Question

When a piezoelectric crystal is deformed by mechanical stress, electricity is produced due to the displacement of the ions. If true enter 1, else enter 0.

Answer 1

Hint: There are two types of piezoelectric effects. (a) Direct piezoelectric effect and (b) Converse piezoelectric effect. The non-Centro symmetric distribution of positive and negative electric charges in the unit cell of piezoelectric materials gives rise to piezoelectricity.

Complete step by step answer:
First let us understand the meaning of piezoelectricity and the source of piezoelectricity.
In 1880, P. Cure and J. Curie observed that an electrical charge was produced when specific materials were subjected to a mechanical force and this is how piezoelectricity came into light. Piezoelectric materials generate an electric charge on application of stress (called direct piezoelectric effect) or exhibit mechanical strain on the application of an electric field (called the converse piezoelectric effect).

Solids have a unit cell. If there is a non-Centro symmetric distribution of positive and negative electric charges in the unit cell, then the material exhibits piezoelectricity. On the application of stress or mechanical vibration on a piezoelectric material, a net electric charge is observed due to a change in the dipole which happens due to the induced displacement of the ions. This change in the dipole develops a piezoelectric potential across the material and the material shows piezoelectricity.

Examples of piezoelectric materials include quartz, zinc oxide, and barium titanate. Quartz has nonpolar crystals that are non-ferroelectric and therefore it cannot have electric net dipole when no stress is applied. However, when stress is applied then electric dipole is generated because of the separation of electric charge centers which further results in a piezoelectric potential. On the other hand, zinc oxide which belongs to the polar crystals has a separation between the positive and the negative charges and therefore it shows a spontaneous polarization in the absence of stress or electric field.

Therefore the answer is 1 i.e. when a piezoelectric crystal is deformed by mechanical stress; electricity is produced due to the displacement of the ions.

Note: Ferroelectric materials belong to polar crystals. These materials exhibit spontaneous polarization that are permanent and the direction of polarization in these materials can be changed by changing the direction of the applied electric field. Their polarization also changes with stress; therefore all ferroelectric materials are piezoelectric.