Strong phase-change magnetoelectric responses have been anticipated by a first-principles investigation of phases in the perovskite BiFeO 3 -BiCoO 3 solid solution, specifically at the morphotropic phase boundary (MPB) between the multiferroic rhombohedral and tetragonal polymorphs. This might be a general property of multiferroic MPBs and a novel promising approach for room temperature magnetoelectricity, which requires the identification of suitable material systems. We present here a comprehensive description of the electrical and electromechanical properties across one such system; the perovskite BiFeO 3 -PbTiO 3 solid solution. All the temperature dependence of dielectric permittivity, ferroelectric hysteresis loops, and piezoelectric coefficients have been obtained, and are discussed in relation to the previously reported perovskite structural evolution. Results show ceramic materials to be very promising for ferroelectric random access memories (remnant polarization as high as 63 lC cm À2 with a comparatively low coercive field of 4.5 kV mm À1 for MPB compositions) and high temperature electromechanical transduction (crystal piezoelectric coefficient of 87 pC N À1 with a Curie temperature above 873 K). Moreover, the occurrence of phase changes between the monoclinic and tetragonal polymorphs under high electric fields is indicated, while the canted antiferromagnetic character of the phases involved is corroborated. V C 2014 AIP Publishing LLC.

We have investigated the occurrence of phase-change functional responses in the BiFeO3-PbTiO3 perovskite solid solution, analogous to those anticipated by a recent first-principles study of BiFeO3-BiCoO3. Like the former system, BiFeO3-PbTiO3 shows a morphotropic phase boundary (MPB) between multiferroic polymorphs of rhombohedral and tetragonal symmetries. MPB BiFeO3-PbTiO3 is a high temperature ferroelectric with the phase transition around 900 K, and a room temperature square-shape hysteresis loop with remnant polarization as high as 62 μC cm−2. Strain under the electric field was studied, and a phase-change response was found. Analogous magnetoelectric effects are expected from the multiferroic nature of this MPB.

Among the recently investigated magnetoelectric materials, those belonging to the solid solution xBiFeO 3 -(1 À x)PbTiO 3 (xBF-(1 À x)PT) seem to be the most promising. However, there is not much information about the characteristics of this system in the whole range of compositions. In this work, the preparation of the system for compositions with 0 # x # 1 is described. The synthesis has been successfully achieved by mechanosynthesis in a high-energy planetary mill. A structural characterization of the mechanosynthesized phases, before and after different thermal treatments, has been carried out by X-ray powder diffraction (XRD), in order to analyze the crystallographic evolution of the phases, correlated to the phase transitions detected by differential thermal analysis (DTA). The structural characterization has allowed the range of compositions of the morphotropic phase boundary (MPB) to be established. First order ferro-paraelectric transitions have been detected by DTA measurements in the whole range of the system and the corresponding Curie temperatures have been determined. Moreover, a comparative microstructural study of the ceramic materials corresponding to the x ¼ 1, 0.7 and 0.6 compositions, prepared by two different processing methods (conventional sintering and spark plasma sintering (SPS)), is reported.

Mineral, complex and chelated micronutrient fertilisers are widely used in agriculture. However, there have been few studies on manganese and zinc fertilisers. In fact, specific chelating agents to provide these micronutrients to plants have not been found, in contrast to iron. This work considers the interactions of novel and traditional ligands in micronutrient mixtures used in hydroponics and fertigation. Theoretical speciation studies comparing the stability in solution have been carried out to simulate the possible interactions that can affect Fe, Mn and Zn in aqueous formulations containing these micronutrients. Unknown stability constants of ligands with Zn and Mn have been determined. Also, theoretical speciation investigations in hydroponic conditions have been carried out. It has been found that the new chelating agents, IDHA and EDDS, and the poorly studied o,p-EDDHA, can be good alternatives to the traditional sources such as EDTA, HEEDTA and DTPA principally for Zn fertilisers. The Mn and Zn chelates with o,p-EDDHA and complexes with lignosulfonate and gluconate have also shown high stability in a hydroponic nutrient solution, maintaining more than 80% Mn in solution until pH 10. The presence of o,o-EDDHA/Fe 3+ and o,p-EDDHA/Fe 3+ enhances the stability of Zn in solution in the mixed fertilisers. More studies with substrates are necessary to confirm these results and to extend them to other agronomic conditions.

International audienceThe BiMnO3+delta phase has been prepared by mechanosynthesis, at ambient pressure and room temperature, as nanocrystalline powders. This oxide exhibits a metastable character, similar to those prepared by high-pressure and high-temperature methods, remaining stable up to 673 K. Nanostructured ceramic materials (92% densification), maintaining the BiMnO3+delta composition, have been successfully processed by the spark plasma sintering technique, at the very low temperature of 673 K, in a time as short as 6 minutes. Conditions of synthesis and sintering are the key factors that determine the actual delta value, or Mn oxidation state. This parameter plays an important role in their magnetic properties, which vary from ferromagnetic for lower delta values (the case of the mechanosynthesized and SPS processed samples) to spin-glass behavior for higher delta values (thermally annealed samples). Electrical measurements, carried out on the dense BiMnO3+delta ceramic material, show no evidence of ferroelectricity down to 77 K, in good accordance with previous structural studies that indicated their centrosymmetric structures