Photoluminescence, Electrical And Magnetic Properties Of Perovskite Oxides

In recent years, perovskite oxides have been a hotspot and attracted much attention due to the physical properties, such as ferroelectricity, ferromagnetism, piezoelectricity, etc.Er-doped 0.94Bi0.5Na0.5TiO3-0.06BaTi03 (BNT-6BT:xEr, x is the mole ratio of Er3+ to BNT-6BT) lead-free piezoceramics with x=0～0.02 have been prepared and the composition-dependent microstructure, photoluminescence, dielectric, piezoelectric and ferroelectric properties are comprehensively investigated. In general, Er-doping has significant effects on photoluminescence, dielectric, and ferroelectric properties. At room temperature, the green (550 nm) emission is enhanced by Er-doping, reaching the strongest emission intensity when x=0.0075. The electric poling results in weakened photoluminescence for compositions with x<0.02, but enhanced photoluminescence for that with x=0.02.As to electrical properties, Er-doping decreases the ferroelectric-relaxor transition temperature (TF-R) and depolarization temperature (Td) significantly, this is due to the Er-doping induced decreased TF-R and Td, which leads to weakened ferroelectricity and the weakened ferroelectricity means decreased contribution of ferroelectric domain to piezoelectricity, for example, the TF-R decreases from 76℃ for the composition with x=0 to 42℃ for that with x=0.02. With increasing x, the piezoelectric and ferroelectric properties tend to weaken. Our results indicate that BNT-6BT with appropriate Er-doping may be a promising multifunctional material with integrated photoluminescence and electrical properties for applications.Single phase BiFeO3 and Bi2Fe4O9 powders have been synthesized via hydrothermal method by carefully controlling the reaction conditions. Their phase purity, morphology, cation’s charge valence, and magnetic property were comparatively investigated. It is found that the BiFeO3 shows dense microstructure with irregular, larger grains, the average grain size is ～5.0μm, whereas the Bi2Fe4O9 displays small, porous microstructure with the sheet shaped grains, the average thickness is ～55 nm and length is ～500 nm. X-ray photoemission spectra confirm that in both compositions, the Bi and Fe cations have the charge valence of +3. The BiFeO3 has weak ferromagnetism even at room temperature, and at 10 K and 20 kOe external field, the maximum magnetization and remnant magnetization are about 0.13 emu/g and 0.004 emu/g, respectively, whereas the Bi2Fe4O9 shows antiferromagnetic nature in the temperature range of 10-300K. The BiFeO3 is antimagnetic within a temperature range of 300 K to Tf, while the BiFeO3 show typical characteristics of spin-glass behavior between the low temperatures and cusps (Tf). The Neel temperature (TN) of Bi2Fe4O9 is around 250 K.0.71BiFeO3-0.29BaTiO3:xCr2O3 (x is the mole ratio of Cr2O3) lead-free piezoceramics with x=0～0.025 have been prepared and their ferroelectric properties have been investigated. It is found that all the ceramics show a perovskite crystal structure without any other detectable phases. The average grain sizes and the ferroelectric properties of 0.71BiFeO3-0.29BaTiO3:xCr2O3 are decreased with the increase of x.