Structural Role of Zirconium in Zirconium-Doped Lithium Silicate/Borate Glass-Ceramics

A series of Zr-doped (~3–10 mol%) lithium silicate (ZRLS) glass-ceramics and their parent glasses and a series of Zr-doped (~2–6 mol% ZrO₂) lithium borate (ZRLB) glasses were investigated using Zr K-edge EXAFS and X-ray Absorption Near Edge Structure (XANES) spectroscopy. Unusual thermo-physical properties of these materials make them good candidates for applications which demand low thermal expansion coefficients. Zirconium ions play an important role in determining those thermos-physical properties. Immediate coordination environments of all ZRLS glasses are remarkably similar for different compositions. For the nearest oxygen shell, the Zr-O coordination number ranges between 6.1 and 6.3 for nucleated and crystallized samples, respectively. Also, the Zr-O mean distance remains similar around ~2.10 Å. For these glasses, the composition dependence of structural parameters was small. Small changes in the coordination environment were observed for ZRLS glass-ceramics after thermal treatments. In contrast, Zr coordination environment in ZRLB glasses appear to depend appreciably on the Zr concentration. For the nearest oxygen shell, the Zr-O coordination number increased from ~6.1 to ~6.8 and the Zr-O distance decreased from ~2.18 to ~2.14 Å with decreasing ZrO₂ content.