Study on Formation Condition and Cation Site Occupancy in Garnets

1. 采用EXAFS光谱、单晶x射线衍射（XRD）和TEM分析方法，研究了三种含铁石榴石（pyrope, Py）、红锰矿（andradite, An）和铝石榴石（almandine, Al）的占位率。XRD结构细化得到的R因子对Py和Al的影响小于2%，对An的影响为4.8%。Py、An和Al的场地占用情况如下：Py = （Fe^2+_）_ < 73 > Ca_0。_ < 61 > Mn_0。10 > _ < Mg_2。_ < 69 >) (Al_3。_ < 98 >铁^ 3 + _。_ (Si_5 < 03 >)。_ < 49 > Al_0。_<58>) _<24>,An: (Fe^2+_。_ < 83 > Ca_5。_ < 6 > Mn_0。20 > _ <) (Al_1。_ < 94 >铁^ 3 + _。_ < 91 >) (Si_5。_ < 99 > Al_0。_<07>) _<24>,Al: (Fe^2+_。_ < 87 > Ca_0。_ < 13 > Mn_0。19 > _ < Mg_0。_ < 91 >) (Al_3。_ < 94 >铁^ 3 + _。_ (Si_5 < 03 >)。_ < 93 > Al_0。24 > _ < 06 >) O_ <。利用K吸收边缘附近的吸收光谱，用EXAFS研究了Fe离子周围的局部结构。Fe-O在Py、An和Al中的原子间距离分别为2.26、2.03和2.29A。由于Mg和Fe^<2+>的离子密度几乎相同，所以Py和Al的x射线衍射结果没有显著差异。另一方面，由于Py和Al的8和6个配位位点上Fe离子的比例不同，EXAFS可以检测到Fe- o距离的一些差异。因此，EXAFS和XRD的检测是非常有效的。稀土石榴石的合成近年来已合成了多种类型的石榴石。切拉尔斯基晶体生长过程中经常报道小面的形成。晶面和非晶面区域之间的微小差异被认为是导致晶体开裂的原因。通过x射线衍射（XRD）对其结构进行了精确的细化，结果表明，两者的化学成分差别不大，但原子间距离差别不大。

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.