The equilibrium shape of NaCl single crystal studied by x-ray reflection on its surfaces
Gu, You-Song
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https://hdl.handle.net/2142/29592
Description
Title
The equilibrium shape of NaCl single crystal studied by x-ray reflection on its surfaces
Author(s)
Gu, You-Song
Issue Date
1992
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
NaCl crystals
equilibrium crystal shapes
X-ray reflection
Language
en
Abstract
The equilibrium shape of NaCl single crystals has been studied by x-ray reflectivity measurements at high symmetric surfaces. The equilibrium shape of a crystal is related to the properties of its surfaces through its surface free energy by means of the Wulff construction. Glancing angle x-ray reflectivity is used to measure the properties of the surfaces. X-ray reflectivities from the NaCl (100), (110) and (111) surfaces are measured during annealing of the samples at high temperatures ranging from 550°C to 700°C. A new method to calculate the x-ray reflectivity has been derived in matrix form for a given arbitrary varying surface layer. With this method, the surface mean width can be obtained by fitting the experimental data of the reflected x-ray intensity to the calculated result for a given surface model. Therefore, the mean width of NaCl surface as a function of annealing time and temperature can be obtained from the experiment. The expe~imental results show that NaCl (100) surface is a perfect, smooth surface, while NaCl (110) and (111) surfaces are stable surfaces when annealing at high temperatures. From the experiments it must be concluded that in the experimental temperature range from 550°C to 700°C the shape of NaCl single crystals is a cube with round edges and blunted corners.
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