Catalyst-Free Synthesis and Structural and Mechanical Characterization of Single Crystalline Ca₂B₂O₅·H₂O Nanobelts and Stacking Faulted Ca₂B₂O₅ Nanogrooves

Single crystalline Ca₂B₂O₅·H₂O (CBOH) nanobelts were synthesized for the first time using a facile catalyst-free hydrothermal method at low temperature. After being annealed at 400 °C for 10 h, the CBOH nanobelts transformed into curve-shaped Ca₂B₂O₅(CBO) nanogrooves with ordered stacking fault arrays along the [1̅10] direction. The single crystalline CBOH nanobelts and the stacking faulted CBO nanogrooves provided a unique platform for investigating the effects of hydrated H₂O and stacking faults on the mechanical properties of nanomaterials. Nanoindentation tests were performed directly on individual CBOH nanobelts and CBO nanogrooves to probe their mechanical properties. It was found that the CBOH nanobelts, with the presence of hydrated H₂O, achieved 28.7% increase in elastic modulus, whereas the stacking faulted CBO nanogrooves, with the absence of hydrated H₂O, exhibited 99% loss in elastic modulus, compared to bulk CBO.