High-Pressure Structural Evolution of Na2ZrSi2O7 and Na2ZrSi2O7.H2O: Topology-Driven Compression Behaviors, Phase Stability, and Electronic Transitions

TL;DR

This study investigates how hydration affects the high-pressure structural, phase, and electronic behavior of Na2ZrSi2O7 using synchrotron X-ray diffraction and electronic calculations, revealing hydration's role in stability and properties.

Contribution

It provides the first comparative analysis of hydrated and anhydrous Na2ZrSi2O7 under high pressure, highlighting topology-driven differences in compression and electronic transitions.

Findings

Na2ZrSi2O7 undergoes a phase transition near 15 GPa, hydrated phase remains stable.

Anhydrous Na2ZrSi2O7 has higher bulk modulus and less anisotropic compression.

Electronic band gap widens with pressure; direct-to-indirect transition in anhydrous phase.

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 Na2ZrSi2O7 and its hydrated analogue Na2ZrSi2O7.H2O up to 30 GPa, combined with electronic structure calculations. At ambient conditions, both phases share the same primary building units (PBUs: [ZrO6] and [SiO4]) but differ in secondary building units (SBUs, M2T4 vs. M2T6). Under compression, Na2ZrSi2O7 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 (B0 = 77.1 GPa) and less anisotropic compression compared with the hydrated phase (B0 = 66.3 GPa). Distinct deformation mechanisms are observed: the anhydrous framework accommodates pressure through [ZrO6] octahedral distortion, whereas the hydrated framework compresses via [Si2O7] group tilting. Electronic structure calculations indicate band gap widening with pressure in both phases; notably, Na2ZrSi2O7 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 secondary building unit scale dictate the pressure-induced structural evolution, phase stability, and electronic properties of zirconosilicate frameworks.