High pressure induced phase transformation of SiO2 and GeO2: difference and similarity

We report high pressure polymorphism of SiO2 and GeO2 at room and high temperatures. It was found that kinetics has a large effect on pressure induced phase transitions of SiO2 and GeO2. The high pressure behavior of SiO2 and GeO2 polymorphs depends on the starting material and pressure–temperature history. Our studies show that SiO2 and GeO2 have a common sequence of high pressure, high temperature structural transformations when the same type of starting material (amorphous or α-quartz) was used: (amorphous or α-quartz)⇒d-NiAs⇒rutile⇒CaCl2⇒α-PbO2⇒pyrite (Pa-3) types. In the case of cristobalite as starting material, the α-PbO2-type phase can be synthesized directly from the high pressure room temperature phase omitting rutile- or CaCl2-type structure. The crystallization of the d-NiAs phase in a narrow temperature interval 1000–1300 K can be used as an indicator of presence of a cation disordered network in both SiO2 and GeO2 materials at high pressure before heating. [Copyright &y& Elsevier]