A Carnegie-led team was able to discover five new forms of silica under extreme pressures at room temperature. Their findings are published by . 
A simulated visual representation of the structural transition from coesite to post-stishovite. The silicon atoms (blue spheres) surrounded by four oxygen atoms (red spheres) are shown as blue tetrahedrons. The silicon atoms surrounded by six oxygen atoms are shown as green octahedrons. The intermediate phases are not filled in with color, showing the four stages that are neither all-blue like coesite nor all-green like post-stishovite. This image is provided courtesy of Ho-Kwang Mao. (Image: Ho-Kwang Mao) Silicon dioxide, commonly called silica, is one of the most-abundant natural compounds and a major component of the Earth's crust and mantle. It is well-known even to non-scientists in its quartz crystalline form, which is a major component of sand in many places. It is used in the manufacture of microchips, cement, glass, and even some toothpaste. Silica's various high-pressure forms make it an often-used study subject for scientists interested in the transition between different chemical phases under extreme conditions, such as those mimicking the deep Earth. The first-discovered high-pressure, high-temperature denser form, or phase, of silica is called coesite, which, like quartz, consists of building blocks of silicon atoms surrounded by four oxygen atoms. Under greater pressures and temperatures, it transforms into an even denser form called stishovite, with silicon atoms surrounded by six oxygen atoms. The transition between these phases was crucial for learning about the pressure gradient of the deep Earth and the four-to-six configuration shift has been of great interest to geoscientists. Experiments have revealed even higher-pressure phases of silica beyond these two, sometimes called post-stishovite. A chemical phase is a distinctive and uniform configuration of the molecules that make up a substance. Changes in external conditions, such as temperature and pressure, can induce a transition from one phase to another, not unlike water freezing into ice or boiling into steam. The team, including Carnegie's Qingyang Hu, Jinfu Shu, Yue Meng, Wenge Yang, and Ho-Kwang, "Dave" Mao, demonstrated that under a range from 257,000 to 523,000 times normal atmospheric pressure (26 to 53 gigapascals), a single crystal of coesite transforms into four new, co-existing crystalline phases before finally recombining into a single phase that is denser than stishovite, sometimes called post-stishovite, which is the team's fifth newly discovered phase. This transition takes place at room temperature, rather than the extreme temperatures found deep in the earth. Scientists previously thought that this intermediate was amorphous, meaning that it lacked the long-range order of a crystalline structure. This new study uses superior x-ray analytical probes to show otherwise--they are four, distinct, well-crystalized phases of silica without amorphization. Advanced theoretical calculations performed by the team provided detailed explanations of the transition paths from coesite to the four crystalline phases to post-stishovite. "Scientists have long debated whether a phase exists between the four- and six-oxygen phases," Mao said. "These newly discovered four transition phases and the new phase of post-stishovite we discovered show the missing link for which we've been searching."
A simulated visual representation of the structural transition from coesite to post-stishovite. The silicon atoms (blue spheres) surrounded by four oxygen atoms (red spheres) are shown as blue tetrahedrons. The silicon atoms surrounded by six oxygen atoms are shown as green octahedrons. The intermediate phases are not filled in with color, showing the four stages that are neither all-blue like coesite nor all-green like post-stishovite. This image is provided courtesy of Ho-Kwang Mao. (Image: Ho-Kwang Mao) Silicon dioxide, commonly called silica, is one of the most-abundant natural compounds and a major component of the Earth's crust and mantle. It is well-known even to non-scientists in its quartz crystalline form, which is a major component of sand in many places. It is used in the manufacture of microchips, cement, glass, and even some toothpaste. Silica's various high-pressure forms make it an often-used study subject for scientists interested in the transition between different chemical phases under extreme conditions, such as those mimicking the deep Earth. The first-discovered high-pressure, high-temperature denser form, or phase, of silica is called coesite, which, like quartz, consists of building blocks of silicon atoms surrounded by four oxygen atoms. Under greater pressures and temperatures, it transforms into an even denser form called stishovite, with silicon atoms surrounded by six oxygen atoms. The transition between these phases was crucial for learning about the pressure gradient of the deep Earth and the four-to-six configuration shift has been of great interest to geoscientists. Experiments have revealed even higher-pressure phases of silica beyond these two, sometimes called post-stishovite. A chemical phase is a distinctive and uniform configuration of the molecules that make up a substance. Changes in external conditions, such as temperature and pressure, can induce a transition from one phase to another, not unlike water freezing into ice or boiling into steam. The team, including Carnegie's Qingyang Hu, Jinfu Shu, Yue Meng, Wenge Yang, and Ho-Kwang, "Dave" Mao, demonstrated that under a range from 257,000 to 523,000 times normal atmospheric pressure (26 to 53 gigapascals), a single crystal of coesite transforms into four new, co-existing crystalline phases before finally recombining into a single phase that is denser than stishovite, sometimes called post-stishovite, which is the team's fifth newly discovered phase. This transition takes place at room temperature, rather than the extreme temperatures found deep in the earth. Scientists previously thought that this intermediate was amorphous, meaning that it lacked the long-range order of a crystalline structure. This new study uses superior x-ray analytical probes to show otherwise--they are four, distinct, well-crystalized phases of silica without amorphization. Advanced theoretical calculations performed by the team provided detailed explanations of the transition paths from coesite to the four crystalline phases to post-stishovite. "Scientists have long debated whether a phase exists between the four- and six-oxygen phases," Mao said. "These newly discovered four transition phases and the new phase of post-stishovite we discovered show the missing link for which we've been searching."
These graphics show the static patterns for 1-D stripy charge order (a) and for 2-D checkerboard charge order (b), within the 2-D Cu-O plane. (Image: R. Comin et al) Riccardo Comin, lead author on a new paper in ("Broken translational and rotational symmetry via charge stripe order in underdoped YBa
Figure 1: Efimov states of neighboring energy always differ by the same scale factor of 22.7, providing evidence of a fundamental university of these exotic states. (Image: Masahito Ueda, RIKEN Center for Emergent Matter Science) Many physical phenomena are based on the forces between two objects—the gravitational attraction between the Earth and the Sun, and the charge that keeps electrons circulating around an atomic nucleus. These two-body interactions are universal, allowing us to predict the behavior of multibody systems. The reverse is also generally true: if the force between two objects is too weak to form a stable system, no stable system can be formed by adding more objects. Yet, around 40 years ago, Vitaly Efimov predicted that under certain circumstances, resonant interactions could allow a system of three particles to form a stable state when two could not. “An Efimov state is a bound state of three particles that exists even if the attraction between two particles is too small to form a bound state,” says Ueda. Efimov states are predicted to occur in a wide range of systems, from groups of identical bosons to macromolecules such as DNA. They were first observed experimentally in 2006 in a gas of cold cesium atoms. Two parameters describe an Efimov state: the strength of the interaction between the particles and a parameter related to the low-energy ground state of the system. The interaction strength was previously found to be a universal parameter, independent of, for example, the type of atoms in a gas. In fact, a deeper universality also appears to be common for all Efimov states—with increasing energy the sizes of Efimov states always differ by a factor of 22.7 (Fig. 1). To further study the properties of different Efimov systems, Ueda and Horinouchi used computer simulations to determine the energetics of systems based on different interaction forces, such as the force between atoms or the force inside an atomic nucleus. Using a method called functional renormalization-group analysis, they found that at low energies, the onset of the Efimov state is characterized by the same parameters irrespective of the system considered. This commonality of both parameters describing Efimov systems suggests an unexpected and fundamental universality that could extend to even more complex systems, comments Ueda. “With our work, one can envisage that not just three-body phenomena but also related four-body or more-body phenomena may be universal.”