Synthesis, X-ray structure and thermal behavior of the new superprotonic conductor Cs2(HSeO4)(H2PO4)

The thermal-differential analysis of the superprotonic transition in Cs2(HSeO4)(H2PO4) showed that the transformation to high-temperature phase occurs at 400 K by one-step process. Thermal decomposition of the product takes place at 471 K. This decomposition occurs in several stages and characterized by weight loss of (CsHSeP). The first two transitions were also studied by X-ray powder diffraction at various temperatures and by impedance and modulus spectroscopy techniques. ac-impedance measurements revealed that, upon heating, the compound undergoes a transformation into a phase of high conductivity at ∼400 K. The activation energy increases from 0.12 to 0.24 eV, while the conductivity jumps from 2.60 × 10−5 Ω−1 cm−1 at 393 K to 2.77 × 10−4 Ω−1 cm−1 at 403 K. Information about charge carrier transport mechanism is obtained by comparison of ΔEf with ΔEσ. The activation energies for the (CsHSeP) compound calculated respectively from the modulus and impedance spectra are approximately close, suggesting that transport properties above and below the superprotonic phase transition (400 K) is probably due to H+ protons hopping mechanism.