High-pressure phase transition is one of the key ways to explore the physical properties, phase transition rules and application performance of materials. Raman spectroscopy is also a way to present the structure and properties of materials well.
Therefore, it is particularly important to understand the laws and mechanisms of the high-pressure phase transition of boron carbide and the evolution of the Raman spectrum to show the physical properties of boron carbide, improve its application performance, and promote the progress of materials science.
In the study, we started from the two aspects of high-pressure phase transition of boron carbide and the evolution of Raman spectrum to explore the changes in the physical properties and phase transition of boron carbide under high pressure, as well as the application and evolution characteristics of Raman spectrum in this process.
Through experimental exploration and theoretical analysis, we hope to more thoroughly understand the physical properties and high-pressure phase transition mechanism of boron carbide, as well as the application significance and characterization ability of the Raman spectrum in a high-pressure environment, and provide useful reference and inspiration for the application of boron carbide and the progress of materials science.
Structure of boron carbide
Research on high-pressure phase transition of boron carbide
Current situation of phase transition of boron carbide under high pressure
The crystal structure of boron carbide is similar to the layered structure of graphene, which is composed of B and C atoms, among which B atoms are arranged in hexagons in the layered structure.
At room temperature, boron carbide crystals are hexagonal, the space group is P63/MMC, and there is a central symmetric point group. However, under high pressure, boron carbide crystals will undergo phase transition and then show different structures and properties.
At present, three high-pressure phase transition structures of boron carbide have been identified, namely: β-BC3 structure, R8 structure and M12 structure.
β-BC3 structure is the first high-pressure phase transition structure of boron carbide, which was discovered in the early 1980s. If boron carbide undergoes phase transition under high pressure of 4.5GPa, its crystal structure will change from a hexagonal system to a structure with multiple hexagonal rings.
Boron Carbide Phase Transition
At this time, the space group of the crystal structure becomes P63/MMC, but the unit cell parameters have changed. The β-BC3 structure is the first structure discovered in the phase transition of boron carbide, and the change of its unit cell parameters is regarded as the beginning of the high-pressure phase transition of boron carbide.
The R8 structure is a high-pressure phase transition structure of boron carbide, which was discovered in 1992. If boron carbide undergoes a phase transition under high pressure of 10GPa, its crystal structure will change from the β-BC3 structure to the R8 structure.
The crystal of the R8 structure belongs to the monoclinic system, the space group is C2/c, and its unit cell parameters are smaller than those of the β-BC3 structure. In this case, the hardness and density of boron carbide are improved, and the thermal conductivity becomes better.
The third high-pressure phase transition structure of boron carbide is the M12 structure, which was discovered in 2001. If boron carbide undergoes a phase transition under a high pressure of 30 to 50GPa, its crystal structure will change from the R8 structure to the M12 structure.
The crystal of the M12 structure belongs to the orthorhombic system, the space group is Pnma, and its unit cell parameter is smaller than that of the R8 structure. In this case, the hardness and density of boron carbide are improved, and it becomes a more stable crystal structure.
Boron Carbide Crystal Structure
Research results on high-pressure phase transition of boron carbide
What is the high-pressure phase transition? After experimental research, it is known that the change in atomic structure causes the high-pressure phase transition of boron carbide. In a high-pressure environment, the arrangement of boron carbide atoms has changed, causing the crystal structure to change.
High-pressure phase transition affects performance: The high-pressure phase transition of boron carbide has a significant effect on its hardness, density, thermal conductivity and electrical conductivity. In the M12 structure, the hardness of boron carbide can be 70-80GPa, and the thermal conductivity will also increase.
Studies have shown that the phase transition temperature of the high-pressure phase transition of boron carbide is related to factors such as pressure, sample preparation method and experimental conditions. Under different experimental conditions, the temperature and pressure of the high-pressure phase transition will also change.
However, in general, the phase transition temperature of high-pressure phase transition of boron carbide is in the range of 2000 to 3000K, and the phase transition pressure is in the range of 30 to 50GPa.
The high-pressure phase transition characteristics of boron carbide have opened up new ways for its application under high temperature, high pressure, high speed and extreme conditions.
For example, the hardness and thermal conductivity of boron carbide under high pressure make it an ideal structural material and sensor material in high temperature, high pressure and ultrasonic waves.
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