Study On Metallization Of Magnesium Silicide And Magnesium Germanide Under High Pressure And Temperature Dependent Grüneisen Parameters Of Aluminum And Sodium Chloride

This paper contains two parts.The first part is to study the metallization phase transition of Mg₂Si and Mg₂Ge under high pressure.The use of two-sided top hydraulic press combined with strip anvil device to measure the Mg₂Si semiconductors the change of electrical resistance under high pressure.The results show that the Mg₂Si had a discontinuous change in resistance at a pressure of about 8.6GPa.According to the theoretical calculation of the predicted 6-8GPa Mg₂Si will occur in the metallization phase transition,we speculated that the Mg₂Si resistance discontinuities may be caused by the metallization.To further validate this speculation,we measured the Mg₂Si in situ Raman spectroscopy and temperature-dependent resistance under high pressure.Mg₂Si high pressure Raman experiments found that the pressure is higher than 9.7GPa Raman peak disappears.When the pressure unloading after the Raman peak again appear,suggesting that the Mg₂Si undergoes a metallization transition at 9.7GPa,and that this phase transition is reversible.Mg₂Si temperature-dependent electrical resistance experiment found that when the pressure is lower than lOGPa resistance decreases with increasing temperature,which is the semiconductor properties,when the pressure is greater than 13GPa with the temperature increases the resistance is increased,this is the metal behavior.In summary,it is speculated that the Mg₂Si undergoes a metallization phase change around 9.7GPa.Followed by the metallization transition of Mg₂Ge under high pressure was studied.The use of two-sided top hydraulic press combined with strip anvil device to measure the Mg₂Ge semiconductors the change of electrical resistance under high pressure.The results show that the Mg₂Ge had a discontinuous change in resistance at a pressure of about 8.7GPa.In order to further verify the pressure of metallization,we carried out the Mg₂Ge high pressure Raman spectroscopy measurement,the first principle to calculate the high pressure band structure.Mg₂Ge high pressure Raman experiment found that the pressure is higher than 9.8GPa Raman peak disappears.when the pressure unloading after the Raman peak reappeared,indicating this transition is reversible.The disappearance of the Raman vibration modes is ascribed to the occurrence of metallization.The rising in the free carrier concentration after metallization prevents the laser light penetration into the sample.The band structure and phase transition of Mg₂Ge under high pressure were studied by using the first-principles method.It was found that the metallization transition of the anti-fluorite structure changed at 7.5GPa,and the structure phase transition to anti-cotunnite structure at 11.0GPa.Combined with the theoretical calculation and related experimental reports,we speculated that the discontinuous change in electrical resistance at 8.7GPa was ascribed to the gap closure and Mg₂Ge may be transformed into the anti-cotunnite structure over 9.8GPa.In the second part of this paper,through rapid compressurization press combined Bridgman anvil measured under high pressure aluminum and sodium chloride Grüneisen parameters change with temperature.Experiments designed a new sample assembly method.First,the sample is heated to the test temperature,then compress through rapid compressurization device,recording rapid compressurization process temperature and pressure curve over time.The temperature curve is modified.Increase the rate in temperature and pressure??T,?P?is calculated using the differential mean value theorem.In this paper,the effect of temperature on the Grüneisen parameters of aluminum in the 297K-494K and sodium chloride in the 312K-608K temperature range was studied.The experimental results show that the ?T/?P values increase with the increase of temperature.The Grüneisen parameters of aluminum are strong negative correlated with temperature in the experimental temperature and the range of 2.17GPa.The Grüneisen parameters of sodium chloride are weakly correlated with temperature in the experimental temperature and the range of 1.46GPa.Which is consistent with the experimental and theoretical calculations reported in the literature.