X-ray Diffraction Study Of Diopside And Spodumene At High Temperature Or High Pressure

The main purpose of this thesis is to discuss the structural stability of diopside and spodumene,which may have a direct influence on the discontinuous surface of the mantle transition zone.The chemical composition and structure of the samples were studied by the methods of electron probe(EPMA),X ray powder diffraction(XRD)and Fourier infrared spectroscopy(IR).The EPMA data shows that the chemical formula of diopside and spodumene samples are(Ca_0.99Na_0.01)(Mg_0.87Fe²⁺_0.06Fe³⁺_0.07)(Si_1.98Al_0.02)O₆ and Li_xAl Si₂O₆ respectively.The cell parameters a=9.7727(?),b=8.9044(?),c=5.2925(?),V=441.4(?)³for diopside,and a=9.472(?),b=8.397(?),c=5.217(?),V=389.6(?)³ for spodumene were calculated using the Unit Cell software and the XRD data.The infrared absorption band of diopside and spodumene is mainly composed of the vibrational mode of Si-O chain group in single chain structure.The high temperature XRD results show that Diopside keeps C2/c structure until 1200?.The axial expansion rate were also calculated.The results show that the b axis of Diopside is easier to be stretched with the increase of temperature,which means the expansion rate of b axis is greater than that of a and c axis.The high pressure XRD experiments were carried out using synchrotron radiation facility and the Diamond Anvil Cell(DAC).In the experimental pressure range,diopside and spodumene maintain the space group C2/c,without structural transformation.But with the increasing pressure,all cell parameters decrease gradually.The axial compressibility of Diopside is?_a=-2.09x10^-3GPa^-1,?_b=-2.85x10^-3GPa^-1,?_c=-2.58x10^-3GPa^-1,which means the a axis is the most difficult to compress.The compression rates of spodumene axes are?_a=-1.72x10^-3GPa^-1,?_b=-1.48x10^-3GPa^-1,?_c=-2.85x10^-3GPa^-1.The isothermal bulk modulus were also fitted by the three order Birch-Murnaghan state equation,with K_0Diopside=119.0 GPa(K'=4,V₀=440.3 3(?)³),and K_0Spodumene=144.6 GPa(K'=4,V₀=387.7 3(?)³).