The High-Pressure Science and Engineering Center (HiPSEC) is dedicated to the investigation of the behavior of materials under extreme conditions, an interplay between high pressures and temperatures. The pressure scales we are able to access in the laboratory permits conditions beyond those found on Earth (3.3 million x atmospheric pressure), and when combined with temperature ranging from a few milliKelvin up to 10,000 Kelvin materials can undergo a plethora of structural and electronic transformations. The ability to tune to these extreme densities often reveals exotic responses such as the transformation of insulators into metals and – remarkably – vice versa. Structural behavior in such tight spaces has significant influences on bonding and hybridization, and destabilizing inner core electrons to participate in chemical bonding. It is behaviors like these which are challenging “classical” textbook chemistry.
HiPSEC researchers apply high pressure techniques to a broad range of scientific disciplines, including fundamental physics and chemistry research and the study of Earth and planetary interiors, each relevant to the National Nuclear Security Administration program.
Studying the behavior of material under extreme conditions is an exciting endeavor. HiPSEC scientists, including about a dozen of senior staff and approximately 40 students, combine experimental and theoretical techniques to understand these problems. The group has very strong ties with U.S. National Laboratories as users of their facilities (APS, ANL, SNS, etc.) and by collaborating with several National Laboratories scientists (LANL, SNL, LLNL, ORNL, INL). Furthermore, the Center enjoys the privilege of HPCAT membership, which translates into secured access to synctrotron beamtime at one of the world greatest high-pressure laboratory.
The first experimental challenge is subjecting the samples to target pressures and temperatures, which typically involves bulky devices and small samples. We generate static high pressures using diamond anvil cells (DAC), the multianvil press and the piston-cylinder press; we also generate dynamic high-pressures using gas-guns and lasers. In combination with high-pressures we achieve temperatures as low as few K using cryostats and temperatures up to several thousands kelvin using laser heating and resistive heating techniques. The second experimental challenge is probing samples in situ, while experiencing extreme conditions. Powerful synchrotron, neutron and laser beams are used to penetrate the high-pressure devices. From the interpretation of the sample-beam interaction we gain knowledge of samples atomic and electronic structures and physical properties. The techniques most extensively used in HiPSEC include diffraction, absorption and emission spectroscopies, Raman spectroscopy, nuclear forward and inelastic scattering, electron microscopy etc. Some propertied can also be measured directly, for instance we measure thermal conductivity, Seebeck coefficient and electric conductivity. HiPSEC laboratories also include equipment for samples synthesis and characterization.
Theoretical and computational studies focus on material properties under extreme conditions such as high pressure, high stress and/or high temperature. Staff in the theory group develop and implement a wide range of first-principles and many-body modeling and simulation approaches in theoretical exploration and also work closely with experimental groups.