Pressure induced transformation and subsequent amorphization of monoclinic Nb₂O₅ and its effect on optical properties

Abstract

Pressure-induced phase transitions of monoclinic H-Nb 2 O 5 have been studied by in situ synchrotron x-ray diffraction, pair distribution function (PDF) analysis, and Raman and optical transmission spectroscopy. The initial monoclinic phase is found to transform into an orthorhombic phase at ~9 GPa and then change to an amorphous form above 21.4 GPa. The PDF data reveal that the amorphization is associated with disruptions of the long-range order of the NbO 6 octahedra and the NbO 7 pentagonal bipyramids, whereas the local edgeshares of octahedra and the local linkages of pentagonal bipyramids are largely preserved in their nearest neighbors. Upon compression, the transmittance of the sample in a region from visible to near infrared (450-1000 nm) starts to increase above 8.0 GPa and displays a dramatic enhancement above 22.2 GPa, indicating that the amorphous form has a high transmittance.The pressure-induced amorphous form is found to be recoverable under pressure release, and maintain high optical transmittance property at ambient conditions. The recoverable pressure induced amorphous material promises for applications in multifunctional materials.

First high-pressure XAFS results at the bending-magnet-based energy-dispersive XAFS beamline BL-8 at the Indus-2 synchrotron facility

“…HPXANES for Nb 2 O 5 demonstrates a significant pressure-dependent increase in intensity of the post-edge first derivative peak, consistent with the reported HPXANES ( Fig. S3 of Guan et al, 2019), and represents improved ordering due to the monoclinic ! orthorhombic transition (Guan et al, 2019;Filonenko & Zibrov, 2001;Tamura, 1972;Zibrov et al, 1998).…”

“…With these strategies, we successfully reproduced the reported XANES spectra of Nb 2 O 5 under pressure (P = 0-16.9 GPa) (http://ixs.iit.edu/ database/data/Farrel_Lytle_data/RAW/Nb/index.html; Fig. S3 of Guan et al, 2019). HPXANES for Nb 2 O 5 demonstrates a significant pressure-dependent increase in intensity of the post-edge first derivative peak, consistent with the reported HPXANES ( Fig.…”

“…However, we selected a standard compound Nb 2 O 5 (Nb +5 ) for our first HPXAFS experiments, for its known pressure-induced structural transition (monoclinic ! orthorhomic) (Guan et al, 2019;Filonenko & Zibrov, 2001;Tamura, 1972;Zibrov et al, 1998) and reported reference XAFS spectra under ambient and highpressure conditions ( Fig. S3 of Guan et al, 2019; http://ixs.iit.…”

“…orthorhomic) (Guan et al, 2019;Filonenko & Zibrov, 2001;Tamura, 1972;Zibrov et al, 1998) and reported reference XAFS spectra under ambient and highpressure conditions ( Fig. S3 of Guan et al, 2019; http://ixs.iit. edu/database/data/Farrel_Lytle_data/RAW/Nb/index.html).…”

“…S3 of Guan et al, 2019), and represents improved ordering due to the monoclinic ! orthorhombic transition (Guan et al, 2019;Filonenko & Zibrov, 2001;Tamura, 1972;Zibrov et al, 1998). This demonstrates a successful initiation of HPXANES at Indus-2; the prospect of improving data quality over the EXAFS regime is addressed.…”