Phase behaviour and superionic phase transition in K3H(SeO4)2

Abstract

The phase behaviour of K 3 H(SeO 4 ) 2 (TKHSe) above room temperature has been studied by differential scanning calorimetric (DSC), thermogravimetric analysis (TGA), simultaneous thermogravimetric and mass spectroscopy analysis (TG-MS), impedance spectroscopy (IS) and X-ray powder diffraction (XRD). Our results show that the previously claimed superionic phase transition in TKHSe at around 388 K (114.85°C) is also the onset temperature of a slow thermal dehydration that occurs at reaction sites distributed over the surface of the crystal. That is, we propose that the TKHSe undergoes simultaneously a superionic phase transition and a decomposition process with a very slow reaction rate that is evident when the sample is pulverized to fine powder, both starting at the same temperature. As a matter of fact, we observe a decrease of the magnitude of the dcconductivity on successive thermal runs in powdered sample attributed to sample decomposition that starts at the surface of the TKHSe grains, but the jump in conductivity is only a consequence of the order-disorder transition in the TKHSe phase that remains inside the grains.

Ion transport mechanism in anhydrous lithium thiocyanate LiSCN part III: charge carrier interactions in the premelting regime

“…5 Comparison of superionic phase transition temperatures for different materials with mobile ions such as F À , 5,9 O 2À , 6,30 Ag + , 5,31 Li + , 7,15,32 Na + , 8,33 K + , 8,9,11,16 and H + . 14,[34][35][36] (a) Superionic transition temperatures T s for various ionic conductors; (b) correlation of T s for selected ion conductors from (a) with the respective melting temperatures T m . The values of T s and T m were either directly taken from literature, or as phenomenological onset temperatures from respective data (intersection point from linear fits before and after transition (cf.…”

Thermal behavior of solid acids in the Rb3H(SO4)2-RbHSO4 system under ambient atmosphere

“…Combinations of these cations or anions at various mole ratios can also give new solid acids in forms of solid solutions with more complex structures [1][2][3][4][5] and alter their thermal and electrical behaviors [4][5][6], for instance (CsxRb1-x)3H(SeO4)2, which will allow more flexibility to utilize this class of materials. Many solid acids undergo polymorphic superprotonic phase transition, giving the increase in conductivity by 3-4 orders of magnitude, at relatively lower temperatures, ~100℃ to 300℃ [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. This fact draws attention from researchers to utilize solid acids as proton-conductors, ultimately in applications like fuel cells or electrolyzers [21,22].…”

Crystal Structure Elucidation of the Novel Molecular-Inorganic Polymer $\mathrm{K_{2}SeO_{4}\cdot H_{2}SeO_{3}}$

“…Values have been reported in the range between 108.1 • C and 122 • C [?, ?, ?, 49]. A recent report [71] claims that TKHSe undergoes a phase transition at around 112 • C and simultaneously decomposes in the temperature range of 110 to 150 • C, starting at the surface of the TKHSe grains. The assumption is that the decomposition is analogous to that reported by Lee [72], for the KDP-type crystals, which suggest that the observed decrease in conductivity on successive thermal runs is a consequence of thermal decomposition (thermally activated).…”

“…O.S. HernÃąndez-Daguer et al [71] , presumes that through variations in the atomic proportions in the M 3 H(AO 4 ) 2 family, that is, by increasing the amount of selenate tetrahedra, one could possibly generate new chemical structures and materials that preserve the electrical properties and lack the thermal instability present in K 3 H(SeO 4 ) 2 (analogous to thermal stability profiles present in ceramic materials [73]). Based on this hypothesis and looking for the superionic phase transition temperatures of the M 4 H 2 (AO 4 ) 3 family [74,75,[75][76][77][78][79], we were able to synthesize a novel compound, K 2 SeO 4 • H 2 SeO 3 .…”