Study On Preparation And Properties Of Perovskite (La,Ca)(Mn,Ti)O₃ Material

Multiferroelectric-magnetoelectric materials have both ferroelectric properties and ferromagnetic properties in a single phase. Due to their unique properties, these materials have been utilized as transducers, waveguides, switches, phase invertors, modulators, etc, playing an increasingly important role in the development of devices in the field of radio-electronics, opto-electronics, micro-wave electronics. Ferroelectronic materials and ferromagnetic materials have similar crystalstructures------perovskite structure (ABO3). Therefore, it is feasible to synthesize atype of perovskite-structured material which has both ferroelectric properties and ferromagnetic properties in the same phase. In the (Re,Ae)TiO₃(Re: La³⁺,Bi³⁺,Y³⁺;Ae: Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺) material, substitution of A niche ions could affect its polarization properties and its resistance properties. Furthermore, introduction of magnetic ions (Mn ion) in to the B niche, would not only affect its dielectric properties, but induce magnetic properties due to double exchange effect caused by Mn³⁺/Mn⁴⁺. Therefore, systematic study on the dielectric and magnetic properties of perovskite-structured (Re,Ae)(Mn,Ti)O₃ is of great significance to the development of Multiferroelectric-magnetoelectric materials.In this article, we synthesized La_0.5Ca_0.5Mn_xTi_1-xO₃ material(La ion and Ca ion in A niche;Mn ion and Ti ion in B niche) by the traditional ceramic process;studied the influence of Mn/Ti ratio on its structure, dielectric properties and magnetic properties. Furthermore we studied the change of microstructures under different sintering conditions and the mechanism resulting in these change. Study found:Under the same sintering conditions, with Mn/Ti ratio increasing, more Ti⁴⁺ cations were substituted by Mn⁴⁺ cation, making the lattice constant decrease. Mn doping could drive the growth of La_0.5Ca_0.5Mn_xTi_1-xO₃ grain, hence with Mn/Ti ratio increasing, grain size increased and material structure became more densified.Higher sintering temperature made it easier for Mn⁴⁺ to substitute Ti⁴⁺, making cell volume of La_0.5Ca_0.5Mn_xTi_1-xO₃ decrease. With sintering time period extending,solid reaction became more complete, and ions had enough time to transit, resulting in the growth of grains.At low Mn/Ti ratio( x < 0.3), there were spatial charge polarization, relaxation polarization and displacement polarization co-existing in the Lao.5Cao.5MnxTi1.xO3material. At higher Mn/Ti ratio ( 0.4 < x < 0.6 ) , (MriTj V'o ) type electric doublets came to being, and comprehensively increased the dielectric constant of the material. As Mn/Ti ratio went even higher, ( MriTi ? V'o ? MriTi) emerged, consumed the ( MnnVo ) type electric doublets, causing decline of the dielectric constant.Elevation of sintering temperature, caused the growth of grain, intensified the ceramic bulk. Large grain size caused more domain in one singal grain. Movement of interface led to the increase of dielectric constant. Density of the bulk also contributed to the increase of dielectric constant.In the Lao.5Cao.5MnxTi1.xO3 system, with the increase of Mn/Ti ratio, the number of 3d electrons increased, meanwhile transition channel of electrons was improved, causing electric-resistivity increase.In the Lao.5Cao.5MnxTi1.xO3 ( 0 < x < 0.7 ) system, as Mn/Ti ratio increasing, ratio of Mn3+/Mn4+increased, causing magnetic conductivity increase.