Structural And Ferroelectric Properties Of A, B Site Doped Hexagonal LuMnO₃

Multiferroics are multifunctional materials, which combine two or more “ferroic”properties such as （anti）ferromagnetism,（anti）ferroelectricity,（anti）ferroelasticity in the samephase. The magnetoelectric multiferroics are particularly appealing due to the so-calledmagnetoelectric effect, a coupling between the magnetic and ferroelectric orders. Due to thismagnetoelectric effect, the spontaneous magnetization could be reoriented by an appliedelectric field and the spontaneous electrical polarization could be tuned by an appliedmagnetic field, which could be applied in spintronics device, information storage, and so on.The hexagonal perovskite structure of LuMnO₃has attracted considerable interests due to thecoexistence of ferroelectric and magnetic order, charge ordering, colossal magnetoresistance,unique characteristics on chemical composition and crystal structure. The ferroelectric Curietemperature TCis750K and the antiferromagnetic Néel temperature TNis90K.In this thesis, we prepare the hexagonal perovskites LuMnO₃via a conventionalsolid-state reaction technique at ambient pressure and investigate the structure and theferroelectric properties of the hexagonal perovskites LuMnO₃systems doped by Ca at A siteor Fe at B site. The main contents of the thesis are as follows:1. Increasing the sintering temperature and doping Fe could suppress the emergence ofthe impurities.2. The lattice constant c of the hexagonal Lu1-xCaxMnO3decreases as x increases, whilethe lattice constant a remains constant. A second phase, orthorhombic structure occurs whenx0.15. The dielectric constant increases with an increasing x in the hexagonal phase anddrops rapidly when the orthorhombic phase emerges.3. There is no structure phase transition in the Fe-doped hexagonal LuMn_1-xFe_xO₃for x0.5. With an increasing x, the lattice constant a decreases while c increases. The dielectricconstant increases linearly with x, which could be contributed to the increase of the tilting ofMnO5bipyramid by Fe doped evidenced by the X-ray diffraction and the Raman data.