Импедансметрия нанокристаллитов Ag-=SUB=-2-=/SUB=-S, внедренных в нанопористые стекла

The temperature dependences of the dielectric spectra of Ag2S nanocrystallites synthesized inside the channels of nanoporous glasses NPG-17 with an average diameter of filamentous pores of 17 nm are studied. The macroscopic mechanism for the occurrence of the frequency dependence of the electrical response of a nanoporous structure NPG+Ag2S is proposed. Formation of the model of mechanism is based superionic phase transition in Ag2S nanocrystallites fixed inside the channels of nanoporous glass is discussed.

Superionic phase transition in individual silver selenide nanowires

The superionic phase transition temperature in Ag2Se nanowires is diameter dependent and suppressed to below 100 °C. An increase in charge carrier density accompanied by a decrease in mobility was observed across the superionic phase transition.

A closer look at superionic phase transition in (NH4)4H2(SeO4)3: impedance spectroscopy under pressure

The proton-conducting material (NH4)4H2(SeO4)3 is examined to check whether its conductivity spectra are sensitive to subtle changes in the crystal structure and proton dynamics caused by external pressure. The AC conductivity was measured using impedance spectroscopy, in the frequency range from 100 Hz to 1 MHz, at temperatures 260 K < T < 400 K and pressures 0.1 MPa < p < 500 MPa. On the basis of the impedance spectra, carefully analyzed at different thermodynamic conditions, the p–T phase diagram of the crystal is constructed. It is found to be linear in the pressure range of the experiment, with the pressure coefficient value dT s/dp = −0.023 K MPa−1. The hydrostatic pressure effect on proton conductivity is also presented and discussed. Measurements of the electrical conductivity versus time were performed at a selected temperature T = 352.3 K and at pressures 0.1 MPa < p < 360 MPa. At fixed thermodynamic conditions (p = 302 MPa, T = 352.3 K), the sluggish solid–solid transformation from low conducting to superionic phase was induced. It is established that the kinetics of this transformation can be described by the Avrami model with an effective Avrami index value of about 4, which corresponds to the classical value associated with the homogeneous nucleation and three-dimensional growth of a new phase.

Rb9– x Ag3+x Sc2(WO4)9: a new glaserite-related structure type, rubidium disorder, ionic conductivity

A new triple tungstate Rb9−x Ag3+x Sc2(WO4)9 (0 ≤ x ≤ 0.15) synthesized by solid state reactions and spontaneous crystallization from melts presents a new structure type related to those of Cs7Na5Yb2(MoO4)9 and Na13Sr2Ta2(PO4)9. The title compound in centrosymmetric space group Cmcm contains dimers of two ScO6 octahedra sharing corners with three bridging WO4 tetrahedra. Three pairs of opposite terminal WO4 tetrahedra are additionally linked by AgO2 dumbbells to form {Ag3[Sc2(WO4)9]}9− groups, which together with some rubidium ions are packed in pseudohexagonal glaserite-like layers parallel to (001), but stacking of the layers is different in these three structures. In the title structure, the layers stack with a shift along the b axis and their interlayer space contains disordered Rb+ cations partially substituted by Ag+ ions. Almost linear chains of incompletely filled close Rb3a–Rb3d positions (the shortest distances Rb–Rb are 0.46 to 0.64 Å) are found to locate approximately along the b axis. This positional disorder and the presence of wide common quadrangular faces of Rb2 and Rb3a–Rb3d coordination polyhedra favor two-dimensional ionic conductivity in the (001) plane with Rb+ and Ag+ carriers, which was confirmed with bond valence sum (BVS) maps. Electrical conductivity measurements on Rb9Ag3Sc2(WO4)9 ceramics revealed a first-order superionic phase transition at 570 K with a sharp increase in the electrical conductivity. The conductivity σi = 1.8 × 10−3 S cm−1 at 690 K is comparable with the value of 1.0 × 10−3 S cm−1 (500 K) observed earlier for rubidium-ion transport in pyrochlore-like ferroelectric RbNbWO6.

Фазовый переход полупроводник--суперионик в пленках сульфида серебра

Frequency dependences of dielectric loss tangent tanδ (f) and Cole-Cole diagram of thin films of silver sulfide at various temperatures in the range 0-200 ° C were studied. A comparison of experimental data with the results of calculation of electrical circuit complex impedance of Ag2S samples is made. The comparison is made for temperatures before and after semiconductor-superionic phase transition. Based on the analysis of experimental results and literature data, a microscopic model of the phase transition in Ag2S is proposed.

Effect of cationic substitution on the double-well hydrogen-bond potential in [K1−x(NH4)x]3H(SO4)2proton conductors: a single-crystal neutron diffraction study

The structure of the mixed crystal [K1−x(NH4)x]3H(SO4)2as obtained from single-crystal neutron diffraction is compared with the previously reported room-temperature neutron structure of crystalline K3H(SO4)2. The two structures are very similar, as indicated by the high value of their isostructurality index (94.8%). It was found that the replacement of even a small amount (3%) of K+with NH4+has a significant influence on the short strong hydrogen bond connecting the two SO42−ions. Earlier optical measurements had revealed that the kinetics of the superionic transition in the solid solution [K1−x(NH4)x]3H(SO4)2are much faster than in K3H(SO4)2; this reported difference in the kinetics of the superionic phase transition in this class of crystal is explained on the basis of the difference in strength of the hydrogen-bond interactions in the two structures.