title: Nb K-edge x-ray absorption investigation of the pressure induced amorphization in A-site deficient double perovskite La1/3NbO3.
abstract: Nb K-edge x-ray absorption spectroscopy is utilized to investigate the changes in the local structure of the A-site deficient double perovskite La1/3NbO3 which undergoes a pressure induced irreversible amorphization. EXAFS results show that with increasing pressure up to 7.5 GPa, the average Nb-O bond distance decreases in agreement with the expected compression and tilting of the NbO6 octahedra. On the contrary, above 7.5 GPa, the average Nb-O bond distance show a tendency to increase. Significant changes in the Nb K-edge XANES spectrum with evident low energy shift of the pre-peak and the absorption edge is found to happen in La1/3NbO3 above 6.3 GPa. These changes evidence a gradual reduction of the Nb cations from Nb(5+) towards Nb(4+) above 6.3 GPa. Such a valence change accompanied by the elongation of the average Nb-O bond distances in the octahedra, introduces repulsion forces between non-bonding adjacent oxygen anions in the unoccupied A-sites. Above a critical pressure, the Nb reduction mechanism can no longer be sustained by the changing local structure and amorphization occurs, apparently due to the build-up of local strain. EXAFS and XANES results indicate two distinct pressure regimes having different local and electronic response in the La1/3NbO3 system before the occurence of the pressure induced amorphization at  ∼14.5 GPa.
authors.affiliation: CELLS-ALBA, Carretera B.P. 1413, Cerdanyola del Valles 08290, Spain. European Synchrotron Radiation Facility, 6 Rue Jules Horowitz, BP220, 38043 Grenoble Cedex, France.
authors.forename: C
authors.initials: C
authors.lastname: Marini
authors.forename: O
authors.initials: O
authors.lastname: Noked
authors.forename: I
authors.initials: I
authors.lastname: Kantor
authors.forename: B
authors.initials: B
authors.lastname: Joseph
authors.forename: O
authors.initials: O
authors.lastname: Mathon
authors.forename: R
authors.initials: R
authors.lastname: Shuker
authors.forename: B J
authors.initials: BJ
authors.lastname: Kennedy
authors.forename: S
authors.initials: S
authors.lastname: Pascarelli
authors.forename: E
authors.initials: E
authors.lastname: Sterer