Superionic Behavior Research Articles

Molecular dynamics simulation of fluoride-perovskites

The authors present the results from constant-pressure constant-temperature molecular dynamics simulations on the fluoride-perovskites: KMnF3, KZnF3 and KCaF3. These simulations lead to the predictions that KMnF3, and KZnF3 are not superionic conductors while KCaF3 shows limited superionic behaviour with a diffusion coefficient of 5.24*10-6 cm2 s-1 ( sigma =0.145 Omega -1 cm-1) and Tc=0.93 Tm. However, these results are only qualitative since the use of the rigid-ion model resulted in simulated temperatures above the experimental melting points.

X-ray diffraction and differential scanning calorimetry of a novel CuI Ag oxysalt solid electrolyte

Abstract Solid electrolytes of the system : xCuI(1−x) (Ag 2 O + MoO 3 ) have been prepared for various values of x, the molar fraction. X-ray Diffraction data has revealed the presence of AgI and Differential Scanning Calorimetry has confirmed this by the presence of an endothermic peak characteristic of the superionic transition of AgI at 150°C. The transport number for silver ions was nearly unity, and preliminary conductivity results showed a value of 10 −3 (Ωcm) −1 at room temperature. The formation of AgI by an exchange reaction between CuI and the silver oxysalt facilitates superionic behaviour similar to AgIag Oxysalts.

Molecular dynamics of the structure and transport properties of amorphous AgI

The potential of Parrinello, Rahman and Vashishta has been used to simulate the behaviour of AgI in the amorphous phase. The pair distribution functions exhibit the type of behaviour expected from amorphous systems. However, the mean square displacement and velocity autocorrelation functions show that amorphous AgI no longer exhibits superionic behaviour.

Defects, phase transitions and dynamical disorder in superionic protonic conductors H3OUO2PO4· 3H2O and CsHSO4

Abstract Specific properties of the hydrogen bond and protons appear to be responsible for the formation of the quasi-liquid state of conducting ions and the resulting superionic behaviour. This state is reached by successive phase transitions involving the mobile species and their interactions with a more or less rigid framework. H3OUO2PO4 · 3H2O (HUP) and CsHSO4 can be considered as models of wet and dry superionic conduction, respectively. Interactions between static effects and dynamical disorder as well as the coupling between sublattices are discussed in relation to results obtained by calorimetry, impedance spectroscopy (up to 10 GHz), vibrational spectroscopy and quasi-elastic neutron scattering.

IV. Order–disorder transitions: solid state kinetics, thermal analyses, X-ray diffraction and electrical conductivity studies in the Ag2SO4–K2SO4 system

Order–disorder transitions occurring in the Ag2SO4–K2SO4 system were investigated by reaction kinetics, thermal analyses, X-ray diffraction, and electrical conductivity techniques. Solid–liquid and solid–solid phase diagrams are reported.The conductivity data in the high temperature phase of the solid resemble superionic conductivity behavior. The higher conductivity of Ag2SO4 with K+ presence relative to pure Ag2SO4 and Ag2−xNaxSO4 compositions support a lattice expansion facilitating higher mobility of ions.The reaction kinetics, X-ray diffraction, and electroconductivity results suggest a relatively open periodic [Formula: see text] sublattice in the high-temperature phase of the sulfate-based systems studied in this series.

Measurements on the conductivity and diffusion of silver ions in Agx–NbSe2

Four probe ion conductivity as well as electrochemical time lag techniques have been applied to study the movement of silver in Agx–NbSe2. The results suggest that a dilute gas phase of silver coexists with a condensed phase in samples intercalated to [Formula: see text] and that a barrier to condensation exists for the silver in the gas phase. The high ion conductivity σi = 3.5 × 10−2 ?−1 cm−1 and diffusion constant D = 3.5 × 10−5 cm−2 s−1 for the gas phase suggests superionic behaviour of silver in NbSe2. Diffusion measurements give activation energies for silver of about 150 meV.

Superionic behavior in CuCl and CuBr at elevated temperatures

EXAFS data on several phases of CuCl and CuBr are analyzed in terms of the various structural models that have been proposed. The one favored is the excluded volume model which has previously given good results on superionic AgI and CuI. It is determined that the Cu ion density peaks at the tetrahedral locations in all phases of CuCl and CuBr and that it spreads substantially toward and through the tetrahedral faces as the temperature is increased. This behavior is qualitatively identical to that in AgI and CuI, and therefore properly regarded as superionic.