Figure 2

Evolution of lattice parameters of epitaxial thin film of \(GeO_2\) on Z-cut quartz substrate (with c-axis, [0001] out-of-plane and a-axis, \([1\bar{2}10]\) in-plane). The sudden drop of out-of-plane \(GeO_2\) film lattice and nearly zero thermal expansion above the \(\alpha\)-\(\beta\) phase transition of the substrate, suggest that the film itself has also undergone an \(\alpha\)-\(\beta\) phase transition. The error bars of the substrate lattice parameters are smaller than the symbols. The lines are guides to the eyes. The data of bulk \(GeO_2\) and \(SiO_2\) are obtained from Refs.^37,39, respectively.