A.F. Orliukas

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).

Relaxation dispersion of ionic conductivity of BICOVOX

Abstract The dispersion of complex dielectric permittivity of BICOVOX (Bi2Co0.1V0.9O5.35) has been investigated between 300 and 800 K in the frequency range from 106 to 109 Hz. The observed relaxation process is attributed to diffusional polarization associated with short range jumping of oxygen vacancies in the crystal lattice. Determination of the conductivity and the relaxation frequency enables estimation of the diffusion coefficient of oxygen vacancies as well as their concentration. A good agreement was found between the activation energy of ionic conductivity and the activation energy of relaxation frequency. It was concluded from the results that the estimated concentration of mobile oxygen vacancies does not change with temperature and is approximately equal to the concentration of oxygen vacancies determined by the refinement of the crystal structure for the high-temperature disordered γ′ phase of the compound. Raman scattering of the samples was also investigated. The maxima of scattering found at around 155 and 240 cm−1 could correspond to the attempt frequency of the mobile oxygen ions.

Broadband Method for the Determination of Small Sample's Electrical and Dielectric Properties at High Temperatures

A model for a measurement circuit consisting of a telescopic coaxial transmission line with the sample placed in the gap of the central conductor has been developed and a measurement method, based on this model, was tested. To determine the samples electrical properties, the method requires the measurement of the two-port scattering matrices of the short-circuited line, the line with one calibration sample, and the line with the sample to be measured inserted. The model takes into account the thermal elongation of the measurement line and can be used for measuring electrical properties of materials at high temperatures in the megahertz and gigahertz ranges. This model also reduces the influence of parasitic reflections in the measuring coaxial line on the measurement results and takes into account a complicated distribution of the electromagnetic field in the measuring capacitor without solving a complicated electrodynamics problem.

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

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.

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.

SINTERING OF OXYGEN ION CONDUCTIVE CERAMICS AND THEIR ELECTRICAL PROPERTIES

Oxygen ion conducting ceramics (Sc2O3)0.1(ZrO2)0.9, (Sc2O3)0.1(CeO2)0.01(ZrO2)0.89 and Ce0.9Gd0.1O1.95 were sintered from powders with different specific surface areas. The produced ceramics were studied by scanning electron microscopy and impedance spectroscopy methods. Impedance spectroscopy measurements were performed in a wide frequency range of 10 Hz–3 GHz at temperatures up to 900 K in air. Temperature dependences of bulk and total ionic conductivities of ceramics were investigated. High bulk ionic conductivity of the order of 1 S/m at 900 K for 10ScSZ and 10Sc1CeSZ ceramics was achieved. Total ionic conductivity for both types of 10GDC ceramics was of the order of 0.1 S/m at 700 K.

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).

Electrical and acoustical relaxation in fast ionic conductors

Abstract The ultrasonic velocity, attenuation coefficient, electric conductivity and dielectric permittivity have been measured in wide temperature and frequency ranges in various crystalline, polycrystalline and glassy solid electrolytes. The high relaxational ultrasonic attenuation maxima and corresponding velocity dispersion have been observed. Such behaviour is supposed to be determined by acoustoionic interactions of two types: (i) the piezoelectric in the piezoelectric superionic; (ii) interaction caused by acoustic wave modulation of chemical potential felt by mobile ions in the centrosymmetric materials. In polycrystalline and glassy superionics the non-Debye behaviour for ultrasonic relaxation has been established. In such materials the characteristic frequency dependencies of ionic conductivity and dielectric permittivity were obtained. A simple theoretical model describing both frequency and temperature dependencies of electrical and acoustical properties of solid electrolytes is proposed. This model is based on continuous distribution of activation energies in a limited interval and describes the experimental data fairly well.