Properties Of Liquid Oxygen Under High Pressure And High Temperature Conditions By Brillouin Scattering

The Brillouin scattering is an inelastic scattering which induced by the interaction between the phonon or magneton in crystal, it can be used to study the acoustic vibration in gas, liquid and solid state. In addition, Brillouin scattering could be used to study other properties such as acoustic velocities, elastic constant, refractive index, adiabatic bulk modulus,polarizability , equation of state(EOS).From these we can get the information about the inner movement and interactions in material.In the present work, we use the Brillouin scattering method and Diamond Anvil Cell (DAC) technique to study the property of the liquid oxygen under high pressure and high temperature (P-T) conditions by background and 60°scattering geometry. The highest P-T is 423K and 8.9GPa. The single-frequency green (532nm) laser is used as Brillouin excitation source, the power of the laser is 200mW. The laser is solid-state dipole-pumped and frequency-doubled, and the Brillouin spectra are collected by a newly developed 3+3 pass tandem Fabry-Perot interferometer, which is designed by JRS scientific instruments. The diamond anvil cell is externally heated with a resistance heater and the temperature is measured by a chromel-alumel thermocouple attached to the side face of the diamond. The pressure is generated by the DAC and measured by the red shift of ruby fluorescence.We have measured the Brillouin scattering spectra of the background scattering geometry and 60°scattering geometry at 298K, 367K and 423K, and also obtain the frequency shift of the Brillouin scattering peak. We find that the influence of temperature to frequency shift of Brillouin scattering of liquid oxygen is slight in both scattering geometry. We also calculate the sound velocity ,refractive index ,elastic constants .At invariable temperature ,the sound velocities increase with the loading of pressure,and the effect of temperature is much more smaller. Our obtained sound velocities have been compared with the other experimental and theoretical results ,which indicate that is more close to the theoretical results that obtained by the EOS, especially in the region of 3-6.5GPa and 423K.When the pressure is up to 6.5GPa, our results and theoretical results that obtained from the EOS become almost the same. In the isothermal situation, the high P-T acoustic velocity and density of liquid oxygen appears to be linear relationship, and the changes of temperature have no effect on the sound velocity and the density.The refractive index of liquid oxygen increases monotonously with the increasing pressure at a constant temperature of 298K, 367K and 423K. At high temperature, the refractive index is larger than that at low temperature and the uncertainty is about 5%. For the liquid, the elastic property is described by only one parameter C11 which is equal to its bulk modulus , and C11 is related to the sound velocity and density by C11=ρV2. The density is obtained from the reported EOS. At the temperature of 298K and 367K, the transformation of elastic constants of liquid oxygen is similar to each other.