A. Kežionis

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.

XRD, XPS, SEM/EDX and broadband impedance spectroscopy study of pyrophosphate (LiFeP2O7 and Li0.9Fe0.9Ti0.1P2O7) ceramics

LiFeP2O7 and Li0.9Fe0.9Ti0.1P2O7 were synthesised by solid-state reaction and ceramics were sintered. The structure of compounds was studied in the temperature range 300–700 K by X-ray diffraction. Ceramics’ surfaces were investigated by scanning electron microscope. Binding energies of Fe 2p, P 2p and O 1s core levels at ceramics’ surfaces have been determined by X-ray photoelectron spectroscopy and different valence states of Fe and P were detected. Elemental compositions of the compounds were studied by energy dispersive X-ray spectrometer. Impedance spectroscopy was performed in the frequency range 10 Hz–3 GHz and in the temperature interval 400–700 K. The changes of the activation energy of ionic conductivity at 528 and 550 K for LiFeP2O7 and Li0.9Fe0.9Ti0.1P2O7, respectively, were found. The phenomena can be related to disordering in the unit cells of the compounds.

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).

Preparation and Characterization of Solid Electrolytes Based on TiP2O7 Pyrophosphate

The Li4xTi1-xP2O7 (x = 0, 0.06, 0.1, 0.2) powders have been synthesized by the solid state reaction and their ceramics have been sintered. The Li4xTi1-xP2O7 (x = 0.06, 0.1, 0.2) compounds have cubic superstructure 3×3×3 (space group Pa-3), which is also typical for TiP2O7 pyrophosphate. The electrical properties of the ceramics were investigated in the frequency range of 10 to 3·109 Hz and temperature interval of 400–720 K by impedance spectroscopy. The relaxation dispersion region in the conductivity and dielectric permittivitty spectra of Li4xTi1-xP2O7 (x = 0, 0.06, 0.1, 0.2) ceramics was found.

Structure and Electrical Properties of Li3–xSc2–xZrx(PO4)3 (x = 0, 0.1, 0.2) Ceramics

At room temperature solid electrolyte Li3−xSc2−xZrx(PO4)3 (x = 0, 0.1) compounds belong to monoclinic symmetry (space group P21/n) and the compound with x = 0.2 belongs to orthorhombic symmetry (Pbcn). At 900 K all the investigated compounds belong to orthorhombic symmetry (space group Pbcn). Anomalies of enthalpy, change of activation energy of ionic conductivity, anomalies of dielectric permittivity in the temperature range 420 K–660 K of investigated compounds with x = 0 and 0.1 were found. The phenomena are related to structure phase transition in the compounds. The relaxation dispersion regions were found in conductivity spectra for the all investigated samples. The frequency dispersion regions are caused by the relaxation processes in grain, grain – boundaries and electrodes. The temperature dependencies of the bulk conductivity and relaxation frequency in the bulk are governed by the same activation energy. It is shown that major role in the temperature dependence of bulk conductivity is played by Li+ ion mobility, which increases as temperature increases.

Impedance spectroscopy study of Cu6PS5I–As2S3 nanocomposites

Nanocrystalline Cu6PS5I powder has been mixed with As2S3 semiconducting glass to obtain nanocomposite. Surface of the obtained sample has been photographed by scanning electron microscope. Electrical properties of Cu6PS5I–As2S3 nanocomposite have been measured using two- and four-probe methods. The obtained results were analyzed by fitting the experimental data to the equivalent circuit model. Warburg impedance element described Cu6PS5I nanoparticles, and the phase transition of this material was indicated.