锐钛矿呈体心四方对称性,因此晶面指标之和h+k+l为奇数时对应衍射线的强度为零,存在系统消光现象,并非所有晶面都能产生XRD、ED斑/峰。SAED可以观测到的只能是晶面指标之和h+k+l为偶数的相应晶面产生的衍射斑或环。如何是对结晶较好的单晶粒进行衍射,可以得到明锐的衍射点阵,具体点阵形式与电子束照射方向或晶面方向直接关联;如果衍射对象是多晶粒,可能获得的是一系列同心的衍射环或呈环状分布的衍射斑,环或斑的宽度与结晶度呈负相关关系。从SAED得出的点阵周期或环半径可以用于与假定物相的晶面间距表对照,以此进行物相定性分析,不过对单晶粒一般需要选取多个方向对不同晶面分别进行衍射才能给出可靠结论,在有多个物相时不宜同时选取多晶粒进行衍射。
以下是锐钛矿的衍射数据:
Card Information
Names: Titanium Oxide
Anatase, syn
Formula: Ti O2
PDF Number: 21-1272
Quality: star
Subfiles: inorganic mineral alloy COR CP EDU FOR NBS
Cell and Symmetry Information
System: tetragonal Space Group: I41/amd (no. 141)
a: 3.7852 c: 9.5139
Density (Dx): 3.893 Z: 4
Instrument Information
Radiation: Wavelength:
Instrument(d): unknown
Instrument(I): unknown I type: unknown
I/Icor: 3.3
Comments and Additional Information
Colour: Colorless
Pattern: See ICSD 9852 (PDF 01-071-1166).
Source: Sample obtained from National Lead Co., South Amboy, New Jersey, USA.
General: Anatase and another polymorph, brookite (orthorhombic), are converted to rutile (tetragonal) by heating above 700 C.
General: Pattern reviewed by Holzer, J., McCarthy, G., North Dakota State Univ, Fargo, North Dakota, USA, ICDD Grant-in-Aid (1990). Agrees well with experimental and calculated patterns.
Pattern: Validated by calculated pattern.
Temperature: Pattern taken at 25 C.