Dielectric Properties and Thermal Decomposition of K^sub 2^Ni(SO^sub 4^)^sub 2^ Crystals

The dielectric properties of K2Ni(SO4)2 crystals have been measured as a function of frequency (100 Hz to 1 MHz) and temperature (400 K to 900 K). The results show that the real part of the conductivity follows the universal dielectric response, where the activation energy varies from 0.72 eV up to 1.08 eV for the temperature range studied. On the other hand, the permittivity and conductivity parameters present a change in their frequency dependence at around 620 K, suggesting that a phase transition might be taking place. To understand this unexpected result, complementary study by thermogravimetric and differential thermal analyses, X-ray powder diffraction analysis, and Raman spectroscopy measurements was carried out. The results suggest thermal decomposition of the original compound at 620 K as follows: 2K2Ni(SO4)2 [arrow right] K2Ni2(SO4)3 + K2SO4.