Prediction of the composition and structure of the Earth's inner core from the first principle calculation

	Prediction of the composition and structure of the Earth's inner core from the first principle calculation
	Cui Hang; Duan ZhenHao; Zhang ZhiGang
刊名	ACTA PETROLOGICA SINICA
	2010-04-01
卷号	26 期号:4 页码:1322-1328
关键词	Earth's deep interior Earth's inner core Ab initio calculation Core composition Core structure
ISSN号	1000-0569
文献子类	Article
英文摘要	The determination of the composition and structure of the Earth's inner core has long been the major subject in the study of the Earth's deep interior. It's widely believed that the Earth's core is formed by iron with a fraction of nickel. However, light elements must exist in the inner core because the earth core is less dense than pure iron-nickel alloy (2% similar to 3% in the solid inner core and 6% similar to 7% in the liquid outer core). The questions are what and how much light element is there in the iron-nickel alloy. Besides the composition, the crystal structure of the iron with or without light element is also not well known. According to the seismological observations, the sound waves propagate 3% similar to 4% faster along the spin axis than in the equatorial plane. That means the inner core is anisotropic. The densest structure of iron-nickel alloy should be h. c. p structure under the very high pressures. However, the h. c. p structure does not propagate waves anisotropic ally. Then what is the structure of the iron-nickel alloy or the iron-nickle-light element alloy. In this study, we tried to predict the composition and the structure of the inner core through ab initio calculation of the Gibbs free energy, which is a function of internal energy, density and entropy. We conclude that the h. c. p structure is more stable than the b. c. c structure under high pressure and 0 K, but with the increase of temperature, the free energy of the b. c. c structure is decreasing much faster than the h. c. p structure caused by the vibration of the atomics, so the b. c. c structure is more stable at high temperatures. With the addition of light elements (S or Si or both), the free energy of b. c. c. decreases even faster, about 3at% of Si not only explains why the inner core is about 2% similar to 3% lighter than the iron-nickle alloy, but also reasons why the inner core is anisotropic, since the b. c. c. structure becomes more stable than the h. c. p structure at 5500 similar to 6000K and b. c. c. is anisotropic in propagating seismic waves. Therefore, we infer that the inner core of the earth is formed by b. c. c iron and a fraction of nickel plus similar to 3.6at. % Si, with a temperature higher than 5500K, which is consistent with the studies from other approaches.
WOS关键词	TEMPERATURE
WOS研究方向	Geology
语种	英语
出版者	SCIENCE PRESS
WOS记录号	WOS:000277950600026
内容类型	期刊论文
源URL	[http://ir.iggcas.ac.cn/handle/132A11/72122]
专题	中国科学院地质与地球物理研究所
通讯作者	Cui Hang
作者单位	CAS, Inst Geol & Geophys, Key Lab Earths Deep Interior, Beijing 100029, Peoples R China
推荐引用方式 GB/T 7714	Cui Hang,Duan ZhenHao,Zhang ZhiGang. Prediction of the composition and structure of the Earth's inner core from the first principle calculation[J]. ACTA PETROLOGICA SINICA,2010,26(4):1322-1328.
APA	Cui Hang,Duan ZhenHao,&Zhang ZhiGang.(2010).Prediction of the composition and structure of the Earth's inner core from the first principle calculation.ACTA PETROLOGICA SINICA,26(4),1322-1328.
MLA	Cui Hang,et al."Prediction of the composition and structure of the Earth's inner core from the first principle calculation".ACTA PETROLOGICA SINICA 26.4(2010):1322-1328.