Broadband impedance spectroscopy of some Li+ and Vo** conducting solid electrolytes

The solid electrolyte Li3Ti1.5(PO4)3 compound has been synthesized by solid state reaction and studied by X-ray diffraction. At room temperature the compound belongs to rhombohedral symmetry (space group R3 ̅c) with six formula units in the unit cell. Li3Ti1.5(PO4)3, Li3xLa2/3–xTiO3 (where x = 0.12) Li+-ion conducting, Ce0.8Gd0.2O1.9, (ZrO2)92(Y2O3)8 with fast oxygen vacancy transport ceramic samples were investigated in the frequency range from 1 Hz to 3 GHz in the temperature interval (300-700) K by impedance spectroscopy methods. Two dispersion regions in ionic conductivity spectra for investigated ceramic samples have been found. The dispersions have been attributed to relaxation processes in grain boundaries and in grains of the ceramics

Broadband impedance spectroscopy of some Li+ and Vo** conducting solid electrolytes

The solid electrolyte Li3Ti1.5(PO4)3 compound has been synthesized by solid state reaction and studied by X-ray diffraction. At room temperature the compound belongs to rhombohedral symmetry (space group R3 ̅c) with six formula units in the unit cell. Li3Ti1.5(PO4)3, Li3xLa2/3–xTiO3 (where x = 0.12) Li+-ion conducting, Ce0.8Gd0.2O1.9, (ZrO2)92(Y2O3)8 with fast oxygen vacancy transport ceramic samples were investigated in the frequency range from 1 Hz to 3 GHz in the temperature interval (300-700) K by impedance spectroscopy methods. Two dispersion regions in ionic conductivity spectra for investigated ceramic samples have been found. The dispersions have been attributed to relaxation processes in grain boundaries and in grains of the ceramics

Microwave sintering improves the mechanical properties of biphasic calcium phosphates from hydroxyapatite microspheres produced from hydrothermal processing

Starting from two microspherical agglomerated HAP powders, porous biphasic HAP/TCP bioceramics were obtained by microwave sintering. During the sintering the HAP powders turned into biphasic mixtures, whereby HAP was the dominant crystalline phase in the case of the sample with the higher Ca/P ratio (HAP1) while alpha-TCP was the dominant crystalline phase in the sample with lower Ca/P ratio (HAP2). The porous microstructures of the obtained bioceramics were characterized by spherical intra-agglomerate pores and shapeless inter-agglomerate pores. The fracture toughness of the HAP1 and HAP2 samples microwave sintered at 1200 A degrees C for 15 min were 1.25 MPa m(1/2). The phase composition of the obtained bioceramics only had a minor effect on the indentation fracture toughness compared to a unique microstructure consisting of spherical intra-agglomerate pores with strong bonds between the spherical agglomerates. Cold isostatic pressing at 400 MPa before microwave sintering led to an increase in the fracture toughness of the biphasic HAP/TCP bioceramics to 1.35 MPa m(1/2)

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 increasesLietuvos energetikos institutasVilniaus universitetasVytauto Didžiojo universitetasŠvietimo akademij

Computational study of hydroxyapatite structures, properties and defects

Hydroxyapatite (HAp) was studied from a first principle approach using the local density approximation (LDA) method in AIMPRO code, in combination with various quantum mechanical (QM) and molecular mechanical (MM) methods from HypemChem 7.5/8.0. The data obtained were used for studies of HAp structures, the physical properties of HAp (density of electronic states - DOS, bulk modulus etc) and defects in HAp. Computed data confirmed that HAp can co-exist in different phases - hexagonal and monoclinic. Ordered monoclinic structures, which could reveal piezoelectric properties, are of special interest. The data obtained allow us to characterize the properties of the following defects in HAp: O, H and OH vacancies; H and OH interstitials; substitutions of Ca by Mg, Sr, Mn or Se, and P by Si. These properties reveal the appearance of additional energy levels inside the forbidden zone, shifts of the top of the valence band or the bottom of the conduction band, and subsequent changes in the width of the forbidden zone. The data computed are compared with other known data, both calculated and experimental, such as alteration of the electron work functions under different influences of various defects and treatments, obtained by photoelectron emission. The obtained data are very useful, and there is an urgent need for such analysis of modified HAp interactions with living cells and tissues, improvement of implant techniques and development of new nanomedical applications

Preparation and characterization of Li2.9Sc1.9-yYyZr0.1(PO4)3 (where y=0, 0.1) solid electrolyte ceramics

The solid electrolyte Li2.9Sc1.9-yYyZr0.1(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)Lietuvos energetikos institutasVilniaus universitetasVilniaus universiteto Medžiagotyros ir taikomųjų mokslų institutasVytauto Didžiojo universitetasŠvietimo akademij