ISSN:
1089-7623
Source:
AIP Digital Archive
Topics:
Physics
,
Electrical Engineering, Measurement and Control Technology
Notes:
In order to study the process of reaction in crystals, it is necessary to observe decomposition of precursor and formation of the product during the transformation. Since such change is related to the structures of both the phases, x-ray diffraction is the most powerful method for this purpose. However, not only Bragg reflections but diffuse scattering or satellite reflections are observed occasionally in the early stage of the process and intensities of those scattering are extremely weak although they are important to analyze the process. Therefore, use of synchrotron radiation is desirable to study those problems. There are many compounds which show topotaxy during phase transformation. Since the product of such transformation is formed in an oriented manner under the influence of the structure of the precursor, diffraction patterns of the product are similar to those of a single crystal and anomaly of the diffraction can be easily detected. We have consequently studied the process of dehydration in α-AlOOH which indicates topotaxy in the process of dehydration. α-AlOOH transforms to α-Al2O3 at about 500 °C when it is heated in air. Lima-de-Faria (1963) found that the products revealed distinct satellite reflections along c* direction on x-ray diffraction patterns when the samples are quenched to room temperature in the early stage of reaction. Similar phenomena are also known in dehydration of α-FeOOH to α-Fe2O3 (both of them are isostructural to α-AlOOH and α-Al2O3, respectively). No interpretation has yet been established to the origin of the satellites. We have analyzed the averaged structure, interpreted the satellite reflections and change of profile of the satellites, and have elucidated the process of the reaction. The results indicate that the origin of the satellites is ascribed to the modulation of Al content along c direction and the change of the profile to the change in the mode of the modulation.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.1140771
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