摘要
Hydrogen incorporation is critical for explaining defect energies, structure parameters and other physical characteristics of minerals and understanding mantle dynamics. This work analyzed the hydrogen complex defects in jadeite by the plane-wave pseudo-potential method based on density functional theory, and optimized the atomic positions and lattice constants in all configurations （different defective systems）. Incorporation mechanisms considered for hydrogen （H） in jadeite include： （1） hydrogen incorporating with the 02 site oxygen and coexisting with M2 vacancy; （2） one H atom combined with an AI atom replacing Si in tetrahedron; （3） 4H atoms directly replacing Si in tetrahedron and （4） 3H atoms replacing Al on the M1 site. The four incorporation mechanisms mentioned above form the corresponding VNa-Hi, Alsi-Hi, Vsi-4Hi and VAr3Hi point defects. The molecular dynamics simulation to the ideal, VNa-Hi, Alsi-Hi, Vsi-4Hi and VAr3Hi point defects under the P-T conditions of 900 K, 2 GPa, the Vsa-Hi and Alsi-Hi point defects under different pressures at T = 900 K, and Alsj-Hj point defects under different temperatures at P = 3 GPa was performed to examine the preferential mode of hydrogen incorporation in jadeite by means of first-principles calculations. The calculations show that the averaged O-H bond-length in the hydrogen point defects system decreased in the order of Alsi-Hi, VNa-HI, Vsl-4Hf and VAI-3Hi. VNa-HI complex defects result in a contraction of the jadeite volume and the presence of Alsi-Hi, Vsi-4H~ and VAI-3Hi defects could increase the superceli volume, which is the most obvious in the VAt-3Hi defects. The energy of formation of Also-HI and VA[-3HI complex defects was much lower than that of other defect systems. The VAI-3Hi defects system has the lowest energy and the shortest O-H bond-length, suggesting that this system is the most favorable. The analytical results of vacancy formation energy, O-H bond- length, and the stability of the hydrogen defects in jadeite have suggested that the preferred hydration incorporation mode in jadeite is VAI-3Hi complex defect.
Hydrogen incorporation is critical for explaining defect energies, structure parameters and other physical characteristics of minerals and understanding mantle dynamics. This work analyzed the hydrogen complex defects in jadeite by the plane-wave pseudo-potential method based on density functional theory, and optimized the atomic positions and lattice constants in all configurations （different defective systems）. Incorporation mechanisms considered for hydrogen （H） in jadeite include： （1） hydrogen incorporating with the 02 site oxygen and coexisting with M2 vacancy; （2） one H atom combined with an AI atom replacing Si in tetrahedron; （3） 4H atoms directly replacing Si in tetrahedron and （4） 3H atoms replacing Al on the M1 site. The four incorporation mechanisms mentioned above form the corresponding VNa-Hi, Alsi-Hi, Vsi-4Hi and VAr3Hi point defects. The molecular dynamics simulation to the ideal, VNa-Hi, Alsi-Hi, Vsi-4Hi and VAr3Hi point defects under the P-T conditions of 900 K, 2 GPa, the Vsa-Hi and Alsi-Hi point defects under different pressures at T = 900 K, and Alsj-Hj point defects under different temperatures at P = 3 GPa was performed to examine the preferential mode of hydrogen incorporation in jadeite by means of first-principles calculations. The calculations show that the averaged O-H bond-length in the hydrogen point defects system decreased in the order of Alsi-Hi, VNa-HI, Vsl-4Hf and VAI-3Hi. VNa-HI complex defects result in a contraction of the jadeite volume and the presence of Alsi-Hi, Vsi-4H~ and VAI-3Hi defects could increase the superceli volume, which is the most obvious in the VAt-3Hi defects. The energy of formation of Also-HI and VA[-3HI complex defects was much lower than that of other defect systems. The VAI-3Hi defects system has the lowest energy and the shortest O-H bond-length, suggesting that this system is the most favorable. The analytical results of vacancy formation energy, O-H bond- length, and the stability of the hydrogen defects in jadeite have suggested that the preferred hydration incorporation mode in jadeite is VAI-3Hi complex defect.
基金
supported by the National Natural Science Foundation of China (grants No.41172051 and 41472042)
the Specialized Research Fund for the Doctoral Program of Higher Education of China (grant No.20060491504)
