On the Functionality of Complex Intermetallics: Frustration, Chemical Pressure Relief, and Potential Rattling Atoms in Y11Ni60C6

Yiming Guo; Daniel C Fredrickson

doi:10.1021/acs.inorgchem.6b01645

On the Functionality of Complex Intermetallics: Frustration, Chemical Pressure Relief, and Potential Rattling Atoms in Y₁₁Ni₆₀C₆

Inorg Chem. 2016 Oct 17;55(20):10397-10405. doi: 10.1021/acs.inorgchem.6b01645. Epub 2016 Sep 28.

Authors

Yiming Guo¹, Daniel C Fredrickson¹

Affiliation

¹ Department of Chemistry, University of Wisconsin-Madison , 1101 University Avenue, Madison, Wisconsin 53706, United States.

PMID: 27680537
DOI: 10.1021/acs.inorgchem.6b01645

Abstract

Intermetallic carbides provide excellent model systems for exploring how frustration can shape the structures and properties of inorganic materials. Combinations of several metals with carbon can be designed in which the formation of tetrahedrally close-packed (TCP) intermetallics conflicts with the C atoms' requirement of trigonal prismatic or octahedral coordination environments, as offered by the simple close-packings (SCP) of equally sized spheres. In this Article, we explore the driving forces that lead to the coexistence of these incompatible arrangements in the Yb₁₁Ni₆₀C₆-type compound Y₁₁Ni₆₀C₆ (cI154), as well as potential consequences of this intergrowth for the phase's physical properties. Our focus begins on the structure's SCP regions, which appear as C-stuffed versions of a AuCu₃-type YNi₃ phase that is not observed on its own in the Y-Ni system. DFT-Chemical Pressure (DFT-CP) calculations on this hypothetical YNi₃ phase reveal large negative pressures within the Ni sublattice, as it is stretched to accommodate the size requirements of the Y atoms. In the Y₁₁Ni₆₀C₆ structure, two structural mechanisms for addressing these CP issues appear: the incorporation of interstitial C atoms, and the presence of interfaces with CaCu₅-type domains. The relative roles of these two mechanisms are investigated with the CP analysis on a hypothetical YNi₃C_x series of C-stuffed AuCu₃-type phases, the Y-Ni sublattice of Y₁₁Ni₆₀C₆, and finally the full Y₁₁Ni₆₀C₆ structure. Through these calculations, the C atoms appear to play the roles of relieving positive Y CPs and supporting relaxation at the AuCu₃-type/CaCu₅-type interfaces, where the cancellation occurs between opposite CPs experienced by the Y atoms in the two parent structures (following the epitaxial stabilization mechanism). The CP analysis of Y₁₁Ni₆₀C₆ also highlights a sublattice of Y and Ni atoms with large negative CPs (and thus the potential for soft vibrational modes), illustrating how frustrated structures could lead to the full realization of the phonon glass-electron crystal concept.