Zircon (ZrSiO4) is a mineral that is widely found in rocks and meteorites on Earth. Zircon has an important role as a “clock” because the uranium contained in trace amounts changes to lead over a geological time of several billion years. In previous studies, the crystal response was observed when zircon was exposed to high temperatures and pressures for a long time. However, a meteorite impact-induced shock only causes high temperature and high pressure for a moment. Therefore, the crystal structure dynamics change, and decomposition under the impact is difficult to observe even with experiments and has not been clarified.

In this study, we performed a laser shock experiment using SACLA to observe the crystal structural response of zircon during shock. The technique generates a shock wave by irradiating a sample with intense laser pulses, and the crystal structure changes before, during, and after the shock are photographed using a bright X-ray pulse. The diffraction peaks of the high-pressure phase, reidite, can be observed at about 28 GPa. At a pressure of about 70 GPa and temperature of 2000 °C, and the material melted and X-ray diffraction peaks of crystals disappeared. The X-ray diffraction image of the shock release process shows that the material crystallized again and returned to a mixed state of zircon and reidite. The results are different from the results of previous experiments conducted under high temperatures and high pressures for a long time, and suggests that decomposition is unlikely to occur in a short time with a laser-induced shock.

The crystal structure of minerals changes depending on the surrounding temperature and pressure. Capturing in detail the phenomena that occur in a very short time, as in this study, has made it clear that time is also a factor in the crystal structure change. In the future, we aim to describe the changes in crystal structure when temperature and pressure are changed on various time scales, and to obtain data that will be useful for estimating the exact scale of meteorite impacts in the past.

Zirconia (ZrO2) ceramics are known to show high-strength and toughness and are used in a wide range of applications including dental materials, medical instruments, jewelry to kitchen knives etc. The reason why zirconia ceramics shows such superior properties is thought to be due to the changes in the crystal structure that occur when cracks are propagating.

However, so far, it has never directly been observed the crystal structure change of zirconia ceramics during breakage. In particular, it has not been clarified that the crystal structure changes when zirconia ceramics are broken by an instantaneous large force such as an impact.

In this study, we investigated shock-loaded zirconia ceramics using time-resolved X-ray observation technique. The experiments were performed at PF-AR, KEK (Japan). As a result, it was demonstrated that the change in crystal structure occurs at the moment of fracture, and the reason why zirconia ceramics exhibit high fracture strength was clarified. This study is elected "featured article" in Applied Physics Letters, and introduced in Scilights. (Press Release) (Scilights and the PDF file) (EurekAlert) (AlphaGalileo)

Baddeleyite is a mineral found in meteorites and on the Earth's surface. Through observations of natural minerals, It has been known that the microstructure of the mineral changes after a meteorite impact (White et al. 2018), but the reason for this change has not been clarified. Clarifying the conditions for this change will allow us to estimate the scale of meteorite impacts in the past, as well as the age of the impact.

In this study, we observed the crystal structure phase transition in ZrO2 mineral, baddeleyite, during shock loading using the shock experimental system at the NW14A beamline of the PF-AR (Japan).

Our shock experiments have revealed that the crystal structure changes to a high-pressure phase immediately after impact, and returns back to its original crystal structure as soon as the shock is released. This reversible change of crystal structure may be the origin of the microstructure exhibited by naturally shocked minerals. In addition, the pressure boundary of the phase transition was determined. (Press Release)

At PF-AR (Photon Factory Advanced Ring) (synchrotron radiation facility of the High Energy Accelerator Research Organization (KEK) in Tsukuba), a powerful and very short (~100 picoseconds) X-ray pulse can be used. Using this advantage, unique time-resolved experiments that capture processes of electrons and atoms in motion have been conducted (e.g., Nozawa et al. 2007, Ichiyanagi et al. 2007, Ichikawa et al. 2011).

In this study, we installed a high-power laser at NW14A beamline for shock experiments, and constructed an experimental system to capture the crystal structure changes in shock-loaded materials using the laser and the synchrotron X-rays. By changing the timing of laser and X-ray irradiation, the dynamics can be investigated with a nanoseconds time resolution.

In 2009, the quasicrystalline mineral icosahedrite was discovered in a meteorite sample (Bindi et al. 2009). Quasicrystals are solids with an atomic arrangement that differs from that of ordinary crystals, and are unique in that they are not found in the rocks that make up the Earth. What are the characteristics of such minerals, how did they form in nature, and through what process did they fall to the earth? Would the atomic arrangement change if it were subjected to the same temperature and pressure conditions that meteorites are subjected to when they hit the earth?

To answer these questions, we used a device called a diamond anvil cell and a laser to pressurize quasicrystalline minerals synthesized in the laboratory to high temperatures and pressures, and investigated their atomic arrangement using X-rays. The experiments were performed at SPring-8 (Japan).

As a result, it was found that the structure was maintained up to a very high pressure of 70 GPa (gigapascals). Later experiments showed that the quasicrystal structure was maintained up to 100 GPa (Stagno et al. 2021).