Pressure-Induced Analysis Of Nano-Oxides (ZrO₂,SiO₂) Phase Transformation And Structural Changes: Molecular Dynamics Simulation

Nanoscale metal oxides (ZrO2, SiO2) are an important nanomaterials in chemical industry, which have been widely applied in functional ceramics, chemical, environmental engineering, cosmetics, and paints, due to their particular characteristic of strong surface effect, quantum size effect, volume effect, and macroscopic quantum tunneling effect. ZrO2 and SiO2 nanoparticles have been reported to experience unique pressure-induced structural changes under high pressure. Therefore, it will be significant to investigate the structure of phase transition.An ideal gas is used as the pressure medium and thermostat in the molecular dynamics simulations, all calculations are performed to use DL_POLY package, and we analyze pressure-induced phase transition of ZrO2 nanoparticles. We have studied three sizes of ZrO2 nanoparticles, and the applied pressures are increasing from 1.0 GPa up to 20 GPa with the interval of 1.0 GPa. Coexistence of the four, five and six coordination of Zr-O unit are observed in the pressure range for smaller nanoparticles. In the ZrO2 nanoparticle with 324 atoms and 768 atoms, the structural transition from tetrahedral to hexahedral dominant structure takes place under 9～10 GPa and 8～11 GPa, respectively. In the case of ZrO2 nanoparticle containing 1500 atoms, there are five kinds of structures coexisting mixture from four to eight coordinate states, displays two structural transformations, occurs at 7-8 GPa and 14～16 GPa, respectively.Using molecular dynamics simulation, two sizes of SiO2 nanoparticles have investigated with the applied pressures from 1.0 GPa to 45 GPa with the interval of 2.0 GPa. Coexistence of the four, five and six coordination of Si-O units are observed in the pressure range of 1.0-45 GPa. In the SiO2 nanoparticles containing 1536 atoms and 3000 atoms, the structural transition from tetrahedral to hexahedral dominant structure takes place under about 31 GPa and 25 GPa, respectively.In addition, we study the modification of Poly(ethylene oxide) on the surface of SiO2 nanoparticles. In this work, the radial distribution functions, mean-square displacement, radial density distribution, and dihedral angle distribution are analyzed. The surface structure of SiO2 nanoparticles is studied. With the variation of temperatures, the movement ability of polymer chains is also analyzied.