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How does quartz produce a voltage when it is compressed?

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Figure 1: Ferroelectric properties of barium titanate (BaTiO3). (Left) Above 120° C the structure of the BaTiO3 crystal is cubic, and there is no net polarization of charge; (right) below 120° C the structure changes to tetragonal, shifting the relative positions of the ions and causing a concentration of positive and negative charges toward opposite ends of the crystal. — capacitor dielectric and piezoelectric ceramics Figure 1: Ferroelectric properties of barium titanate (BaTiO₃). (Left) Above 120° C the structure of the BaTiO₃ crystal is cubic, and there is no net polarization of charge; (right) below 120° C the structure changes to tetragonal, shifting the relative positions of the ions and causing a concentration of positive and negative charges toward opposite ends of the crystal.

Quartz produces a voltage when compressed due to the piezoelectric effect, a phenomenon occurring in certain crystals that lack a centre of symmetry within their crystal lattice.12

When mechanical stress—such as squeezing or compression—is applied to a quartz crystal, it causes small, relative displacements of ions within the lattice structure. This displacement separates the centres of positive and negative electric charge, resulting in electric polarization. This internal shift creates a potential difference across the crystal, which can be measured as a voltage when the crystal is placed between two electrodes.123

Because the magnitude of the generated charge is proportional to the applied pressure, quartz is effectively utilized in various applications, including pressure gauges and precision clocks.13