Abstract The Raman spectra and in-situ X-ray diffraction patterns of synthetic merrillite, Ca9NaMg(PO4)7, have been measured up to 1173 K at ambient pressure. No phase transformation was observed in this study. The effect of temperature on the Raman spectra shows that all observed active bands continuously shift to lower wavenumber with increasing temperature. The temperature dependences of v3 anti-symmetric P O stretching modes are larger than those of v1 symmetric P O stretching, v4 and v2 O P O bending modes and the external modes. Lattice parameters and volume were analyzed, and the thermal expansion coefficients were obtained as 4.86(5) × 10−5 K-1, 1.46(1) × 10−5 K-1 and 1.94(5) × 10−5 K-1 for V, a and c, respectively. Thermal expansion of merrillite shows an axial anisotropy with a smaller expansion coefficient along the a-axis. The average isobaric mode Gruneisen parameter for the internal PO4 modes of merrillite has been calculated as 0.57.

中文翻译：

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不同温度下镁晶石的拉曼光谱和 X 射线衍射

摘要 在环境压力下，在高达 1173 K 的温度下测量了合成磷灰石 Ca9NaMg(PO4)7 的拉曼光谱和原位 X 射线衍射图。在这项研究中没有观察到相变。温度对拉曼光谱的影响表明，随着温度的升高，所有观察到的活性谱带不断地向较低波数移动。v3 反对称 PO 拉伸模式的温度依赖性大于 v1 对称 PO 拉伸、v4 和 v2 OPO 弯曲模式以及外部模式的温度依赖性。分析晶格参数和体积，得到热膨胀系数为 4.86(5) × 10−5 K-1、1.46(1) × 10−5 K-1 和 1.94(5) × 10−5 K-1分别为 V、a 和 c。merrillite 的热膨胀表现出轴向各向异性，沿 a 轴具有较小的膨胀系数。