Abstract
Tetrahedral units can transport oxide anions via interstitial or vacancy defects owing to their great deformation and rotation flexibility. Compared with interstitial defects, vacancy-mediated oxide-ion conduction in tetrahedra-based structures is more difficult and occurs rarely. The isolated tetrahedral anion Scheelite structure has showed the advantage of conducting oxygen interstitials but oxygen vacancies can hardly be introduced into Scheelite to promote the oxide ion migration. Here we demonstrate that oxygen vacancies can be stabilized in the BiVO4 Scheelite structure through Sr2+ for Bi3+ substitution, leading to corner-sharing V2O7 tetrahedral dimers, and migrate via a cooperative mechanism involving V2O7-dimer breaking and reforming assisted by synergic rotation and deformation of neighboring VO4 tetrahedra. This finding reveals the ability of Scheelite structure to transport oxide ion through vacancies or interstitials, emphasizing the possibility to develop oxide-ion conductors with parallel vacancy and interstitial doping strategies within the same tetrahedra-based structure type.
Highlights
Tetrahedral units can transport oxide anions via interstitial or vacancy defects owing to their great deformation and rotation flexibility
Multiple complementary techniques, including synchrotron powder diffraction and neutron powder diffraction (SPD and NPD), solid-state 51V nuclear magnetic resonance (NMR) spectroscopy, density functional theory (DFT) calculations and interatomic-potential-based molecular dynamic (MD) simulations, evidence that the oxygen vacancies in Bi1−xSrx VO4−0.5x are accommodated via formation of corner-sharing tetrahedral V2O7 dimers and the oxygen vacancy migration in the Scheelite structure involves V2O7-dimer breaking and reforming process assisted by cooperative rotations and deformations of isolated neighboring tetrahedra
The solid solution limit in Bi1−xSrxVO4−0.5x can be extended significantly from x = 0.1 using solid-state reaction synthesis to x = 0.3 via direct crystallization from the melt, using aerodynamic levitation (ADL) coupled to laser heating system as an original elaboration method
Summary
Tetrahedral units can transport oxide anions via interstitial or vacancy defects owing to their great deformation and rotation flexibility. We demonstrate that oxygen vacancies can be stabilized in the BiVO4 Scheelite structure through Sr2+ for Bi3+ substitution, leading to corner-sharing V2O7 tetrahedral dimers, and migrate via a cooperative mechanism involving V2O7-dimer breaking and reforming assisted by synergic rotation and deformation of neighboring VO4 tetrahedra This finding reveals the ability of Scheelite structure to transport oxide ion through vacancies or interstitials, emphasizing the possibility to develop oxide-ion conductors with parallel vacancy and interstitial doping strategies within the same tetrahedra-based structure type. Multiple complementary techniques, including synchrotron powder diffraction and neutron powder diffraction (SPD and NPD), solid-state 51V nuclear magnetic resonance (NMR) spectroscopy, density functional theory (DFT) calculations and interatomic-potential-based MD simulations, evidence that the oxygen vacancies in Bi1−xSrx VO4−0.5x are accommodated via formation of corner-sharing tetrahedral V2O7 dimers and the oxygen vacancy migration in the Scheelite structure involves V2O7-dimer breaking and reforming process assisted by cooperative rotations and deformations of isolated neighboring tetrahedra
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