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High-Pressure Structural Evolution of Na 2 ZrSi 2 O 7 and Na 2 ZrSi 2 O 7 ·H 2 O: Topology-Driven Compression Behaviors, Phase Stability, and Electronic Transitions

Year: 2025

Type: article

Abstract: High Resolution Image Download MS PowerPoint Slide 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.

Source: Inorganic Chemistry

DOI: 10.1021/acs.inorgchem.5c04119