Thermal behavior of mullite between 4 K and 1320 K
Thermal behavior of mullite between 4 K and 1320 K
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DOI：
10.1111/jace.15028
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发表时间：
2017-11-01
影响因子：
3.9
通讯作者：
Gesing, Thorsten M.
中科院分区：
文献类型：
--
作者：
Murshed, Mohammad Mangir;Sehovic, Malik;Gesing, Thorsten M.
使用中子和 X 射线粉末衍射测量了 2:1 和 3:2 莫来石在 4 K 至 1320 K 之间的公制参数的演变。在低温下观察到 a 泡孔参数以及泡孔体积的负热膨胀，2:1 莫来石比 3:2 莫来石更明显。每个参数均使用 0 K 零压力状态方程的 Gruneisen 一阶近似进行模拟，其中振动能量使用微观方法计算。虽然 b 细胞和 c 细胞参数仅需要一个德拜项，但需要具有负格鲁内森参数的第二个德拜谱才能拟合 a 细胞参数以及细胞体积。在 4 K、300 K 和 1320 K 下，模型分别计算出 2:1 莫来石的体积热膨胀系数为 0.09x10(-6) K-1、9x10(-6) K-1 和 17.3x10(-6) K-1，以及 0.09x10(-6) K-1、8.7x10(-6) K-1， 3:2 莫来石为 17.3x10(-6) K-1。温度相关的拉曼光谱和声子态密度暗示了低温下细胞收缩的可能微观来源。提出了一种简单的多项式方法来计算 3:2 莫来石的弹性刚度系数，该系数无法从实验中获得。
The evolution of metric parameters of 2:1 and 3:2 mullites have been measured between 4 K and 1320 K using neutron and X-ray powder diffraction. Negative thermal expansion was observed at low temperature for the a-cell parameter and consequently for the cell-volume, which is more pronounced for 2:1 mullite than those for 3:2 mullite. Each parameter is simulated using Gruneisen first-order approximation for the zero pressure equation of state at 0 K, where the vibrational energy was calculated using microscopic approach. While the b- and c-cell parameters require only one Debye term, a second Debye spectrum with negative Gruneisen parameter was required to fit the a-cell parameter as well as the cell volume. At 4 K, 300 K and 1320 K the model, respectively, calculates the volume thermal expansion coefficients of 0.09x10(-6) K-1, 9x10(-6) K-1, and 17.3x10(-6) K-1 for 2:1 mullite, and 0.09x10(-6) K-1, 8.7x10(-6) K-1, and 17.3x10(-6) K-1 for 3:2 mullite. Temperature-dependent Raman spectra and phonon density of states hint for the possible microscopic sources of the cell contraction at low temperature. A simple polynomial approach is presented to calculate the elastic stiffness coefficients of the 3:2 mullite, which are not available from experiments.