Investigating the Local Structure of Lanthanoid Hafnates Ln₂Hf₂O₇ via Diffraction and Spectroscopy

Abstract

The lanthanoid hafnates Ln 2 Hf 2 O 7 (Ln = La, Pr, Nd, Sm−Tm) were studied using a combination of synchrotron X-ray and neutron powder diffraction together with X-ray absorption and Raman spectroscopy. Spectroscopic methods revealed a gradual increase in disorder from the ideal pyrochlore structure to the defect fluorite structure as the size of the Ln cation increases. The line shape of the Hf L 3 -edge X-ray absorption near edge spectra which is sensitive to the local coordination environment changed with increasing disorder. The general line shape of the O K-edge XANES and Raman spectra also indicated an increase in disorder across the Ln 2 Hf 2 O 7 series. Differences in the diffraction and spectroscopy analysis reflect the greater sensitivity of the spectroscopy techniques to local ordering.

Candidate quantum spin ice in the pyrochlorePr2Hf2O7

“…A nonmagnetic reference sample, La 2 Hf 2 O 7 , was prepared via the same route, starting from La 2 O 3 . Both powder samples were characterized by x-ray diffraction at room temperature and found to be single phase with the Pr 2 Hf 2 O 7 lattice parameter refined to 10.6842 ± 0.0002Å, in agreement with other reports that have established that it crystallizes in the pyrochlore structure [33,34]. A parallelepiped sample of mass m = 79.5 mg was cut from a single crystal of several grams, oriented using a Laue camera, and used for macroscopic measurements.…”

An investigation of the electronic structure and structural stability of RE2Ti2O7 by glancing angle and total electron yield XANES

“…The super structural peaks (odd planes) from the XRD patterns were used to differentiate the pyrochlore-phase materials from the defect-fluorite phase materials [59][60][61][62]. A decrease in the intensity of the superstructural peaks is generally indicative of cation anti-site disorder; however, the intensities of these peaks relative to the other peaks are also affected by the differences in the scattering power between the A-and B-site cations [33,63]. Rietvield refinement results of the powder XRD patterns collected from some of the undamaged RE 2 Ti 2 O 7 (RE = Sm, Gd, Yb) materials are presented in Fig.…”

Phase evolution and chemical durability of co-doped Gd2Zr2O7 ceramics for nuclear waste forms

“…Generally, A 2 B 2 O 7 oxides can adopt pyrochlore or defect fluorite structure due to the ionic radius ratio of cations (r A /r B ) [13,14]. Pyrochlore is a superstructure of the fluorite phase (AO 2 space group Fm-3m).…”