Interstitial Oxide Ion Order and Conductivity in La1.64Ca0.36Ga3O7.32 Melilite.

Man-Rong Li, Xiaojun Kuang, Samantha Y. Chong, Zhongling Xu, Christopher I. Thomas, Hongjun Niu, John B. Claridge, Matthew J. Rosseinsky

Research output: Contribution to journalArticleScientificpeer-review


Previously, we demonstrated that A-site substitution in melilite LaSrGa3O7 affords La1.54Sr0.46Ga3O7.27, in which interstitial oxygen atoms (Oint) are located in the 5-rings of the 2-dimensional tetrahedral network, gives pure oxide ion cond. of 0.02-0.1 over 600-900° temp. range. LaCaGa3O7 also adopts the tetragonal melilite structure found for the Sr phase. When doped to introduce oxide charge carriers in the La1+xCa1-xGa3O7+0.5x series, the tetragonal structure is retained to x=0.5. Herein, we address the impact on the phys. properties of a new lower-sym. phase formed to accommodate the high interstitial doping levels 0.55≤x≤0≅ X-ray powder diffraction from La1.64Ca0.36Ga3O7.32 indicates that the lowering of sym. at high doping levels occurs by formation of an orthorhombic cell with expansion of the ab plane contg. the B3O7 network. The refined structure of this interstitial-ordered orthorhombic phase reveals how the distortions required to stabilize the interstitial oxides at both the tetrahedral and the larger A sites become coupled at large interstitial densities to prevent unfavorable local interactions between carriers. Although the refined cell would need to be doubled again to allow for total carrier order, thus explaining the rather high residual ionic conductivities, the effect on interstitial mobility of the need to rearrange the complex relaxation around a mobile carrier without adversely affecting potential neighbors in the surrounding 5-rings can be gauged by the extent of the displacements required between the interstitial-contg. and interstitial-free parts of the superstructure, and the requirement to order the La dopants on the A site around the interstitial oxides. [on SciFinder(R)]
Original languageEnglish
Pages (from-to)2362-2366, S2362/1-S2362/52
JournalAngewandte Chemie
Issue number13
Publication statusPublished - 28 Feb 2010
MoE publication typeA1 Journal article-refereed


  • calcium lanthanum gallate melilite interstitial oxide ion order cond


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