Noncrystalline ceramics have lower heat transport largely due to

• A. More free electrons
• B. Reduced lattice vibrations
• C. More effective phonon scattering due to disorder
• D. Electron hopping dominates

Answer: (C)

Heat transfer in solids is carried mainly by lattice vibrations, or phonons. In noncrystalline (amorphous) ceramics there is no long-range atomic order, so the structure is highly disordered. This disorder disrupts the propagation of phonons, causing them to scatter very frequently and drastically shorten their travel distances (mean free path). Because heat transport in these materials relies on phonons, this heavy scattering severely lowers thermal conductivity. In ceramics, there aren’t many free electrons to contribute to heat flow like in metals, so electron-based mechanisms aren’t helping much anyway. Lattice vibrations aren’t simply reduced; they are present, but their transport is hindered by disorder. Hence the dominant reason for the lower heat transport is more effective phonon scattering due to disorder.