From an engineering perspective, practical Ivacaftor ic50 thermoelectric device requires a significant
volume of material. To realize this objective, nanostructuring using ball milling followed by hot pressing was shown to have a significant reduction in the thermal conductivity of thermoelectric materials especially silicon [7–10]. Similarly, mechanical deformation using high pressure was adopted to improve the Seeback coefficient of Bi2Te3 and PbTe [11, 12]. Valiev et al. [13] demonstrated a novel technique using high-pressure torsion (HPT) to create a high density of lattice defects such as grain boundaries and dislocations on nanometer length scales [13]. Ikoma et al. [14, 15], using HPT processing, reported detailed structural characterization of bulk crystalline silicon by X-ray diffraction spectroscopy, Raman spectroscopy, photoluminescence find more spectroscopy, and transmission electron microscopy and discussed the mechanism behind the nanograin formation in detail [14, 15]. Intrinsic high thermal conductivity of single crystalline silicon limits its application in thermoelectric systems. In this work, we show that bulk single crystalline silicon, when subjected to intense plastic strain through HPT processing, shows a dramatic reduction in room temperature thermal conductivity from its intrinsic single crystal value of 142 W m−1 K−1
to a low thermal conductivity of approximately 7.6 W m−1 K−1. The experimental thermal conductivity results are comparable to nanostructured silicon prepared by ball milling and spark plasma sintering approach reported in the literature [7–10]. Considering the widely adopted method of ball milling followed by plasma sintering in thermoelectric literature to form bulk samples, the current approach could be a promising alternative for such applications. Methods Sample preparation Montelukast Sodium Single crystalline Si (100) wafers of size 5 × 5 mm2 and thickness 640 μm were subjected to HPT processing. Details of the HPT processing in Si was described elsewhere14. Briefly, the HPT facility comprises of upper and lower anvils made of tungsten carbide with flat bottomed spherical depressions to
mount the test sample. During experiments, the test samples were placed in the lower anvil and the pressure was applied on the upper anvil. The HPT facility was operated at a pressure of 24 GPa (loading time approximately 7 s and unloading time approximately 2 s) and at room temperature. Torsional straining is achieved by rotating the lower anvil with respect to the upper anvil at a rotation speed of 1 rpm. HPT-processed samples with 0, 10, and 20 torsion cycles were prepared using this process. The samples were further annealed at 873 K for 2 h (0 and 10 torsion cycles) and 3 h (20 torsion cycles) in nitrogen atmosphere. We performed Raman and X-ray diffraction characterization independently and found that the experimental results were similar to previous literature results [14, 15].