M. Zdanowska-Frączek

Kinetic Monte Carlo simulations of proton conductivity.

The kinetic Monte Carlo method is used to model the dynamic properties of proton diffusion in anhydrous proton conductors. The results have been discussed with reference to a two-step process called the Grotthuss mechanism. There is a widespread belief that this mechanism is responsible for fast proton mobility. We showed in detail that the relative frequency of reorientation and diffusion processes is crucial for the conductivity. Moreover, the current dependence on proton concentration has been analyzed. In order to test our microscopic model the proton transport in polymer electrolyte membranes based on benzimidazole C(7)H(6)N(2) molecules is studied.

The proton conductivity in benzimidazolium azelate under moderate pressure

Abstract The kinetic Monte Carlo method is applied to examine effects of hydrostatic pressure on the benzimidazolium azelate (BenAze) proton conductivity. Following the experimental indications the recently proposed model has been modified to simulate the transport phenomena under moderate pressure, resulting in a very good agreement between numerical and experimental results. We demonstrate that the pressure-induced changes in the proton conductivity can be attributed to solely two parameters: the length of the hydrogen bond and the amplitude of lattice vibrations while other processes play a minor role. Furthermore, in high-pressure regime we anticipate the crossover from the increasing to decreasing temperature dependence of the proton conductivity arising from the changes in the hydrogen-bond activation barrier with increased pressure.

The superionic phase transitions in (NH4)3H(SeO4)2 under hydrostatic pressure up to 400 MPa

The effect of hydrostatic pressure on proton conductivity of (NH4)3H(SeO4)2 superionic crystal was studied in a wide temperature range and different isobaric conditions by means of impedance spectroscopy method. The measurements were performed along the trigonal c axis of the crystal, i.e., along the direction perpendicular to the plane in which, in the superionic phases, a dynamically disordered H-bond network is formed. The obtained pressure-temperature phase diagram is linear with increasing pressure. The triple point, which is the point of coexistence of the three phases: ferroelastic phase IV, ferroelastic phase III, and superionic phase II was found at p = 116.3 MPa and T = 287.3 K. High pressure leads to increase in the temperature range of stability of both superionic phases and to a drastic decrease in the temperature width of the ferroelastic phase III. With increasing pressure, the range of the superionic phase II expands at the expense of the range of the ferroelastic phase III, which is unsta...

The effect of pressure on the conductivity behavior of the (NH4)3H(SeO4)2 superprotonic crystal

The impedance spectra of (NH4)3 H(SeO4)2 in low and high-conductive phases under various thermodynamic conditions were analyzed. The measurements were performed by the ac admittance technique along the trigonal c axis of the crystal, i.e., along the direction perpendicular to the plane in which, in the superionic phases, a dynamically disordered H-bond network was formed. Activation energies and activation volumes were calculated for different phases of the (NH4)3 H(SeO4)2 crystal from the baric dependencies of dc conductivity and they were correlated with pressure coefficients of the phase transitions. The experimental results were analyzed within the classical hopping model, in terms of the strong proton–phonon coupling and polaronic effect.

Effect of Hydrostatic Pressure on the Phase Transition Temperature in [NH2(CH3)2]3Sb2Cl9

Effect of hydrostatic pressure up to 400 Mpa on the electric permittivity in [NH2(CH3)2]3 Sb2Cl9 was studied. The transition temperature (T c ) was found to increase with increasing pressure up to 150 MPa, passed through a maximum and than decrease with increasing pressure. Unexpected nonlinear decreasing of T c with increasing pressure above 150 Mpa indicates the different mechanism of ferroelectric phase transition than that considered till now.

High pressure NQR study of ferroelectric N(CH3)4H(Cl3CCOO)2

Abstract The effect of pressure up to 300 MPa on the 35Cl NQR spectra in N(CH3)4H(Cl3CCOO)2 has been studied at 77K. The results are suitable for an interpretation based on Matsushita and Matsubara theory and reflect the proton migration within hydrogen bond