Thermal conductivity of dense and porous yttria-stabilized zirconia

The thermal conductivity of dense and porous yttria-stabilized zirconia (YS Z) ceramics has been measured as a function of temperature in the range 25 to 1000 degreesC. The dense specimens were either single crystal (8 mol% YS Z) or sintered polycrystalline (3 mol% and 8 mol% YSZ). The porous specimen s (3 mol% YSZ) were prepared using the "fugitive" polymer method, where dif ferent amounts of polymer spheres (of two different average sizes) were inc luded in the starting powders before sintering. This method yielded materia ls with uniformly distributed porosities with a tight pore-size distributio ns. A theory has been developed to describe the thermal conductivity of den se YSZ as a function of temperature. This theory considers the reduction in the intrinsic thermal conductivity due scattering of phonons by point defe cts (oxygen vacancies and solute) and by the "hopping" of oxygen vacancies. It also considers an increase in the effective thermal conductivity at hig h temperatures due to radiation. This theory captures the essential feature s of the observed thermal conductivity. The Maxwell theory has been used to analyze the thermal conductivity of the porous materials. An adequate agre ement was found between the theory and experiment. (C) 2001 Kluwer Academic Publishers.