The Structural Investigation Of Vanadinite?Montebrasite And Turquoise At The Upper Mantle Temperature And Pressure Conditions

The in-situ high-pressure structure of vanadinite is studied by synchrotron radiation X-ray diffraction(SRXRD)and Diamond Anvil Cell(DAC)device,and the highest experimental pressure was 8.13 GPa.No phase transition was observed during the experiment.Third-order Birch-Murnaghan Equaton of State(Eos)was used to fit the P-V data,with V₀=675.0(8)?³,K₀=53.0(2.7)GPa,K'=7.1(9)and V₀=673.0(6)?³,K₀=63.2(1.0)GPa,K'=4.The axial compressibility of a and c in vanadinite were also fitted using the Eos Fit software and the fitting results are as follows,a₀=10.2935(70)?,K₀(a)=47.4(4.1)GPa,K₀'(a)=6.4(1.4);c₀=7.3637(57)?,K₀(c)=59.2(8.6)GPa,K₀'(c)=11.7(3.7).The axial compressibility(?_a=7.03×10^-3GPa^-1;?_c=5.63×10^-3GPa^-1)indicates that vanadinite has a strong anisotropic compression model.The intensity of the peak shape and the change of the curve shape are small in the high temperature infrared spectrum of the vanadinite,proving that the structure of[VO₄]is relatively stable.The in situ high pressure structure of the montebrasite was studied using SRXRD and DAC device.The experimental results show that its structure is stable up to 12.71 GPa.With the increasing of pressure,the unit cell parameters are gradually decreasing step by step.The parameters such as bulk moduls were fitted by the the second-order B-M EOS with K'=4(fixed),V₀=161.6(3) ?³,K₀=138.0(5.2)GPa.The axial compressibility was also obtained with K'=4(fixed),a₀=5.1693(72)?,K₀(a)=120.7(9.8)GPa;b₀=7.1807(69)?,K₀(b)=132.0(8.0)GPa;c₀=5.085(101)?,K₀(c)=123.1(14.8)GPa.The in situ high pressure X-ray diffraction study of turquoise shows that turquoise undergo phase transition from 1.17 GPa to 9.24 GPa.However,the pattern has small changes from 10.85 to 15.95 GPa,which indicates its structure is fairly stable then.Since the XRD pattern are similar beween the adding and releasing process,turquoise undergo reversible phase transions.