Question

Explain why all ferroelectric crystals behave as piezoelectric crystals but the reverse is not true.

Answer 1

1. All ferroelectric crystals behave as piezoelectric crystals because they possess a spontaneous electric polarization that changes when mechanical stress is applied, generating an electric charge which is the basic property of piezoelectricity.
2. However, the reverse is not true because not all piezoelectric crystals have spontaneous and reversible polarization, which is a defining feature of ferroelectric materials.
3. In other words, while all ferroelectric substances show piezoelectric behaviour, not all piezoelectric materials can reverse their polarization under an electric field, so they cannot be classified as ferroelectric.