Crystal structure change of katoite, Ca3Al2(O4D4)3, with temperature at high pressure
Crystal structure change of katoite, Ca3Al2(O4D4)3, with temperature at high pressure
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卡托石 Ca3Al2(O4D4)3 晶体结构随高压温度的变化
DOI：
10.1007/s00269-018-1016-4
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发表时间：
2019
影响因子：
1.4
通讯作者：
Takanori Hattori
中科院分区：
文献类型：
--
作者：
Atsushi Kyono;Masato Kato;Asami Sano-Furukawa;Shin-ichi Machida;Takanori Hattori
为了揭示水晶石Ca3Al2(O4D4)3在高压下的高温分解机理，用高压高温中子衍射法研究了水晶石Ca3Al2(O4D4)3的结构。在空间群Iad的约束下，用Rietveld方法研究了晶体结构。在约8 Gpa的压力下，卡托石的晶胞体积随着温度的增加而增加。虽然在200℃至400℃的温度范围内观察到异常的膨胀行为，但晶胞不断膨胀至850℃。900℃时，加托石分解，残留物完全溶解在脱水水中。结果表明：在300~900℃温度范围内，高压对碳酸钙石脱水温度的提高有很强的影响，降温减压至常温后，碳酸钙石与刚玉Al_2O_3和钙铝榴石Ca(OH)_2的峰一起重新出现。在8℃时，CaO_8十二面体和Al_2O_6八面体的体积随着温度升高到850℃时分别膨胀约8%和13%。另一方面，四面体空隙收缩约10%：由于CaO_8十二面体和Al_2O_6八面体的膨胀，四面体空隙受到等渗挤压。在此温度范围内，相邻的D-D键距离几乎保持不变，而O-D键距离在分解前急剧缩小。结果表明，D-D排斥力引起的O-D距离的缩短破坏了O-D键的稳定性，从而导致卡托石的热分解。
To reveal the decomposition mechanism with temperature under high pressure, crystal structure of a hydrogrossular, katoite Ca3Al2(O4D4)3has been studied by high-pressure and high-temperature neutron diffraction technique. The crystal structure was investigated using Rietveld method under a constraint of the space groupIad. At pressure of approximately 8 GPa, the unit cell volume of katoite increased as a function of temperature. Although unusual expansion behavior was discerned in a temperature range between 200 and 400 °C, the unit cell was continuously expanded up to 850 °C. At 900 °C, katoite was decomposed and the residuals were dissolved completely in the dehydrated water. The results show that high-pressure strongly affects the increase of the katoite dehydration temperature from 300 to 900 °C. After cooling and decompression to ambient conditions, the peaks of katoite reappear together with those of corundum Al2O3and portlandite Ca(OH)2. At 8 GPa, the volume of CaO8dodecahedron and AlO6octahedron expands with temperature up to 850 °C by about 8% and 13%, respectively. That of tetrahedral interstice, on the other hand, contracts by about 10%: the tetrahedral interstices are squeezed isotopically by the expansion of CaO8dodecahedra and AlO6octahedra. The neighboring D–D distance remains almost unchanged in this temperature range, while the O–D bond distance shrinks drastically just before decomposition. It is suggested that the shortening of O–D distance caused by the D–D repulsion destabilizes the O–D bond that results in the thermal decomposition of katoite.