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The velocity interferometer system for any reflector (VISAR) and pyrometric measurements in dynamic highpressure experiments require the use of an optical window, and Alumina (Al2O3) or sapphires is often considered as a window material due to its high shock impedance and excellent transparency. Consequently, understanding the characteristics of its transparency and refractive index change under shock loading is crucial for explaining such experimental data. Experimental studies indicate optical transparency loss in shocked Al2O3. The mechanisms for the phenomenon are some interesting issues. A first-principles study suggests that shock-induced VO+2 (the +2 charged O vacancy) defects in Al2O3 could be an important factor causing the transparency loss. Recently, the red shift of the extinction curve (i.e., the wavelength dependence of the extinction coefficient) with increasing shock pressure has been observed. It is needed to ascertain whether this behavior is also related to shock-induced vacancy point defects. In addition, up to now, information about Al2O3 refractive index at a wavelength of 532 nm under strong shock compression (the optical source wavelength in VISAR measurement is usually set at 532 nm) has been unknown, and neither the effects of structural transitions nor vacancy point defects on the refractive index of shocked Al2O3 are determined. Here, to investigate the above-mentioned questions, we perform first principles calculations of optical absorption and refractive index properties of Al2O3 crystal without and with VO+2 and VAl3 (the -3 charged Al vacancy) defects in a pressure range of 180 GPa (the calculations in CASTEP are carried out by the plane-wave pseudo potential method in the framework of the density functional theory). Our absorption data show that the observed optical extinction in shocked Al2O3 cannot be explained by only considering pressure and temperature factors, but shock-induced VO+2 should be an important source for this behavior. On the basis of these results, we may judge that 1) the transparency loss explanation for shocked Al2O3 in the view of vacancy point defects is reasonable; 2) the absorption extinction should dominate the extinction phenomenon observed in shocked Al2O3. Our calculations find that high-pressure structural transition in Al2O3 causes an obvious enhancement of its refractive index. The refractive index decreases with increasing shock pressure in corundum and Rh2O3 regions, and decreases slightly below 172 GPa and increases slowly above 172 GPa with increasing shock pressure in CalrO3 region. The VO+2 and VAl3 defects in Al2O3 have apparent influences on the shock pressure dependence of its refractive index. These results mean that the information about Al2O3 refractive index under strong shock loading cannot be obtained simply by extrapolating its low pressure data. Our prediction could be of importance for future experimental study and new window-material development.
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Keywords:
- high pressure /
- first-principles calculations /
- optical properties /
- sapphire
[1] Oganov A R, Ono S 2005 Proc. Natl. Acad. Sci. USA 102 10828
[2] Ono S, Oganov A R, Koyama T, Shimizu H 2006 Earth Planet. Sci. Lett. 246 326
[3] Zhou X M, Wang X S, Li S N, Li J, Li J B, Jing F Q 2007 Acta Phys. Sin. 56 4965 (in Chinese) [周显明, 汪小松, 李赛男, 李俊, 李加波, 经福谦 2007 物理学报 56 4965]
[4] Lin J F, Degtyareva O, Prewitt C T, Dera P, Sata N, Gregoryanz E, Mao H K, Hemley R J 2004 Nat. Mater. 3 389
[5] Weir S T, Mitchell A C, Nellis W J 1996 J. Appl. Phys. 80 1522
[6] He L, Tang M J, Fang Y, Jing F Q 2008 Europhys. Lett. 83 39001
[7] Zhang D Y, Hao G Y, Zhang M J, Liu F S 2007 Journal of Synthetic Crystals 36 531 (in Chinese) [张岱宇, 郝高宇, 张明建, 刘福生 2007 人工晶体学报 36 531]
[8] Cao X X 2011 M. S. Thesis (Chengdu: Sichuan University) (in Chinese) [操秀霞 2011 硕士学位论文 (成都: 四川大学)]
[9] Hare D E, Webb D J, Lee S H, Holmes N C 2002 Optical Extinction of Sapphire Shock-Loaded to 250-260 GPA. In Shock Compression of Condensed Matter-2001 : 12th APS Topical Conference Atlanta, Georgia (USA), June 24-29, 2001 p1231
[10] He L, Tang M J, Yin J, Zhou X M, Zhu W J, Liu F S, He D W 2012 Physica B 407 694
[11] He X, He L, Tang M J, Xu M 2011 Acta Phys. Sin. 60 026102 (in Chinese) [何旭, 何林, 唐明杰, 徐明 2011 物理学报 60 026102]
[12] Li X M, Yu Y Y, Li Y H, Zhang L, Ma Y, Wang X S, Fu Q W 2010 Acta Phys. Sin. 59 2691 (in Chinese) [李雪梅, 俞宇颖, 李英华, 张林, 马云, 汪小松, 付秋卫 2010 物理学报 59 2691]
[13] LaLone B M, Fat'yanov O V, Asay J R, Gupta Y M 2008 J. Appl. Phys. 103 093505
[14] Wise J L, Chhabildas L C 1986 Laser Interferometer Measurements of Refractive Index in Shock-Compressed Materials (New York: Springer US) pp441-454
[15] Setchell R E 2002 J. Appl. Phys. 91 2833
[16] Fratanduono D E, Eggert J H, Akin M C, Chau R, Holmes N C 2013 J. Appl. Phys. 114 043518
[17] He L, Tang M J, Zeng M F, Zhou X M, Zhu W J, Liu F S 2013 Physica B 410 137
[18] Matsunaga K, Tanaka T, Yamamoto T, Lkuhara Y 2003 Phys. Rev. B 68 085110
[19] Segall M D, Lindan P J D, Probert M J, Pickard C J, Hasnip P J, Clark S J, Payne M C 2002 J. Phys. : Condens. Matter 14 2717
[20] Kohn W, Sham L J 1965 Phys. Rev. 140 A1133
[21] Vanderbilt D 1990 Phys. Rev. B 41 7892
[22] Perdew J P, Burke K, Ernzerhof M 1996 Phys. Rev. Lett. 77 3865
[23] Fischer T H, Almlof J 1992 J. Phys. Chem. 96 9768
[24] Zhang D Y, Liu F S, Hao G Y, Sun Y H 2007 Chin. Phys. Lett. 24 2341
[25] Ching W Y, Xu Y N 1994 J. Am. Ceram. Soc. 77 404
[26] Wu J, Walukiewicz W, Shan W, Yu K M, Ager III J W, Li S X, Haller E E, Lu H, Schaff W J 2003 J. Appl. Phys. 94 4457
[27] Holm B, Ahuja R, Yourdshahyan Y, Johansson B, Lundqvist B I 1999 Phys. Rev. B 59 12777
[28] Meyers M A 1994 Dynamic Behavior of Materials (New York: Wiley-IEEE) p413
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[1] Oganov A R, Ono S 2005 Proc. Natl. Acad. Sci. USA 102 10828
[2] Ono S, Oganov A R, Koyama T, Shimizu H 2006 Earth Planet. Sci. Lett. 246 326
[3] Zhou X M, Wang X S, Li S N, Li J, Li J B, Jing F Q 2007 Acta Phys. Sin. 56 4965 (in Chinese) [周显明, 汪小松, 李赛男, 李俊, 李加波, 经福谦 2007 物理学报 56 4965]
[4] Lin J F, Degtyareva O, Prewitt C T, Dera P, Sata N, Gregoryanz E, Mao H K, Hemley R J 2004 Nat. Mater. 3 389
[5] Weir S T, Mitchell A C, Nellis W J 1996 J. Appl. Phys. 80 1522
[6] He L, Tang M J, Fang Y, Jing F Q 2008 Europhys. Lett. 83 39001
[7] Zhang D Y, Hao G Y, Zhang M J, Liu F S 2007 Journal of Synthetic Crystals 36 531 (in Chinese) [张岱宇, 郝高宇, 张明建, 刘福生 2007 人工晶体学报 36 531]
[8] Cao X X 2011 M. S. Thesis (Chengdu: Sichuan University) (in Chinese) [操秀霞 2011 硕士学位论文 (成都: 四川大学)]
[9] Hare D E, Webb D J, Lee S H, Holmes N C 2002 Optical Extinction of Sapphire Shock-Loaded to 250-260 GPA. In Shock Compression of Condensed Matter-2001 : 12th APS Topical Conference Atlanta, Georgia (USA), June 24-29, 2001 p1231
[10] He L, Tang M J, Yin J, Zhou X M, Zhu W J, Liu F S, He D W 2012 Physica B 407 694
[11] He X, He L, Tang M J, Xu M 2011 Acta Phys. Sin. 60 026102 (in Chinese) [何旭, 何林, 唐明杰, 徐明 2011 物理学报 60 026102]
[12] Li X M, Yu Y Y, Li Y H, Zhang L, Ma Y, Wang X S, Fu Q W 2010 Acta Phys. Sin. 59 2691 (in Chinese) [李雪梅, 俞宇颖, 李英华, 张林, 马云, 汪小松, 付秋卫 2010 物理学报 59 2691]
[13] LaLone B M, Fat'yanov O V, Asay J R, Gupta Y M 2008 J. Appl. Phys. 103 093505
[14] Wise J L, Chhabildas L C 1986 Laser Interferometer Measurements of Refractive Index in Shock-Compressed Materials (New York: Springer US) pp441-454
[15] Setchell R E 2002 J. Appl. Phys. 91 2833
[16] Fratanduono D E, Eggert J H, Akin M C, Chau R, Holmes N C 2013 J. Appl. Phys. 114 043518
[17] He L, Tang M J, Zeng M F, Zhou X M, Zhu W J, Liu F S 2013 Physica B 410 137
[18] Matsunaga K, Tanaka T, Yamamoto T, Lkuhara Y 2003 Phys. Rev. B 68 085110
[19] Segall M D, Lindan P J D, Probert M J, Pickard C J, Hasnip P J, Clark S J, Payne M C 2002 J. Phys. : Condens. Matter 14 2717
[20] Kohn W, Sham L J 1965 Phys. Rev. 140 A1133
[21] Vanderbilt D 1990 Phys. Rev. B 41 7892
[22] Perdew J P, Burke K, Ernzerhof M 1996 Phys. Rev. Lett. 77 3865
[23] Fischer T H, Almlof J 1992 J. Phys. Chem. 96 9768
[24] Zhang D Y, Liu F S, Hao G Y, Sun Y H 2007 Chin. Phys. Lett. 24 2341
[25] Ching W Y, Xu Y N 1994 J. Am. Ceram. Soc. 77 404
[26] Wu J, Walukiewicz W, Shan W, Yu K M, Ager III J W, Li S X, Haller E E, Lu H, Schaff W J 2003 J. Appl. Phys. 94 4457
[27] Holm B, Ahuja R, Yourdshahyan Y, Johansson B, Lundqvist B I 1999 Phys. Rev. B 59 12777
[28] Meyers M A 1994 Dynamic Behavior of Materials (New York: Wiley-IEEE) p413
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