Infrared and Raman spectra of ZrSiO₄ experimentally shocked at high pressures

Zirco- and reidite-type ZrSiO₄ produced by shock recovery experiments at different pressures have been studied using infrared (IR) and Raman spectroscopy. The v₃ vibration of the SiO ₄ 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 (I4₁/amd) to reidite (I4₁/a) is proven by the occurrence of additional IR and Raman bands. Although the SiO ₄ group 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.