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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]

Ferroelectric property that induces electrocaloric effect was investigated in Ba(Ge x Ti 1- x )O 3 ceramics, known as BTGx. X-ray diffraction analysis shows pure perovskite phases in tetragonal symmetry compatible with the P 4 mm (No. 99) space group. Dielectric permittivity exhibits first-order ferroelectric-paraelectric phase transition, confirmed by specific heat measurements, similar to that observed in BaTiO 3 (BTO) crystal. Curie temperature varies weakly as a function of Ge-content. Using the direct and indirect method, we confirmed that the adiabatic temperature change Δ T reached its higher value of 0.9 K under 8 kV/cm for the composition BTG6, corresponding to an electrocaloric responsivity Δ T / Δ E of 1.13 × 10 -6 K.m/V. Such electrocaloric responsivity significantly exceeds those obtained so far in other barium titanate-based lead-free electrocaloric ceramic materials. Energy storage investigations show promising results: stored energy density of ~17 mJ/cm 3 and an energy efficiency of ~88% in the composition BTG5. These results classify the studied materials as candidates for cooling devices and energy storage applications.

High-performance lead-free multiferroic composites are desired to replace the lead-based ceramics in multifunctional device applications. Laminated compounds were prepared from ferroelectric and ferromagnetic materials. In this work, we present the laminated ceramics compound by considering the ferromagnetic La 0.5 Ca 0.5 MnO 3 (LCMO) and the ferroelectric BaTi 0.8 Sn 0.2 O 3 (BTSO) in two different proportions. Compounds ( 1-x ) LCMO-( x ) BTSO with x = 1 and 0 (pure materials) were synthesized by the sol-gel method, and x = 0.7 and 0.5 (laminated) compounds were elaborated by welding appropriate mass ratios of each pure material by using the silver paste technique. Structural, dielectric, ferroelectric, microstructure, and magnetic characterizations were conducted on these samples. X-ray scattering results showed pure perovskite phases confirming the successful formation of both LCMO and BTSO. Scanning electron microscope (SEM) images evidenced the laminated structure and good quality of the interfaces. The laminated composite materials have demonstrated a multiferroic behavior characterized by the ferroelectric and the ferromagnetic hysteresis loops. Furthermore, the enhancement of the dielectric constant in the laminated composite samples is mainly attributed to the Maxwell-Wagner polarization.