A New Family of Ternary Intermetallic Compounds with Dualistic Atomic Ordering - The ZIP Phases.

Abstract

A new family of nanostructured ternary intermetallic compounds - named the ZIP phases - is introduced in this work. The ZIP phases exhibit dualistic atomic ordering, i.e., they form two structural variants: one with the fcc diamond cubic structure (space group Fd <math xmlns="http://www.w3.org/1998/Math/MathML"> <semantics><mover><mn>3</mn> <mo>¯</mo></mover> <annotation>$\bar 3$</annotation></semantics> </math> m) and one with the hexagonal structure (space group P6₃/mmc). They are also characterized by metallic behavior, ionic bonding, and atomic zigzagging. Powder metallurgical routes involving pressure-assisted densification are adopted to demonstrate ZIP phase synthesis in the Nb-Si-Ni, Nb-Si-Co, Ta-Si-Ni, V-Si-Ni, and Nb-Si-Fe ternary systems. Crucially, reactive hot pressing is capable of producing high-purity ZIP phase materials after the judicious, elemental system-specific optimization of the processing route. Synthesis of phase-pure materials - demonstrated in the Nb-Si-Ni ternary system by the synthesis of quasi phase-pure Nb₃SiNi₂ and Ni₃SiNb₂ ZIP phase-based materials - is a steppingstone to the prospective exploitation of the ZIP phases. Characterization of Nb₃SiNi₂ and Ni₃SiNb₂ involves crystal structure determination, spatially resolved chemical analysis, and determination of select thermal, electrical, magnetic, mechanical, and physical properties. Density functional theory is used to assess the stability of Nb₃SiNi₂ & Ni₃SiNb₂ and derivative binary compounds at different temperatures, also exploring the exfoliation of these two ZIP phases along specific surfaces to produce 2D derivatives.