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Multiferroic composites with the composition (1 − x) BaTi0.8Sn0.2O3–(x) La0.5Ca0.5MnO3 (x = 0, 0.3, 0.5, 0.7, 0.9 and 1) were prepared by sol–gel techniques. Rietveld refinements of the composites with 0–3 and 3–0 type connectivities exhibit the formation of pure phases and confirm the fraction of the composite samples. It was found that the composites grain size decreases slightly with increasing the La0.5Ca0.5MnO3 content. Magnetic measurements of the composite ceramics exhibit a gradual increase in saturation and remanent magnetization with increasing La0.5Ca0.5MnO3 content. Dielectric data demonstrate that the composite materials show high values of the dielectric constant in comparison with the parent compound BaTi0.8Sn0.2O3 (BTSO). In addition, an attempt is made to measure the magnetoelectric coupling coefficient and to explain the negative permittivity and losses occurring in these materials at a certain frequency and temperature conditions. [ABSTRACT FROM AUTHOR]

Perovskite manganite La0.5Ca0.5−x□xMnO3 (LCMO) nanomaterials were elaborated using the sucrose modified auto combustion method. Rietveld refinements of the X-ray diffraction patterns of the crystalline structure confirm a single-phase orthorhombic state with Pbnm space group (No. 62). The Ca-vacancies were voluntarily created in the LCMO structure in order to study their influence on the magnetic behaviour in the system. The magnetic susceptibility was found to be highly enhanced in the sample with Ca-vacancies. Paramagnetic-to-ferromagnetic phase transition was evidenced in both samples around 254 K. This transition is, characterized by a drastic jump of the susceptibility in the sample with Ca-vacancies. The maximum of entropy change, observed for both compounds at magnetic field of 6 T was 2.30 J kg−1 K−1 and 2.70 J kg−1 K−1 for the parent compound and the lacunar one respectively. The magnetocaloric adiabatic temperature change value calculated by indirect method was 5.6 K and 5.2 K for the non-lacunar and Ca-vacancy compound, respectively. The Ca-lacunar La0.5Ca0.5−x□xMnO3 (x = 0.05) reported in this work demonstrated overall enhancement of the magnetocaloric effect over the LCMO. The technique used to elaborate LCMO materials was beneficial to enhance the magnetocaloric effect and magnetic behaviour. Therefore, we conclude that this less costly environmentally friendly system can be considered as more advantageous candidate for magnetic refrigeration applications then the commonly Gd-based compounds. [ABSTRACT FROM AUTHOR]

Glass-ceramics in the system xBaTiO3-(1-x)NaPO3 (0 ≤ x ≤ 14, x in mol%) have been prepared and characterized. The structural organization of the glass-ceramics has been studied using XRD diffraction and infra-red (FTIR), 31P Magic angle spinning (MAS-NMR) and dielectric spectroscopies. Results suggest two distinct regions comprising the glass structure, one with low-BaTiO3 content and the other with higher content of the ferroelectric compound BaTiO3. The depolymerisation effects and the structure changes, promoted by BaTiO3 addition, are evidenced by means of the IR and NMR results. Dielectric permittivity shows that the ferroelectric-paraelectric transition temperature of each glass-ceramic appears at the same temperature for a pure BaTiO3 ceramic. [ABSTRACT FROM AUTHOR]

Glasses belonging to the series yA2O-(1-y)[0.25(WO3)2-0.75P2O5] ( y=0.10-0.60) are elaborated. DTA experiments reveal that the glass-network of the glasses are broken with increasing of modifier content. EPR spectra show the presence of two signals due to W5+ and Mo5+, as impuritie. The intensity of these EPR centres decreases when the concentration of A2O increases. The variation of Tg upon the modifier content is ascribed to structural changes occurring in the matrix of these glasses. [ABSTRACT FROM AUTHOR]

Abstract: The present study concerns the system 0.5[xNa2O–(1− x)Li2O]–0.5[0.4(MoO3)2–0.6P2O5], with x varying between 0 and 1. The elaborated glass samples have been characterised using powder X-ray diffraction (XRD), differential thermal analysis (DTA) and impedance spectroscopy. The total alkali oxide content is chosen in order to ensure that the electrical conductivity of the glasses under study is entirely ionic. It was evidenced that the conductivity minimum corresponds to the maximum of the activation energy. The glass transition temperature seems to present a minimum for the ratio Na/(Na+Li)=0.5. On the other hand, the density appears very linearly versus Na/(Na+Li). The mixed alkali effect (MAE) is resulting here in a conductivity minimum observed for the composition corresponding to Na/(Na+Li)=0.5, (x =0.5). It could be attributed to the fact that the two types of alkali ions are randomly mixed and have distinct conduction pathways. This implies that Li ions tend to block the pathways for the Na ions and vice versa. [Copyright &y& Elsevier]