Structural Phase Transition and Metallization of Nanocrystalline Rutile Investigated by High-Pressure Raman Spectroscopy and Electrical Conductivity

Abstract

We investigate the structural, vibrational, and electrical transport properties of nanocrystalline rutile and its high-pressure polymorphs by Raman spectroscopy, and AC complex impedance spectroscopy in conjunction with the high-resolution transmission electron microscopy (HRTEM) up to ~25.0 GPa using the diamond anvil cell (DAC). Experimental results indicate that the structural phase transition and metallization for nanocrystalline rutile occurred with increasing pressure up to ~12.3 and ~14.5 GPa, respectively. The structural phase transition of sample at ~12.3 GPa is confirmed as a baddeleyite phase, which is verified by six new Raman characteristic peaks. The metallization of the baddeleyite phase is manifested by the temperature-dependent electrical conductivity measurements at ~14.5 GPa. However, upon decompression, the structural phase transition from the metallic baddeleyite to columbite phases at ~7.2 GPa is characterized by the inflexion point of the pressure coefficient and the pressure-dependent electrical conductivity. The recovered columbite phase is always retained to the atmospheric condition, which belongs to an irreversible phase transformation.

Pressure-Induced Structural Phase Transition and Metallization of CrCl3 under Different Hydrostatic Environments up to 50.0 GPa

“…Noteworthily, when the pressure was enhanced up to 31.2 GPa, the electrical conductivity of CrCl 3 raised steeply by about 3 orders of magnitude and then rose gently from 0.40 to 1.38 S/cm in the pressure range of 31.2–44.5 GPa. In fact, our previous high-pressure electrical conductivity studies have already disclosed that the noticeable jump in electrical conductivity is a typical characteristic of the semiconductor-to-metal transition. − Besides, above 31.2 GPa, the feeble electrical conductivity dependence relation with pressure provides another credible proof of metallization. Furthermore, the pressure point of metallization accords with that of the ETT, and thus, it is reasonable to speculate that the ETT may be accompanied by the metallization of CrCl 3 .…”

Some Remarks on the Electrical Conductivity of Hydrous Silicate Minerals in the Earth Crust, Upper Mantle and Subduction Zone at High Temperatures and High Pressures

“…have already studied from Dai Lidong's high-pressure research group in HTHPSEI, at the Institute of Geochemistry, Chinese Academy of Sciences [73][74][75][76][77]. In addition, some important semiconducting materials including the binary metallic oxides, AB-type structural layered metallic compounds, AB2-type structural transition-metal dichalcogenides (TMDs), and ABO3type structural perovskite compounds are paid attention in regards to their structural phase transition, amorphization, and metallization, and investigated under conditions of HP-HT conditions in detail [78][79][80][81][82][83][84][85][86][87][88][89][90][91][92][93][94][95][96][97].…”

Chemical Synthesis and High-Pressure Reaction of Nb5+ Monodoped Rutile TiO2 Nanocrystals

“…The HP reaction of nano R-TiO 2 , however, just began in the 2000s accompanied by the rapid progress of nanoscience and nanotechnology. Nano R-TiO 2 directly transformed to the baddeleyite-like structure without passing the α-PbO 2 -like intermediate phase during pressurization and thus presented an abnormal phase transition behavior compared to its bulk counterpart (Figure a). − This abnormality is believed to be related to the size effects of nano R-TiO 2 due to the intrinsic lattice relaxation of nanomaterials.…”