Effect of cation substitution in Cs1–2x Ba x H2PO4 on structural properties and proton conductivity

Abstract

We synthesized compounds with partial substitution of Cs+ cations in CsH2PO4 by Ba2+ cations. The structural, electron transport and thermodynamic properties of Cs1–2x Ba x H2PO4 (x = 0–0.15) were studied for the first time with the help of a set of physicochemical methods: infrared and impedance spectroscopy, X-ray diffraction and synchronous thermal analysis. The proton conductivity of Cs1–2x Ba x H2PO4 at 50–230°C was investigated in detail by impedance measurements. The formation of solid substitution solutions isostructural with CsH2PO4 (P21/m) is observed in the range of substitution degrees of x = 0–0.1, with a slight decrease in the unit cell parameters and some salt amorphization. The conductivity of disordered Cs1–2x Ba x H2PO4 in the low-temperature region increases by two orders of magnitude at x = 0.02 and increases with an increasing fraction of barium cations by three or four orders of magnitude at x = 0.05–0.1; the superionic phase transition practically disappears. At x = 0.15, heterophase systems based on salts are formed, showing high conductivity and a further decrease in the activation energy of conductivity to 0.63 eV. The conductivity of the high-temperature phase of Cs1–2x Ba x H2PO4 does not change with increasing fraction of the substituent.