黑柱石的高压相变及其压缩性研究

利用金刚石压腔(DAC)和原位同步辐射X射线衍射(XRD)技术, 研究天然黑柱石单晶室温下的高压结构稳定性和压缩性, 实验最高压力为39.5 GPa。实验中观察到黑柱石在19.2 GPa 时从斜方晶系α相(空间群Pnam)转变为单斜晶系β相(空间群P2₁/a), 转变过程中晶胞体积没有明显的不连续变化。利用Birch-Murnaghan状态方程, 对黑柱石单胞体积随压力的变化关系(P-V)进行拟合, 得到α相黑柱石状态方程参数为K₀=118(4) GPa, V₀=671.9(5) A³, K₀′=6.6(7); β相黑柱石初始相变压力P_r=19.2 GPa, 状态方程参数为K_r=157(3) GPa, V_r=599.3(6) A³, K_r′=4 (固定)。此外, 确定了α相和β相黑柱石的轴压缩系数, 并从化学组成和晶体结构压缩性各向异性的角度讨论相变机理。

Phase Transitions and Compressibility of Ilvaite at High Pressures

The high-pressure phase stability and compressibility of a natural orthorhombic symmetry ilvaite are investigated up to 39.5 GPa at room temperature using diamond anvil cell (DAC) combined with in-situsynchrotron radiation single-crystal X-ray diffraction. Experimental results show that ilvaite undergoes a structural transition from an orthorhombic α-phase (Pnam) to a monoclinic β-phase (P2₁/a) at 19.2 GPa. This structural transformation from α to β phase is displaced without any obvious discontinuity in volume across the transition. The pressure-volume data of ilvaite are described by the third-order Birch-Murnaghan equation of state, yielding K₀=118(4) GPa,V₀=671.9(5)A³,K₀′=6.6(7)for α-ilvaite and K_r=157(3) GPa, V_r=599.3(6) A³, K₀′=4(fixed) with a phase transition pressure P_r=19.2 GPa for β-ilvaite. In addition, the axial compression coefficients for both α- and β-ilvaites are determined, and the mechanism of the pressure-induced Pnam to P2₁/a phase transition is discussed in the views of crystal structure and the anisotropy of compressibility.