Research Of Multiferroic Properties Of Cr/Fe Codoped BaTiO₃and Electrochemical Properties Of Multielement Hydrogen Storage Alloy

1Research on BaTiO₃-based multiferroic materialIn this work, the incorporation of transition metal elements in the ferroelectric materialBaTiO₃has both ferromagnetic and ferroelectric properties of the composite multiferroicmaterials. The multiferroic properties of Fe/Cr co-doped BaTiO₃was studied systematically.The multiferroic performance of BaTiO₃was improved significantly. The results are asfollows:1.1BaTi（1-x）Cr_xO₃samples （x=1.0%、2.5%、5.0%、7.5%）These samples （x≤2.5%） are crystallized in a tetragonal perovskite structure （t-BaTiO₃）at room temperature; With the Cr doping content increasing, BaCrO3phase appears. Theappearance of BaCrO3indicates that Cr has a low solubility in BaTiO₃lattice. The XPS resultof the sample at x=2.5%shows that Cr exists as a single state of Cr³⁺, considering the XRDtest results, we believe that Cr ion which is in the samples at low doping content then replacesat Ti. Those ferroelectric test data indicate that these samples have good ferroelectricproperties at room temperature. With the increasing Cr doping content, the leakage current inthese samples increased and the ferroelectric properties decreased. Magnetic measurementresults indicate that these BaTi（1-x）Cr_xO₃samples all have demonstrated room temperatureferromagnetism. With the increasing Cr doping content, the specific saturation magnetizationof these samples first increases and then decreases, maximum value appears at x=5.0%, butthe magnetization is still weak. Combining with the XRD test results, the change of specificsaturation magnetization indicates that Cr3+is the primary cause of sample’s ferromagnetismat room temperature. The hops of specific saturation magnetization at the Curie temperatureof BaTiO₃（400K） proved the existence of magnetoelectric coupling in these samples. Afterannealing in N2atmosphere, the reduction of the magnetic parameters and disappearance ofBaCrO3phase proved that: The origin of magnetization in Cr doped BaTiO₃samples is thesuper-exchange interactions between Cr ions which depending on O ions.1.2BaTi1-xFexO3samples （x=1.0%、2.5%、5.0%、7.5%） and BaTi0.95-xFexCr0.05O3samples （x=2.5%、5.0%、7.5%）.In order to overcome the weak ferromagnetism in BaTi（1-x）Cr_xO₃, we have prepared Fe/Cr codoped BaTiO₃samples, and compared with Fe doped BaTiO₃samples. Combination of theXPS results, X-ray diffraction （XRD） patterns show that both BaTi1-xFexO3andBaTi_0.95-xFe_xCr₍0.05_O3samples are crystallizing in a hexagonal perovskite （h-BaTiO₃） andtetragonal perovskite （t-BaTiO₃） coexistence structure at room temperature. Fe exists in thesesamples with a single state of Fe³⁺. Fe doped into BaTiO₃lattice and then replaced at Ti aswell. The XRD result can prove that codoping BaTiO₃with Fe/Cr can improve the solubilityof Cr ions in the BaTiO₃. From the analysis of ferroelectric and magnetic properties of thesesamples, we can find that: With the increasing Fe doping content, the specific saturationmagnetization of BaTi_1-xFe_xO₃samples first increases and then decreases, the ferroelectricproperties decreased until disappeared; the specific saturation magnetization ofBaTi0.95-xFexCr0.05O3samples increases linearly and the ferroelectric properties decrease tosome extent. From this, we can infer that codoping BaTiO₃with Fe/Cr can significantlyimprove the ferromagnetic properties at no expense of rapid decline in ferroelectricperformance at the same time. Codoping is an effective way to synthesis the multiferroicmaterial which has better ferroelectric and magnetic propertiesIn summary, we successfully prepared Cr doped BaTiO₃multiferroic materials, andcodoped BaTiO₃with Fe/Cr significantly improved the ferroelectric properties of Fe-dopedBaTiO₃multiferroic materials. We believed that the super-exchange interaction of transitionmetal ions which depending on oxygen ions as a medium was a direct origin of theferromagnetic and enhanced it then. This exchange would make the Ti3d shell being notcompletely empty which would destroy the time reversal symmetry, and then led to thedisappearance of the ferroelectric.2Effect of annealed treatment and elemental composition on microstructure andelectrochemical properties for multielement hydrogen storage alloy.In this work, we prepared multielement hydrogen La-Mg-Ni-Co alloy, and study theeffect of annealed treatment and elemental composition on both microstructure andelectrochemical properties for multielement hydrogen storage alloy.2.1The (La_0.83Mg_0.17)Ni_3.9alloy were prepared by induction melted method, then it washeated for different days. The XRD patterns show that these alloys consist of LaNi₅, Pr5Co₁₉Ce2Ni7and PuNi3-type phase. The mass fraction of each phase in these alloys varies after annealing. The hydriding capacity of annealing alloy was higher than as-cast alloy. Estimatingfrom pressure-composition isotheral curves, it was considered that the hydriding is governedby two processes, which has the close relationship with the phase abundance of each phasevaried.2.2The LaNi_3.8-xAl_x（0≤x<0.5） alloy was prepared by arc melting under argonatomosphere. The electrochemical result showed that, both full Co substitution of Ni and theincreasing doping content of Mg will decrease the discharge capacity. It means the HRD （highrate discharge） property of La-Mg-Ni alloy is better than La-Mg-Co alloy. High elementcontent of LaNi5and PuNi₃will make cyclic stability better. Full Co substitution of Ni willmake the activation is extremely difficult. Mg substitution of La will make cyclic stabilitybetter, make the activation easier and decrease the HRD property. The addition of Co reducesthe lattice defects, which can imporve the ability of corrosion-resistant. Comparing the curveof HRD-I0（exchange current density） with the curve of HRD-D （hydrogen diffusioncoefficient）, we can find that the hydrogen diffusion coefficient is a key factor for the highrate discharge performance.