An experimental investigation unravelling the aberrant thermo-mechanical behaviour of Re-loaded zeolite Na-A

Abstract

Materials that defy conventional lattice expansion at elevated temperatures and compression at high pressures hold immense potential for forefront functional applications, yet they remain unexplored. We present a rhenium-loaded zeolitic-A framework (Re-ZTA) that co-exhibits negative thermal expansion (NTE) and exceptional negative volumetric compressibility (NVC)-two rare, counterintuitive properties. These exotic phenomena manifested by Re-ZTA are ascribed to the occupation of the guest moieties, NH₄ReO₄ and NH₄NO₃, on the surface and within the pores. While the intrinsic NTE of the guest moieties and their anchoring effect on the bridging oxygen atoms of Re-ZTA trigger the tetrahedral rotation to facilitate the NTE behaviour until 205 °C, the progressive intrusion of the guest moieties into the pores from the surface of Re-ZTA is responsible for the observed switching from conventional compression to NVC above a critical pressure of 1.4 GPa. The framework structure was irreversibly amorphized at 4.6 GPa due to the accumulation of pressure-induced structural disorder, while the same was evident at a temperature beyond 205 °C due to the local instability of the framework. Remarkably, isothermal high-pressure diffraction studies at 70 °C and 130 °C exhibited the unexpected loss of NVC to typical compression owing to the thermal degradation of guest moieties while demonstrating enhanced structural stability by minimizing the structural disorder. These findings position Re-ZTA as a promising candidate for next-generation functional materials that offer tunable thermo-mechanical response under extreme conditions, paving the way for contemporary materials exhibiting simultaneous NTE, exceptional NVC and temperature-induced switching for structural, electronic and energy-related applications.