Structure imaging and vanadium substitution in cubic TiCr₂ Laves phase

Abstract

Properties of Laves phase compounds can be tailored by alloying and microstructural engineering. V-substituted cubic TiCr₂ Laves phase has been studied to understand the location of V atoms in the lattice, by structural imaging and first-principle computations. Even though Ti, V and Cr appear next to each other in the periodic table, V preferentially replaces the Ti lattice producing anti-site defects. The defect formation energy for V substitution in Ti and in Cr lattice is 0.29 and 0.40 eV, respectively. V replacement in the Ti lattice generates atomic scale strain. Atomic numbers of V, Ti and Cr being very close, this phase is not quite suitable for incoherent imaging for understanding the structure and the chemistry. Instead, difference in channelling behaviour of electron waves along the Ti columns and along the Cr columns could be exploited to preferentially image the individual atom columns. Nature of the exit phase wave, phase and amplitude has been used to understand the contrast qualitatively. The intensity distribution of any particular atom column that is disturbed by the presence of foreign atom has been used to detect the position of V atoms. This method could be extended to study other Laves phases and complex intermetallic structures to understand their structure, defects and interfaces.

Keywords:

• Laves phase
• V–Ti–Cr alloy
• high-resolution electron microscopy
• multislice simulation
• first-principle

Acknowledgement

The authors would also like to acknowledge UGC-DAE-CSR for providing the experimental support for the work. Stimulating discussion on various occasions with Shabana Khan, Bhabha Atomic Research Center, Mumbai, is thankfully acknowledged. Encouragement and support from Prof. Rampi Ramprasad, University of Connecticut, is thankfully acknowledged.

Disclosure statement

No potential conflict of interest was reported by the authors.