| Shock temperature measurement is a crucial subject in equation-of-state and high-pressure phase transition investigations. So, the shock temperature experimental techniques have been developed for a long time both in theory and experiment for condensed matter, particularly the non-transparent materials, at high pressures and high temperatures, but yet it has been not solved up to now. Among issues of shock temperature measurements by the radiometry means, the optical transpareny of window material under shock condition is a much concerned problem to be solved urgently, since it is closely related to proper interpretation for the measured thermal radiation profile record. For the commonly used window materials of LiF and sapphire, we always confront the trouble of rattier large impedance and temperature mismatching situations aross sample/window interface if the sample is with intermediate impedance (say p0~7.0 g/cm3) because under such condition large error would be introduced in data processing. In this article, the LiTaO3 single crystal (p0=7.46g/cm3) is selected as a candidate window materials for measuring shock temperature of Fe sample (p0=7.853 g/cm3) in order to reduce both impedance and temperature mismatch levels across the sample/window interface, and accordingly the Hugoniot locus and and optical transpareny of LiTaO3 under shock compression have been measured.A comparative study of the optical transparency under shock compression condition for LiF, sapphire and LiTaO3 is conducted by using two-stage light-gas gun with bore diameter of 35 mm as loading device, a modified Mallory's sample configuration as tested sample assembly, and high-speed electronic camera as the optical transparency measuring apparatus. The results demonstrate that LiF can remain its optical transparency a sufficient time duration at 102 GPa which is consistent with the common view of good transparency at high pressure for LiF, and, sapphire and LiTaO3 can remain their optical transparency only a time duration of ~300ns at 130 GPa and 140 GPa, respectively, and followed a continuous degradation manner.In order to estimate the levels of impedance mismatching and temperature mismatching between Fe and LiTaO3 window, the Hugoniot data of LiTaO3 is measured in the pressure range of 77-227 GPa. The result is C0=(3.53+0.24) km/s and =1.317+0.086, here Co and X are two constants in the shock velocity (D)-particle velocity (a) relation of D=C0+u, and shows that the shock impedance of LiTaO3 is higher than those of LiF and sapphire, close to those of Zn and Sn, and more approaching to Fe in comparison with LiF and sapphire windows. The above data could be used to analyze the impedance and temperature mismatching levels between the non-transparent sample material being studied and the window material as a partly data base. Among the sample materials with intermediate impedances, using LiTaO3 as window material to measure shock temperature of Fe is benificial to realyze fairly good impedance and temperature match situations and, therefore, to conduct precise shock temperature determination for Fe.Based on the analysis above-mentioned, the shock temperature measurements of Fehave been performed in this work, using LiTaO3 as the window material. The preliminary results demonstrate the measured shock temperatures are in fairly good agreement with the data previously published, and, therefore, implys that the technical approach proposed in the work is reasonal and workable. It is worth to notice that the important significance of above work, in spite of the support is coming from the data previously published as mentioned above, is that our result possesses rather higher confidence level than that case providing LiF or sapphire is used as the window material, which is just the value of our work for developing the technique of shock temperature determination. But, the above achievement is relatively preliminary since experimental data obtained by us are rather limited due to the allowable working period for ours. Much additional works (... |
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