Ferroelectric vs. Piezoelectric Materials: Key Differences Explained

This article clarifies the differences between ferroelectric and piezoelectric materials, both of which possess unique structural and electrical properties. As the names suggest, both material types exhibit distinct electrical characteristics.

Piezoelectric Materials

Piezoelectric materials have the remarkable ability to convert mechanical energy into electrical energy, and vice versa.

They are broadly classified into two main categories:

• Crystals
• Ceramics

Direct Piezoelectric Effect

Direct Piezoelectric Effect

When subjected to mechanical stress, piezoelectric materials generate an electrical potential. This phenomenon, known as the direct piezoelectric effect, finds applications in:

• Strain sensors
• Gas lighters
• Microphones
• Ultrasonic detectors

The direct piezoelectric effect manifests differently under compression and tension, as depicted in the figure above:

• Compression Effect: Decreasing the volume results in a voltage with the same polarity as the material.
• Tension Effect: Increasing the volume produces a voltage with the opposite polarity as the material.

Inverse Piezoelectric Effect

Inverse Piezoelectric Effect

Conversely, when a piezoelectric material is exposed to an electric field (voltage), it either lengthens or shortens proportionally to the applied voltage. This is termed the inverse piezoelectric effect and is utilized in:

• Crystal speakers
• Crystal oscillators
• Actuators
• Record player pick-ups

As illustrated in the figure above:

• (A) Applying a voltage with the same polarity causes the material to expand.
• (B) Applying a voltage with the opposite polarity causes the material to contract.

Ferroelectric Materials

Ferroelectric Material

• All ferroelectric materials exhibit the piezoelectric effect due to their lack of symmetry.
• These materials form a special class within piezoelectric materials, possessing additional unique characteristics.
• They exhibit spontaneous polarization, meaning polarization occurs even in the absence of an external electric field.
• Ferroelectrics are the electrical analogue of ferromagnets, which may display permanent magnetic behavior. Rochelle Salt was the first ferromagnetic material discovered by Valasek.
• A key characteristic of ferroelectrics is that their polarization can be changed and reversed by applying an external electric field, as shown in the figure below.

Ferroelectric vs Piezoelectric

It’s important to note that many ferroelectric materials are also piezoelectric. However, the reverse isn’t always true.

Ferroelectric vs. Piezoelectric: A Comparison