Evidence of a Thermal Diffusivity Gap in Sintered Li-Co-Sb-O Solid Solutions.

In this work, the thermal properties of ternary Li 3 x Co 7-4 x Sb 2+ x O 12 solid solutions are studied for different concentrations in the range 0 ≤ x ≤ 0.7. Samples are elaborated at four different sintering temperatures: 1100, 1150, 1200 and 1250 °C. The effect of increasing the content of Li + and Sb 5+ , accompanied by the reduction of Co 2+ , on the thermal properties is studied. It is shown that a thermal diffusivity gap, which is more pronounced for low values of x , can be triggered at a certain threshold sintering temperature (around 1150 °C in this study). This effect is explained by the increase of contact area between adjacent grains. Nevertheless, this effect is found to be less pronounced in the thermal conductivity. Moreover, a new framework for heat diffusion in solids is presented that establishes that both the heat flux and the thermal energy (or heat) satisfy a diffusion equation and therefore highlights the importance of thermal diffusivity in transient heat conduction phenomena.