ABSTRACT The compressibility and effect of pressure on the vibrations of merrillite, Ca9NaMg(PO4)7, were studied by using diamond anvil cell at room temperature combined with in-situ synchrotron X-ray diffraction and Raman spectroscopy up to about 18 and 15 GPa, respectively. The pressure-volume data was fitted by a third-order Birch–Murnaghan equation of state to determine the isothermal bulk modulus as K0 = 87.2(32) GPa with pressure derivative K0′ = 3.2(4). If K0′ = 4, the isothermal bulk modulus was obtained as 81.6(10) GPa. The axial compressibility was estimated and an axial elastic anisotropy exists since a-axis is less compressible than the c-axis. The Raman frequencies of all observed modes for merrillite continuously increase with pressure, and the pressure dependences of stretching modes (v 3 and v 1) are larger than those of the bending modes (v 4 and v 2) and external modes. The isothermal mode Grüneisen parameters and intrinsic anharmonicity of merrillite were also calculated.

中文翻译：

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高压下磷灰石的 X 射线衍射和拉曼光谱

摘要 利用金刚石砧室在室温下结合原位同步加速器 X 射线衍射和拉曼光谱高达约 18 和 15 GPa，研究了压力对钙钛矿 Ca9NaMg(PO4)7 振动的压缩性和影响，分别。压力-体积数据通过三阶 Birch-Murnaghan 状态方程拟合，以确定等温体积模量 K0 = 87.2(32) GPa，压力导数 K0' = 3.2(4)。如果 K0' = 4，则获得的等温体积模量为 81.6(10) GPa。估计轴向压缩率并且存在轴向弹性各向异性，因为 a 轴的可压缩性小于 c 轴。所有观察到的墨晶石模式的拉曼频率随着压力不断增加，并且拉伸模式（v 3 和v 1）的压力依赖性大于弯曲模式（v 4 和v 2）和外部模式的压力依赖性。还计算了等温模式 Grüneisen 参数和磷灰石的固有非谐性。