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Perovskite La2Ti2O7 nanocrystalline powder was obtained through the shock synthesis method. In the study, La2O3 and TiO2 powders were mixed through ball milling and, subsequently, shocked by a flyer at a velocity of 3.2 km/s. After shock treatment, the sample was recovered and characterized via various techniques, such as x-ray diffraction, Raman, scanning electron microscope, transmission electron microscope, and ultraviolet-visible diffuse reflection spectrum analysis, to find the presence of La2Ti2O7 nanocrystalline powder with an average grain size of approximately 30 nm in the recovered samples with different yields. Moreover, the results further confirm that the high shock temperature and long ball milling treatment induce higher activation of precursors to improve the La2Ti2O7 content in the recovered samples. By adjusting the relative density of precursor and the ball milling period, pure La2Ti2O7 nanocrystalline powder was obtained. The formation mechanism of La2Ti2O7 was carefully illustrated. This study presents a new method to synthesize La2Ti2O7 nanocrystalline powder by detonation-driven flyer impact.

Fast deformations in the quartz crystals during shock compression process have been investigated with two time-resolved methods of in-situ diffractions by x-ray free electron laser (XFEL) and large-scale molecular dynamic (MD) simulations in order to get insights in planar deformation feature (PDF) mechanism. PDFs in quartz provide strong evidence for impact and are used to estimate the impact conditions. The present experimental results on X-cut and Y-cut quartz single crystals at pressures below phase transition indicate ideal uniaxial compression and rotation of fractured grains to a direction to heat up locally due to dispersed particle velocity distribution in the dynamic movement. This could explain the observed disordering at given planes, as supported by the MD simulations.

We determined the shock equation of state of CaF2 at pressures of ∼0.4–1.5 TPa using high-power laser shock techniques. The shock velocity-particle velocity was approximated by the universal Hugoniot relationship known to metallic fluids. Our results do not support the incompressible behavior above ∼100 GPa claimed previously. Warm dense CaF2 is a bonded liquid above the melting point and approaches an ideal fluid above ∼1 TPa. The measured reflectivity change of CaF2 at the shock front, similar to the other semiconducting liquids in the warm dense region, suggests a gradual metallization process due to the presence of delocalized electrons at high shock-front temperatures.

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.

Real-time vibrational spectra of shock-compressed nitromethane-d3 (CD3NO2) up to 10 GPa have been measured using a single-pulse laser Raman spectrometer in conjunction with a propellant gun and vibrational mode-dependent behavior has been examined. The NO2 stretching mode shows small frequency shift compared to other stretching modes, which may be attributed to increased intermolecular interaction under pressure. Pressure-induced Raman frequency shift of all the investigated stretching modes shows monotonic increase up to ∼5.0 GPa. Above 5 GPa, however, an abrupt drop in Raman frequency shift is observed for the CN and the CD3 stretching modes. At higher pressures, Raman frequencies of these two modes increase again until all Raman bands disappear at above ∼8.5 GPa, where a strong background emerges over the whole spectral range (500–2600 cm−1). This strong emission appears to indicate an onset of a single shock induced chemical reaction at ∼8.5 GPa.

The phase transformation behavior of hexagonal germanium nitride, including both α- and β-Ge3N4, has been studied under shock wave compression. The shock compressed quenched samples indicate phase transformation from hexagonal into a cubic spinel structure (γ-Ge3N4). This transformation is completed with increasing shock pressure up to 40–46 GPa (temperature of 1300–1500 K). The lattice constant of γ-Ge3N4 is measured to be 0.820 63±0.000 19 nm, and the crystal density 6.581 g/cm3, by the powder x-ray diffraction. The stability of γ-Ge3N4 also has been investigated under shock wave compression. It is found that the spinel structure is very stable, and up to at least 63 GPa (temperature of ∼1700 K) there is no indication of the formation of a postspinel phase.

Inclined-mirror Hugoniot measurements were performed on pure AlN polycrystals in the pressure range up to 150 GPa to study the yield properties, phase transition, and equation of state. The Hugoniot-elastic limit (HEL) stress was approximately 9.4 GPa. Above the HEL, the Hugoniot data converged to a static compression curve despite the high thermal conductivity, which indicated that the thermal property is not an important factor in determining the shock yield property. The phase transformation from wurtzite-type (B4) to rock salt-type (B1) structure took place at approximately 19.4 GPa, and was completed by about 75 GPa. The corrected transition pressure at 298 K was 19.2 GPa. Shock velocity (Us) versus particle velocity (Up) relation of the final phase was given by Us=3.27+1.81Up km/s. The Birch–Murnaghan fitting curve of the calculated isothermal compression curve of the B1-type phase roughly coincided with the recent static x-ray diffraction data up to over 100 GPa. The Gruneisen parameter, bulk moduli (K0), and the pressure derivative (K0′) at zero pressure of the B1-type phase were estimated to be 1.51±0.03, 304±4 GPa, and 3.9±0.2 (K0″=−0.02), respectively.

Rhombohedral forms of layered boron nitride (r‐BN) as mixtures with copper powders were shock compressed and quenched from pressures in the range 8–50 GPa. Recovered specimens were investigated by x‐ray diffraction and electron microscopy. The graphite‐like BN (h‐BN) and turbostratic BN (t‐BN) phases are observed in the pressure range 8–22 GPa and wurtzite‐type BN (w‐BN) in the range 17–39 GPa. The zincblende‐type BN (c‐BN) phase is identified from specimens subjected to high shock temperatures and consists of very fine grains mostly less than 10 nm. The mechanism of phase transformation of r‐BN to c‐BN is proposed to occur through two paths: (i) direct conversion by relatively strong shocks and (ii) indirect, kinetically controlled conversion via intermediate phases by shock loadings generating relatively weak pressures (

The Hugoniot data for zinc oxide (ZnO) single crystals were measured up to 80 GPa along both the ⟨ 112¯0⟩ (a-axis) and ⟨0001⟩ (c-axis) directions using a velocity interferometer system for any reflector and inclined-mirror method combined with a powder gun and two-stage light gas gun. The Hugoniot-elastic limits of ZnO were determined to be 10.5 and 11.5 GPa along the a- and c-axes, respectively. The wurtzite (B4) to rocksalt (B1) phase transition pressures along the a- and c-axes are 12.3 and 14.4 GPa, respectively. Shock velocity (Us) versus particle velocity (Up) relation of the final phase is given by the following relationship: Us (km/s) = 2.76 + 1.51Up (km/s). Based on the Debye-Gruneisen model and Birch-Murnaghan equation of state (EOS), we discuss the EOS of the B1 phase ZnO. The bulk modulus (K0) and its pressure derivative (K0′) are estimated to be K0 = 174 GPa and K0′ = 3.9, respectively.

The particle velocity profiles of an MgO single crystal under shock compression were measured up to a pressure of 35 GPa by a velocity interferometer system for any reflector using a LiF window combined with a powder gun. The Hugoniot-elastic limit (HEL) of MgO along the ⟨100⟩ direction was 2.9–4.3 GPa and the initial elastic waves contain some oscillations. Along the ⟨110⟩ direction, the HEL was higher than along the ⟨100⟩ direction and anomalous, two-step-structure elastic waves were observed. These characteristics are discussed based on the slip system of the MgO crystal.

An approach is developed to investigate the dynamic tensile fracture of nanocrystalline copper by laser irradiation loading. A push-pull type velocity interferometer system for any reflector is used to measure the rear free surface velocity profiles. The dynamic tensile strength of nanocrystalline copper films is determined from these velocity profiles as a function of the tensile strain rate. Results show that the dynamic tensile strength of nanocrystalline copper film is about 3 GPa, which is much higher than that of polycrystalline bulk copper, but lower than that of single crystal copper. This dynamic tensile strength increase may be attributed to constraints on dislocation motion by more grain boundaries in nanocrystalline materials.

A diagnostic technique with high time resolution in the velocity-history measurement is presented by coupling an electronic streak camera with a push-pull type velocity interferometer system for any reflector. This technique has been applied to investigate the dynamic tensile spall induced by laser irradiation in pure aluminum by measuring the free surface velocity profiles of samples. Laser irradiation intensities are in the range of 1010–1012W∕cm2. Spall strength in pure aluminum is calculated from the measured free surface velocity profile as a function of the tensile strain rate. The results show a rapid increase with the tensile strain rate more than 106s−1. The damage influence on the tensile spall of laser-irradiated pure aluminum is analyzed by experimental and numerical studies. In the frame of percolation theory, a physical model is proposed to describe the rapid stress release due to void coalescence. A good agreement between the calculation and the experiment is obtained.

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.

Hugoniot measurements on the highly dense, pure B4C polycrystal were performed by the inclined-mirror method to study the elastoplastic transition and to search phase transition. In inclined-mirror streak photographs, the smoothly jagged structure was observed at the free-surface shape in the plastic region. The Hugoniot-elastic limit (HEL) has been determined to be approximately 19.5GPa. In the plastic region, a kink was observed at a particle velocity of around 1.26km∕s. The shock velocity (US)–particle velocity (UP) Hugoniot relations in the plastic region were given by US=3.7+5.4UPkm∕s in the Up range of 0.54–1.26km∕s and US=9.61+0.73UPkm∕s in the Up range of 1.26–4.3km∕s. The S value (0.73) in US=C0+SUP above UP=1.26km∕s is significantly small compared with the result of Vogler et al. [J. Appl. Phys. 95, 4173 (2004)], and was much smaller than those of many oxides and nitrides. This material behaved as an elastoisotropic solid above the HEL and showed a large and linear change in the pressure-density...

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.