Pressure Induced Stability Enhancement of Cubic Nanostructured CeO₂ †

Ceria (CeO₂) is a versatile material used in catalytic and electronic applications. Its cubic fluorite structure is known for stability across various conditions. Prior research has shown that CeO₂ can undergo a structural phase transition to an orthorhombic phase under pressure. However, the behavior of nanoscale CeO₂ under pressure remains less understood. While microscale and single-crystal CeO₂ exhibit a clear phase transition, the nanoscale material behaves differently. This gap motivated the current investigation into how grain size affects phase stability under high pressure. The study aims to clarify whether nanoscale CeO₂ resists structural changes due to internal constraints. Understanding this could inform the design of pressure-resistant materials. The use of helium as a pressure medium allows precise control. The findings may help in tailoring CeO₂ for specific technological uses.

The goal is to compare the structural behavior of CeO₂ under pressure across different grain sizes. The researchers aim to determine if nanoscale CeO₂ resists phase transitions more than larger grains. They hypothesize that internal constraints in nanoscale CeO₂ may suppress phase changes. The study uses hydrostatic pressure up to 110 GPa to test this. The focus is on how grain size influences phase stability. The researchers also examine stacking fault density as a potential stabilizing factor. The work addresses a specific question about nanoscale CeO₂'s response to pressure. The results could clarify the role of grain size in phase transitions.

The study uses hydrostatic pressure up to 110 GPa to examine CeO₂. Three forms of CeO₂ are tested: nanoscale powder, micrometer-scale powder, and single crystals. X-ray diffraction is used to monitor structural changes. Helium is the pressure-transmitting medium. The experiments are conducted at room temperature. The first-order phase transition is tracked in micrometer and single-crystal samples. For nanoscale powder, no transition is observed up to 110 GPa. Stacking fault density is measured as a possible constraint. The method ensures consistent pressure application across all samples.

Micrometer-scale CeO₂ and single crystals show a first-order phase transition at high pressure. The nanoscale powder does not exhibit this transition up to 110 GPa. The stacking fault density increases significantly in the nanoscale material. This increase is two orders of magnitude higher than in larger grains. The higher fault density may act as an internal constraint. This constraint could prevent the nucleation of the high-pressure phase. The results suggest that grain size strongly influences phase stability. The suppression of the phase transition is specific to nanoscale CeO₂.

The study shows that nanoscale CeO₂ resists phase transitions under pressure. This resistance is not observed in micrometer-scale or single-crystal samples. The increase in stacking fault density in nanoscale CeO₂ is notable. The authors propose that this increase may act as an internal constraint. The constraint could prevent the nucleation of the high-pressure phase. The findings suggest that grain size plays a key role in phase stability. The results are specific to CeO₂ under hydrostatic pressure. The study does not generalize to other materials or conditions.