Masaki Fujikane

Thermophysical properties of BaZrO3 and BaCeO3

Abstract Polycrystalline perovskite type oxides, BaZrO 3 and BaCeO 3 , have been prepared by mixing the appropriate amounts of ZrO 2 , CeO 2 , and BaCO 3 followed by reacting at 1273 K and sintering at 1773 K. The thermophysical properties, viz. the thermal expansion coefficient, melting point, elastic moduli, Debye temperature, and Vickers hardness, of BaZrO 3 and BaCeO 3 have been measured. The harmonic and dilatational terms of the heat capacity have been evaluated by using the values of the thermal expansion coefficient, compressibility, and Debye temperature measured in the present study, The relationships between several properties of BaZrO 3 and BaCeO 3 show the typical characteristics of the perovskite type oxides.

Nanoindentation study on insight of plasticity related to dislocation density and crystal orientation in GaN

Yield shear stress dependence on dislocation density and crystal orientation was studied in GaN by nanoindentation examination. The yield shear stress decreased with increasing dislocation density, and it decreased with decreasing nanoindentation strain-rate. It reached and coincided at 11.5 GPa for both quasi-static deformed c-plane and m-plane GaN. Taking into account theoretical Peierls–Nabarro stress and yield stress for each slip system, these phenomena were concluded to be an evidence of heterogeneous mechanism associated plastic deformation in GaN crystal. Transmission electron microscopy and molecular dynamics simulation also supported the mechanism with obtained r-plane dislocation line.

Anisotropic effect of piezoelectric polarization on Schottky barrier height in elastically deformed bulk GaN crystal

We studied electrical characteristics in c-pane (0001) and m-plane (10−10) GaN by nanoindentation examination with a conductive diamond indenter. At constant voltage during partial indentation, the current density increased stepwise as the loading–unloading cycle went by in c-plane GaN and was constant in m-plane GaN. During several constant-indentation loads, the turn-on voltage decreased with increasing indentation load in c-plane GaN and was constant in m-plane GaN. We investigated the piezoelectric polarization anisotropy by in situ electric measurement while controlling strain in GaN crystals.

Strain Rate Controlled Nanoindentation Examination and Incipient Plasticity in Bulk GaN Crystal

Yield shear stress dependence on dislocation density and crystal orientation was studied in bulk GaN crystals by nanoindentation examination. The yield shear stress decreased with increasing dislocation density, and it decreased with decreasing nanoindentation strain-rate. It reached and coincided at 11.5 GPa for both quasi-static deformed c-plane (0001) and m-plane (100) GaN. Taking into account theoretical Peierls–Nabarro stress and yield stress for each slip system, these phenomena were concluded to be an evidence of heterogeneous mechanism associated plastic deformation in GaN crystal. Transmission electron microscopy and molecular dynamics simulation also supported the mechanism with obtained r-plane (012) slip line right after plastic deformation, so called pop-in event. The agreement of the experimentally obtained atomic shuffle energy with the calculated twin boundary energy suggested that the nucleation of the local metastable twin boundary along the r-plane concentrated the indentation stress, leading to an r-plane slip.

Fabrication of Metastable Oxide Ceramics with Oxygen Vacancy

Metastable ZrO 2 -x particles were successfully prepared by inert gas condensation (IGC) process. To control oxygen vacancies in metastable ZrO 2 -x, samples were annealed between 100°C and 400°C for 2 h under low oxygen partial pressures (PO 2 = 10-15 Pa). Therefore, metastable ZrO 2 -x samples with various oxygen vacancies (0.26 < x < 0.81) were successfully fabricated by IGC method; also, the particle sizes were less than 10 nm.