Structure ofGeO2glass at pressures up to 8.6 GPa

Abstract

The structure of ${\text{GeO}}_{2}$ glass at pressures extending from ambient to 8.6(5) GPa was measured at $\ensuremath{\simeq}25\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$ by using in situ neutron diffraction. The results show a gradual change in the intermediate range order with increasing density as manifested by an increase in position and reduction in height of the first sharp diffraction peak in the total structure factor. By contrast, the local ordering, as characterized by the Ge-O bond length and coordination number, remains constant for the pressure range from ambient to $\ensuremath{\simeq}5\text{ }\text{GPa}$. As the pressure is increased further to 8.6(5) GPa, however, a steady increase from 4.0(1) to 4.9(1) is observed in the Ge-O coordination number as the corresponding distance increases from 1.73(2) to $1.77(2)\text{ }\text{\AA{}}$. The results are therefore consistent with the operation of two densification mechanisms, the low-pressure one associated with squeezing the open network of corner-linked tetrahedral motifs and the high-pressure one associated with a transformation of those motifs. There is no evidence in support of an abrupt transformation of the network structure over the investigated pressure range. The structure of permanently densified ${\text{GeO}}_{2}$ glass was also investigated by high-energy x-ray diffraction. The results show that there is a threshold pressure at $\ensuremath{\simeq}5\text{ }\text{GPa}$ below which the structure of a recovered glass is similar to that of the high-pressure material. Above the threshold pressure there is, however, a reorganization of both the local and intermediate range ordering once the pressure is released and the Ge-O coordination number returns to 4.