What is piezoelectricity?

Piezoelectricity is a physical property of certain materials, such as quartz crystals and specific ceramics, that relates mechanical stress to electrical voltage. When you physically squeeze, bend, or stress a piezoelectric material, it generates a small electrical voltage across its surfaces. Conversely, when an electrical voltage is applied across these materials, they mechanically flex or deform. This dual, reversible property is what allows quartz crystals to act as highly stable frequency-determining components in oscillators and electronic filters. Distractors that mention generating electromagnetic waves directly or changing the index of refraction refer to completely different physical phenomena, such as the electro-optic effect, and entirely miss the mechanical-electrical relationship fundamental to piezoelectricity.