Raman Spectroscopy Study Of Sodium Perchlorate Under High Pressure And High Temperature

Anhydrous sodium perchlorate(NaClO4),one of the anhydrite-type ABO4 compond linked with CaSO4,CaSeO4,and zircon-type phases,has abundant phase transition under high pressure and high temperature.It is possible that the anhydritetype turns into monazite-type,barite-type or AgMnO4-type under high pressure and high temperature.However,the exiting of AgMnO4-type structure is controversial.Instead of AgMnO4-type phase,CaSO4 forms monazite-type phase under high pressure.Compared with the monazite-type and AgMnO4-type,it is similar structural parameters and activation energy between each other.It should be easy to transform into AgMnO4-type.There are different views on the existence of AgMnO4-type.On the one hand,the barite-type phase is distorted to metastable AgMnO4-type structure.On the other hand,although atomic arrangement of those two phases has resemblance,it is great different with tetrahedron orientation.So AgMnO4-type should not be the distorted barite-type.This suggests that the existence of AgMnO4-type is still a confused question.Moreover,the phase diagram of NaClO4 reveals that anhydrite-type NaClO4 may turn into AgMnO4-type and then shift into barite-type with the compression.It is necessary for researching the phase transition of NaClO4 under high temperature and high pressure.The pressure and temperature-induced phase transition of anhydrite-type Soduim perchlorate(NaClO4)were investigated by in-situ Raman spectrum methods at high pressures and temperature in Mao-Bell type and external resistive heating heating-I type diamond anvil cell(DAC).The Raman spectra of anhydrite-(Cmcm),monazite-(P21/n),AgMnO4-(P21/n),and barite-type(Pnma)structure of NaClO4 were calculated by density function theory.Distribution map of three different strctures of NaClO4 was observed within pressure range of 0.1 MPa~20 GPa and temperature range of 30 ?~500 ?.Phase diagram of NaClO4 was recognized within the same pressure and temperature range.The present dissertation focuses on the Raman vibration message and phase transition of NaClO4 under different temperature and pressure.The specific content of the dissertation includes that:Four different types of NaClO4 are calculated using first principles calculation.Raman spectra of NaClO4 are measured under different temperature and pressure conditions.Based on the above studies,the following conclusions were obtained:(1)The experimental data shows that anhydrite-type NaClO4 undergoes a structural transition at ~3.7 GPa.The phase transformation is completed at~5.7 GPa,and remains stable up to 47 GPa.The high pressure structure can be recovered at~3.1 GPa upon decompression.Reconstructive phase transition occurs between anhydrite type and monazite type of NaClO4 within the pressure range of 0.1 MPa ~47 GPa.It is different with the phase transition sequence that anhydrite type turns into AgMnO4 type at ~2 GPa and then changes into barite type at ~3 GPa.(2)According to the initial pressure,the phase transition sequence of anhydrite type of NaClO4 changes obviously during the temperature increasing from 30 ? to 500 ?.The anhydrite-type NaClO4 changes into cubic Na Cl phase when the initial pressure located in the pressure range of 0.1 MPa ~ 1.7 GPa;As the temperature increasing,anhydrite-type NaClO4 changes partly into monazite-type and then barite-type occurs slightly at the higher temperature.Raman peak(~470 cm-1)at the corresponding wavenumbers of the ClO internal modes(?2)emerged represents the generating of barite-type of NaClO4.Finally,anhydrite-and monazite-type NaClO4 turn into the high pressure and temperature barite-type NaClO4 completely.The initial pressure impacts the temperature of phase transition from anhydrite-type to barite-type directly at the initial pressure range of 2.6 GPa~3.0 GPa.(3)At the initial pressure range of 3.7 GPa~5.6 GPa,anhydrite-and monazite-type NaClO4 turn into barite-type partly with the increasing temperature and then transform into barite-type totally at the higher temperature within the temperature range of 30 ?~500 ?.Higher initial pressure inhibits the phase transition when the process of heating.As the initial pressure at 4.5 GPa,the temperature value of completely forming the barite-type NaClO4 is 280 ?.At the same time,the temperature value elevates into 300 ? when the initial pressure at 5.6 GPa.(4)At the initial pressure range of 5.6 GPa~10.9 GPa,monazite-type NaClO4 turn into barite-type partly with the increasing temperature and then transform into baritetype totally at the higher temperature within the temperature range of 30 ?~450 ?.However,monazite-and barite-type of NaClO4 coexist at the initial pressure of 10.9 GPa when temperature increased into 450 ?.Moreover,at the initial pressure of 43 GPa,monazite-type NaClO4 transforms into barite-type suffering from quenching at the high temperature of ~1800 K.As the above,the temperature of forming barite-type NaClO4 has a positive relationship with the initial pressure.(5)Barite-type NaClO4 maintains stably at the process of cooling.Otherwise,the experimental data shows that barite-type NaClO4 retains stably when compressing up to 41.8 GPa under ambient temperature conditions.However,The barite structure undergoes the phase transition at~2.2 GPa upon decompression.Partial barite-type NaClO4 turns into anhydrite-type NaClO4 upon decompression.Finally,anhydrite-type NaClO4 can be recovered.(6)The above conclusions reveal the phase transition of anhydrous sodium perchlorate under high pressure and temperature and consummate the phase diagram of NaClO4 at the temperature and pressure range of 0.1 MPa~20 GPa and 30 ?~500 ?.The dissertation provides the phase transition model for the anhydrite-type ABO4 ternary compounds under high pressure and temperature.