Papers by Keyword: Single Crystal

Abstract: In this study, to clarify the effects of Mo addition on deformation behavior of Ti-Mn alloys, the mechanical properties and the deformation structures of the alloys were investigated using Ti-Mn and Ti-Mn-Mo alloys polycrystals and single crystals. We found that the elongation of Ti-Mn alloys are improved from approximately 5% to 30% by Mo addition, with maintaining ultimate tensile strength of 900 MPa. The excellent strength-ductility balance of Ti-Mn-Mo alloys is caused by {332}<113> twinning, which is unique twinning for metastable β-type titanium alloys. Additionally, the deformation behavior of Ti-Mn and Ti-Mn-Mo alloys was investigated in detail by using single crystals focusing on a critical resolved shear stress (CRSS). As a result, we found for the first time that CRSS for {332}<113> twinning in Ti-Mn-Mo alloy was lower than that in Ti-Mn alloy. Moreover, in Ti-Mn-Mo alloy, CRSS for {332}<113> twinning was lower than that for {112}<111> slip. These results suggest that CRSS for {332}<113> twinning in Ti-Mn alloys is decreased by Mo addition.

Abstract: Ni-based single crystal superalloy turbine blades have excellent mechanical strength and resistance to corrosion and oxidation due to a uniformly distributed gamma prime phase in a gamma matrix. However, defect grains have been often found on the surface of turbine blades after manufacturing, which can be potential sites of crack initiation. In this study, several different types of surface defect grains formed in third generation Ni-based single crystal turbine blades, such as stray grains, freckle chain grains, equiax grains, and a new grain formed in surface scale, had been investigated. The grain boundary regions were observed by high resolution electron microscopy. Although the formation mechanism of each grain defect is different, secondary phases, such as rhenium-rich particles, have been always found in each grain boundary. In addition, depending on the existence of the secondary phases as well as the size of defect grains, different microstructures were observed even in the same defect grain boundary. Finally, the observed results suggest that if there is any boundary region in a turbine blade, secondary phases, such as Re-rich particles, can be found.

Abstract: Single crystals of lead germanate are obtained by the Czochralski technique. The dimensions of hexagonally shaped crystals are up to 25 × 25 × 5 mm³. According to X-ray diffraction measurements the grown crystals respond to lead germanate Pb₅Ge₃O₁₁ structure. Curie temperature was also measured.

Abstract: (300Å)Fe films were deposited, on MgO (001) single crystalline substrate with various buffer layer thickness t_Ag (Å) / (75Å) Cr. The magnetic properties of the Fe films were measured by magneto-optic Kerr effect (MOKE) technique. The MOKE measurements provided the t_Ag buffer layer thickness dependence of the hysteresis loops and the change of loop shapes with the surface roughness. It was found that the magnetization reversal process changed with the surface roughness. Magnetization rotation dominated the magnetization reversal for the smoothest films. As the films roughened, the domain-wall pinning set in, eventually dominating the magnetization reversal for the roughest films. Additionally, the magnetic uniaxial anisotropy in the Fe films disappeared as the roughness parameters increased. It was also found from MOKE that the surface roughness strongly affected the coercivity.

Abstract: Aluminum nitride (AlN) single crystal boules were grown by physical vapor transport (PVT). Diameter expansion during boule growth, without the introduction of low angle grain boundaries (LAGB) around the boule periphery, was confirmed by crossed polarizer imaging, synchrotron white beam x-ray topography (SWBXT), and synchrotron monochromatic beam x-ray topography (SMBXT). The densities of basal plane dislocations (BPD) and threading edge dislocations (TED) averaged from high-magnification topographs of five regions of a high-quality substrate were 0 cm^-2 and 992 cm^-2, respectively. Substrates fabricated from AlN boules possessed excellent surface finishes suitable for epitaxy.

Abstract: A successful growth of the titanium-doped lithium niobate (Ti: LiNbO₃) single crystal by Czochralski method is reported. By preserving an effective control of growth parameters such as maintaining accurate temperature gradient by controlling its output power and growth rate as well as wisely choosing the right pulling rate and speed rotation, the Ti:LiNbO₃ single crystal successfully produced using Automatic Diameter Control-Crystal Growth System (ADC-CGS). The structural and optical analyses have been done by using X-ray Diffractometer (XRD), Differential Thermal Analyzer (DTA) and Ultraviolet-Visible (UV-Vis) spectroscopy. The crystallinity of the sample has been confirmed using XRD and DTA has been used to determine the crystal nature of the sample. The position of fundamental absorption edge was recorded via transmission spectra in UV and visible region.

Abstract: Currently, novel method to synthesize diamond film on material substrate called as in-liquid microwave plasma CVD (IL-MPCVD) has been achieved. It has been studied and improved in addition expected as new method instead of conventional gas phase microwave plasma CVD (MPCVD). The purpose of this study is to synthesize single crystal diamond using IL-MPCVD in high speed deposition. The experimental conditions, methanol was poured in to the reactor. Each of diamond particles (100) and (111) was embedded on the stainless steel substrates (SUS632J2). It was mounted to the substrate holder of in-liquid plasma equipment and installed on the top cover. The distance between the tip of the electrode and the substrate was kept to 1.5mm. A microwave of 2.45GHz was irradiated into the quartz glass tube reactor from the rectangular cavity resonator with 4 mm diameter tungsten electrode and the plasma was generated at its tip. The microwave was adjusted in appropriate power to maintain a certain substrate temperature. Diamond films were evaluated by Raman spectroscopy, Scanning Electron Microscope (SEM) and Laser Microscope (LM). As a result, the best orientation for epitaxial growth was found to be (100) which have film growth gradually and smooth surface. Whereas (111) face has polycrystalline film with irregularity growth and rough surface. The remaining H and C after CO synthesis satisfying H/C>20 is necessary to synthesized diamond using IL-MPCVD. The deposition rate was about 32 μm/h when both single crystal and polycrystalline diamond film were synthesized.

Abstract: It was shown in Ni₅₃Mn₂₅Ga₂₂ single crystals that the annealing at 1273 K for 1 h followed by slow cooling, at which the (L2₁+γ)-structure is formed, provides the increase of crystals plasticity as compared with the brittle initial L2₁-single crystals. The increase of critical stresses by more than 2 times (up to σ > 150 MPa), at which the cooling/heating cycles under stress are accompanied by sample destruction, is observed. Moreover, the value of thermal hysteresis is increased by 1.5 times and the perfect curve of superelasticity is observed at T=423 K.

Abstract: Single crystal TiO₂ nanorod (TNR), aligned vertically and packed with the length up to 10 μm on the surface of FTO glass, are prepared hydrothermal method, without any surfactant materials. By adjusting reaction time and concentration of titanium precursor solution, the morphology of TNRs is controlled and result in 20-50 nm of diameters, 4-10 μm length and the inter-distance between TNRs are approximately 3.8 nm. Morphology-controlled TNR arrays are applied to a photoanode in photovoltaic cell. photo-conversion efficiency of Packed TNRs with 10 μm length reached 4.2%.

Abstract: We report the electrical-transport and magnetic properties of the hole doped La_0.7Ca_0.3MnO₃ (LCMO-1) and La_0.88Ca_0.12MnO₃ (LCMO-2) single crystals, prepared using floating zone technique. The metal to insulator transition (T_MI) occurs at 211 K along c-axis and T_MI = 185 K along ab-plane for LCMO-1 single crystal. No electronic transition was observed over the whole temperature range under the magnetic field up to 8 T for LCMO-2 single crystal. It is observed that the T_MI is higher along c-axis as compared to that in the ab-plane, consequently signifying more favorable hoping of electrons is along c-axis in LCMO-1. The ac-susceptibility measurement shows that ferromagnetic to paramagnetic transition temperature (T_C) at 206 K for LCMO-1 and T_C = 118 K for LCMO-2 single crystals which is seemingly related to notable change of resistance at 120 K in LCMO-2 single crystal. The maximum MR of 98% for LCMO-1 and 59% for LCMO-2 single crystals up to 8 T applied magnetic field along c-axis and ab-plane, respectively are observed.