THERMAL-CONDUCTIVITY AND DIFFUSIVITY OF KH2PO4 AND NH4H2PO4 POLYCRYSTALLINE SAMPLES NEAR THEIR PHASE-TRANSITIONS

Simultaneous measurements of thermal conductivity and diffusivity of f erroelectric polycrystalline samples of the KDP family type have been performed with the transient plane source (TPS) technique over the tem perature range 88-300 K. The thermal conductivity behavior resembles t hat of the corresponding single crystals, but with values a factor of three lower. This decrease in thermal conductivity of the polycrystall ine 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 de duced from the x-ray analysis and the apparent densities. The data ind icate that the phase transition mechanisms (displacement type and orde r-disorder type) still dominate the conduction processes in spite of t he presence of other scattering mechanisms due to the imperfection of the microstructure in the polycrystalline form of these materials.