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1. chinaXiv:201703.00562 [pdf]

Temperature dependent defects evolution and hardening of tungsten induced by 200 keV He-ions

M. H. Cui; Z. G. Wang; L. L. Pang; T. L. Shen; C. F. Yao; B. S. Li; J. Y. Li; X. Z. Cao; P. Zhang; J. R. Sun; Y. B. Zhu; Y. F. Li; Y. B. Sheng
Subjects: Physics >> Condensed Matter: Structural, Mechanical and Thermal Properties

Tungsten has been selected as one of the potential candidate materials to cover some parts of the divertor in the future International Thermonuclear Experimental Reactor (ITER). The accumulation of defects and He induced by neutron irradiation and their impact on the mechanical properties of tungsten are of very importance. In this work, the high pure polycrystalline tungsten samples were implanted by 200 keV He+ with a fluence of 5016 He+/cm2 at temperatures of room temperature(RT), 200, 400 and 800oC. Vacancy-type defects were detected in all implanted samples by means of positron annihilation spectroscopy. Vacancy-type defects produced by He implantation exist in the damaged layer and are decorated by He atoms. With increasing implantation temperature, more He atoms fill in the vacancy-type defects and make for the formation of larger defects. The nano-hardness values were measured by nano-indentation technique. It is observed that implantation hardening occurred for all the implanted samples. With increasing implantation temperature from 200 to 800 oC, the change of the average hardness values which are lower than the value at RT has a tendency of enhancement for the shallower layer and degradation for the deeper layer. The hardness variations are discussed to be the pinning effects of the defects with different density or size.

submitted time 2017-03-26 Hits1313Downloads755 Comment 0

2. chinaXiv:201703.00558 [pdf]

Study of defect types and room-temperature ferromagnetism in undoped rutile TiO2 single crystals

LI Dong-Xiang; QIN Xiu-Bo; ZHENG Li-Rong; LI Yu-Xiao; CAO Xing-Zhong; LI Zhuo-Xin; YANG Jing; WANG Bao-Yi
Subjects: Physics >> Condensed Matter: Structural, Mechanical and Thermal Properties

Room-temperature ferromagnetism has been experimentally observed in annealed rutile TiO2 single crystals when magnetic field is applied parallel to the sample plane. By combining X-ray absorption near edge structure spectrum and positron annihilation lifetime spectroscopy, Ti3+-VO defect complexes (or clusters) have been identified in annealed crystals at high vacuum. We elucidate that the unpaired 3d electrons in Ti3+ ions provide the observed room-temperature ferromagnetism. Besides, excess oxygen ions in TiO2 lattice could induce a number of Ti vacancies which increase magnetic moments obviously.

submitted time 2017-03-26 Hits1205Downloads687 Comment 0

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