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Shocked forsterite above 250 GPa indicates incongruent crystallization of MgO, its phase transition, and remelting., Forsterite (Mg2SiO4) is one of the major planetary materials, and its behavior under extreme conditions is important to understand the interior structure of large planets, such as super-Earths, and large-scale planetary impact events. Previous shock compression measurements of forsterite indicate that it may melt below 200 GPa, but these measurements did not go beyond 200 GPa. We report the shock response of forsterite above ~250 GPa, obtained using the laser shock wave technique. We simultaneously measured the Hugoniot and temperature of shocked forsterite and interpreted the results to suggest the following: (i) incongruent crystallization of MgO at 271 to 285 GPa, (ii) phase transition of MgO at 285 to 344 GPa, and (iii) remelting above ~470 to 500 GPa. These exothermic and endothermic reactions are seen to occur under extreme conditions of pressure and temperature. They indicate complex structural and chemical changes in the system MgO-SiO2 at extreme pressures and temperatures and will affect the way we understand the interior processes of large rocky planets as well as material transformation by impacts in the formation of planetary systems.

Earth’s outer core is liquid and dominantly composed of iron and nickel (~5–10 wt%). Its density, however, is ~8% lower than that of liquid iron, and requires the presence of a significant amount of light element(s). A good way to specify the light element(s) is a direct comparison of density and sound velocity measurements between seismological data and those of possible candidate compositions at the core conditions. We report the sound velocity measurements of a model core composition in the Fe-Ni-Si system at the outer core conditions by shock-wave experiments. Combining with the previous studies, we found that the best estimate for the outer core’s light elements is ~6 wt% Si, ~2 wt% S, and possible ~1–2.5 wt% O. This composition satisfies the requirements imposed by seismology, geochemistry, and some models of the early core formation. This finding may help us to further constrain the thermal structure of the Earth and the models of Earth’s core formation.

Shock-recovery and annealing experiments on basalt-baddeleyite mixtures were undertaken to evaluate shock effects on U–Pb isotopic systematics of baddeleyite. Shock pressures up to 57 GPa caused fracturing of constituent phases, mosaicism of olivine, maskelynitization of plagioclase, and melting, but the phase transition from monoclinic baddeleyite structure to high-pressure/temperature polymorphs of ZrO2 was not confirmed. The U–Pb isotopic systems of the shock-loaded baddeleyite did not show a large-scale isotopic disturbance. The samples shock-recovered from 47 GPa were then employed for annealing experiments at 1000 or 1300 °C, indicating that the basalt-baddeleyite mixture was almost totally melted except olivine and baddeleyite. Fine-grained euhedral zircon crystallized from the melt was observed around the relict baddeleyite in the sample annealed at 1300 °C for 1 h. The U–Pb isotopic systems of baddeleyite showed isotopic disturbances: many data points for the samples annealed at 1000 °C plotted above the concordia. Both radiogenic lead loss/uranium gain and radiogenic lead gain/uranium loss were observed in the baddeleyite annealed at 1300 °C. Complete radiogenic lead loss due to shock metamorphism and subsequent annealing was not observed in the shock-loaded/annealed baddeleyites studied here. These results confirm that the U–Pb isotopic systematics of baddeleyite are durable for shock metamorphism. Since shergottites still preserve Fe–Mg and/or Ca zonings in major constituent phases (i.e. pyroxene and olivine), the shock effects observed in Martian baddeleyites seem to be less intense compared to that under the present experimental conditions. An implication is that the U–Pb systems of baddeleyite in shergottites will provide crystallization ages of Martian magmatic rocks.

Shock-recovery experiments on mixtures of olivine and water with gas (air) were performed in a previous study to demonstrate water-mineral interactions during impact events (Furukawa et al., 2007). The products of these former experiments were investigated in the present study using transmission electron microscopy, scanning electron microscopy, and X-ray powder diffraction with the aim of finding evidence of aqueous alteration. Serpentine formed on the surface of shocked olivine with well-developed mosaicism. The yield of serpentine depended on the water/olivine ratio in the starting material, indicating progressive serpentinization under water-rich conditions. Comminution and mosaicism were developed in shocked olivine grains. The temperature and pressure changes of the samples during the experiments were estimated by constructing Hugoniots for mixtures of olivine and water, combined with the results of an additional fracturing experiment on a shocked container. Pressures and temperatures reached 4.6-7.2 GPa and at least 230-390 degrees C, respectively, for 0.7 mu s during in-shock compression. Post-shock temperatures reached a maximum of similar to 1300 degrees C, when the shock wave reached the gas in the sample cavity. The serpentine formed after the post-shock temperature maximum, most likely when temperatures dropped to between 200 and 400 degrees C. This is the first experiment to demonstrate the formation of phyllosilicates using heat supplied by an impact. The present results and estimations suggest that phyllosilicates could form as a result of impacts into oceans as well as by impacts on terrestrial and Martian crustal rocks, and on some asteroidal surfaces, where liquid or solid H(2)O is available. A significant amount of phyllosilicates would have formed during the late heavy bombardment of meteorites on the Hadean Earth, and such phyllosilicates might have affected the prebiotic carbon cycle. (C) 2011 Elsevier Ltd. All rights reserved.

In situ time-resolved measurements of shock wave profiles for anisotropic fluorite crystals with two different crystal orientations were carried out up to a pressure of 34 GPa that is above the transition pressure for the fluorite to cotunnite phase. They indicate that the Hugoniot elastic limit varies with the crystal orientation and final pressure and that high-pressure phase transition from fluorite to a cotunnite-type structure occurs at 13 GPa in 10–20 ns for CaF2 [100]-oriented crystals and at 17 GPa in more than 50 ns for CaF2 [111]-oriented crystals, respectively. These results are in disagreement with those from static compression. The phase transition at static pressures has been known to be very sluggish, but the present results indicate a large sensitivity of kinetics to the relationship between crystallographic orientation and shock direction, supporting a martensitic mechanism for the fluorite to cotunnite phase transition that is enhanced by the effect of shock-induced shear. It is also helpful to explain the observation that the in situ emission spectra for shocked Eu-doped fluorite became weak and had no shift above ~15 GPa.

Moganite, a monoclinic SiO2 phase, has been discovered in a lunar meteorite. Silica micrograins occur as nanocrystalline aggregates of mostly moganite and occasionally coesite and stishovite in the KREEP (high potassium, rare-earth element, and phosphorus)–like gabbroic-basaltic breccia NWA 2727, although these grains are seemingly absent in other lunar meteorites. We interpret the origin of these grains as follows: alkaline water delivery to the Moon via carbonaceous chondrite collisions, fluid capture during impact-induced brecciation, moganite precipitation from the captured H2O at pH 9.5 to 10.5 and 363 to 399 K on the sunlit surface, and meteorite launch from the Moon caused by an impact at 8 to 22 GPa and >673 K. On the subsurface, this captured H2O may still remain as ice at estimated bulk content of >0.6 weight %. This indicates the possibility of the presence of abundant available water resources underneath local sites of the host bodies within the Procellarum KREEP and South Pole Aitken terranes., 月の地下に大量の氷が埋蔵されている可能性 --月隕石から氷の痕跡である「モガナイト」を発見、月で利用可能な水資源に期待--. 京都大学プレスリリース. 2018-05-09.

Shock recovery experiments were conducted on porous mixtures (initial porosity 35 ± 5%) in silicate–metal and silicate–metal–sulfide systems in an attempt to simulate impact phenomena of unconsolidated porous materials similar to ordinary chondrites in a wide range of shock pressures from 20 to 70 GPa. The textures and chemical compositions of shocked samples were investigated in detail. Features such as grain deformation, fracture density decrease, and heterogeneous meltings are found. At

Shock waves in solids are more complex than those in gases, because a solid behaves as elastic and plastic media depending upon the stress level and strain rate.

A series of shock recovery experiments up to ~50 GPa were performed on reactions to form carbon nitrides. Nitrogen-rich starting materials, included a C-N-O amorphous precursor, dicyandiamide, melamine, and a mixture of carbon tetrahalide and sodium dicyanoamide, were used and the recovered samples were investigated by X-ray diffraction technique, elemental analysis, transmission electron microscopy and so on. Experimental results showed formation of a new carbon nitride, high stability of melamine up to a shock pressure of 37 GPa, and production of amorphous C-N materials with a highest N/C ration of 1.26 from the reaction between carbon tetrahalide and sodium dicyanoamide. We extended to the system C3N4-Si3N4 based on the recent results on synthesis of spinel-type nitrides. Shock wave chemical reactions provide a route for synthesizing novel materials including not only high-pressure phases but also metastable, unique substances.

Changes in the anisotropy of the low-field magnetic susceptibility (AMS) of basaltic andesite were induced by decaying stress waves and subsequently quantified. An initial shock pressure of 5 GPa was generated in a block of the target rock through impacting with a cylindrical projectile. Following the impact, the maximum or minimum principal susceptibility axes of the target were reoriented toward the shock direction at low (0.5–3 GPa) or high (>3 GPa) estimated shock pressures, respectively. Subtraction of the initial AMS demonstrated a parallelism between the induced susceptibility axes and the shock direction. These results suggest a potential application of AMS as an indicator of the propagation directions of stress waves generated in rocks at terrestrial impact structures.

The time-resolved emission spectra of the CaF2(Eu) crystal subjected to impact-induced shock compression in the inelastic region have been measured up to 31.6 GPa and the effect of shock and release waves on the Eu emission spectrum has been recorded. The Eu2+ spectrum centered at ~425 nm shifts toward the longer wavelength with a shock pressure of up to ~15 GPa, but no further shift has been observed at higher pressures. Emission spectra under static pressure have also been measured up to 10.2 GPa and compared with those under shock compression. A blue Eu2+ emission at ~425 nm and a sharp orange Eu3+ emission at ~590 nm are observed under static pressure. A large pressure shift of ~2.2 nm/GPa is observed for the blue emission at pressures of up to ~10 GPa, but the orange emission spectrum hardly moves against pressure. The Hugoniot determined for the CaF2(Eu) single crystal is Us=5.15+1.18Up.

The high stress Us-Up Hugoniot equation of state (EOS) of a zirconium-based bulk metallic glass (BMG, Zr57Nb5Cu15.4Ni12.6Al10) was determined using plate impact experiments on disk-shaped samples of 10-mm diameter and 2-mm thickness. The National Institute for Materials Science (NIMS) two-stage light-gas gun was used for the high stress measurements (∼26 to 123 GPa), and the Georgia Institute of Technology (GT) single-stage gas gun was used for the lower stress measurements (∼5 to 26 GPa). The NIMS experiments were instrumented with streak photography and used the inclined mirror (IM) method to simultaneously measure shock velocity and free surface velocity. The GT experiments used polyvinylidene fluoride (PVDF) stress gages and velocity interferometry (VISAR) to simultaneously measure the shock velocity, free surface velocity, and stress. Results from the streak camera records and PVDF gages + VISAR traces, as well as impedance matching calculations, were used to generate the Us-Up Hugoniot EOS for the BMG over a wide range of stresses. The Us-Up data show evidence of a low pressure phase, a transition to a mixed phase region at ∼26 GPa, followed by transition at ∼67 GPa to a high-pressure phase of bulk modulus of 288 GPa.

Shock recovery experiments on MgSO4, CaSO4, and their hydrates (kieserite, epsomite, and bassanite) were performed to investigate shock-induced dehydration and decomposition at shock pressures up to 36 GPa. The recovered solid samples indicated dehydration at pressures below 24 GPa, but no clear evidence was found for possible decomposition of MgSO4 and CaSO4 to produce MgO or CaO as final products. These sulfates and hydrates have been observed on the surface of Mars, and the present experimental results can be applied towards understanding the presence of surface water on Mars and the recycling of water by impacts. This finding that the sulfate hydrates undergo dehydration upon impact, as well as the fact that the sulfates CaSO4 and MgSO4 absorb moisture, suggests the total amount of water on Mars has remained almost unchanged since the time of formation of the planet.

Shock-recovery experiments were performed targeting an olivine, iron, and water mixture to simulate a low-velocity ocean impact event. The maximum pressure in the sample container reached 20 GPa during the experiments. Ultrafine particles (UPs) of olivine and metal oxides were newly formed, even at pressures less than their vaporization pressure (150–200 GPa). Impedance-match and thermodynamic calculations suggest that supercritical water formed during the shock wave traversal. Such supercritical water dissolves impacted materials and precipitates UPs. Results of our experiments further suggest that many extraterrestrial objects that have impacted on oceans might have been converted to large masses of UPs and probably influenced the climate and UV shielding, especially during the late Hadean and early Archean eras.

Current trends in research on shock experiments to understand the fundamentals of impact phenomena were briefly reviewed. It was addressed that dynamic behavior of volatile-bearing materials is important although many experimental difficulties are recognized technically. The subject under various initial conditions will become more critical for detailed understanding of the impact phenomena in the universe. Overhauling of the current attitude in this research area and new development with a long-term perspective are required in Japan.

Since the discovery of spinel nitrides in 1999, there has been a lot of effort in basic science to further develop advanced nitrides and electronic nitrides. The aim and scope of the research in this field is to synthesize novel nitrides for structural and functional applications. Silicon-based spinel nitrides combine ultrahigh hardness with high thermal stability against decomposition in different environments, suggesting potential applications as cutting tools. These materials are also expected to show interesting optoelectronic properties, which may lead to applications in light-emitting diodes. The synthesis of spinel silicon and germanium nitrides at ultrahigh pressures and temperatures, as well as the successful synthesis of tin nitride at ambient pressure, has created an enormous impact on both the basic science and technological development of advanced nitrides. Moreover, the discovery of novel phases of transition metal nitrides, such as Zr3N4 and Hf3N4 with a Th3P4 structure, as well as the recently reported nitrides of Pt and Mo, demonstrates the scientific potential of highpressure synthesis techniques in the field of materials science. Here, the state of the art in the field of novel hard materials based on nitrides synthesized reproducibly under high pressure is reviewed.

Hugoniot equation-of-state and release adiabat results are presented for magnesite to a pressure of ~140 GPa. A sharp change in the shock velocity and particle velocity relation suggests that a phase transition to a high-pressure phase occurs at 107±10 GPa. Decomposition of magnesite was observed by abrupt volume expansion during the pressure release from a pressure over the phase transition and by investigating post-shock magnesites recovered from hypervelocity impacts of mini-flyers performed using a laser-driven acceleration. Post-shock magnesites above 95 GPa contained MgO crystallites and the amount of MgO increased with increasing shock pressure.

Shock reactions between CX4 (X=Br or I) and NaN(CN)2 were investigated to prepare carbon nitrides. The post shock samples were characterized by the powder X-ray diffraction (XRD) technique. The XRD spectrum of the product showed a peak in the range of 0.324–0.336 nm in d -value corresponding to the (002) basal plane diffraction in graphitic structure. Elemental analysis (C, H, N, O) of the product showed that the atomic ratio of nitrogen to carbon (N/C) ranged from 0.38 to 1.3. Analysis of data revealed that the d -value increased and the nitrogen content decreased with the increase of the impact velocity.

Shock recovery experiments of sinoite (Si 2 N 2 O) were carried out in a pressure range of 28–64 GPa. Post-shock samples were investigated by optical microscopy, X-ray diffraction, micro Raman spectroscopy, and transmission electron microscopy coupled with energy dispersive X-ray analysis. Sinoite was stable up to ~28 GPa, being partially amorphous at 34 GPa, and almost completely amorphized above 41 GPa. These results are consistent with the observation that sinoite is found in enstatite chondrites classified into shock stage S2, and imply that sinoite may not be a crystallization product from impact melts and that it may be a metamorphic product of high temperatures and relatively low pressure.

A series of shock recovery experiments up to ∼50 GPa were carried out on three nitrogen-rich materials of a C–N–O amorphous precursor, dicyandiamide and melamine. The powder X-ray diffractions (XRD) of recovered samples show that carbon nitride phases are formed. They are β-C 3 N 4 and a new crystalline phase. The new phase is indexed as a monoclinic cell with a =0.981 nm, b =0.723 nm, c =0.561 nm, β =95.2° and V cell =0.3966 nm 3 . Melamine was very stable and did not decompose up to ∼37 GPa. This new phase is considered to form during the adiabatic release process with an extremely high quenching rate (∼10 9 K/s) and shock compression may provide a novel synthesis route for various C–N phases from appropriate organic materials.

High-temperature oxide melt drop solution calorimetry was used to study the energetics of formation of cubic silicon nitride prepared at high pressure. The standard enthalpy of formation of c-Si3N4 is −776.3 ± 9.5 kJ/mol. The calorimetric measurement of Si3N4 in 3Na2O·4MoO3 solvent was validated by comparing the enthalpy of formation for β–Si3N4 with previous work using alkali borate solvent. The enthalpy of transformation from β– to c-Si3N4 is 80.2 ± 9.6 kJ/mol. This value appears consistent with the observed synthesis conditions, which do not represent reversed equilibrium reactions.

The excellent shock-absorbing performance of WS2 and MoS2 nanoparticles with inorganic fullerene-like structures (IFs) under very high shock wave pressures of 25 GPa is described. The combined techniques of X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, thermal analysis, and transmission electron microscopy have been used to evaluate the diverse, intriguing features of shock recovered IFs, of interest for their tribological applications, thereby allowing improved understanding of their antishock behavior and structure-property relationships. Two possible failure mechanisms are proposed and discussed. The supershock-absorbing ability of the IF-WS2 enables them to survive pressures up to 25 GPa accompanied with concurrent temperatures of up to 1000 degrees C without any significant structural degradation or phase change making them probably the strongest cage molecules now known.

Ammonia is a necessary precursor of amino acids in terms of the origin of life on the early Earth. However, the formation of ammonia is problematic in the non-reducing atmosphere that presently believed on the early Earth. The abiotic reduction of nitrogen is, therefore, debated currently in the oceanic and hydrothermal conditions [[J.A. Brandes, N.Z. Boctor, G.D. Cody, B.A. Cooper, R.M. Hazen, H.S. Yoder Jr., Abiotic nitrogen reduction on the early Earth, Nature 395 (1998), 365–367; D.P. Summers, S. Chang, Prebiotic ammonia from reduction of nitrite by iron (II) on the early Earth, Nature 365 (1993), 630–633; M. Dorr, J. Kaessbohrer, R. Grunert, G. Kreisel, W.A. Brand, R.A. Werner, H. Geilmann, C. Apfel, C. Robl, W. Weigand, A possible prebiotic formation of ammonia from dinitrogen on iron sulfide surfaces, Angew. Chem. Int. Ed. 42 ( 2003), 1540–1543 [1] , [2] , [3] ]. Here we perform shock experiments with Cu3N (nitrogen source), Fe and H2O, supposing an impact event of an extraterrestrial object to the ocean. The results demonstrate clearly the formation of ammonia in high yields. This reduction process from nitrogen to ammonia is highly probable as “local and transitional” phenomena on the early Earth when the heavy bombardment by extraterrestrial objects had become less intense but still continued in the period from 4.3 to 3.5 Gyr ago.

The phase transitions of α-Si 3 N 4 and β-Si 3 N 4 have been investigated by shock compression through the recovery technique and Hugoniot measurements. α- and β-Si 3 N 4 are transformed into a cubic spinel structure (c-Si 3 N 4 ). The yield of c-Si 3 N 4 increases with increasing shock pressure and reaches 100% at 63 GPa. The shock-synthesized c-Si 3 N 4 powders are nanocrystals and display a high-temperature metastability up to about 1620 K. c-Si 3 N 4 is one of the hard materials based on the measured equation of state, c-Si 3 N 4 powders have been characterized by electron microscopy and 29 Si magic angle spinning NMR spectroscopy. The purification and separation method has been developed to obtain pure c-Si 3 N 4 powders.

γ-Si3N4 is a nitrogen-based ultra-hard ceramic with Si atoms occupying both tetrahedral and octahedral sites in a spinel structure. Soft-x-ray emission and absorption spectra of γ-Si3N4 are presented, which together provide an experimentally determined bandgap of 4.30 ± 0.25 eV. Information about localized partial density of states (LPDOS) of the non-equivalent Si sites is presented.

A new high-pressure phase of LiAlO 2 has been recovered through a shock recovery technique at pressures above 9 GPa. This new phase has been refined as a tetragonal structure with lattice parameters of a =0.38866(8) nm and c =0.83001(18) nm. Its calculated density is 3.51 g/cm 3 , about 34% denser than γ -LiAlO 2 . The aluminum and lithium cations in this new phase are six-fold coordinated, as in α -LiAlO 2 and the structure of this new phase is similar to tetragonal LiFeO 2 . This new high-pressure phase is stable at temperatures up to 773 K.

Shock compression of a TiN and CuO mixture up to 48 GPa and characterization of post shock samples by Raman spectroscopy and X-ray diffraction techniques have realized a fast redox reaction that yields well-crystallized rutile (TiO2) in less than 1 μs. Experimental results indicate that TiN itself is stable at high nitrogen pressure and does not decompose into Ti3N4+Ti at shock pressure up to 42 GPa.

We have developed laser-driven shock compression and sample recovery techniques for exploring novel materials. Strong shock waves are generated by hypervelocity impacts of mini-flyer accelerated by pulsed laser ablation. We have measured the mini-flyer velocity using a time-resolved velocimeter (VISAR), with the impact pressures estimated by means of the impedance match solution method. Through sample recovery techniques, the high-pressure phase transitions and dynamic stability of cubic diamond and hexagonal BN are investigated and compared in terms of shock compression durations.

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.

New phases of Si 3 N 4 that may be stable at higher pressure than spinel have been searched using a first-principles plane-wave pseudopotential method. The CaTi 2 O 4 -type phase is found to be the prime candidate for the post-spinel phase among six phases selected on the analogy to high-pressure oxides. The phase transformation from the spinel is predicted to occur at 210 GPa. All silicon atoms of the new phase are coordinated by six anions, similar to the case of the high-pressure forms of SiO 2 and SiC. Because of its high energy at zero pressure, this new phase may be difficult to quench. The bandgap increases with an increase of pressure when compared in the same polymorph. However, the bandgap and the net charge decrease in the order of β, spinel, and CaTi 2 O 4 -type phases at zero pressure. The theoretical bulk modulus of the CaTi 2 O 4 -type phase is comparable with that of spinel.

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.

We present the formation of cubic Si6−zAlzOzN8−z (z=1.8 and 2.8) spinels by shock compressions from the corresponding β-sialon. Formed sialon spinels coexist with considerable amounts of the amorphous phase. The amorphization is considered to be a solid–solid reaction due to the sluggish phase transition under shock compression. The lattice parameter of the spinel increases and the density decreases with increasing z parameter. Shock-synthesized sialon spinels are nanocrystals with most grain sizes less than 30 nm and consist of main units of SiN4, SiN6 and AlO6.

Spinet-type Si3N4 has been synthesized under high pressures and high temperature conditions. Some structural characteristics have been investigated. Recent results are reviewed and compared with those of compounds containing six-fold coordinated Si. Some perspective will be given.

Shock-recovery experiments were carried out on the Allende CV carbonaceous chondrite using a single-stage propellant gun. Allende samples were impacted at room temperature with peak shock pressures of 11 and 21 GPa. Another samples were impacted twice from the same direction at room temperature with first/second shock pressures of 11/11 GPa and 21/21 GPa to study shock effects by multiple impacts. The other samples were preheated and impacted at 300°C and 11 GPa, 300°C and 21 GPa, and 600°C and 21 GPa to study shock effects at high temperature. In all recovered samples, chondrules were flattened perpendicular to the direction of shock wave propagation and showed alignment. The whole shapes and microtextures of flattened chondrules are very similar to those observed in naturally shocked CV chondrites. The degree of chondrule flattening increases with shock intensity, initial temperature, and the number of impacts. Silicate minerals in chondrules shocked at high temperatures were blackened due to injection of Fe, Ni, and S-rich melt into fine fractures. The matrix was compressed to varying degrees by impacts. Matrices that were impacted at high temperatures melted partially to form veins filled by a mixture of silicate fragments and Fe, Ni, and S-rich melt. A detailed comparison of textures between experimentally shocked Allende and naturally shocked CV chondrites indicates that the Allende sample impacted twice at 21 GPa and room temperature is very similar to the Leoville and Efremovka CV chondrites that have experienced the highest level of impacts among carbonaceous chondrites of petrologic type 3. The Allende sample impacted once at 21 GPa and room temperature is similar to the Gronsnaja CV chondrite. The Allende samples impacted at 300 and 600°C differ in texture from any naturally shocked CV chondrite. These results suggest that CV carbonaceous chondrites found so far on the Earth have undergone mild impacts on cold meteorite parent bodies.

Shock recovery experiments of plagioclase feldspar in contact with pyroxene, shock-loaded at 36–53 GPa, showed that monomineralic glass of plagioclase was mixed with brecciated pyroxenes with virtual absence of mixed-mineral melts. This amorphous phase of plagioclase produced at 36–42 GPa displays enormously high ductility although the amorphous phase is less likely to be a quenched high-pressure melt because both shock and post-shock bulk temperature cannot exceed the melting point. The results suggest that alkaline components in feldspar can be extensively mobilized even in a very short duration of shock, which can never be achieved by normal diffusion in the same time scale. Since feldspar is a major carrier phase of alkaline volatiles, shock mobilization mechanism may explain shock disturbance of Rb–Sr and 39 Ar– 40 Ar ages of basaltic shergottites.

Synthetic single crystal forsterites have been shocked up to 82GPa and examined by profile analysis of Raman spectra. Raman bands due to Si–O external vibrations of translational and rotational modes are shifted to higher frequencies with the increase of shock pressure without band broadening. At the internal vibration of Si–O stretching modes, the bands show no shift up to 46GPa, while above that pressure they are shifted to the higher frequencies with distinguishable band broadening. Although Mg(M2)–O translational band is not shifted, its band broadening increases linearly with increasing shock pressure. Over the shock pressure of 46GPa, the Mg–O band is shifted gradually to the lower frequencies as opposed to that all of the internal bands of υ 1 to υ 4 have tendency to move to higher frequencies, whereas the Mg–O band width is doubled. These variations indicate that the lattice deformation resides heterogeneously in the crystal structure of the shocked forsterite, in which the SiO4 tetrahedron is compressed differently between the pressure ranges below and above the 46GPa in the plastic region. In the lower shock region, plastic deformation is caused mainly by the translational and rotational strain, while over the shock pressure of 46GPa, abrupt plastic changes occur in both tetrahedral and octahedral polyhedra, causing positive and negative residual stresses in the structure, respectively. The transition pressure of 46GPa coincides nearly with the onset pressure of phase transition, 50GPa, on the pressure-density Hugoniot of shocked forsterite (Syono et al., 1981).

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.

A series of shock-recovery experiments were carried out on the Murchison CM carbonaceous chondrite by using a single-stage propellant gun. The Murchison samples were shocked in nine experiments at peak pressures from 4 to 49 GPa. The recovered samples were studied in detail by using an optical microscope, a scanning electron microscope and an electron-probe microanalyzer. Chondrules are flattened in the plane of the shock front at 4 to 30 GPa. The mean aspect ratio of chondrules increases from 1.17 to 1.57 roughly in proportion to the intensity of shock pressure up to ∼25 GPa. At 25 to 30 GPa, the mean aspect ratio does not increase further, and chondrules show increasingly more random orientations and degrade their preferred orientations, and at ∼35 GPa, they are extensively disrupted. Most coarse grains of olivine and pyroxene are irregularly fractured, fracture density increases with increasing shock pressure and at ∼30 GPa almost all are thoroughly fractured with subgrains of Local shock melting occurs as melt veins and pockets at 20 to 30 GPa. Fracture-filling veins of fine grains of matrix are also produced at 25 to 30 GPa. The melts and the fine grains seem to result mainly from frictional heating due to displacement along fractures. At ∼35 GPa, melting occurs pervasively throughout the matrix. The melts are mainly produced from the matrix; however, they are consistently more enriched in Fe, S, and Ca, which indicates that these elements are selectively incorporated into the melts. The melts contain tiny spherules of Fe-Ni metal, Fe sulfide, and numerous vesicles. At 49 GPa, the matrix is totally melted and coarse grains of olivine are partially melted. The melts contain much larger vesicles (50–300 μm in diameter) than those in the samples shocked at lower pressures, which indicates that much more intense devolatilization and gas expansion took place. For the purpose of comparing shock thermal effects between the experimentally shocked samples and naturally shocked targets (surface materials in the Murchison parent body), we calculated internal energy increase for compression by multiple shock wave reflections (experimental case) and for compression by a single shock wave (natural case). The results suggest that postshock thermal effects observed at each experiment may be attained by impact on the natural targets at a considerably lower shock pressure than the peak shock pressure. From the results of our experiments and calculations, we conclude that if the Murchison parent body were shocked on the surface at pressures higher than ∼25 GPa, shocked material would probably undergo drastic increase in the degree of comminution and simultaneous generation of strong expansive forces on pressure release. Thus the results support the hypothesis of Scott et al. (1992) that volatile-rich carbonaceous chondrites shocked above 20 to 30 GPa escaped from the parent body and formed particles that are too small to survive as meteorites.

We have carried out impact experiment of Al mini-flyers, which have been accelerated by high intensity pulsed lasers to generate ultra-high, dynamic pressures. A laser intensity of about 50 TW/cm2 can achieve an impact velocity of 40 km/s, corresponding to a terapascal range of pressure. Laser-shock recovery experiments of hBN and SiC were investigated up to 650 GPa, and recovered samples were compared with previousresults by conventional shock experiments. Analyses of recovered samples reveal some differences in the quenched phase, which may apparently be attributed to short durations of laser-shock compressions.

We have examined synthetic single crystals of forsterites shocked up to 82GPa using a single stage propellant gun. Even in forsterites shocked to 82GPa, any decomposition phases such as spinels or silica glasses and fine-grained MgO could not be detected by X-ray diffraction and EPMA methods. Profile analysis of X-ray diffraction peaks of the shocked forsterites using a Gandolfi camera has been done to detect the maximum strain. The maximum strain derived from Williamson-Hall plot of about 20 diffraction angles and their integral maximum breadths had a linear relation to the shock pressures, in which the elastic limit could not be detected. Unit cell dimensions did not show any changes against the shock pressures, however the increasing broadening of X-ray diffraction peaks occurred with the increase of shock pressures, indicating the homogeneous lattice distortion due to shock pressures. This is the first quantitative analysis that enables us to estimate an experienced shock pressure from the X-ray peak broadening, and is applied to the Dhurmsala LL6 chondrite; the pressure estimated in this study is ranging from 24.0 to 37.8GPa in contrast to the range of 5 to 20 GPa (shock stage S3 by Stoffler et al., 1991) estimated from the texture of olivine in the chondrite.

Synthetic single crystals of forsterite shocked up to 82.0GPa have been examined by the profile analysis of photo-luminescence spectra. The forsterites give rise eight broad bands in photo-luminescence spectra in contrast to unshocked forsterite having usually faint and obscure luminescence. Their intensity increases linearly with increasing the pressure up to 46.2GPa, while over the pressure the intensity abruptly decreases. The intensity variation also has a close relationship to Raman band shift and broadening, implying the variable degree of lattice deformation in shocked forsterites. The critical shock pressure of 46.2 GPa nearly corresponds to the onset shock pressure of phase transition (50GPa) on the Hugoniot curve of forsterite (Syono et al., 1981). Luminescence mechanism in the shocked forsterite may be the emission transition between the deformed electron levels with vibrational sub-levels in its [SiO4]4− molecular orbitals. This is a new type of photo-luminescence in silicate minerals that can be called as the deformation luminescence.The correlation between the intensity of photo-luminescence and shock pressure loaded on the forsterites is formulated, and applied to estimate the shock pressure of Dhurmsala LL6 chondrite; it ranges from 26 to 29 GPa.

A series of recovery experiments was conducted using a propellant single-stage gun on starting materials of both α-SiC and β-SiC. X-ray examination on the recovered samples indicated that obvious polytype transformations among 3C, 6H, and 15R took place. To the α-SiC starting material, 15R tends to increase and 6H tends to decrease, while a small amount of α-SiC form transforms to 3C type, along with increasing the shock temperature and pressure. X-ray diffraction analysis showed that the β-SiC polytype is transformed into rhombohedral forms. From results of both types of SiC samples, rhombohedral polytypes seem to be the favored shock modification. The effects of shock pressure and shock temperature and their heterogeneous distribution on these polytype transitions are discussed in detail. Analysis showed that these polytype transitions resulted from the stacking sequence changes of SiC atom layers.

Silicon nitride thin film was fabricated by pulsed laser deposition using KrF excimer laser and a silicon nitride compact as a target. The deposition was carried out on Al 2 O 3 (0001) at 1173K in N 2 gas pressure of 0.27 Pa. The X-ray diffraction did not provide any structural information of the deposited thin films except that it is composed of amorphous and/or micro-crystalline structure. X-ray absorption near edge structures at Si-K edge revealed that local arrangement of Si is not random. It should be composed of SiN 4 unit similar to the case of α-Sι 3 N 4 crystal. Metallic Si component cannot be found in XANES.

T. A. Pikuz, A. Ya. Faenov, N. Ozaki, N. J. Hartley, B. Albertazzi, T. Matsuoka, K. Takahashi, H. Habara, Y. Tange, S. Matsuyama, K. Yamauchi, R. Ochante, K. Sueda, O. Sakata, T. Sekine, T. Sato, Y. Umeda, Y. Inubushi, T. Yabuuchi, T. Togashi, T. Katayama, M. Yabashi, M. Harmand, G. Morard, M. Koenig, V. Zhakhovsky, N. Inogamov, A. S. Safronova, A. Stafford, I. Yu. Skobelev, S. A. Pikuz, T. Okuchi, Y. Seto, K. A. Tanaka, T. Ishikawa, and R. Kodama, "Indirect monitoring shot-to-shot shock waves strength reproducibility during pump–probe experiments", Journal of Applied Physics 120, 035901 (2016) https://doi.org/10.1063/1.4958796., We present an indirect method of estimating the strength of a shock wave, allowing on line monitoring of its reproducibility in each laser shot. This method is based on a shot-to-shot measurement of the X-ray emission from the ablated plasma by a high resolution, spatially resolved focusing spectrometer. An optical pump laser with energy of 1.0 J and pulse duration of ∼660 ps was used to irradiate solid targets or foils with various thicknesses containing Oxygen, Aluminum, Iron, and Tantalum. The high sensitivity and resolving power of the X-ray spectrometer allowed spectra to be obtained on each laser shot and to control fluctuations of the spectral intensity emitted by different plasmas with an accuracy of ∼2%, implying an accuracy in the derived electron plasma temperature of 5%-10% in pump-probe high energy density science experiments. At nano- and sub-nanosecond duration of laser pulse with relatively low laser intensities and ratio Z/A ∼ 0.5, the electron temperature follows Te ∼ Ilas2/3. Thus, measurements of the electron plasma temperature allow indirect estimation of the laser flux on the target and control its shot-to-shot fluctuation. Knowing the laser flux intensity and its fluctuation gives us the possibility of monitoring shot-to-shot reproducibility of shock wave strength generation with high accuracy.

The Hugoniot data for TeO2 single crystals were obtained for pressures up to ~85 GPa along both the 〈100〉 (a-axis) and 〈001〉 (c-axis) directions using a velocity interferometer system for any reflector and inclined-mirror method combined with a powder gun or two-stage light gas gun. The Hugoniot-elastic limit of TeO2 was determined to be 3.3–4.3 GPa along the c-axes. The shock velocity (U s) versus particle velocity (U p) relation for TeO2 shows a kink around U p = 1.0 km s−1, which suggests a phase transition completes at ~26 ± 2 GPa. The Hugoniot relations of the low and high pressure phase are given by U s = 3.13(5) + 1.10(6)U p for U p 1.0 km s−1, respectively. First-principles geometry optimizations based on the generalized gradient approximation after Perdew, Burke and Ernzerhof method were also performed on TeO2. It suggested that a continuous structure distortion occurs up to 22 GPa, and the lattice parameters b and c abruptly increase and decrease at 22 GPa, respectively, indicating a first-order phase transition to the cotunnite structure phase. The equation of state of the cotunnite phase TeO2 is discussed based on the experimental and simulation results.

— We have carried out shock-recovery experiments on the Allende CV3 carbonaceous chondrite using a single-stage propellant gun and succeeded in reproducing oriented, flattened chondrules like those observed in some natural CV3 chondrites. The Allende samples were shocked at equilibrium pressures of 11 and 21 GPa, which are close to the highest values in shock stages S2 and S3, respectively (Stoffler et al., 1991). Chondrules are flattened nearly perpendicular to the compaction axis with mean aspect ratios of 1.34 and 1.62 at pressures of 11 and 21 GPa, respectively; thus, the degree of chondrule flattening is proportional to the shock intensity. The chondrule flattening and foliation are mainly due to collapse of pores in the matrix under shock pressure. High matrix abundance of CV3 chondrites could result in much apparent chondrule flattening relative to ordinary chondrites. Optical and electron microscope observations show that textural and mineralogical characteristics of chondrules and matrix in the shock-loaded samples are very similar to those observed in naturally shocked CV3 chondrites. Our results provide strong support for the interpretation that the chondrule flattening and foliation in CV3 chondrites were caused by shock-induced pressure due to hypervelocity impacts on the meteorite parent bodies.