Vibrational spectroscopy of fast-quenched ZrSiO₄ melts produced by laser treatments: Local structures and decomposed phases

Rapidly quenched ZrSiO₄ melts produced by CO₂ and pulsed YAG lasers have been analysed using infrared (IR) and Raman spectroscopy. The quenched melts exhibit decomposition into binary oxides (ZrO₂ and SiO₂), while other phases or complex SiO₄ tetrahedron networks are also observed. The local structures and the phases of the quenched melts depend strongly on the quenching rate and melting conditions. Monoclinic ZrO₂ are found to be the main ZrO₂ phase in the samples treated by CO₂ laser, although tetragonal ZrO₂ was found near boundaries between the untreated and melted regions. High concentrations of tetragonal ZrO₂ were detected in the samples treated by pulsed YAG lasers. Our observations indicate that the formation of tetragonal ZrO ₂ is related to relatively high quench rates. Micro-IR and Raman data from areas near the boundaries between the quenched melts and untreated zircon show systematic variations of local structures and compositions. We observe a small region with relatively low density between the untreated and melted boundaries, which consists of tetragonal ZrO₂ or glassy ZrO ₂, and SiO₂. Broad vibrational bands occur in the wavenumber region where the characteristic frequencies of zircon are located. This observation could indicate the possible existence of small amounts of glassy ZrSiO₄ in the melt state of zircon, although zircon tends to decompose above the melting point. These observations are in sharp contrast with the behaviour of radiation-damaged zircon, the so-called metamict zircon, where no phase separation occurs in samples which have not been subsequently annealed.