Effect of Stress-Strain Profile on Bulk Thermal Conductivity

Thermal conductivity reduction via stress-strain engineering has serious implications in the fabrication of high efficiency thermoelectric generators due to the introduction of additional lattice defects (increased phonon scattering) and decreasing of the speed of sound (lattice softening). Here, we systematically study the effect of stress-strain profile on thermal conductivity through experiments. We fabricate bulk buttons of porous silicon (∼3 cm³) from micropowders (∼50 µm size) under different initial pressure conditions using plasma-assisted sintering. We then obtain the stress-strain and hardness profiles of the substrates using nanoindentation. After obtaining the mechanical properties, we perform laser flash analysis and differential scanning calorimetry to obtain the bulk thermal conductivity of the samples. Our preliminary results show that higher strain (i.e. lower initial pressure) yields lower bulk thermal conductivity due to the better preservation of nanoscale properties. Furthermore, we see a reduction in speed of sound with higher strain, highlighting the effect lattice softening. This study sheds light on the effect of mechanical properties on thermal conductivity and offers insights into new avenues for the design of low thermal conductivity nanomaterials.