# 28.7: Temperature Dependence of the Hysteresis Loop

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We have now seen the way in which the hysteresis loop arises. However, there are more aspects to the hysteresis loop.

We have only observed it at one particular temperature, one at which the material is ferroelectric. What happens if the temperature is raised? The hysteresis loop changes with temperature, becoming sharper and thinner, and eventually disappearing, i.e.: As you can see, the polarisation increases at 90°C, as a result of a phase transition. Between this temperature and room temperature, the polarisation increases steadily, as a direct relation with temperature, such that:

ΔP = p ΔT

where p = pyroelectric coefficient (C m-2 T-1).