Xijun Li

High pressure behavior of titanium–silicon carbide (Ti3SiC2)

The dynamic high-pressure behavior and phase stability of titanium–silicon carbide (Ti3SiC2), a unique ceramic having metal-like properties, was investigated in this study. Time-resolved measurements of the Hugoniot equation of state, employing a plate impact geometry, were conducted on the Ti3SiC2 samples in the pressure range of 50–120 GPa using a two stage light gas gun. At pressures around 90–120 GPa, Ti3SiC2 was found to transform to a more compressed state. Shock-recovery experiments were also performed on Ti3SiC2 powders at impact velocities of 1.5–2 km/s using a single capsule geometry, with and without the addition of copper powder to vary the shock-loading pressure (calculated to be 22–58 GPa) and temperature (calculated to be up to 3250 °C) in the sample. No evidence of shock-induced decomposition was observed in these recovery experiments performed on the Ti3SiC2 powders.

Aluminum oxynitride at pressures up to 180 GPa

Hugoniot equation-of-state data of shock compressed aluminum oxynitride (AlON), consisting of 64.1 mol% Al2O3⋅35.9 mol% AlN with a density of ∼3.68 g/cm3, have been determined to 180 GPa. The relationship between shock velocity (Us) and particle velocity (Up) is expressed by a straight line: Us(km/s)=8.08+0.761Up(km/s). Although there is no evidence of phase transition in the data, the determined Hugoniot of AlON has been compared with those of oxide spinels such as MgAl2O4 and Fe3O4. We discuss the systematics of high pressure phase transitions of spinels that indicate a phase transition to CaTi2O4-type phases. The phase transition to CaTi2O4-type structures implies that the recently discovered Si3N4 spinel also may be transformed into a CaTi2O4-type phase with increasing pressure.

Electron-Beam Domain Writing in Stoichiometric LiTaO3 Single Crystal by Utilizing Resist Layer

Ferroelectric crystals with patterned domain structures, such as LiTaO3, show excellent optical properties and have thus been used as materials for functional photonic devices. The effect of a resist layer on microscale domain engineering by electron-beam direct writing was examined using stoichiometric LiTaO3 single crystals. It was demonstrated that using an electron-beam (e-beam) resist to spatially confine the beam electrons, a regular, uniform dot array of domains (with a size of 1 µm) could be fabricated along the z-axis throughout the crystal. Ring-shaped domains could be fabricated by this technique. Our experiments pave the way for improving the e-beam domain fabrication method by utilizing a resist covering.

Domain patterning thin crystalline ferroelectric film with focused ion beam for nonlinear photonic integrated circuits

Domain patterning thin ferroelectric films creates nonlinear optical devices. Unfortunately, pinholes cause conventional electrical domain-poling methods to short circuit when used on thin film. We have applied a focused ion beam (FIB) to pattern the ferroelectric domains of LiNbO3 single crystalline films with thicknesses of 800nm–2μm. FIB can fabricate domains 100 times faster than a scanning probe microscope and can be applied to irregular surface structures. Furthermore, FIB is compatible with semiconductor device processing techniques, which paves the way for monolithic nonlinear photonic integrated circuits in ferroelectrics.

Hugoniot of beta-SiAlON and high-pressure phase transitions

Hugoniot equation-of-state data of shock compressed β‐Si4Al2O2N6 have been determined to a pressure of 120 GPa. The relationship between shock velocity (Us) and particle velocity (Up) is expressed by a linear equation Us(km∕s)=5.62+0.96Up(km∕s) above a pressure of ∼40GPa beyond the Hugoniot elastic limit (15–16 GPa). A phase transition to spinel is observed at the onset pressure of 32 GPa. According to the systematics of high-pressure phase transitions of spinels that indicate a phase transition to CaTi2O4-type phases at high pressures, β‐Si4Al2O2N6 may also be transformed into a CaTi2O4-type phase with further increasing pressure. The previous recovery experiments on β-SiAlON indicated the formation of spinel and amorphous phases at shock pressures of 41–63 GPa. A comparison of the Hugoniot data and recovered samples suggests that the high-pressure CaTi2O4-type phase is not quenchable and quenched as an amorphous phase although a large hysteresis is detected in the release path.

Domain engineering in LiTaO 3 by focused charge beam: From micro to nano scale

In this study, 1-mum-dot domain by resist-assisted electron beam writing and 100-nm-wide line domain by focused ion beam domain patterning techniques have been demonstrated in LiNbO3 and LiTaO3 crystals thicker than tens of mum.

Hugoniot Measurements of High Pressure Phase Stability of Titanium‐Silicon Carbide (Ti3SiC2)

Hugoniot measurements of the high‐pressure phase stability of titanium‐silicon carbide (Ti3SiC2) were performed in this study. Ti3SiC2 is a unique ceramic having high stiffness, but low hardness. Time‐resolved measurements employing plate‐impact geometry were conducted on Ti3SiC2 samples in the pressure range of 50 to 120 GPa using the NIMS two‐stage light‐gas‐gun. Experiments performed in the lower pressure range followed the continuous pressure‐volume compressibility trend reported by Onodera, et al. in static high‐pressure experiments. At pressures around 80–120 GPa, deviation in pressure‐volume compressibility to a more compressed state was observed indicating evidence of a possible phase change. Streak camera records of the free surface velocity measured using the inclined mirror method also showed discontinuous slope, indicating a possible pressure‐induced phase transformation.

Shock Response of Ruby Crystal Studied by Pulsed Excitation Luminescence Spectroscopy

Time-resolved luminescence spectroscopy with a pulsed excitation method has been applied to investigate the elastoplastic deformation in shocked ruby single crystal. The ruby luminescence is induced by a nanosecond laser pulse, and before the luminescence decays significantly, a shock wave generated by plate impact is introduced into the sample. The elastoplastic deformation and its effect on the wave propagation have been recorded as streak images.