Inorganic Ionic Compound Materials with Structural Flexibility

Abstract

Inorganic ionic compounds are widely existed in nature and applied in construction, energy, biomedical and optical fields. However, the inherent ionic bonding characteristics lead to brittle fracture of these inorganic materials under mechanical force, which significantly limits their application scopes. Overcoming the inherent brittleness of these materials represents a long-standing challenge in chemistry and materials science. In recent years, significant advances have been made to turn inorganic materials into flexible ones. In this review, we summarize the emerging strategies for enhancing the flexibility (e.g., deformability, resilience, plasticity, ductility, etc.) of inorganic materials composited by inorganic ionic compounds, by the regulation of bulk solid phase structures and morphologies. For the regulation of bulk solid phase structures, specific strategies involve regulating ionic bonding and slip systems, alongside leveraging dynamic phase transition. Among these, modulating ionic bonds reduces the stiffness of inorganic ionic materials by weakening the interactions between ions, thereby enhancing their moldable ability. Regulating slip systems improves ductility and plasticity by increasing dislocation density and the number of effective slip systems while maintaining the integrity of structure to facilitate slip. Utilizing dynamic phase transition of materials enhances plasticity by dissipating stress through stress- or thermally-induced dynamic cyclic phase transformations. For the regulation of morphologies, approaches focus on constructing nanowires, sub-1 nm architectures, and molecular-scale structures. High aspect ratios and amplified surface effects endow one-dimensional nanowires with exceptional bending flexibility. This feature becomes even more pronounced in sub-1 nm and molecular-scale structures, even imparting polymer-like characteristics. In this review, we aim to deepen the fundamental understanding in turning brittle inorganic ionic compounds to flexible one from a structural-property relationship view, and creates avenues for their potential applications in structural materials, flexible electronics and novel biomaterials.

Keywords

Inorganic ionic compound / Materials science / Flexibility / Bulk phase regulation / Morphology regulation / Crystal engineering / Nanostructures / Microstructures

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