-B compounds.

Main Methods:

• Ab initio evolutionary simulations were employed to explore Zr-B phase space up to 18 atoms per unit cell.
• Mechanical stability was assessed using elastic constants, and dynamical stability through phonon dispersion calculations.
• Electronic structure and bonding characteristics were analyzed using electronic density maps and crystal orbital Hamilton population (COHP) diagrams.

Main Results:

• Two new stable Zr-B phases, Zr2B3 and Zr3B2, were identified, alongside known phases like ZrB, ZrB2, ZrB12, oP8-ZrB, and Zr3B4.
• Calculated formation enthalpies suggest the new phases are experimentally synthesizable, with pressure generally aiding synthesis.
• The novel Zr2B3 and Zr3B2 compounds exhibit low hardness (<10 GPa) and high ductility, contrasting with harder known Zr-B phases.
• Electronic structure calculations indicate metallic behavior with significant ionic bonding between Zr and B atoms.

Conclusions:

• The discovery of Zr2B3 and Zr3B2 expands the known phase diagram of the Zr-B system.
• These new phases offer potential for applications requiring ductile metallic materials.
• Computational methods effectively predict novel stable materials and their properties, guiding experimental synthesis efforts.