What happens to a materials temperature when it is changing state

When thermal energy is added to a substance, its temperature increases, which can change its state from solid to liquid (melting), liquid to gas (vaporization), or solid to gas (sublimation) ... Decreasing pressure can cause it to vaporize. For some types of rock, decreasing pressure can also cause them to melt.

When a substance changes from one state of matter to another it undergo a change of state. These changes of state always occur with a change of heat which is energy. It comes into the material during a change of state or heat comes out of the material during this change. the heat content of the material changes but the temperature does not.