E. Kazakevičius

Synthesis, structure and peculiarities of ionic transport of Li1.6Mg0.3Ti1.7(PO4)3 ceramics

Abstract The solid electrolyte Li1+2xMgxTi2−xP3O12 compounds were synthesized by a solid state reaction. The ceramic samples were sintered for 0.2, 0.5, 1 and 3 h and studied by X-ray and complex impedance spectroscopy in the frequency range 10 Hz–1.2 GHz in the temperature range 300–600 K. Two regions of relaxation dispersion were found, the dispersions were related to the fast Li+ ion transport in the bulk and grain boundaries. Varying of the sintering time affects the density, values of grain boundary conductivity (σgb), its activation energy (ΔEgb) and relaxation frequency (fgb). The activation energy (ΔEb) of bulk conductivity (σb) and activation energy (ΔEf) of relaxation frequency (fb) in the bulk are the same. That can be attributed to the fact that the temperature dependence of the bulk conductivity is caused only by the mobility of the fast Li+ ions, while a number of charge carriers remains constant with temperature.

Electrical conductivity dispersion in Co-doped NASICON samples

Impedance spectra of Co-doped NASICON polycrystalline samples (x = 2.0) were measured in the frequency range 0.5 MHz-1.2 GHz and analyzed in terms of the conductivity dispersion. The dispersion of bulk electrical conductivity obeys the power law frequency dependence σ(ω) = σ 0 + Kω n . It is observed from room temperature up to 450 K, i.e. up to the temperature of phase transformation of NASICON. The activation energy of the conductivity of grain interiors and the activation energy of the frequency, at which the dispersion sets on, have the same value of 0.313 eV. The activation energy value of the frequency dependent part of conductivity (0.077 eV) constitutes the proper fraction of the activation energy of the dc conductivity. Similar dispersion is found at lower frequencies for the grain-boundary conductivity. It extends in temperature up to 550 K, well over the temperature of phase transformation of NASICON. The phase transformation, taking place in the crystal grains of the material, does not influence the electrical behavior of grain boundaries. The activation energies for the grain boundary conductivity and for the grain-boundary onset frequency also have equal values (0.440 eV).

Electrical conductivity studies in (Ag3AsS3)x(As2S3)1−x superionic glasses and composites

Compositional, frequency, and temperature studies of impedance and electrical conductivity in (Ag3AsS3)x(As2S3)1−x superionic glasses and composites were performed. Frequency range from 10 Hz to 3 × 109 Hz and temperature interval 300–400 K were used for the measurements. Compositional dependences of electrical conductivity and activation energy are analyzed; the most substantial changes are observed with the transition from (Ag3AsS3)0.4(As2S3)0.6 glass to (Ag3AsS3)0.5(As2S3)0.5 composite. With increase of Ag3AsS3 content, the investigated materials are found to have crystalline inclusions and show the two-phase composite nature. Addition of Ag3AsS3 leads to the increase of electrical conductivity whereas the activation energy decreases.

Structural and electrical investigation of (Ag3AsS3)x(As2S3)1−x superionic glasses

Structural studies of (Ag3AsS3)x (As2S3)1−x chalcogenide superionic glasses in the compositional range x = 0.3–0.9 were performed by scanning electron microscopy. Temperature and compositional dependences of transmission coefficient, electrical conductivity, and activation energy were investigated

Characterization of NASICON-type Na solid electrolyte ceramics by impedance spectroscopy

Na solid electrolytes are cheaper than the ones of Li and could be of interest to apply in secondary batteries and gas sensors. In the present work, the NASICON-type Na1.3Ti1.7Al0.3(PO4)3 compound has been synthesized by Pechini method and the phase purity of the compound was confirmed by XRD. Ceramics of the compound were prepared in several different sintering temperatures and the morphology of the samples was examined by SEM. The investigation of the electrical properties was performed in 10 Hz to 3 ⋅ 109 Hz and 300–500 K frequency and temperature ranges by means of impedance spectroscopy. The impedance spectra were analyzed and observed dispersions were related to microstructure of the ceramics.

Preparation and characterization of Li2.9Sc1.9−y Y y Zr0.1(PO4)3 (where y = 0, 0.1) solid electrolyte ceramics

The solid electrolyte Li2.9Sc1.9− y Y y Zr0.1(PO4)3 (where y = 0, 0.1) compounds belong to monoclinic symmetry (space group P21/n) at room temperature. The Zr 3d, Sc 2p, P 2p, Y 3d, O 1s, and Li 1s core level X-ray photoelectron spectra (XPS) were fitted. The Li ions in ceramics without Y occupy two different positions and in the ceramics with Y they occupy one position in the lattice. The deconvolutions of the Zr 3d, P 2p, Sc 2p, and Y 3d core level XPS are associated with different valence states on the surfaces of the investigated ceramics. Anomalies of enthalpy, change of activation energy of ionic conductivity, anomalies of dielectric permittivity in the temperature range 420–520 K of investigated compounds were found. The phenomena are related to diffuse structure phase transition in the compounds. At temperatures 600 and 900 K, the compounds belong to orthorhombic symmetry (space group Pbcn).

Some aspects of charge transport in Li0.5-xNaxLa0.5TiO3 (x = 0, 0.25) ceramics

In this work, the influence of partial substitution of Li to Na in Li0.5La0.5TiO3 (LLTO) compound was investigated by broad frequency range impedance spectroscopy (IS). The equivalent circuit method was used to relate the electric modulus spectra with confinement of mobile Li ions by rigidly arranged Na in the lattice of LLTO.