What physical phenomenon does a piezoelectric material exhibit?

A piezoelectric material exhibits the ability to generate an electrical charge in response to mechanical stress or deformation. This phenomenon occurs due to the asymmetric arrangement of atoms within the crystal structure of the material. When the material is deformed—whether through compression, stretching, or bending—electrical charges are displaced, resulting in a measurable voltage across the material. This unique characteristic makes piezoelectric materials valuable in various applications, such as sensors, actuators, and transducers.

In contrast, the other choices do not accurately reflect the properties of piezoelectric materials. Increased thermal conductivity when heated pertains to thermal properties, rather than the electrical response to mechanical stress. Permanent shape changes when cooled refer more closely to materials exhibiting shape memory or certain phase changes, not the piezoelectric effect. Lastly, color shifts in response to temperature changes are typically associated with thermochromic materials and are unrelated to the behavior of piezoelectric materials.