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標題Title: X-ray and resistance studies of the melting and freezing
作者Authors: 林開政,E V Charnayayx..等
上傳單位Department: 機械工程系
上傳時間Date: 2010-6-30
上傳者Author: 林開政
審核單位Department: 機械工程系
審核老師Teacher: 林開政
檔案類型Categories: 論文Thesis
關鍵詞Keyword: x-ray, phase transitions
摘要Abstract: Abstract. The melting and freezing processes and the structure of gallium in an opal were
studied using x-ray powder diffraction within the temperature range 10 to 320 K. Four different
modifications of solid confined gallium were found. Two of these modifications did not coincide
with any known gallium structures; another two coincided with -Ga and disordered -Ga. The
broadening of the total melting and freezing processes and reduction of the phase transition
temperatures compared to bulk -Ga phase were obtained. The size of confined gallium
crystallites corresponding to the different modifications was estimated for cooling and warming.
The reproducible freezing was treated as a result of the steep temperature dependence of the
nucleation rate in supercooled melts. Additional measurements of resistance for the opal filled
with gallium revealed that it was sensitive mainly to the melting and freezing within the gallium
modification coinciding with disordered -Ga. Melting–freezing hysteresis for this modification
was found to depend on temperatures of pre-warming. It was suggested that the freezing of this
modification is driven by the amount of frozen crystallites of the phase with the highest onset
of freezing. The melting broadening and the lowering of the phase transition temperatures for
the confined gallium modifications were discussed.

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