1990 Fiscal Year Final Research Report Summary
Study on Formation Condition and Cation Site Occupancy in Garnets
| Project/Area Number |
63460052
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
鉱物学(含岩石・鉱床学)
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| Research Institution | Tokyo Institute of Technology |
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Principal Investigator |
OKADA Kiyoshi Tokyo Institute of Technology, Faculty of Engineering, Associate Professor, 工学部, 助教授 (80114859)
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| Co-Investigator(Kenkyū-buntansha) |
MORIKAWA Hideki Tokyo Institute of Technology, Res. Lab. of Eng. Mater., Associate Professor, 工業材料研究所, 助教授 (80016815)
HAYASHI Shigeo Tokyo Institute of Technology, Faculty of Engineering, Research Associate, 工学部, 助手 (20218572)
TANAKA Kiyoaki Tokyo Institute of technology, Res. Lab. of Eng. Mater., Research Associate, 工業材料研究所, 助手 (00092560)
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| Project Period (FY) |
1988 – 1990
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| Keywords | Garnets / Rare earth garnets / Crystal structure / EXAFS spectroscopy |
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| Research Abstract |
1. Natural garnets
Site occupancies in three kinds of Fe including garnets, i. e., pyrope(Py), andradite(An) and almandine(Al), have been investigated by EXAFS spectroscopy, single crystal X-ray diffraction (XRD) and analytical TEM methods. The R factors obtained by XRD structural refinement were under 2% for Py and Al but 4.8% for An. Site occupancies for Py, An and Al are as follows ;
Py : (Fe^2+_. _<73>Ca_0. _<61>Mn_0. _<10>Mg_2. _<69>)(Al_3. _<98>Fe^3+_. _<03>)(Si_5. _<49>Al_0. _<58>)O_<24>,
An : (Fe^2+_. _<83>Ca_5. _<06>Mn_0. _<20>)(Al_1. _<94>Fe^3+_. _<91>)(Si_5. _<99>Al_0. _<07>)O_<24>,
Al : (Fe^2+_. _<87>Ca_0. _<13>Mn_0. _<19>Mg_0. _<91>)(Al_3. _<94>Fe^3+_. _<03>)(Si_5. _<93>Al_0. _<06>)O_<24>.
Local structure around Fe ion has been examined by EXAFS using absorption spectra in the vicinity of K absorption edge. Interatomic distances of Fe-O in Py, An and Al were 2.26, 2.03 and 2.29A, respectively. Since the ionic dadii of Mg and Fe^<2+> are almost same, those obtained from XRD in Py and Al showed no significant difference. On the other hand, some difference in Fe-O distance can be detected by EXAFS because there is a difference in the ratio of Fe ion in 8 and 6 coordination sites for Py and Al. In this way, examination by both EXAFS and XRD was found to be very effective.
2. Synthetic rare earth garnets
Recently various kinds of garnets have been synthesized. Formation of facet is usually reported in the Czechralski crystal growth. The slight difference of crystals between facet and off facet regions is considered to yield cracking in the crystals. It was clarified from the precise structure refinemnt by XRD that there is little difference in chemical composition but a small difference in interatomic distances.
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