A quantum of crystal lattice vibrational energy having a magnitude hf, where h is the Planck constant and f is the frequency of the vibration. Phonons are analogous to the quanta of light, i.e. photons. The concept of phonons is useful in the treatment of the thermal conductivity of nonmetallic solids and, through consideration of electron–phonon interactions, the temperature dependence of the electrical conductivity of metals and understanding the phenomenon of superconductivity.