In-Situ High-Pressure Synchrotron X-Ray Diffraction of Natural Epidote
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摘要: 在金刚石压腔高压装置(DAC)上采用同步辐射角度色散X射线衍射技术，在室温、最高压力9.16 GPa条件下，对天然绿帘石进行了状态方程研究。在实验压力范围内，未观察到绿帘石发生相变。通过Birch-Murnaghan状态方程，对所获得的实验数据进行了状态方程拟合，获得了天然绿帘石的体弹模量值为116(7) GPa，体弹模量的压力导数值为7.8(8)，若将体弹模量的压力导数值固定为4，获得绿帘石的体弹模量值为132(4) GPa。另外，绿帘石存在较为明显的轴向压缩各向异性：c轴方向压缩系数最大，b轴方向压缩系数最小，说明天然绿帘石在c轴方向更易于压缩，而b轴方向最抗压。Abstract: In situ angle dispersive X-ray diffraction measurements for a natural epidote were performed with diamond anvil cell instrument and synchrotron radiation at NSLS (National Synchrotron Light Source).The maximal pressure in the experiment was 9.16 GPa.At experimental pressures, no evidence of phase transition of the epidote was observed.A fit to the third-order Birch-Murnaghan equation of state yielded an isothermal bulk modulus of 116(7) GPa and its pressure derivative of 7.8(8).The isothermal bulk modulus of epidote is determined to be 132(4) GPa, assuming that its first pressure derivative is 4.Furthermore, we confirm that the linear compressibilities along a, b, and c directions of epidote are elastically anisotropic.Consequently, it can be concluded that the compressibility of epidote under high pressures has been accurately constrained.
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Key words:
- equation of state /
- natural epidote /
- X-ray diffraction /
- synchrotron radiation
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图 1 绿帘石在不同压力下的代表性X射线衍射谱
Figure 1. Representative X-ray diffraction patterns of the epidote at pressures up to 9.16 GPa
表 1 绿帘石在不同压力下的晶胞参数
Table 1. Cell parameters versus pressure for epidote
p/(GPa) a/(nm) b/(nm) c/(nm) β/(°) V/(nm3) 0.0001 0.891 8(8) 0.563 9(7) 1.018 8(6) 115.39(4) 0.463 5(4) 1.40 0.889 7(8) 0.562 9(4) 1.013 8(7) 115.35(6) 0.458 8(5) 2.40 0.887 7(9) 0.561 6(5) 1.011 1(8) 115.38(7) 0.455 4(5) 3.34 0.885 7(8) 0.560 4(6) 1.007 9(9) 115.37(8) 0.452 1(6) 4.47 0.883 1(7) 0.559 1(6) 1.004 8(8) 115.35(9) 0.448 3(7) 5.53 0.880 8(9) 0.557 9(6) 1.002 1(9) 115.33(9) 0.445 1(6) 6.54 0.877 9(8) 0.557 1(7) 0.999 7(7) 115.33(8) 0.441 9(7) 8.26 0.875 5(9) 0.556 0(7) 0.996 2(8) 115.28(9) 0.438 5(7) 9.16 0.874 8(7) 0.555 4(6) 0.995 7(9) 115.31(7) 0.436 8(8) 
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表 2 绿帘石和斜黝帘石的弹性参数值
Table 2. The elastic parameters of epidote and clinozoisite
Samples K0/(GPa) K0′ References Epidote 162(4) 4(Fixed) Holland, et al.[3] Epidote 207(15) 4(Fixed) Qin, et al.[4] Epidote 111(3) 7.6(7) Gatta, et al.[5] Epidote 124(1) 4(Fixed) Gatta, et al.[5] Clinozoisite 138(3) 4(Fixed) Fan, et al.[12] Epidote 116(7) 7.8(8) This study Epidote 132(4) 4(Fixed) This study
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