An improved technique was used to prepare the ceramic samples of Bi_(5.75)R_(0.25)Fe_(1.4)Ni_(0.6)Ti_(3)O_(18)(BRFNT,R=Eu,Sm,Nd,Bi,and La).The five-layer Aurivillius phase of the samples was confirmed by X-ray diffraction(XRD)without detectable impurities.BRFNT samples exhibit the pseudo-tetragonal except the orthorhombic BSmFNT samples.The characteristic plate-like morphology was revealed by field emission transmission electron microscopy(FETEM)images.At ambient tempe rature,all the samples present both ferroelectric and magnetic properties and BEuFNT shows the best ferroelectric behavior with its remanent polarization as high as 14.9μC/cm^(2)under 155 kV/cm,which is three times higher than that of Bi_(5.75)R_(0.25)Fe_(1.4)Ni_(0.6)Ti_(3)O_(18).Moreover,the remanent magnetization of BEuFNT is increased up to 1.20 emu/g compared to that of Bi_(5.75)R_(0.25)Fe_(1.4)Ni_(0.6)Ti_(3)O_(18)which is only 0.53 emu/g.With increasing radius of the introduced A-site ions,the ferroelectric phase transition temperature(T_(CE))is decreased while the magnetic phase transition temperature(T_(CM))fluctuates.The decrease in both T_(CE)and T_(CM) corresponds to the upward shift of the related Raman modes and vice versa,indicating that the T_(CE)and the T_(CM) depend not only on the t factor,but also on the strength of the covalent bonds.
用传统固相烧结法制备了Bi5–xEuxFe0.5Co0.5Ti3O15(BEFCT–x:x=0,0.35,0.55,0.85)陶瓷样品,对比研究了它们的结构和电磁性能。X射线衍射分析表明:掺杂未导致明显杂相,材料的剩余极化(2Pr)随掺杂量的增加呈先增加后减小的变化趋势,在Eu掺杂量为0.55时,材料的2Pr达到最大值,为11.2μC/cm2,升幅达143%,可以由Eu掺杂导致氧空位的抑制和铋氧层的破坏所形成的竞争机制解释。随Eu含量的增加,材料的剩余磁化单调上升,最大达到0.28 A m2/kg,比未掺杂时增加了2个数量级,从晶格失配、耦合增强以及共生结构等方面的综合效果解释了这一现象。材料的介电温度谱显示,Eu掺杂未明显损害材料的热稳定性,Eu掺杂所导致的介电损耗行为可能与氧空位或其他点缺陷有关联。
As a novel structure, inverse opal, with threedimensional periodic macropore and mesopore and huge specific surface area, has great promising applications. In this paper, tin dioxide (SnO_(2)) inverse opal films were prepared with sol–gel method by cooperative opal template. The surface morphologies of SnO_(2)inverse opal films were examined by scanning electron microscopy (SEM), the inner structure of SnO_(2)inverse opal films was examined by transmission electron microscopy (TEM), the optical properties of SnO_(2)inverse opal films were studied and discussed in detail. Optical reflectance spectra reveal that, for the opal films, the wavelengths of the reflectance peak confirmed by the experimental reflectance spectra are consistent with the theoretical values;for the SnO_(2)inverse opal films, the wavelengths of the reflectance peak confirmed by the experimental reflectance spectra deviate from theoretical values largely.
Co-doped BisFeTi3O15 thin films （BFCT-x, Bi5Fe1-xCoxTi3O15） were prepared using a sol-gel technique. XRD patterns confirm their single phase Aurivillius structure, and the corresponding powder Rietveld analysis indicates the change of space group around x ： 0.12. The magnetic hysteresis loops are obtained and ferromagnetism is therefore confirmed in BFCT-x thin films. The remanent magnetization （Mr） first increases and reaches the maximum value of 0.42 emu/cm^3 at x = 0.12 due to the possible Fe^3＋-O Co^3＋ ferromagnetic coupling. When x = 0.25, the Mr increases again because of the dominant Fe^3＋-O Co^3＋ ferromagnetic coupling. The remanent polarization （2Pr） of BFCT-0.25 was measured to be as high as 62 μC/cm2, a 75% increase when compared with the non-doped BFCT-0 films. The 2Pr remains almost unchanged after being subjected to 5.2 × 10^9 read/write cycles. Greatly enhanced ferroelectric properties are considered to be associated with decreased leakage current density.
