Original implementation of low-temperature SPS for bioactive glass used as a bone biomaterial.

Alkali borated bioactive glasses powders with compositions based on the SiO2-Na2O-CaO-P2O5-x B2O3 system (0 < x < 20 wt%); have been consolidated at low temperature using Spark Plasma Sintering (SPS). Through SPS technique under 50 MPa, it was possible to achieve fully dense and completely amorphous borated glasses at temperatures as low as 420 °C. By increasing the sintering temperature up to 430 °C, the dense samples crystallized which is mostly achieved at higher temperatures. This study reveals that the mechanical properties of these new borated biomaterials are suitable to be used as a promising candidate for repairing defects in non-load-bearing bones as well as for coating on the metallic surface implants to improve the bioactivity process bone/implant. The pressure had a weak effect on the crystallization and densification of the glass compared to the temperature during the powder consolidation by SPS. Moreover, by increasing the boron content, the compressive strength and the elastic modulus of the elaborated glasses decreased for being close to those of the natural.

Study of complex impedance spectroscopic properties of La0.7-x Dy x Sr0.3MnO3 perovskite oxides.

The dysprosium perovskite La0.7-x Dy x Sr0.3MnO3 (x = 0.00 [LSMO] and 0.03 [LDSMO]) compounds were prepared by the sol-gel reaction and characterized by the X-ray diffraction technique. The electrical conductivity and modulus characteristics of the system have been investigated in the temperature and the frequency range 311-356 K and 209-5 × 107 Hz, respectively, by means of impedance spectroscopy. The ac and dc conductivities were studied to explore the mechanisms of conduction of LSMO and LDSMO. The insertion of a small amount of Dy3+ in the La-site of LSMO perovskite oxide increases the value of the activation energy from 0.2106 to 0.5357 eV and enhances electrical resistivity values for almost two orders of magnitude.

Analysis based on scaling relations of critical behaviour at PM-FM phase transition and universal curve of magnetocaloric effect in selected Ag-doped manganites.

The critical behaviour of Pr0.5Sr0.5-x Ag x MnO3 (0 ≤ x ≤ 0.2) samples around the paramagnetic-ferromagnetic phase transition is studied based on isothermal magnetization measurements. The assessments based on Banerjee's criteria reveal the samples undergoing a second-order magnetic phase transition. Various techniques such as modified Arrott plot, Kouvel-Fisher method, and critical isotherm analysis were used to determine the values of the ferromagnetic transition temperature T C, as well as the critical exponents of ß, γ and δ. The values of critical exponents, derived from the magnetization data using the Kouvel-Fisher method, are found to be (ß = 0.43 ± 0.002, 0.363 ± 0.068 and 0.328 ± 0.012), (γ = 1.296 ± 0.007, 1.33 ± 0.0054 and 1.236 ± 0.012) for x = 0.0, 0.1 and 0.2, respectively. This implies that the Pr0.5Sr0.5-x Ag x MnO3 with 0 ≤ x ≤ 0.2 systems does not belong to a single universality class and indicates that the presence of magnetic disorder in the system must be taken into account to fully describe the microscopic interaction of these manganites. With these values, magnetic-field dependences of magnetization at temperatures around T C can be well described following a single equation of state for our samples. From magnetic entropy change (ΔS M), it was possible to evaluate the critical exponents of the magnetic phase transitions. Their values are in good agreement with those obtained from the critical exponents using a modified Arrott plot (MAP). We used the scaling hypotheses to scale the magnetic entropy change and heat capacity changes to a universal curve respectively for Pr0.5Sr0.5-x Ag x MnO3 samples.

Structural and magnetic properties of mixed Co-Ln (Ln = Nd, Sm, Eu, Gd and Ho) diethyleneglycolate complexes.

New hybrid compounds LnCoCl(deg)2 (deg = diethyleneglycolate; Ln = Nd, Sm, Eu, Gd and Ho) have been synthesized by mixing cobalt and rare earth cations in a boiling diethyleneglycol (degH2) medium. Their crystallographic structures have been ab initio solved from synchrotron powder diffraction data. They consist of edge sharing tetrameric sub-units [(Ln2Co2)(deg)4(Cl)2] forming 1D infinite chains along the c parameter of a monoclinic unit cell (SG = C2/c). The five- and seven-coordination of Co(2+) and Ln(3+) cations inferred from the crystallographic results is confirmed by UV-visible absorption and Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy. In the LnCoCl(deg)2 (Ln = Nd, Sm, Eu, Gd, Ho) series, weak antiferromagnetic superexchange interactions have been evidenced, between high spin Co(2+) and Ln(3+) orbitally degenerate cations. These materials are considered as potential precursors for the simultaneous reduction of Co-Ln-glycolate species into bimetallic nanoparticles by the polyol process.