Synchrotron X-rays Uncover Crystalline Phase and Fine Structure of Zirconia

Yttria-stabilized zirconia (YSZ) has become indispensable in restorative dentistry; however, the influence of yttria content on its crystalline phases and fine structure remains incompletely understood. This study investigated how variations in yttria content (3–8 mol%) and low-temperature degradation (LTD) influence the crystalline phase composition and local atomic structures of dental zirconia using synchrotron-based X-ray diffraction (XRD) and X-ray absorption fine structure (XAFS) spectroscopy. Forty-two sintered disc-shaped specimens were prepared from zirconia powders stabilized with 3–8 mol% yttria (3–8YSZ). Half of the specimens were polished, while the other half underwent autoclaving to induce LTD. Synchrotron XRD showed that 3–5YSZ contained 2 tetragonal ( t and t′ ) phases, while 8YSZ contained a cubic ( c ) phase. The t -phase fraction decreased markedly with increasing yttria content, from 83.1 mass% in 3YSZ to 25.3 mass% in 5YSZ. LTD induced monoclinic ( m ) and rhombohedral ( r ) phases in 3YSZ and 4YSZ but not in 5YSZ, indicating improved LTD resistance at higher yttria contents. XAFS showed that the dual-peak white-line profile of zirconia specimens varied with yttria content, reflecting the t -to- t′ phase transition, and transformed into a single broadened peak after LTD, consistent with structural disorder induced by phase transformation. Fine structural analysis revealed 2 main coordination shells, Zr–O and Zr–Zr. In the Zr–Zr shell, the Debye–Waller factors changed systematically with yttria content, reflecting structural disorder associated with oxygen vacancies. In conclusion, a combined synchrotron XRD and XAFS approach elucidated the phase composition and atomic-scale structural disorder in dental zirconia across different yttria contents. These insights provide a foundation for the rational design of next-generation translucent dental zirconia, in which crystalline phase composition and local atomic disorder are deliberately tailored to achieve durable clinical performance.