Why are crystalline ceramics typically better thermal conductors than noncrystalline ceramics?

• A. Because electrons dominate heat transfer in crystals
• B. Phonon scattering is reduced in crystalline order
• C. Noncrystalline materials have more grain boundaries
• D. Crystalline ceramics are more porous

Answer: (B)

Heat transfer in ceramics is mainly through lattice vibrations called phonons. In a crystalline lattice, atoms are arranged in a regular, repeating pattern, allowing phonons to propagate over long distances with relatively few interruptions. This minimizes scattering and lets heat flow efficiently, so crystalline ceramics tend to have higher thermal conductivity.

In contrast, noncrystalline (amorphous) ceramics lack this long-range order. The disorder creates many irregularities in bonding and structure, which scatter phonons and disrupt their travel, leading to lower thermal conductivity.

Electrons typically carry heat in metals, not ceramics, so electron-based transfer isn’t the driving factor here. Porosity usually lowers conductivity, and grain boundaries pertain more to polycrystalline materials than to amorphous ones. The key idea is that crystalline order reduces phonon scattering, enabling better heat conduction.