Abstract
Silicate frameworks exhibit diverse structural responses under extreme conditions, which are strongly influenced by hydration. Here, we present a comparative high-pressure synchrotron X-ray diffraction study of Na(2)ZrSi(2)O(7) and its hydrated analogue Na(2)ZrSi(2)O(7)·H(2)O up to 30 GPa, combined with electronic structure calculations. At ambient conditions, both phases share the same primary building units (PBUs: [ZrO(6)] and [SiO(4)]) but differ in secondary building units (SBUs, M(2)T(4) vs M(2)T(6)). Under compression, Na(2)ZrSi(2)O(7) undergoes a phase transition near 15 GPa, while the hydrated phase remains stable throughout the pressure range. The anhydrous compound exhibits a higher bulk modulus (B(0) = 77.1 GPa) and less anisotropic compression compared with those of the hydrated phase (B(0) = 66.3 GPa). Distinct deformation mechanisms are observed: the anhydrous framework accommodates pressure through [ZrO(6)] octahedral distortion, whereas the hydrated framework compresses via [Si(2)O(7)] group tilting. Electronic structure calculations indicate band gap widening with pressure in both phases; notably, Na(2)ZrSi(2)O(7) shows a direct-to-indirect band gap transition, whereas the hydrated phase retains a direct gap. These results reveal how hydration-driven topological modifications at the SBU scale dictate the pressure-induced structural evolution, phase stability, and electronic properties of zirconosilicate frameworks.