Anisotropy of the Electric Field Gradient in Two-Dimensional α-MoO3 Investigated by 57Mn(57Fe) Emission Mössbauer Spectroscopy
Fecha
2022-07-04Autor
Schell, Juliana
Zyabkin, Dmitry
Bharuth-Ram, Krish
Gonçalves, João N.
Díaz-Guerra, Carlos
Gunnlaugsson, Haraldur Páll
Tarazaga Martín-Luengo, Aitana
Schaaf, Peter
Bonanni, Alberta
Masenda, Hilary
Dang, Thien Thanh
Mølholt, Torben E.
Ólafsson, Sveinn
Mantovan, Roberto
Johnston, Karl
Gíslason, Hafliði Pétur
Krastev, Petko B.
Naidoo, Deena
Qi, Bingcui
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Crystals 12(7) : (2022) // Article ID 942
Resumen
Van der Waals α-MoO3 samples offer a wide range of attractive catalytic, electronic, and optical properties. We present herein an emission Mössbauer spectroscopy (eMS) study of the electric-field gradient (EFG) anisotropy in crystalline free-standing α-MoO3 samples. Although α-MoO3 is a two-dimensional (2D) material, scanning electron microscopy shows that the crystals are 0.5–5-µm thick. The combination of X-ray diffraction and micro-Raman spectroscopy, performed after sample preparation, provided evidence of the phase purity and crystal quality of the samples. The eMS measurements were conducted following the implantation of 57Mn (t1/2 = 1.5 min), which decays to the 57Fe, 14.4 keV Mössbauer state. The eMS spectra of the samples are dominated by a paramagnetic doublet (D1) with an angular dependence, pointing to the Fe2+ probe ions being in a crystalline environment. It is attributed to an asymmetric EFG at the eMS probe site originating from strong in-plane covalent bonds and weak out-of-plane van der Waals interactions in the 2D material. Moreover, a second broad component, D2, can be assigned to Fe3+ defects that are dynamically generated during the online measurements. The results are compared to ab initio simulations and are discussed in terms of the in-plane and out-of-plane interactions in the system.
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