Study On The Structure And Properties Of Rare Earth LnFeO₃?Ln=La,Nd,Sm,Eu? And NaNbO₃

The rare earth ferrite LnFeO₃?Ln=La?Nd?Sm?Eu?with perovskite structure and NaNbO₃ have many novel properties such as ferromagnetism,ferroelectricity and photocatalysis for their unique structures.Exploring their structures and properties has become an interesting issue,recently.Based on literatures and experimental data,feasible solid-state sintering procedures were adopted to prepare LnFeO₃ ceramics,and their ferromagnetisms were characterized.The characteristics of megnetic moment switching and domain structures were determined to explain the mechanism of experimental phenomena and properties.The results are listed as follows:Firstly,to design the sintering procedure of LnFeO₃ ceramics,by combining the relevant literatures and differential thermogravimetric curves of powder samples,the ranges of sintering temperatures were determined;and by comparing the shrinkage rates of samples,the precise sintering temperatures were obtained.The XRD data of sintered samples were determined and analyzed,andno second phases were shown in the four formulas by comparing their XRD data.The samples with uniform and dense grains and without obvious pores were observed with scanning electron microscopy,indicating that prepared ceramics were of high quality.In order to investigate their ferromagnetism,the hysteresis loop s at room temperature and the spectrum of magnetic properties versus temperature during high and low temperature ranges were measured.At room temperature,the elongated waist-like magnetic hysteresis loops reflect their weak ferromagnetic or antiferromagnetic properties;and their magnetic phase transitions were shown b y the changes of the magnetic spectrum during high and low temperature ranges.Those magnetic phase transitions are related with the internal magnetization reversals,i.e.internal spin reorientations.To determine the relationship between their microstructure and magnetic properties,the domain on the surfaces were observed.Their results of atomic force microscopy reflected the accordant grain size with those observed by scanning electron microscopy.Simultaneously,a large number of striped domains were observed and distributed uniformly on the grain surfaces.The magnetic distributions were consistent with the domains of grains shown by the magnetic microscope image,indicating that the coupling between magnetic and electric properties in multiferroic materials was certainly correlated with their domains.Nextly,NaNbO₃ transparent ceramics were prepared by delicate-controlled solid state reaction method.The structures and properties of the sample were determined using XRD,SEM,ferroelectric hysteres is loops and UV�Vis spectroscopy.XRD results showed that the antiferroelectic phase Pbcm and ferroelectric phase R3c coexist in NaNbO₃ ceramics.NaNbO₃ ceramic presented the compact microstructure with fewer pores among grains from SEM images,enhancing the light transmission and weakening the absorption and reflection,which was confirmed by the UV-Vis spectroscopy.The tunic-shaped hysteresis loops of NN ceramic illustrated that two phases co-contributed to its ferroelectricity,and its high storage energy density and breakdown voltage of were obtained.Resultly,NaNbO₃ transparent ceramic has potential practical applications in the capacitor for energy storage.