Study on Formation Condition and Cation Site Occupancy in Garnets

1.天然石榴石用EXAFS光谱、单晶X射线衍射仪(XRD)和分析电子显微镜研究了三种铁榴石(Py石榴石、An石榴石和Al石榴石)中的位置。经X射线衍射仪结构修正后，Py和Al的R因子均小于2%，而An的R因子仅为4.8%。Py、An和Al的场地占有率如下：Py：(Fe^2+_._&lt；73&gt；Ca0。_&lt；61&gt；mN_0。(Al_3._&lt；98&gt；Fe^3+_)。_&lt；03&gt；)(Si_5._&lt；49&gt；Al_0._&lt；58&gt；)O_&lt；24&gt；，an：(Fe^2+_。_&lt；83&gt；Ca_5._&lt；06&gt；Mn_0。20&gt；)(Al_1._&lt；94&gt；Fe^3+_。_&lt；91&gt；)(Si_5._&lt；99&gt；Al_0._&lt；07&gt；)O_&lt；24&gt；，Al：(Fe^2+_。_&lt；87&gt；Ca_0。_&lt；13；mN_0。_&lt；19&gt；mg_0。_&lt；91&>)(Al_3._&lt；94&gt；Fe^3+_。_&lt；03&gt；)(Si_5._&lt；93&gt；Al_0.利用K吸收边附近的吸收光谱，用EXAFS研究了Fe离子周围的局域结构。Fe-O在Py、An和Al中的原子间距分别为2.26、2.03和2.29A。由于Mg和Fe~(2+)、Lt~(2+)和Gt~(2+)的离子强度几乎相同，所以用X射线衍射法测得的Py和Al的离子强度没有显著差异。另一方面，由于Py和Al的8个配位和6个配位上的Fe离子比例不同，EXAFS可以检测到Fe-O距离的一些差异。这样，EXAFS和X射线衍射仪的检测都被发现是非常有效的。合成稀土石榴石最近合成了各种类型的石榴石。捷克勒斯基晶体生长过程中常有小面形成的报道。小面区和非小面区晶体的细微差别被认为是晶体中产生裂纹的原因。由X射线衍射仪的精确结构分析表明，这两种材料的化学成分差别不大，但原子间距离相差很小。

1. Natural garnetsSite 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 garnetsRecently 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.