Structural variations induced bv heat treatment in allanite and REE-bearini piemontite
Structural variations induced bv heat treatment in allanite and REE-bearini piemontite
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铜锰矿和稀土贝里尼皮蒙特矿热处理引起的结构变化
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BoNlizzt.
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作者：
P.lor;BoNlizzt.
在绿帘石族的含稀土矿物中，三价稀土元素取代Ca的存在需要二价阳离子（Fe 2+，Mn 2+，Mg）进入八面体位置。在空气中加热褐帘石和含稀土的硬锰矿时，Fe 2+和Mn 2+氧化;然而，电荷平衡由相应的H损失维持。目前的工作涉及这一进程所涉及的结构调整。为此，选择了两种单晶（褐帘石和含稀土的硬硅钙石）进行热处理和结构研究。晶体在空气中在380和900 ℃之间的几个温度下退火48小时。每次热处理后，测定晶胞参数。每当晶格参数发生显着变化时，进行结构细化，并检查随着加热温度的升高而发生的结构变化。氧化主要导致平均M3-O八面体距离的缩短，并在较小程度上，平均M1-O距离;脱氢是明显的显着延长的供体受体的距离，以及通过补偿缩短的键距离，涉及的OH中的O 1 0。热处理也引起了轻微的迁移八面体阳离子，推断从电子的数量变化来自占位细化。氧化-脱氢过程引起晶胞参数的变化。特别是，缩短的b（这是平行于八面体链）中观察到处理的褐帘石晶体。在含稀土的锰铁矿样品中，由于氧化作用，
In REE-bearing minerals of the epidote group, the presence of trivalent rare earth elements substituting for Ca requires the entry of divalent cations (Fe2+, Mn2+, Mg) in the octahedral sites. Upon heating allanite and REE-bearing piemontite in air, Fe2+ and Mn2+ oxidize; however, the charge balance is maintained by a corresponding H loss. The present work deals with the structural adjustments involved in this process. To this purpose, two single crystals (allanite and REE-bearing piemontite) were selected for heat treatments and structural study. Crystals were annealed in air for 48 h at several temperatures between 380 and 900'C. After each heat treatment, unit-cell parameters were determined. Structure refinements were performed whenever significant variations in the lattice parameters took place, and structural changes occurring with the increase of the heating temperature were examined. Oxidation mainly resulted in a shortening of the mean M3-O octahedral distances and, to a lesser extent, of the mean Ml-O distances; dehydrogenation was made evident by a dramatic lengthening of the donor to acceptor distance, as well as by the compensational shortening of the bond distances involving the Ol0 in OH. Heat treatments also induced a minor migration of octahedral cations, as inferred from changes in the number of electrons deriving from the site-occupancy refinement. The oxidation-de-hydrogenation process caused variations in the unit-cell parameters. In particular, a shortening ofb (which is parallel to the octahedral chains) was observed in the treated allanite crystal. In the sample of REE-bearing piemontite, the increase of Mn3*, due to the oxidation