Nb K-edge x-ray absorption investigation of the pressure induced amorphization in A-site deficient double perovskite La_1/3NbO₃

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.

Probing the electronic and local structure of Sr$_{2-x}$La$_x$CoNbO$_6$ using near-edge and extended x-ray absorption fine structures

“…2(a, b) of [45]. Further, two prominent features 1 and 2, which are separated by ∼ 13 eV, can be attributed to the 1s →5p transition and the resonance due to multiple scattering of the photoelectrons from the neighboring atoms, respectively [46][47][48]. It is interesting to note that the intensity of the feature 2 remains almost invariant up to the x = 0.4 and then increases monotonically with further increase in the La substitution for the x 0.6 samples [see inset (a1) of Fig.…”

Ce(iv)-centered charge-neutral perovskite layers topochemically derived from anionic [CeTa2O7]−layers

“…The average oxidation state in the mixed-valence compounds could be estimated from the peak position of the derivative XANES spectra, namely, the shi of the absorption edge. 23,24 Generally, the absorption edge should shi to a higher energy as the oxidation state increases. Indeed, the derivative peak position of RbLaTa 2 O 7 (Ta 5+ ) was observed at higher energy than that of TaS 2 (Ta 4+ ) (Fig.…”

Exploring the Interplay between Structure and Electronic Behavior across Pressure-Induced Isostructural and Structural Transitions in Weyl-Type Semimetal NbAs

“…In this sense, pressure initially confines the Nb-As vibration (hardening effect) and, subsequently, induces a change at ~25 GPa in the bond topology, leading to an increase in σ 2 Nb-As(1) . Near pressure-induced structural transitions, indeed, typical anomalies in pair-distance variance may occur in several compounds, as, for example, in YH 3[57], CuO[58], and La 1/3 NbO 3[59]. For the pair Nb-Nb(1) in Figure7b, it is noteworthy that the formation of both the C 3h axis and horizontal mirror (σ h ) continuously alters the vibrational patterns, which may explain the increase in the value of σ 2 Nb-Nb(1) above ~25 GPa.…”