Which action is necessary to create a potential difference in crystals?

Creating a potential difference in crystals involves manipulating the arrangement of atoms or the electrical charges within the material. Bending or twisting the crystal alters its structure and can generate internal stress, which affects the distribution of charge carriers. This mechanical change can lead to the piezoelectric effect, where the application of mechanical force results in the separation of electrical charges, thereby creating a potential difference.

For example, in piezoelectric materials, when mechanical stress is applied through bending or twisting, it can cause a shift in the position of positive and negative charge centers within the crystal lattice. This shift leads to the development of an electric field and a corresponding voltage across the material. This principle is essential in various applications, including sensors and actuators, where the conversion of mechanical energy to electrical energy is crucial.

Other options like heating, compressing, or molding may impact the material properties but don’t directly create the same type of potential difference through charge separation as bending or twisting does in the context of piezoelectric properties.