Piezoelectricity is generated by:

The piezoelectric effect is a physical property of certain crystalline materials, such as quartz. When mechanical stress or pressure (deformation) is applied to these crystals, it causes an electrical charge to build up across the material. Conversely, when an electrical voltage is applied across the crystal, it deforms mechanically. This unique electromechanical interaction is what allows crystals to serve as highly precise oscillators and filters in radio circuits. Adding impurities relates to semiconductor doping, and magnets relate to electromagnetism, neither of which is involved in generating piezoelectricity.