Structural And Void Analysis Of Amorphous Metal Oxides (ZrO₂, GeO₂): Molecular Dynamics Simulations

ZrO₂ has been widely used for its excellent chemical and physical properties in special ceramics,electronic material,solid oxide fuel cell etc. The mechanism of its high oxygen ionic conductivity at high temperature is not clear.Also,the research of how to increase its re-crystallization temperature during the heat treatment in the industrial process is highlighted.GeO₂ has similar structure with SiO₂.And both of them are archetypical glass material existed in nature.In addition,GeO₂ has been reported to experience extinct pressure-induced structural changes under high pressure.MD simulations by using of "quech-and-melt" mechanics with two cooling rates of 0.1K/ps and 1K/ps has been used to generate and study the structure and further void analysis of amorphous ZrO₂(a-ZrO₂). Based on the analysis of the relationships of potential energy and average coordination number with the temperature,we have found that the glass transition temperature is 2200K～2000K.The algorithm developed by Gianluca Malavasi etal has been employed in our work to study the void characteristics during the glassified process of ZrO₂.The results of interstitial void distribution(R_i) has shown that the state in the glass transition temperature (2200K～2000K) is more looser thanα-ZrO₂.The R_i ofα-ZrO₂ presents a double-peak distribution with the largest fraction peak at 0.8(?).The R_i of l-ZrO₂ presents a single-peak distribution with the peak at larger position. Thus,the liquid state is looser than amorphous state.R_b has been calculated to characterize the moving path among particles.The largest fraction peak ofα-ZrO₂ presents to be 0.8(?),and the largest value of R_b shows at 2.2(?).By comparison,the liquid state has larger interstitial volume fraction than the amorphous state,and the systems around the glass transition temperature,2200-2000 K are smaller.We reported the structural transitions and void analysis during the densification of the amorphous GeO₂ by using molecular dynamics simulation under the applied pressures from 1 GPa to 25 GPa. Coexistence of the four,five and six coordination of Ge-O was observed in the pressure range of 1～25 GPa.The relaxation of the intra-tetrahedral basic units was observed under the pressure below 5 GPa through both the density changes and the bond-angle distributions of O-Ge-O.The bond-angle distributions revealed the relaxation of Ge-O-Ge to a large value under 11～13 GPa.The structural transition from tetrahedral to pentahedral dominant structure takes place under about 13～15 GPa.The highest fractions of the Ri,Riw and Rb shift to smaller values and present narrower distributions as pressure goes higher.The largest void channel decreases the radius from 3.9 under 1 GPa to 1.2 under 25 GPa.