Anomalous behavior at the I2/a to Imab phase transition in SiO2-moganite:: An analysis using hard-mode Raman spectroscopy
Anomalous behavior at the I2/a to Imab phase transition in SiO2-moganite:: An analysis using hard-mode Raman spectroscopy
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DOI：
10.2138/am.2007.2184
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发表时间：
2007-04-01
影响因子：
3.1
通讯作者：
Post, Jeffrey E.
中科院分区：
文献类型：
--
作者：
Heaney, Peter J.;McKeown, David A.;Post, Jeffrey E.
二氧化硅多晶型摩根石通常与年龄小于 100 Ma 的微晶二氧化硅品种中的石英共生。同步加速器 X 射线衍射表明，当莫干石被加热到大约 570 K 以上时，会发生位移相变，并且对称性从 I2/a 到 Imab 增加。在本研究中，我们采用硬模式拉曼光谱来确认α-β莫干石转变的存在，并为转变机制提供补充见解。我们对 501 Delta cm(-1) 对称拉伸弯曲振动（B-3g，模式）随温度变化的位移的分析有力地支持了 570 至 590 K 之间单斜相到斜方相变的存在。然而，在 593 至 723 K 之间，模式保持固定在 496 Delta cm(-1)。这种行为在冷却时重复，但滞后超过 100 K。我们提出了三个假设来解释这一观察结果：（1）IP 莫干石内纳米级石英片层的共生可能会产生抑制转变的应变； (2) 该转变可能表现出马氏体特征，其特征是在有限的温度区间内α-莫干石和β-莫干石共存； (3)α-和β-莫干石转变可以通过中间相发生。
The silica polymorph moganite is commonly intergrown with quartz in microcrystalline silica varieties that are less than similar to 100 Ma in age. Synchrotron X-ray diffraction suggests that a displacive phase transition occurs when moganite is heated above similar to 570 K, with an increase in symmetry from I2/a to Imab. In the present study, we employed hard-mode Raman spectroscopy to confirm the existence of the alpha-beta moganite transformation and to offer complementary insight into the transition mechanism. Our analysis of the displacement of the 501 Delta cm(-1) symmetric stretching-bending vibration (B-3g, mode) with changing temperature strongly supports the existence of a monoclinic-to-orthorhombic phase transition between 570 and 590 K. Between 593 and 723 K, however, the mode remained fixed at 496 Delta cm(-1). This behavior was repeated on cooling, but with a hysteresis of over 100 K. We offer three hypotheses that may explain this observation: (1) the intergrowth of nanoscale quartz lamellae within I P moganite may exert a strain that inhibits the transition; (2) the transition may exhibit a martensitic character marked by the co-existence of alpha- and beta-moganite over a finite temperature interval; and (3) the alpha- and beta-moganite transition may occur via an intermediate phase.