Premium
Influence of Valence Electron Concentration on Laves Phases: Structures and Phase Stability of Pseudo‐Binary MgZn 2– x Pd x
Author(s) -
Thimmaiah Srinivasa,
Miller Gordon J.
Publication year - 2015
Publication title -
zeitschrift für anorganische und allgemeine chemie
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.354
H-Index - 66
eISSN - 1521-3749
pISSN - 0044-2313
DOI - 10.1002/zaac.201500197
Subject(s) - crystallography , valence electron , valence (chemistry) , laves phase , materials science , crystal structure , atom (system on chip) , chemistry , electron , alloy , intermetallic , metallurgy , physics , organic chemistry , quantum mechanics , computer science , embedded system
A series of pseudo‐binary compounds MgZn 2– x Pd x (0.15 ≤ x ≤ 1.0) were synthesized and structurally characterized to understand the role of valence electron concentration ( vec ) on the prototype Laves phase MgZn 2 with Pd‐substitution. Three distinctive phase regions were observed with respect to Pd content, all exhibiting fundamental Laves phase structures: 0.1 ≤ x ≤ 0.3 (MgNi 2 ‐type, hP 24; MgZn 1.80 Pd 0.20(2) ), 0.4 ≤ x ≤ 0.6 (MgCu 2 ‐type, cF 24; MgZn 1.59 Pd 0.41(2) ), and 0.62 ≤ x ≤ 0.8 (MgZn 2 ‐type, hP 12: MgZn 1.37 Pd 0.63(2) ). Refinements from single‐crystal X‐ray diffraction indicated nearly statistical distributions of Pd and Zn atoms among the majority atom sites in these structures. Interestingly, the MgZn 2 ‐type structure re‐emerges in MgZn 2– x Pd x at x ≈ 0.7 with the refined composition MgZn 1.37(2) Pd 0.63 and a c / a ratio of 1.59 compared to 1.64 for binary MgZn 2 . Electronic structure calculations on a model “MgZn 1.25 Pd 0.75 ” yielded a density of states (DOS) curve showing enhancement of a pseudogap at the Fermi level as a result of electronic stabilization due to the Pd addition. Moreover, integrated crystal orbital Hamilton population (ICOHP) values show significant increases of orbital interactions for (Zn,Pd)–(Zn,Pd) atom pairs within the majority atom substructure, i.e., within the Kagomé nets as well as between a Kagomé net and an apical site, from binary MgZn 2 to the ternary “MgZn 1.25 Pd 0.75 ”. Multi‐centered bonding is evident from electron localization function (ELF) plots for “MgZn 1.25 Pd 0.75 ”, an outcome which is in accordance with analysis of other Laves phases .