The microstructure of Ce-TZP ceramics processed by a coating technique, compared to co-precipitated powder-based Ce-TZP, was analysed using a combination of XRD, SEM, TEM, etc. The results showed that CeO2-coated powder-based zirconia ceramics exhibited higher fracture toughness than co-precipitated powder-based zirconia ceramics in spite of a little decreasing hardness. Besides, a small amount of alumina addition can significantly improve the fracture toughness of CeO2-coated powder-based zirconia ceramics. In contrast with homogeneous grain size and stabilizer content distribution of co-precipitated powder-based Ce-TZP ceramics, SEM and EPMA analysis revealed that coating process resulted in wider grain size and stabilizer content distribution in this Ce-TZP ceramics. The superior fracture toughness of CeO2-coated Ce-TZP ceramics was mainly attributed to a fraction of highly transformable tetragonal ZrO2 grains with low ceria content. The residual stress existing between anisotropic monoclinic and tetragonal grains, and the thin glass films containing alumina and silica at grain boundary observed by TEM, were believed to benefit the preservation more tetragonal grains during sintering, contributing to the stress-induced martensitic phase transformation.
Experiments of X-ray diffraction at room temperature, on water confined in silica gel powder (hydrophilic surface) at three levels of hydration (18, 25 and 50%) are presented and analysed. The structural modifications of water when absorbed in silica gel are determined.
The structural and superconducting properties of Cu–Co and coupled Gd–Ca/Cu–Co substitution in GdBa2Cu3O7−δ have been studied by X-ray diffraction for crystal structure determination, resistivity, a.c. susceptibility for Tc determination and iodometry for oxygen content measurements. The oxides (Gd1−yCay)Ba2(Cu1−xCox)3O7−δ have been synthesised for 0.0≤x≤0.15 and 0.0≤y≤0.45. The effect of increasing Co-concentration in GdBa2(Cu1−xCox)3O7−δ for 0.0≤x≤0.15 is to lower the carrier concentration and decrease Tc which is attributed to the hole filling by Co. This suppression in Tc has been compensated for by appropriate hole doping with Ca, in (Gd1−yCay)Ba2(Cu1−xCox)3O7−δ which shows that for a fixed Co-content Tc increases dramatically as the Ca-content increases leading for instance to the oxides x=0.1, y=0.3; x=0.12, y=0.36 and x=0.15, y=0.45 with respective Tc’s of 83 K, 68 K and 63 K whereas the nonsubstituted phases x=0.1, 0.12, 0.15, y=0.0 don’t superconduct.
By replacing of the carbon atoms with boron and nitrogen in the crystalline phase of fcc diamond, new candidates for ultra-hard materials have been proposed in the BC2N stoichiometry. Their characterisation is here performed using methods based on density functional theory in its local density approximation. Full geometry relaxation of the substituted diamond gives the possibility to discover metastable systems which are isoelectronic with diamond and cubic boron nitride (c-BN). Such a kind of alloys are expected to be thermally and chemically (i.e. versus oxidation) more stable than diamond and harder than c-BN. That is, ternary B–C–N compounds could likely supersede the expensive diamond in various applications. In the present work we also employ first-principles methods to predict the mechanical properties of the achieved three-dimensional BC2N phases. Calculations of the cohesive properties, bulk and elastic moduli are presented. Considering the correlation between the hardness and the shear modulus and the values of the bulk moduli, we predict that the phases I and II of BC2N could be harder than c-BN. Electronic properties were studied in detail by means of density of states and band structure analysis. The calculation of the C, N and B K ELNES spectra is also shown for the presented phases.
The synthesis of monometallic hydrotalcite-like compounds (MHLC) type Co(II)–Co(III) materials was achieved by precipitation of a solution of cobalt nitrate(II) followed by microwave irradiation during the hydrothermal treatment step. The effects of irradiation time, precipitant agent and atmosphere were studied in order to establish the preparation conditions and the stability of these materials. As expected, these materials required careful preparation conditions, mainly a very slow addition of the precursors. NH4OH had to be used as precipitant agent in an air atmosphere. Short microwave irradiation times during the hydrothermal treatment provided a better crystallization of MHLC. The low stability of these compounds (∼200°C) was explained by the presence of several Co-complexes between the layers of the laminar structure. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), differential thermal analysis and thermogravimetric analysis (DTA/TGA), and thermoprogrammed oxidation (TPO) were used as characterization techniques.
