Crystal structures at high pressures and temperatures
- 出版日期：2000.
- 页数：80 p. :
- 第一责任说明：Wendel Alexander Caldwell.
- 分类号：a323
- ISBN：0599874023(ebk.) :
MARC全文
62h0021666 20140522150115.0 cr un||||||||| 101221s2000 xx ||||f|||d||||||||eng | AAI9981123 0599874023(ebk.) : CNY371.35 UnM UnM NGL a323 Caldwell, Wendel Alexander. Crystal structures at high pressures and temperatures [electronic resource] / Wendel Alexander Caldwell. 2000. 80 p. : digital, PDF file. Source: Dissertation Abstracts International, Volume: 61-07, Section: B, page: 3476. ; Chair: Raymond Jeanloz. Thesis (Ph.D.)--University of California, Berkeley, 2000. The diamond anvil cell (DAC) is a unique instrument that can generate pressures equivalent to those inside planetary interiors (pressures on the order of 1 million atmospheres) under sustained conditions. When combined with a bright source of collimated x-rays, the DAC can be used to probe the structure of materials in-situ at ultra-high pressures. An understanding of the high-pressure structure of materials is important in determining what types of processes may take place in the Earth at great depths.;Motivated by previous studies showing that xenon becomes metallic at pressures above ∼1 megabar (100 GPa), we examined the stable structures and reactivity of xenon at pressures approaching that of the core-mantle boundary in the Earth. Our findings indicate the transformation of xenon from face-centered cubic (fcc) to hexagonal close-packed (hcp) structures is kinetically hindered at room temperature, with the equilibrium fcc–hcp phase boundary at 21 (±3) gigapascals, a pressure lower than was previously thought. Additionally, we find no tendency on the part of xenon to form a metal alloy with iron or platinum to at least 100 to 150 gigapascals, making it unlikely that the Earth's core serves as a reservoir for primordial xenon.;Measurements of the compressibility of natural (Mg.75,Fe .25)2SiO4 γ-spinel at pressures of the Earth's transition zone yield a pressure derivative of the bulk modulus K0 ′ = 6.3 (±0.3). As γ-spinel is considered to be a dominant mineral phase of the transition-zone of the Earth's mantle (400–670 km depth), the relatively high value of K0′ for γ-spinel may help explain the rapid increase with depth of seismic velocities through the transition zone.;The thermodynamics, mechanisms and kinetics of pressure-induced amorphization are not well understood. We report here new studies indicating little or no entropy difference between the crystalline and glassy states of Ca(OH) 2 (portlandite). Additional work on the pressure-induced amorphization of AlPO4 (berlinite) shows that this material, which is a close analog to quartz, shows a rich behavior that is dependent upon the pressure, temperature, stress-state and time-scales of the experimental conditions. Crystallography. University of California, Berkeley. aCN bNGL http://pqdt.bjzhongke.com.cn/Detail.aspx?pid=EPUdgfxji6g%3d NGL Bs697 rCNY371.35 ; h1 bs1101