Infrared and Raman spectra of ZrSiO4 experimentally shocked at high pressures

Zircon- and reidite-type ZrSiO4 produced by shock recovery experiments at different pressures have been studied using infrared (IR) and Raman spectroscopy. The nu(3) vibration of the SiO4 group in shocked natural zircon shows a spectral change similar to that seen in radiation-damaged zircon: a decrease in frequency and increase in linewidth. The observation could imply a possible similar defective crystal structure between the damaged and shocked zircon. The shock-pressure-induced structural phase transition from zircon (I4(1)/amd) to reidite (I4(1)/a) is proven by the occurrence of additional IR and Raman bands. Although the SiO4 groups in both zircon- and reidite-ZrSiO4 are isolated, the more condensed scheelite gives rise to Si-O stretching bands at lower frequencies, suggesting a weakening of the bond strength. Low-temperature IR data of the reidite-type ZrSiO4 show an insignificant effect of cooling on the phonon modes, suggesting that the structural response of reidite to cooling-induced compression is weak and its thermal expansion is very small.