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Chemical Bonding Effect on the Incorporation and Conduction of Interstitial Oxide Ions in Gallate Melilites
Author(s) -
Xu Jungu,
Li Yanchang,
Zhou Lijia,
Tang Xin,
Kuang Xiaojun
Publication year - 2019
Publication title -
advanced theory and simulations
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.068
H-Index - 17
ISSN - 2513-0390
DOI - 10.1002/adts.201900069
Subject(s) - antibonding molecular orbital , crystallography , oxygen , ion , chemical bond , interstitial defect , ionic radius , lone pair , materials science , density functional theory , ionic bonding , oxide , chemical physics , chemistry , computational chemistry , atomic orbital , electron , molecule , physics , metallurgy , optoelectronics , organic chemistry , doping , quantum mechanics
The ability to incorporate high content of interstitial oxygen ions (O i ) in La 1+ x Sr 1‐ x Ga 3 O 7+0.5 x melilite owing to the good size match between La 3+ and Sr 2+ ions is well documented. Here, the complete substitution of Sr 2+ by Pb 2+ lone‐pair cations results in a significant loss of this ability, even though Sr 2+ and Pb 2+ have almost the same effective ionic radius. To explore the fundamental mechanism underlying this result, density functional theory (DFT) calculations are performed on both the LaSrGa 3 O 7 ‐based and LaPbGa 3 O 7 ‐based materials, revealing a new chemical bonding effect on the incorporation of mobile oxygen interstitial defects in melilites. For LaSrGa 3 O 7 ‐based melilites, the interstitial oxygens have cooperatively weak antibonding interactions with the framework oxygen atoms (O f ). This antibonding O i ‐O f interaction pushes O i toward a 3‐linked Ga ion, enhancing the covalent bonding between this Ga ion and O i . In addition, the antibonding O i –O f interaction makes the oxygen interstitial defects and framework atoms highly active, benefiting the migration of defects. In contrast, for LaPbGa 3 O 7 ‐based materials, the 6s 2 electrons of Pb 2+ point toward the c ‐axis and form antibonding with framework O 2− . This antibonding projects into the tunnel void, thereby directly hindering the entrance of interstitial oxygen atoms into the pentagonal rings.