In this review the phenomenon of proton conductivity in materials and the elements of proton conduction mechanismsproton transfer, structural reorganization and diffusional motion of extended moietiesare discussed with special emphasis on proton chemistry. This is characterized by a strong proton localization within the valence electron density of electronegative species (e.g., oxygen, nitrogen) and self-localization effects due to solvent interactions which allows for significant proton diffusivities only when assisted by the dynamics of the proton environment in Grotthuss and vehicle type mechanisms. In systems with high proton density, proton/proton interactions lead to proton ordering below first-order phase transition rather than to coherent proton transfers along extended hydrogen-bond chains as is frequently suggested in textbooks of physical chemistry. There is no indication for significant proton tunneling in fast proton conduction phenomena for which almost barrierless proton transfer is suggest...

Proton Conductivity: Materials and Applications

Ultra-Cold Neutrons is the complete, self-contained introduction and review of the field of ultra-cold neutron (UCN) physics. It is suitable as an introduction to the field for research students, as a useful compendium of results and techniques for researchers and is of general interest to non-specialists in other areas of physics such as neutron, atomic and fundamental physics and neutron scattering.

https://iopscience.iop.org/article/10.1088/0034-4885/42/3/002/pdf

Ultra-Cold Neutrons

Raman and IR-measurements on the high- T c material series La 2 CuO 4 and YBa 2 Cu 3 O 7 are reviewed. This summary focuses on lattice vibrations in these superconducting systems, on impurity phases, the influence of oxygen stoichiometry and element substitution. The determination of the superconducting gap, the phonon renormalization in the superconducting state, and the isotope effect with its implications on the theory of superconductivity in these materials are discussed. In addition, the measured lattice vibrations are compared with the results of lattice dynamics calculations.

Lattice vibrations in high-Tc superconductors: Optical spectroscopy and lattice dynamics☆

Proton exchange membranes for fuel cells operated at medium temperatures: Materials and experimental techniques

The high-temperature behavior of CsH₂PO₄ has been carefully examined under both ambient and high pressure (1.0 ± 0.2 GPa) conditions. Ambient pressure experiments encompassed thermal analysis, AC impedance spectroscopy, ¹H NMR spectroscopy, and polarized light microscopy. Simultaneous thermogravimetric analysis, differential scanning calorimetry, and evolved gas analysis by mass spectroscopy demonstrated that a structural transition with an enthalpy of 49.0 ± 2.5 J/g occurred at 228 ± 2 °C, just prior to thermal decomposition. The details of the decomposition pathway were highly dependent on sample surface area, however the structural transformation, a superprotonic transition, was not. Polarized light microscopy showed the high temperature phase to be optically isotropic in nature, consistent with earlier suggestions that this phase is cubic. The conductivity of CsH₂PO₄, as revealed by the impedance measurements, exhibited a sharp increase at the transition temperature, from 1.2 × 10⁻⁵ to 9.0 × 10⁻³ Ω¹⁻cm⁻¹, followed by a rapid decline due to dehydration. In addition, chemically adsorbed surface water was shown to increase the conductivity of polycrystalline CsH₂PO₄ over well-dried samples, even at mildly elevated temperatures (>200 °C). At high pressure an apparent irreversible phase transition at 150 °C and a reversible superprotonic phase transition at 260 °C were observed by impedance spectroscopy. At the superprotonic transition, the conductivity increased sharply by ~3 orders of magnitude to 3.5 × 10⁻² Ω¹⁻cm⁻¹ at 275 °C. This high conductivity phase was stable to the highest temperature examined, 375 °C, and exhibited reproducible and highly Arrhenius conduction behavior, with an activation energy for charge transport of 0.35 eV. Upon cooling, CsH₂PO₄ remained in the high-temperature phase to a temperature of 240 °C.

High-Temperature Behavior of CsH2PO4 under Both Ambient and High Pressure Conditions

A considerable enhancement of the superconducting transition temperature Tc in perovskite-type oxides is explained in the framework of the anharmonic model for superconductors with structurally unstable lattices. It is shown that the interaction of electrons with highly anharmonic oxygen-ion vibrations of a rotational type results in a sufficiently large coupling constant λ. The obtained estimation for Tc is in agreement with experimental data for La(Y)BaCuO systems.

ANHARMONIC MODEL FOR HIGH-Tc SUPERCONDUCTORS.

The theory of lattice dynamics of an anharmonic crystal is developed without using the harmonic approximation as starting point. On the basis of the double-time Green's function method the self-consistent system of equations determining the equilibrium parameters of the lattice, the vibrational frequency and their damping is obtained. The free energy and the internal energy of an anharmonic crystal are calculated.



[Russian Text Ignored].

Theory of Anharmonic Crystals. I. General Formulation

The properties of the f.c.c. lattice with central nearest neighbour interaction are investigated on the basis of the dynamical theory of the anharmonic crystal developed in [1]. It is shown that in the case of constant external pressure the lattice becomes unstable at sufficiently high zero point energy or temperature. The behaviour of the physical quantities in the vicinity of the unstability point is investigated.



[Russian Text Ignored.]

Theory of Anharmonic Crystals. III. Three‐Dimensional Lattice

The phonon dispersion curves in solid biphenyl are calculated. It is shown that the commensurate-incommensurate phase transition is induced by mixing of anharmonic molecular torsion and acoustic phonons. The parameters of the anharmonic potential for torsion vibrations and temperature dependence of the soft mode are obtained.



Phononendispersionskurven in festem Biphenyl werden berechnet. Es wird gezeigt, das der Ubergang: kommensurable-inkommensurable Phase durch Mischung von anharmonischer Molekultorsion und akustischen Phononen induziert wird. Die Parameter des anharmonischen Potentials fur die Torsionsschwingungen und die Temperaturabhangigkeit der soft-Mode werden erhalten.

N. M. Plakida

Papers

ANHARMONIC MODEL FOR HIGH-Tc SUPERCONDUCTORS.

Theory of Anharmonic Crystals. I. General Formulation

Theory of Anharmonic Crystals. III. Three‐Dimensional Lattice

The Internal Soft‐Mode Phase Transition in Solid Biphenyl

The Isotope Effect within the Anharmonic Model for High-Tc Superconductors