The science and technology related with light has revolutionized modern society, and understanding the effects of light on semiconducting materials has become crucial to current science and technology. Although much research has been done on the effects of light on the electronic and optical properties of materials, the effects of light on the mechanical properties of materials are not well understood. It was recently found that extraordinarily large plasticity appears in bulk compression of single-crystal ZnS in complete darkness even at room-temperature. This is believed to be due to the less interactions between dislocations and photo-excited electrons and/or holes. However, methods for evaluating dislocation behavior in such semiconductors with small dimensions under a particular light condition had not been well established. Here we show a new nanoindentation method that incorporates well designed lighting system for exploring dislocation behavior depending on the light conditions in advanced semiconductors. We used single-crystal ZnS as a model material because its bulk deformation behavior has been well investigated. It is confirmed that the decrease of dislocation mobility with light observed in conventional bulk deformation tests can be understood even by the nanoindentation tests at room-temperature. It is remarkable that we experimentally demonstrate that dislocation mobility appears to be more sensitive to light exposure than dislocation nucleation.

Pulsed electric current sintering (PECS) technique, which can highly control sintering conditions with uniaxial pressing under vacuum, is effective in fabricating various functional materials. Particularly, high densification rates attained by this sintering technique enable suppressed grain growth during sintering process results in fine-grained microstructures. For laser optics, we show that PECS is also effective for fabricating non-cubic laser materials with fine microstructure, and sapphire/Nd:YAG ceramic composite materials. In this paper, we describe the microstructure, optical characteristics, and lasing properties for the fabricated materials and discuss the future possibility of PECS for applying to laser optics.

Shrinkage behaviors during shrinkage rate-controlled flash (SCF) sintering were investigated for 8 mol% Y₂O₃–ZrO₂ (8YSZ) when shrinkage rates were varied between 60 and 300 μm/min under alternating current fields of 50 V_rms/cm, 1200 mA_rms, and 1000 Hz at a furnace temperature of approximately 870°C. Volumetric power dissipation and electrical conductivity were shown to exhibit similar dependencies against linear shrinkages even if the shrinkage rates were changed. The 8YSZ polycrystals, with similar microstructure and density, could be produced under all SCF conditions used in this study, which was confirmed as a characteristic feature of SCF sintering. Finally, the 8YSZ polycrystals with a density of 5.91–5.93 g/cm³ and a grain size of 2.2–2.6 μm could be produced with a shrinkage process period of 15–65 min at a furnace temperature of approximately 870°C.

The uniformity of shrinkages and the distribution of grain sizes were investigated for flash-sintered 3 mol%Y₂O₃-ZrO₂ compacts in direct current and alternating current (AC) electric fields using rectangular-shaped and circular truncated cone-shaped green compacts. The use of a high-frequency AC electric field enough to suppress electrode overvoltage was confirmed to be advantageous for uniform shrinkages, regardless of the shapes of the green compacts. However, the grain size distribution became larger in cone-shaped green compacts, the cross-sectional areas of which varied along the compact. The grain sizes in flashed cone-shaped green compacts were found to exhibit a near linear relation to current density, which provides a means for determining the grain size distribution upon the flash sintering of green compacts with different cross-sectional areas along an electric field.

The effect of alternating current electric field on the densification behavior and microstructural evolution in flash sintering of Li_1.5Al_0.5Ge_1.5(PO₄)₃ (LAGP) is investigated in this study. With an increase in the applied electric field, the onset temperature of flash sintering was lowered and the density of the sintered sample was decreased. Maximum density of 90% was obtained under 50 V_rms/cm and 30 mA_rms/mm². Based on X-ray diffraction results, the crystal phase of the sample has a NASICON-type phase, and no phase transformation was observed in the samples after flash sintering. Spherical-shaped holes were observed in the sample flash-sintered at the higher electric field. A well-developed structure with faceted grains was observed in the high magnification image at the spherical holes. It was suggested that thermal runaway during flash sintering caused a partial melt in the sample while the recrystallization of LAGP from the melt caused the formation of large spherical holes.

In order to improve IR transparency of the Y₂O₃-MgO composite, the effect of powder calcination conditions was investigated. The absorption intensity of carbonate peaks sensitively changes with the powder calcination conditions, such as temperature and time, before the pulsed electric current sintering (PECS). The calcination at 1150°C for 8 h can eliminate the contamination of the carbonate groups pre-existing in the starting Y₂O₃ and MgO powders. The composites fabricated from the powders, which were calcinated at the optimum conditions, can attain high IR transparency with maintaining the fine and dense microstructures. This indicates that the pre-calcination of the powders is an effect method to remove the carbonate contamination without causing significant powder coarsening and agglomeration in the Y₂O₃-MgO composites. During the PECS processing, however, a small amount of carbon contaminations occurs additionally from the graphite die/paper and remains even in the post-annealed Y₂O₃-MgO composite. It can be concluded that for the Y₂O₃-MgO composites, although the carbonate related contaminations are succeeded to remove from the starting power mixture, the carbon contamination occurs additionally from the graphite die/paper during the PECS processing and degrades the IR transparency.