Structural insights from multivariate analysis of XANES and Raman Spectra in ZrO2–R2O–CaO–SiO2 Glasses (R = Na, K) prepared by high-throughput melting

Multivariate analysis of X-ray absorption and Raman spectra from samples prepared by a high-throughput melting system was conducted to investigate the effects of ZrO 2 concentration ( x ) on the Zr coordination environment and the glass network structure in ZrO 2 -doped R 2 O–CaO–SiO 2 glasses ( R = Na, K). The hundreds of samples were synthesized using a slurry-based combinatorial method involving Pt-Au microwells, followed by measurements of their Zr K-edge X-ray absorption near-edge structure and Raman spectra. Principal component analysis and non-negative matrix factorization revealed distinct structural evolution depending on the alkali species. For R = K , at x < 5 mol%, Zr predominantly adopted a highly symmetric six-coordinated environment. The spectral analysis suggests that this environment is stabilized by preferential charge compensation by Ca 2+ ions. This regime showed an increase in Q 3 (Zr) units without Q 2 formation. As x increased, the results indicate that K + ions participated in charge compensation, reducing Zr site symmetry and promoting Q 2 formation. Consequently, only tetragonal ZrO 2 precipitated at x > 13 mol%. In contrast, for R = Na, a less symmetric Zr environment and the simultaneous formation of Q 2 and Q 3 (Zr) units were observed across all concentrations, implying mixed charge compensation by Na + and Ca 2+ ions. These structural differences led to the precipitation of both monoclinic and tetragonal ZrO 2 phases at x > 16 mol%. The results demonstrate that the competition between network modifiers for charge compensation governs the glass structure and crystallization behavior.