We collected in situ high-temperature powder X-ray diffraction (XRD) patterns, as well as Raman and Fourier transform infrared (FTIR) spectra on a natural serandite sample. The volumetric thermal expansion coefficient αV (K−1) is determined as a linear function of T (K): 37.6(5) × 10−9 × T + 11.1(3) × 10−6, with an averaged value of 31.7(10) × 10−6 K−1, while the anisotropy of axial thermal expansivities shows the order of αa > αb > αc. The isobaric Grüneisen parameters γiP are constrained as: 0.2–1.6 for most of the lattice vibrations below 500 cm−1; while 0–0.6 for the O–Si–O bending and Si–O stretching modes inside the Si3O9 chains above 500 cm−1. As compared with common silicate phases in the upper mantle and the transition zone, the γiP parameters for the internal vibrations are significantly smaller in silicate chains (serandite, enstatite) than those in Si2O7 groups (wadsleyite) and isolated SiO4 units (forsterite, pyrope), since the rotation of the bridging O atoms (in the direction perpendicular to Si–O–Si) could relax the SiO4 tetrahedra at elevated temperature. The OH-bending vibration of serandite is observed in both Raman-active (1378 cm−1) and IR-active (1389 cm−1) modes, with a temperature-dependence of − 0.07 and − 0.09 cm−1/K, respectively. The red-shift of these OH-bending modes with increasing temperature indicates that the hydrogen bond gets weaker as the O3…O4 distance becomes larger during thermal expansion. Additionally, our polarized FTIR spectra confirm that the stretching mode of the very strong hydrogen bond, a broad absorption region (1400–3300 cm−1), is polarized in the direction of E//b, as reported by Hammer et al. (Am Mineral 83:569–576, 1998).

中文翻译：

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绢云母的高温 X 射线衍射、拉曼和红外光谱

我们收集了天然绢云母样品的原位高温粉末 X 射线衍射 (XRD) 图案，以及拉曼和傅里叶变换红外 (FTIR) 光谱。体积热膨胀系数 αV (K−1) 确定为 T (K) 的线性函数：37.6(5) × 10−9 × T + 11.1(3) × 10−6，平均值为 31.7( 10) × 10−6 K−1，而轴向热膨胀率的各向异性显示为αa > αb > αc。等压 Grüneisen 参数 γiP 被限制为：对于低于 500 cm-1 的大多数晶格振动为 0.2–1.6；而 0-0.6 对于 500 cm-1 以上的 Si3O9 链内的 O-Si-O 弯曲和 Si-O 拉伸模式。与上地幔和过渡带中常见的硅酸盐相相比，硅酸盐链（serandite, 顽火石）比 Si2O7 基团（wadsleyite）和孤立的 SiO4 单元（镁橄榄石、镁橄榄石）中的那些，因为桥接 O 原子的旋转（在垂直于 Si-O-Si 的方向上）可以在高温下松弛 SiO4 四面体。在拉曼活性 (1378 cm-1) 和 IR 活性 (1389 cm-1) 模式下观察到丝绿岩的 OH 弯曲振动，温度依赖性分别为 - 0.07 和 - 0.09 cm-1/K . 随着温度升高，这些 OH 弯曲模式的红移表明氢键在热膨胀过程中随着 O3…O4 距离变大而变弱。此外，我们的偏振 FTIR 光谱证实了非常强的氢键的拉伸模式，一个宽吸收区（1400-3300 cm-1），在 E//b 的方向上偏振，如 Hammer 等人报道的那样。(Am Mineral 83:569–576, 1998)。