Thermal behaviour of polycrystalline [Ba(H2O)3](ClO4)2 and [Ba(NH3)4](ClO4)2

Phase transitions, melting processes and thermal decompositions of [Ba(H2O)3](ClO4)2 and [Ba(NH3)4](ClO4)2 were studied by differential scanning calorimetry (DSC) and thermogravimetric analysis connected with quadruple mass spectrometer (TGA/QMS). The phase transition at TCh=304.0K (on heating) and at TCc=286.8K (on cooling) was detected for [Ba(NH3)4](ClO4)2 by means of DSC, but none phase transition at that temperature range has been registered for [Ba(H2O)3](ClO4)2. The decomposition process of the [Ba(H2O)3](ClO4)2 supervene in the three main stages. In stage I (305-520 K) dehydration of [Ba(H2O)3](ClO4)2 to anhydrous Ba(ClO4)2 undergoes in two steps, in which consecutively 1/3 (at 305-360 K) and 2/3 (at 361-520 K) of all H2O molecules are liberated. In stage II (521-740 K) anhydrous Ba(ClO4)2 has two solid-solid phase transitions: at TC1 = 566.6 K and at TC2 = 641.7 K. Next it melts at Tm = 760 K. Stage III (above 761 K) is connected with decomposition and explosion of melted Ba(ClO4)2. The decomposition process of the [Ba(NH3)4](ClO4)2 supervene in the three main stages, too. Stage I (310-520 K) is connected with deammination of [Ba(NH3)4](ClO4)2 to Ba(ClO4)2 and all NH3 molecules are liberated. Stages II and III (521-850 K) are exactly the same as they were observed for [Ba(H2O)3](ClO4)2.