Phase transitions in [Ca(H₂O)₄](NO₃)₂ studied by differential scanning calorimetry, X-ray single crystal diffraction and neutron powder diffraction: Part I

详细信息	查看全文 | 推荐本文 |

• 作者：Anna Migda&#x142 ; -Mikuli ; Joanna Hetma&#x144 ; czyk ; Wojciech Nitek ; Edward Mikuli ; &#x141 ; ukasz Hetma&#x144 ; czyk
• 关键词：Tetraaquacalcium nitrate(V) ; Phase transitions ; Structural changes ; Differential scanning calorimetry ; X-ray single crystal diffraction ; Neutron powder diffraction
• 刊名：Journal of Alloys and Compounds
• 出版年：2007
• 期刊代码：45_09258388
• 类别：ms
• 出版时间：25 April 2007
• 卷：432
• 期：1-2
• 页码：232-240
• 文件大小：594 K

摘要

Two phase transitions at: and (on heating) and at: and (on cooling) were determined for [Ca(H₂O)₄](NO₃)₂ between 90 and 300 K by means of differential scanning calorimetry (DSC). Large thermal hysteresis (22 K) of T_C1 phase transition is characteristic for similar compounds indicating high degree of dynamical disorder of NO₃⁻ anions. Phase transition discovered at T_C2 is connected with small change of the crystal structure. Namely, at low temperature phase the unit cell is doubled and there are scant but statistically significant differences between atom positions at 100 and 215 K. The space group (P2₁/n; No. 14) is the same for high, intermediate and low temperature phase, however, changes of water molecules orientations and changes in the net of hydrogen bonds are distinctly visible.