Static and Dynamic High Pressure Mineral Physics

Book Preface

High-pressure mineral physics focuses on the physical properties of materials at high pressure, a field that has shaped our understanding of deep planetary interiors and revealed new material phenomena appearing at extreme conditions. Beginning in the early 1970s, the field has made major contributions to Earth and planetary sciences, condensed matter physics, and high-pressure materials synthesis, through ever-expanding capabilities for reaching higher pressures and probing smaller samples. Ho-Kwang “Dave” Mao has been at the forefront and led the growth of the field since its beginning. Dave started his epic adventure in high-pressure research as a doctoral student at the University of Rochester working in the lab of William A. “Bill” Bassett. After graduating in 1968, Dave began as a postdoctoral fellow at the Geophysical Laboratory (GL) of the Carnegie Institution of Washington, working closely with GL staff scientist Peter Bell. Shortly thereafter, in 1972, Dave was appointed as a staff scientist by GL Director Hatten Yoder, and he retired in 2019 after more than 50 years of discovery, innovation, impact, and influence applying mineral physics in the realms of Earth and planetary science and fundamental materials science.
While a graduate student in Rochester, Dave was first introduced to an entirely new high-pressure technology, the diamond anvil cell, which had recently been developed at the National Institute of Standards and Technology (NIST)/National Bureau of Standards (NBS) (Piermarini, 2001). Dave’s graduate work, measuring lattice parameters of iron and iron oxides using in situ X-ray diffraction, working together with diamond anvil cell (DAC) pioneer Bill Bassett and fellow student Taro Takahashi, set him on his path of high-pressure discovery (Mao et al., 1967, 1974). Upon his arrival at the Geophysical Lab, Dave worked together with Peter Bell (Figure 1.1) on improvements to the original lever-arm DAC design (Piermarini, 2001), and they were the first to achieve pressures of a megabar and above (Mao and Bell, 1978), opening up the lower mantle and core to relatively routine exploration by other eager high-pressure Earth scientists. Dave recognized that measuring pressure quickly and reliably was a prerequisite for this device to take hold in the high-pressure community, and Dave again leaped on a new method, the ruby fluorescence pressure scale developed at NIST/NBS, calibrating the scale using specific volume meas-urements of four metals combined with their shock wave equations of state to provide a reliable, quasihydrostatic in situ pressure scale that is still widely used today (Mao et al., 1978, 1986).
The use of the DAC as a high-pressure device to address problems in Earth and planetary sciences, condensed matter physics, and materials sciences has drastically expanded by combining the DAC with laser heating to achieve simultaneous high pressure and temperature and coupling the DAC with synchrotron X-radiation for in situ measure-ments. Dave led both expansions to address a wide range of scientific questions in high-pressure science. Together with GL postdoctoral fellow Takehiko Yagi at the Geophysical Lab in the late 1970s, Dave was among the first to combine laser heating with the DAC to synthesize and investigate the structure and crystal chemistry of minerals at lower mantle conditions (Bell et al., 1979; Yagi et al., 1978, 1979), following the successful synthesis of the MgSiO3-perovskite phase (bridgmanite) (Liu, 1976). The development of the double-sided laser-heating technique (Shen et al., 1996) and the symmetric DAC (Shen and Mao, 2017) further advanced the application of DAC techniques.
Dave recognized early on that the ability to probe samples in the DAC with focused energy at infrared, optical, and X-ray wavelengths permits a vast landscape of possible measurements to be made in situ at high pressure and often at high temperature. From his first forays into coupling synchrotron radiation with high-pressure experiments at the Brookhaven National Lab in the 1980s to his vision and dedication to the construction of large facilities dedicated to high-pressure science at the Advanced Photon Source (High Pressure Collaborative Access Team [HPCAT], HPSynC) and most recently the Shanghai Synchrotron Radiation Facility (SSRF), Dave and like-minded colleagues have led the community to its current state, where making measurements at megabar pressures and extreme temperatures while probing with energetic beams at scales reaching to the nanometric in scale has become commonplace and, importantly, easily accessible (Mao and Hemley, 1996; Shen et al., 1996, 2010; Mao et al., 2001a;Zhaoetal.,2004; Hemley et al., 2005; Mao et al., 2016;Shenand Mao, 2017; Goncharov et al., 2019).
In the realm of Earth sciences, Dave has spent a career investigating the fundamental phase equilibria, thermodynamic, and physical properties of solid and liquid phases at pressure–temperature conditions relevant to Earth’s lower mantle and core – his body of work is truly remarkable and has been tremendously impactful. From his studies on deep mantle silicates and oxides to his extensive investigations on iron and iron alloys, there can be little doubt that our current understanding of Earth’s deep interior has Dave’s footprints all over the territory, and it is hard to find a path Dave has not trodden (Yagi et al., 1978; Mao and Bell, 1979; Jephcoat et al., 1986; Mao et al., 1989, 1997, 1998, 1990, 2001b, 2006b; Stixrude et al., 1992; Fei and Mao, 1994; Duffy et al., 1995; Saxena et al., 1995; Shen et al., 1998; Shieh et al., 1998; Badro et al., 1999; Hirose et al., 1999; Zha et al., 2000; Merkel et al., 2002; Li et al., 2004; Lin et al., 2005). One might argue that Dave’s most recently discovered path leading to new high-pressure hydrous phases and superoxide iron-rich phases, potentially tying together the Earth’s surface, mantle, and core, represents a fitting destination that began with his studies on iron and iron oxide phases as a graduate student (Hu et al., 2016; Liu et al., 2017, 2019; Mao et al., 2017; Zhang et al., 2018 Lin et al., 2020).

Expanding his horizons beyond the terrestrial landscape, Dave ventured into the realm of gas giants early in his career, aiming to probe the high-pressure behavior of hydrogen and leading the elusive search for its metallicity, the “holy grail” in high-pressure physics (Sharma et al., 1980; Hemley and Mao, 1988; Mao et al., 1988a, 1988b; Badding et al., 1991; Mao and Hemley, 1994; Loubeyre et al., 1996; Gregoryanz et al., 2003). This ultimately led to numerous investigations of a vast array of molecular compounds, explor-ation of novel new materials, and the search for room temperature superconductivity in materials at high pressure (Mao et al., 1988a, 2006a; Vos et al., 1993; Goncharov et al., 1996; Eremets et al., 2001; Meng et al., 2004; Yoshimura et al., 2006; Gregoryanz et al., 2007; Chen et al., 2008; Somayazulu et al., 2010; Zhu et al., 2013; Zhou et al., 2016; Zeng et al., 2017; Wang et al., 2018; Ji et al., 2019).
Perhaps the greatest legacy of Dave’s epic journey is the vast number of scientists (Figure 1.2) who he has trained, collaborated with, mentored, interacted with, and paved the way for over the last 50-plus years, a tradition that he continues to this day. The operation of the dedicated high-pressure beamline (HPCAT) at the Advanced Photon Source has further expanded Dave’s collaborations with researchers around the globe (Figure 1.3). This volume, Static and Dynamic High-Pressure Mineral Physics, represents an outgrowth of the workshop held in Dave’s honor at the Geophysical Lab in 2018 (Figure 1.4) celebrating his half-century journey in high-pressure science. Many of those who attended the workshop have contributed chapters to this book, together with collabor-ators and colleagues both old and new who have the pleasure of tagging along on Dave’s journey of discovery in high-pressure science.