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Why can a peak in dielectric constant near the Curie point be a problem for capacitors?

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Figure 1: Ferroelectric properties of barium titanate (BaTiO3). (Left) Above 120° C the structure of the BaTiO3 crystal is cubic, and there is no net polarization of charge; (right) below 120° C the structure changes to tetragonal, shifting the relative positions of the ions and causing a concentration of positive and negative charges toward opposite ends of the crystal. — capacitor dielectric and piezoelectric ceramics Figure 1: Ferroelectric properties of barium titanate (BaTiO₃). (Left) Above 120° C the structure of the BaTiO₃ crystal is cubic, and there is no net polarization of charge; (right) below 120° C the structure changes to tetragonal, shifting the relative positions of the ions and causing a concentration of positive and negative charges toward opposite ends of the crystal.

A peak in the dielectric constant near the Curie point is considered problematic for capacitors because it results in a lack of stability in the material's performance.1

In ferroelectric materials like barium titanate, the dielectric constant—which measures a material's ability to store electric charge—exhibits a large, sharp increase at the temperature where the material transitions from a tetragonal to a cubic crystal structure. Because the dielectric constant is highly sensitive to temperature changes near this point, the capacitance of the device becomes unstable, making it unsuitable for applications requiring consistent performance across varying temperatures.1

To mitigate this issue, engineers use chemical substitutions to modify the material's properties:
* Lead (Pb²⁺) is substituted to increase the Curie point.1
* Strontium (Sr²⁺) is substituted to lower the Curie point.1
* Calcium (Ca²⁺) is substituted to broaden the temperature range over which the peak occurs, thereby improving overall stability.1