Research On The Structural Behavior Of Several Typical Non-metal Hydrides Under High Pressure

The electrical behavior and structure transition of hydrides under high pressure has attracted a great deal of attentions since they were predicted that could become superconductor under high pressure.Although,phosphine(PH3)and silane(SiH4)have been reported could become at high pressure,the PH3 phase under compression has remained unknown and no relevant experimental studies have been reported.The structure behaviors of SiH4 under high pressure are still under debate.In this thesis,we systematically studied the structure behaviors and stoichiometry evolution of PH3 and SiH4.PH3 is stable below 11.7 GPa and then it starts to dehydrogenate through two dimerization processes at room temperature and pressures up to 25 GPa.Two resulting phosphorus hydrides,P2H4 and P4H6,were verified experimentally and can be recovered to ambient pressure.Under further compression above 35 GPa,the P4H6 directly decomposed into elemental phosphorus.Low temperature can greatly hinder polymerization/decomposition under high pressure,and retain P4H6 up to at least 205 GPa.The superconductivity transition temperature of P4H6 is predicted to be 67 K at 200 GPa,which agrees with the reported result,suggesting that it might be responsible for superconductivity at higher pressures.Our results clearly show that P2H4 and P4H6 are the only stable P-H compounds between PH3 and elemental phosphorus,which is helpful for shedding light on the superconducting mechanism.X-ray can significantly accelerate the polymerization and decomposition of PH3.At 9 GPa,PH3 polymerized into P4H6 and completely decomposed into elemental phosphorus at 22 GPa.For SiH4,temperature can affect the high pressure phase transition of SiH4.At room temperature,a liquid-liquid transition happened at 3.9 GPa.And it became solid at 5.5 GPa.The structure of SiH4 at room temperature is different of that at low temperature.And the low temperature can be quenched to room temperature at above 9 GPa.At above 26.2 GPa,SiH4 starts to polymerize and the polymer phase only is stable at high pressure.During the decompression,the polymer phase SiH4 decomposed into elemental Si and H2.By using high pressure laser heating system,we studied the reaction of phosphorus and hydrogen.At 9 and 15 GPa,phosphorus is stable and cannot react with hydrogen.But for silicone,it can react with hydrogen at 7.9 GPa and the product is SiH4.At above 17.5 GPa,silicone is stable and cannot react with hydrogen any more.