Laser-field-induced superionic transition

Abstract

A possible mechanism of the laser-field-induced superionic transition in the near-surface region is proposed theoretically in ionic-electronic materials, i.e. , mixed conductors. The laser field does not expose ions immediately but via intermediate interaction with conduction electrons and induces many nonequilibrium defects in the Ag sublattice. These processes cause the decreasing of activation energy of stable Frenkel defects and, consequently, the decreasing of the superionic transition temperature. I. BV. I. aODUtmIONHegels' law that quantitative changes lead to change of some quality is embodied in the process of modification of crystal properties as the crystal becomes more and more imperfect. Given a small concentration of defects in a solid, it is possible to examine their contribution to its features by means of expansion in a perturbation series of a suSciently small parameter. However, in a crystal with many defects, the disordering of the structure becomes considerable, to the extent that a lot of properties of the constituent particles become liquidlike. A situation where the number of allowable sites is much greater than the number of particles may occur at lower temperatures than the ordinary superionic transition temperature in superionic conductors (SIC's). In SIC's a phase transition of the ionic subsystem to a liquidlike state often follows the melting of one of the ionic sublattices. Frenkel defects randomly occupy the numerous fine local minima of the potential. These minima are closely connected with the diffusion paths of mobile ions. The transition of a crystal into the superionic state takes place due to the stepwise growth in the concentration of Frenkel defects (in a cation-type conductor) stemming from their interaction with each other through the mediation of the lattice distortion' and the direct Coulomb interaction.The role of electrons in the superionic transition is considered to be important. In AgI-family materials their influence is neglected usually, because of the relatively low concentration of conduction electrons in comparison with the concentration of mobile ions (10 cm ), while articles exist where the electron-electron correlations are assumed to be responsible for formation of the superionic state. ' In a mixed SIC, such as the Ag chalcogenides (Ag2S, Ag2Se, AgzTe), the electronic conductivity plays an essential part in the total conductivity of the crystal and the electron-electron and electron-ion interaction effects also are indubitably important.As was discussed by Bondarev and Kuklov, the formation of a superionic state near the surface in an ionic crystal is preferable to inside the crystal, on account of the presence of an electric double layer. In Ref. 5 the possibility of inducing the superionic state was suggested by application of an external static electric field, which leads to decrease in the surface barrier for ionic diffusion.In this paper, we discuss a credible mechanism of inducing a superionic state in the region near the surface of a mixed SIC with...

Gating processes in Na-channel of biological membrane from the standpoint of superionic phase transition

“…The evaluation performed for different superionic-related materials yields the activation energy gain Ae a falling approximately in the range -1 eV to -5 eV at room temperature [14,15,21]. Thus, the lattice potential being screened by local dipoles, the drastic flattening of relief occurs.…”

“…The effective charges ei and ej can be the same [15] or can be different [14] depending on the relative positions of particles. The integral in eq.…”

“…2) Assuming that the appearance of this local potential minimum is the crucial prerequisite for the superionic transition, we recognize the super-or non-superionic materials mainly by the correlation extent of p and d electrons; 3) The superionic transition has been believed to happen in the system of interacting Frenkel defects [18], where the local minimum acts as an interstitial site [15]. But microscopically, without statistical averaging, the transition can be considered as a redistribution of probabilities to find the particle in one of the potential minima, when the local minimum gets the absolute and vice versa.…”

“…Both in the case of ferroelectrics [13] and for SIC and related materials [14], the spacing of double-well minima can fall far short of the lattice parameter. In other words the microscopic dipoles seem to be not stable but rather flickering near the lattice sites [ 12,15]. The microscopic mechanisms which are responsible for the double-well potential can vary essentially for different materials [16].…”

“…The local dipoles, provided their concentration is sufficient, are able to decrease the activation energy substantially for Frenkel pair formation. The gain in activation energy can be estimated as (kB = 1) [14,15], a8. = 47rN oT I dRR~ (Uo -2(U.,, )).…”