Glasslike thermal conductivity of tourmaline at low temperatures

Thermal conductivity measurements parallel and perpendicular to the c-axis in tourmaline single crystals are reported in the range of 1.7 – 35K. The spontaneous polarization is constrained to the c-axis in tourmaline. The thermal conductivity (K) follows the glasslike K ∝ T^1.9 below 6K in both crystallographic directions, and the magnitude of K is in the upper range found in glasses. It is concluded that the glasslike thermal properties associated with the spontaneous polarization in ferroelectric - type solids occur isotropically throughout the crystal and are not limited to the polarization direction.