Proton conduction in the binary system (1 − x)CsHSeO4–xKHSeO4 studied with a free-energy model

Electrical Impedance Spectroscopy (EIS) was used to study the electrical properties of the (1???x)CsHSeO₄–xKHSeO₄ binary system with concentrations x?=?0.0 and 0.1. The results show a higher proton-conduction phase above 80°C for both concentrations, however, while DC conductivity of CsHSeO₄ shows a gradual change to higher values in the 80–118°C temperature range, the 0.9CsHSeO₄–0.1KHSeO₄ concentration reveals an abrupt change at about 80°C to an intermediate temperature phase. The observed behavior for the doped sample was modeled using a trial free-energy density, based on the concentration of mobile ions, that takes into account the formation of defects, configurational and phonon entropies, and defect-defect interactions. By minimising the free-energy density one obtains two roots for the carrier concentration at a given temperature, which corresponds to a stable and metastable configuration. It is possible to characterise the phase behavior of the system by means of temperature and two model parameters, which depend on the crystalline properties of the system, but not on temperature. One can successfully explain the conductivity behavior of the system by changing the model parameters if it is assumed that its variations are due to the carriers density.     

Dielectric relaxation in single crystal NH4H2PO4 in the high-temperature regime

The dispersion curves of the dielectric response in single crystal NH₄H₂PO₄ were obtained in the radio frequency range and below the high-temperature transition at T_p−160 °C. The results reveal dielectric relaxation at low frequency, which is about 10⁵ Hz at 70 °C, and it shifts to higher frequencies (∼3×10⁶ Hz) as the temperature increases. The relaxation frequency was determined from the peak obtained in the imaginary part of the permittivity as well as from the derivative of the real part of the permittivity. The activation energy E_a=0.55 eV, obtained from the relaxation frequency is very close to that derived from the dc conductivity. We suggest that this dielectric relaxation could be due to the proton jump and phosphate reorientation that cause distortion and change the local lattice polarizability inducing dipoles like      

Effect of H<Subscript>3</Subscript>PO<Subscript>2</Subscript> on the mechanical,thermal, and electrical properties of polymers based on poly (vinyl alcohol) (PVA) and chitosan (CS)

A polymer based on poly (vinyl alcohol) (PVA) and chitosan (CS) with a weight ratio of 80:20 was prepared by solvent casting processes, and the effect of H₃PO₂ was investigated. Thermal analysis shows miscibility of the two polymer amorphous phases since a single T_g was located between those of the individual components and the melting point of the crystalline phase was depressed to 189 °C. It was found that the acid acts as a plasticizer for the PVA-CS blends and its T_g is depressed significantly to 23 °C as the acid concentration increases to 50%. Strain-stress tests also corroborate this effect. The DC conductivity of the blends follows an Arrhenius-type thermal activation behavior with activation energy of 0.1 eV in the 30–90 °C temperature range. Moreover, the conductivity increases with increasing acid content up to a maximum value of approximately 1.4 × 10^?2 S/cm for the blend with an acid concentration of 50%.