相变及空位缺陷对高压下GeO_2光学性质的影响

本文采用第一性原理方法,在100 GPa的压力范围内,计算了GeO_2理想晶体和含锗、氧空位点缺陷晶体的光学性质.吸收谱数据表明,压力诱导的三个结构相变对GeO_2晶体的吸收谱均有影响:第一个相变将导致其吸收边蓝移,而第二和第三相变将使得其吸收边红移.锗和氧空位点缺陷的存在将导致GeO_2的吸收边红移,但氧空位点缺陷引起的红移更明显.尽管如此,分析发现,在100 GPa的压力范围内,压力、相变以及空位点缺陷等因素都不会导致GeO_2晶体在可见光区出现光吸收现象(是透明的).波长在532 nm处的折射率数据显示,在GeO_2的四个相区,其折射率均随压力增加而降低;而且,GeO_2的三个结构相变以及锗、氧空位点缺陷都会导致其折射率有所增大.本文预测,GeO_2有成为冲击光学窗口材料的可能.

Effects of phase transitions and vacancy defects on the optical properties of GeO2 under high pressure

The optical properties of GeO2 crystal without and with and vacancy defects within pressure 100 GPa were calculated by using the first-principles method. The absorptive data show that the three pressure-induced structural phase transitions in GeO2 have the influences on the absorption spectra: the first transition causes a blue-shift of its absorption edge, but the second and third transitions lead to the red-shifts of its absorption edge. The existence of and vacancy defects results in the absorption edge red-shift, but the influence of is more obvious. However, within 100 GPa, pressure, transition, and vacancy factors do not give rise to its optical absorption in the visible region. The refractive-index data of GeO2 at 532 nm indicate that, in its four structural phase regions, the refractive index decreases with increasing pressure, but the three high-pressure structural transitions as well as and vacancy defects in GeO2 cause an increase in refractive index. We predict that GeO2 is likely to be an optical window material in shock experiments.