Layered LaSrGa₃O₇‐Based Oxide‐Ion Conductors: Cooperative Transport Mechanisms and Flexible Structures

Abstract

Novel melilite-type gallium-oxides are attracting attention as promising new oxide-ion conductors with potential use in clean energy devices such as solid oxide fuel cells. Here, an atomic-scale investigation of the LaSrGa 3 O 7 -based system using advanced simulation techniques provides valuable insights into the defect chemistry and oxide ion conduction mechanisms, and includes comparison with the available experimental data. The simulation model reproduces the observed complex structure composed of layers of corner-sharing GaO 4 tetrahedra. A major finding is the first indication that oxide-ion conduction in La 1.54 Sr 0.46 Ga 3 O 7.27 occurs through an interstitialcy or cooperative-type mechanism involving the concerted knock-on motion of interstitial and lattice oxide ions. A key feature for the transport mechanism and high ionic conductivity is the intrinsic flexibility of the structure, which allows considerable local relaxation and changes in Ga coordination.

Localization of Oxygen Interstitials in CeSrGa3O7+δ Melilite

“…The oxygen interstitial enters into a four-linked Ga1O 4 bonding environment and transforms it into a distorted five-coordinate trigonal bipyramid (Figure 9c). Similar GaO 5 geometry has been observed in La 1+x A 1−x Ga 3 O 7+0.5x (A = Sr, Ca), 11,32,35,36 Ga 2 Te 4 O 11 , 37 and NaGa 2 (OH)(PO 4 ) 2 . 38 The stabilization of interstitial oxygen in CeSrGa 3 O 7.39 is different from that observed in the La 1+x A 1−x Ga 3 O 7+0.5x (A = Sr, Ca) 11,32,35,36 melilites.…”

Cooperative mechanisms of oxygen vacancy stabilization and migration in the isolated tetrahedral anion Scheelite structure

“…In order to elucidate how the oxygen vacancies migrate in the Scheelite structure, atomistic static lattice and MD simulations based on the interatomic potential method were performed, as previously successfully applied in other structure types based on tetrahedral units, for example, apatite-based 9 , melilite-based 12 , and LaBaGaO 4 -based 3 oxide ion conductors. The potential parameters listed in Supplementary Table 5 well reproduce the Scheelite BiVO 4 structure.…”

Interstitial oxide ion migration in scheelite-type electrolytes: a combined neutron diffraction and computational study

“…12 In such systems, ionic conduction is frequently based on anisotropic ions migration via interstitial or interstitialcy mechanism. [13][14][15][16][17][18] Nevertheless, their final performances are competitive with those of the 3D ionic conductors. The scheelite ABO 4 class of ternary oxides is a wide family of materials with several fields of applications, ranging from solid state scintillators, 19,20 to laser materials 21 and catalysts.…”