High Temperature And High Pressure Synthesis And Properties Of Perovskite-type Manganites Yb_1-xDy_xMnO₃（0.1≤x≤0.5）

The perovskite-type structure materials have accounted for a significantproportion of multi-functional materials, which have the properties of piezoelectric,superconducting, magnetic resistance, catalysis, ionic conductor and so on. Due to thestructural stability of perovskite-type manganites, it can be doped with differentelements, and then regulated its properties. For perovskite-type manganites, it can beapplied in solid fuel cells, high-temperature heating materials, sensors, electrolyte,solid resistors, precious metals redox catalysts and many other areas. Therefore,perovskite-type manganites have been considered as a hot topic in physics, chemistry,materials science, and many other interdisciplinary fields. My paper are mainlyincluding these two results as follow：(1) A series of hexagonal perovskite-type compounds Yb1-xDyxMnO3(0.1≤x≤0.5)have been firstly prepared by the traditional solid-state reaction method at1573K for20h. Final products are fully characterized by the X-ray Powder Diffractometer(XRD), Energy Dispersive Spectrometer (EDS), X-ray Photoelectron Spectroscopy(XPS) analyses, and then subject to magnetic measurements (SQUID). The results ofXRD patterns of hexagonal Yb1-xDyxMnO3(0.1≤x≤0.5) manganites show that allcompounds have been pure phase and they crystallize in the hexagonal perovskitestructure with a space group of P63cm; With the increasing of larger Dy ions, thestructures of Yb1-xDyxMnO3(0.1≤x≤0.5) start to transfer from hexagonal to orthorhombic. It is noteworthy that the refinement of cell parameters increasing withthe rise of Dy content, prove that Dy ions have been doped into the crystal lattice. TheEDS results show the existence molar ratio of Yb, Dy and Mn, presumably, is almostconsistent with the theoretical stoichiometric ratio. The XPS spectra of Yb1-xDyxMnO3(0.1≤x≤0.5) samples show that this system could only exist as Mn3+. The magnetismof this series compounds can be explained by the chiral3D Heisenberg model.Therefore, the temperature dependence of magnetization (M-T) and the hysteresisloops of the Yb1-xDyxMnO3(0.1≤x≤0.5) have been investigated in detail. These resultsindicate that the Yb1-xDyxMnO3(0.1≤x≤0.5) system should exhibit antiferromagneticproperties but with spin canting ferromagnetism. The Néel temperature (TN) wasfound to be4.5K, which is lower than that of others reports of YbMnO3. Moreover,with the increasing of the Dy ions, the susceptibilities of Yb1-xDyxMnO3aresignificant grown, however, the Néel temperature is still around4.5K.(2) Using KCl as flux, the orthorhombic perovskite-type compounds ofYb1-xDyxMnO3(0.1≤x≤0.4) have been also obtained by a high-pressure fluxmethod at1273K for20h under5GPa high pressure, and single crystal ofo-Yb0.5Dy0.5MnO3has also obtained by this method. Subsequently, themolecular structure and magnetic properties of o-Yb1-xDyxMnO3(0.1≤x≤0.5) havebeen investigated in detail. The results of XRD patterns of orthorhombicYb1-xDyxMnO3(0.1≤x≤0.4) show that they have been pure phase and they crystallizein the orthorhombic perovskite structure with a space group of Pnma, and itsstructural distortion appears to increase gradually with the increasing of Dy ions. Also,I conduct single crystal XRD analysis on suitable Yb0.5Dy0.5MnO3single crystals,which the crystal structure can be characterized by tilting the ideal MnO6octahedralstructure of perovskite to afford a distorted hexagonal structure, with a typicaldimension of0.12×0.09×0.05mm. The results of EDS show the existence molarratio of Yb, Dy and Mn, presumably, corresponds to the theoretical stoichiometricratio. Because valence states can play influential roles on magnetic properties, thevalence state of Mn ions have been determined by XPS analysis. The XPS resultsprove that the Mn3+ions are the major Mn species present in the single crystal of orthorhombic Yb1-xDyxMnO3(0.1≤x≤0.5). After analyzing the valence state of Mnions, the magnetic properties have been tested. The magnetism ofo-Yb1-xDyxMnO3(0.1≤x≤0.5) can be explained by the typical3D Heisenberg model.According to previous reports, the magnetism of o-RMnO3exhibits antiferromagneticbehavior. Notably, typical paramagnetic characteristics are evident that are differentfrom o-RMnO3. The disappearance of antiferromagnetism could be due to highpressure flux method and the increase of average radius of rare earth ions that caninduce pronounced structural distortion. In general, this disappearance ofantiferromagnetic may be beneficial to understanding the mechanism ofperovskite-type rare earth manganites.Overall, we synthesized a novel series of hexagonal or orthorhombic structureYb1-xDyxMnO3(0.1≤x≤0.5). Also, the results of the relationship between the structureand magnetic properties of perovskite-type rare earth manganites could not onlyprovide a new ideas and methods for further researches, but it also could provide atheoretical basis and experimental data for future studies of perovskite-type rare earthmanganites.