Thermal conductivity and diffusivity of KH₂PO₄ and NH₄H₂PO₄ polycrystalline samples near their phase transitions

Abstract

Simultaneous measurements of thermal conductivity and diffusivity of ferroelectric polycrystalline samples of the KDP family type have been performed with the transient plane source (TPS) technique over the temperature range 88-300 K. The thermal conductivity behavior resembles that of the corresponding single crystals, but with values a factor of three lower. This decrease in thermal conductivity of the polycrystalline form is attributed to scattering mechanisms due to microstructural imperfections such as point defects, grain boundaries, etc. Values of porosity have been estimated using the dimensions of the unit cell deduced from the x-ray analysis and the apparent densities. The data indicate that the phase transition mechanisms (displacement type and order-disorder type) still dominate the conduction processes in spite of the presence of other scattering mechanisms due to the imperfection of the microstructure in the polycrystalline form of these materials.