Structural Phase Transitions And Optical Properties Of Nb₂O₅ Under High Pressure

As is well-known,Nb₂O₅ has various applications in special optical glasses,chemical fiber panels,monolithic capacitors and piezoelectric ceramic elements because of its high dielectric constant,high refractive index,outstanding photoelectric properties,and high chemical stability.As a new means of material research,high pressure technique has been widely used in various fields such as physical,earth sciences and materials science.Based on the basic physics research,the main purpose of high pressure technology research is to find out the phase transition process of lattice structure under pressure and understand the phase change mechanism.From the point of view for application,the key purposes of high-pressure studies are aimed at discovering new high-pressure phases with novel properties and understanding phase transition mechanisms.If a high-pressure phase can be preserved at ambient conditions,its novel properties could be retained,which provides a new pathway to design materials with tailored properties.Thus,the high-pressure technique is a powerful way to synthesize new materials with novel properties.Pressure-induced phase transitions of monoclinic H-Nb₂O₅ have been studied by in situ synchrotron X-ray diffraction?XRD?,pair distribution function?PDF?analysis,UV-visible transmission spectroscopy,Raman spectroscopy and X-ray absorption spectroscopy?XAFS?.This work aims to study the structure transformation of Nb₂O₅,provide insights into the understanding phase transformation mechanisms of Nb₂O₅ and explore materials with novel properties.The research results are as follows:1.The initial monoclinic phase is found to transform into an orthorhombic phase at⁹ GPa and then change to an amorphous form above 21.4 GPa.The PDF and XAFS data reveal that a part of NbO₆ octahedra are destroyed and converted to NbO₇ pentagonal bipyramids with the 1^stt structural transformation,and the amorphization is associated with disruptions of the long-range order of the NbO₆octahedra and the NbO₇ pentagonal bipyramids,whereas the local edge-shares of octahedra and the local linkages of pentagonal bipyramids are largely preserved in their nearest neighbors.2.Upon compression,the transmittance of the sample in a region from visible to near infrared?450¹000 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 maximum transmittance can reach 52%.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.