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Phase transitions in [Ca(H2O)4](ClO4)2 studied by differential scanning calorimetry, X-ray single crystal diffraction and neutron powder diffraction

✍ Scribed by Joanna Hetmańczyk; Łukasz Hetmańczyk; Anna Migdał-Mikuli; Edward Mikuli; Wojciech Nitek

Publisher
Elsevier Science
Year
2008
Tongue
English
Weight
646 KB
Volume
891
Category
Article
ISSN
0022-2860

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✦ Synopsis

Four phase transitions at: T h C1 ¼ 267:1 K, T h C2 ¼ 258:8 K, T h C3 ¼ 254:1 K and T h C4 ¼ 195:4 K (on heating) and at T c C1 ¼ 263:8 K, T c C2 ¼ 255:4 K, T c C3 ¼ 246:0 K (on cooling) were determined for [Ca(H 2 O) 4 ](ClO 4

) 2 between 90 and 295 K by means of differential scanning calorimetry (DSC). Phase transitions discovered at T C1 , T C2 and T C3 are connected with small change of the crystal structure. Namely, there are scant but statistically significant differences between unit cell parameters (angles: a, b, c) and torsion angles in the structure of [Ca(H 2 O) 4 ](ClO 4 ) 2 at 293 and 240 K. The space group (P 1; No. 2) is the same for high, intermediate and low temperature phase, however, changes of perchlorate anions orientations are distinctly visible.

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