A phase transition is the physical process in which a substance undergoes a change in its state of matter, such as from solid to liquid or from liquid to gas.
Pressure is defined as the force exerted on a surface per unit area. In the context of phase transition, pressure refers to the external force applied to a substance that can cause it to change its state of matter.
Pressure plays a crucial role in phase transition as it can change the thermodynamic conditions of a substance, altering its state of matter. For example, increasing pressure can cause a solid to melt into a liquid, or a liquid to vaporize into a gas.
High-pressure phase transition refers to the process of changing a substance's state of matter under high levels of pressure. This can result in the formation of new phases or the suppression of existing phases, leading to unique material properties.
Some examples of phase transition under pressure include the melting of ice into water at high pressures, the formation of diamonds from carbon under extreme pressure and temperature, and the transformation of graphite into graphene under high-pressure conditions.