Multiferroic YMn₂O₅ Fine Powders Derived From Hydrothermal Process

Multiferroic materials have been the subject of intensive research due to their interesting magnetic and ferroelectric properties and the mutual correlation between magnetic and ferroelectric orderings in the same phase, and they have potential applications in many fields, such as information storage, integrate circuits and magnetic sensors, et al. It is unusual that ferroelectricity and magnetism coexist in one system, while RMn₂O₅ (R stands for rare earth) materials have become one of the most important research topics.This dissertation focused on the preparations and properties of multiferroic YMn₂O₅ prepared by hydrothermal method. XRD, SEM, TEM, PPMS measurements were employed to characterize their properties. The effects of synthetic conditions such molar ration of starting materials, reaction temperature, mineralizer concentrations on the morphologies, structures and properties were studied, and methods of morphology control and new-phase synthesis were tried to optimize the properties of as-prepared products. Moreover, the "dissolution and recrytallization" model was used to explain the nucleation and growth processes of YMn₂O₅. And the results are as follows:(1) Single phase YMn₂O₅ fine particles with orthorhombic structure were successfully prepared with one-step hydrothermal route. It was found that the particle sizes and morphologies of YMn₂O₅ were strongly influenced by the reaction temperature and mineralizer concentrations. The phase composition remained the same while molar ratio of starting materials changed.(2) Well-dispersive and regular YMn₂O₅ crystals with controllable size and shape were synthesized through a simple hydrothermal reaction, and the optimal experimental conditions were found when the mineralizer concentration is 1 mol/L and reaction was processed at 523 K for 6 h.(3) Magnetic measurement shows that the Neel temperature of YMn₂O₅ powders is about 45 K. It shows paramagnetism at room temperature and weak ferromagnetism at temperature below 45 K. (4) The formation mechanism and growth process of YMn₂O₅ ceramic powders were studied based on knowledge of crystal physics, solution chemistry and crystallography, and it was found the nucleation and growth processes were probably carried out according to the "dissolution and recrytallization" mechanism.