A high-temperature and high-pressure Raman spectroscopic study of CaGeO3 garnet
A high-temperature and high-pressure Raman spectroscopic study of CaGeO3 garnet
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DOI：
10.1007/s002690050009
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发表时间：
2000-02
影响因子：
1.4
通讯作者：
T. Chaplin;Nancy L. Ross;Bruno Reynard
中科院分区：
文献类型：
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作者：
T. Chaplin;Nancy L. Ross;Bruno Reynard
在11.5 GPa和1225 K的温度下，分别采集了cageo3四方石榴石的高压和高温拉曼光谱，以研究其可能的本征非调和行为。在研究范围内，观察到拉曼峰的位置随压力和温度呈线性变化，高能量峰比低能峰表现出更大的p和t诱导位移。观察到的汞诱导的位移与报道的镁铝榴石和铁长石相似，而观察到的磷诱导的位移通常比铝硅酸盐和镁sio3majorite石榴石大（Gillet等）。1992年;Rauch等人。1996)，因为cageo3石榴石的体积模数较大。利用观察到的cageo3石榴石的模式位移来确定该相的等温和等压模式grisen参数。这些参数的值与先前报道的粗砂和andradite相似（Gillet等）。1992)。计算出的cageo3石榴石的本征非调和参数ai为非零，表明该相具有明显的非调和行为。这些值的范围从−3.8 × 10−5K−1到−1.3 × 10−5K−1，也与报道的andradiite和grossular的值相似，但小于为pyrope测定的值（Gillet等）。1992)。因此，我们期望MgSiO3majorite表现出比我们研究的日耳曼酸盐类似物更大的非调和性。为cageo3方形石榴石确定的非调和参数现在可以引入准调和振动热容模型，以解释所观察到的非调和行为。
High-pressure and high-temperature Raman spectra of CaGeO3tetragonal garnet have been collected to 11.5 GPa and 1225 K, respectively, in order to investigate possible intrinsic anharmonic behaviour in this phase. The Raman peak positions were observed to vary linearly with pressure and temperature within the ranges studied, with the higher-energy peaks showing largerP- andT-induced shifts than the low energy modes. The observedT-induced shifts are similar to those reported for grossular and andradite, while the observedP-induced shifts are generally larger than those of aluminosilicate and MgSiO3majorite garnets (Gillet et al. 1992; Rauch et al. 1996) due to the larger bulk modulus of CaGeO3garnet. The observed mode shifts of CaGeO3garnet were used to determine the isothermal and isobaric mode Grüneisen parameters for this phase. These parameters are similar in value to those reported previously for grossular and andradite (Gillet et al. 1992). The calculated intrinsic anharmonic parameters,ai, for CaGeO3garnet were determined to be nonzero, indicating significant anharmonic behaviour for this phase. These values, which range from −3.8 × 10−5K−1to −1.3 × 10−5K−1, are also similar to those reported for andradite and grossular, but smaller than those determined for pyrope (Gillet et al. 1992). Hence, we expect MgSiO3majorite to show greater anharmonicity than the germanate analogue studied by us. The anharmonic parameters determined for CaGeO3tetragonal garnet may now be introduced into quasiharmonic vibrational heat capacity models to account for the observed anharmonic behaviour.