Electron microscopic study on high-pressure induced deformation of nano-TiO<sub>2</sub>
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2022-12-03 |
| Journal | Acta Physica Sinica |
| Authors | Fei Wang, Quanjun Li, Kuo Hu, Bingbing Liu |
| Institutions | Jilin University |
| Citations | 1 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis study investigates the high-pressure induced plastic deformation and phase transformation of anatase TiO2 nanospheres, yielding the visible-light active a-PbO2 phase.
- Core Achievement: Successfully synthesized the high-pressure a-PbO2 phase of TiO2 using non-hydrostatic compression/decompression in a Diamond Anvil Cell (DAC), confirming its stability at ambient pressure.
- Deformation Mechanism: High pressure induces plastic deformation in TiO2 via mechanisms (deformation twinning and stacking fault slip) previously observed mainly in metals.
- Size Effect Discovery: A strong size effect governs the deformation: submicron grains (500-1000 nm) exhibit high plasticity with lens-shaped lamellar twins, while nanocrystalline grains (100-150 nm) show reduced plasticity and form fan-shaped multiple twins and increased stacking faults.
- Phase Sequence: Raman analysis confirmed the transition sequence: Anatase â Zircon-like phase (at 14.6 GPa) â a-PbO2 phase (stable upon decompression below 7.7 GPa).
- Microstructure Control: The ability to control the size-dependent deformation microstructure (twin density and type) provides a new method for preparing twin-rich a-PbO2 TiO2, potentially enhancing its photocatalytic and mechanical performance.
- Engineering Relevance: The findings offer a new perspective for studying the size effect on high-pressure phase transformations and optimizing synthesis parameters for functional oxide nanomaterials.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Initial Material Purity | 99.9 | % | Anatase TiO2 powder |
| Maximum Applied Pressure | 31.9 | GPa | Peak compression pressure |
| DAC Culet Diameter | 300 | ”m | Diamond Anvil Cell setup |
| Gasket Hole Diameter | 100 | ”m | Sample chamber size |
| Anatase â Zircon-like Transition | 14.6 | GPa | Pressure where new Raman peaks appear |
| Zircon-like â a-PbO2 Transition | 7.7 | GPa | Pressure during decompression |
| a-PbO2 Stability Pressure | 1.3 | GPa | Pressure where Zircon-like phase fully disappears |
| Submicron Grain Size Range | 500-1000 | nm | Exhibits lamellar deformation twins |
| Nanocrystalline Grain Size Range | 100-150 | nm | Exhibits fan-shaped multiple twins |
| Anatase Eg(1) Raman Peak | 144 | cm-1 | Characteristic peak of initial phase |
| a-PbO2 Raman Peaks (Strong) | 314, 437 | cm-1 | Characteristic peaks of recovered phase |
| Submicron Twin Plane (Example) | (101) | N/A | Observed in 1# and 2# grains |
| Nano Twin Planes (Example) | (110), (011) | N/A | Observed in 4# grain (multiple twins) |
| Excitation Wavelength | 514 | nm | Raman spectroscopy source |
Key Methodologies
Section titled âKey Methodologiesâ- Initial Sample: Used commercial anatase TiO2 nanospheres (99.9% purity) with a broad size distribution (4 nm to 1000 nm).
- High-Pressure Application: Samples were loaded into a Diamond Anvil Cell (DAC) using a 304 stainless steel gasket (100 ”m hole). No pressure transmitting medium was used, ensuring non-hydrostatic compression.
- Pressure Cycle: Samples were compressed up to approximately 31.9 GPa, followed by full decompression back to ambient pressure. Ruby fluorescence was used for pressure calibration.
- In-Situ Phase Monitoring: High-pressure Raman spectroscopy (Renishaw InVia, 514 nm laser) was used to track the phase transitions during both compression (Anatase â Zircon-like) and decompression (Zircon-like â a-PbO2).
- TEM Sample Extraction: Post-mortem samples were extracted from the DAC chamber surface using a Dual-beam Scanning Electron Microscope (FEI scios) for microstructure analysis.
- Microstructure Characterization: High-resolution Transmission Electron Microscopy (HRTEM, JEOL JEM-2200FS) and Selected Area Electron Diffraction (SAED) were employed to analyze the morphology, crystal structure, deformation twins, and stacking faults in the recovered a-PbO2 phase.
- Deformation Analysis: Eccentricity (ratio of short axis to long axis) was calculated for recovered grains to quantify the degree of non-hydrostatic deformation and correlate it with grain size.
Commercial Applications
Section titled âCommercial ApplicationsâThe successful synthesis and microstructural control of the twin-rich a-PbO2 phase TiO2 are relevant to several high-performance material sectors:
- Visible Light Photocatalysis: The a-PbO2 phase is highly valued for its suitable band gap, enabling efficient photocatalytic degradation of pollutants under visible light, applicable in Wastewater Treatment and Air Purification Systems.
- Advanced Structural Materials: Controlling the density and type of deformation twins (similar to metallic hardening) can significantly enhance the Mechanical Strength and Toughness of TiO2-based ceramics and composites, suitable for high-wear or high-stress applications.
- Energy Storage: The presence of high-density twin boundaries and stacking faults may create fast ion diffusion pathways, potentially improving the performance and cycling stability of Lithium-Ion Battery Anodes or Solid-State Electrolytes based on TiO2.
- High-Pressure Materials Synthesis: The methodology provides a blueprint for controlling microstructure (e.g., inducing specific twin types) in other functional oxide nanomaterials synthesized via Non-Hydrostatic High-Pressure Techniques.
- Sensor Technology: The size-dependent deformation and resulting microstructures can be leveraged to tune the electronic properties of TiO2, relevant for developing next-generation Gas Sensors and Chemical Sensors.
View Original Abstract
The high-pressure <i>α</i>-PbO<sub>2</sub> phase of TiO<sub>2</sub> has suitable band gap and photocatalytic capability in the visible light range, which is an environmentally friendly and efficient photocatalytic material. In this work, <i>α</i>-PbO<sub>2</sub> phase of TiO<sub>2</sub> is obtained by the pressure-relief treatment of anatase nanospheres through using diamond anvil cell, and transmission electron microscope (TEM) observation shows the obvious deformation of TiO<sub>2</sub> nanospheres. High-esolution TEM shows that there are a large number of stacking faults along the [100] direction and deformation twins in the grain. Specifically, the deformation twin band with lens lamellar structure is formed in the submicron grain. The fan-shaped multiple deformation twins are formed in the nanocrystalline grains. This study shows that anatase TiO<sub>2</sub> can be deformed under high pressure, and its micro mechanism of deformation is similar to metalâs, mainly including deformation twins and stacking fault slip. There is obvious size effect in the formation of deformation twins. These results provide a new breakthrough point for the study of the size effect of high-pressure phase transformation of TiO<sub>2</sub>, and also point out an experimental direction for preparing the twin high-pressure <i>α</i>-PbO<sub>2</sub> phase.