| Multiferroics refer those materials which process two or more primary ferroics in the same phase. The so-called primary ferroics refer ferroelectricity, ferromagnetism and ferroelasticity, which have been widely studied. What’s more, ferromagnetic and ferroelectric ordering exist coupling, which means that magnetic field can control polarization and electric field can control magnetization. The features described above make it possible to be applied in the new multi-functional devices. In recent years, multiferroics have been of particular interest in the field of condensed matter physics and materials science. Rare earth titanate R2Ti2O7(R=rare earth) has many physical properties and broad application prospects. If R is La or Nd, it has a perovskite layered structure. While R is Sm-Lu or Y, it has a pyrochlore-type structure. For La2Ti2O7with monocline, people have more focused on its photocatalytic properties and photoluminescent properties. But its multiferroic properties are less studied.This article has studied the effect of sintering condition on ferroelectric properties of La2Ti2O7ceramic. On above base, we prepare doped La2Ti2O7to make it have outstanding multiferroic properties at room temperature. The main contents are as follows:(1) A series of La2Ti2O7ceramics are prepared by conventional solid-state reaction. Effect of sintering temperature and durations on the phase, ferroelectric properties is investigated in detail, together with dielectric properties. It can be found from the result that when sintering temperature and durations are1400℃and24hours respectivly, La2Ti2O7ceramic shows the best ferroelectric properties. La2Ti2O7ceramic has an invariable dielectric constant and dielectric loss at room temperature in the frequency range of2～10MHz, which increase with the increasing of temperature.(2) A series of Mn and Fe doped La2Ti2O7respectivly are prepared by conventional solid-state reaction. Firtly, effect of Mn doped La2Ti2O7on the phase, microstructure, multiferroic and dielectric properties is investigated in detail. XRD results show that all samples (La2Ti2-xMnxO7(0≤x≥0.16)) are phase pure. Doping Mn decreases the average grain size of La2Ti2O7, revealing that doping Mn restrains the growth of La2Ti2O7grains. Compared with La2Ti2O7, remnant polarization of all doped samples decreases, but it decreases at first and increases with the doping level increasing. What’s more, all doped samples show ferromagnetism at room temperature and the maximum can be observed for x=0.08, of which remanent magnetization and coercive field are0.0018emu/g and0.38μC/cm2respectivly. Then, effect of Fe doped La2Ti2O7on the phase, ferroelectric and ferromagnetism is studied in detail. The results show that when samples with small doping contents are pure, and when doping contents is not less than0.04samples have the second phase La2/3TiO3. Compared with La2Ti2O7, remnant polarization of all doped samples decreases, but it increases with the doping level increasing, which results from the second phase. From the result of hysteresis loop, it can be seen that ferromagnetic ordering increases gradually with the contents of Fe increasing.(3) Effect of Nd and Mn together doped La2Ti2O7on the multiferroic properties is studied. A series of La2-xNdxTi1.92Mn0.0807(0≤x≤0.4) ceramics are prepared by conventional solid-state method. XRD results show that all samples are pure, which indicates that Nd and Mn ions can completely locate in the lattice of La2Ti2O7. Compared with La2Ti1.92Mn0.08O7, doping Nd can increase ferroelectric ordering. From the result of hysteresis loop, it can be seen that doping Nd makes La2Ti1.92Mn0.08O7change from ferromagnetic ordering to paramagnetism ordering. |
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