Shengwen Yu

Dielectric and magnetic enhancements in BiFeO3–PbTiO3 solid solutions with La doping

Solid solutions of 0.45(Bi1−xLax)FeO3–0.55PbTiO3 (BLFPTx) for x=0.1, 0.2, and 0.3 were prepared by the mixed oxide method. BLFPTx showed the tetragonal perovskite structure of which the c∕a ratio and Curie temperature decreased with the increase of La content. Significant dielectric and magnetic enhancements were observed for BLFPTx with La doping. The ferroelectric and ferromagnetic hysteresis loops revealed the maximum remanent polarization and magnetization of 28μC∕cm2 and 0.14emu∕g, respectively, for BLFPTx of x=0.3. Results indicated that BLFPTx was of the insulating and switchable multiferroics with both ferroelectric and ferromagnetic properties.Solid solutions of 0.45(Bi1−xLax)FeO3–0.55PbTiO3 (BLFPTx) for x=0.1, 0.2, and 0.3 were prepared by the mixed oxide method. BLFPTx showed the tetragonal perovskite structure of which the c∕a ratio and Curie temperature decreased with the increase of La content. Significant dielectric and magnetic enhancements were observed for BLFPTx with La doping. The ferroelectric and ferromagnetic hysteresis loops revealed the maximum remanent polarization and magnetization of 28μC∕cm2 and 0.14emu∕g, respectively, for BLFPTx of x=0.3. Results indicated that BLFPTx was of the insulating and switchable multiferroics with both ferroelectric and ferromagnetic properties.

Enhanced tunable properties of Ba0.6Sr0.4TiO3 thin films grown on Pt∕Ti∕SiO2∕Si substrates using MgO buffer layers

Ba0.6Sr0.4TiO3 (BST) thin films were prepared on MgO buffered Pt(111)∕Ti∕SiO2∕Si substrates by pulsed laser deposition. The crystallographic structure, interface characteristics, and dielectric properties of BST thin films are strongly dependent on MgO thickness. BST thin films exhibit (111) preferred orientation when MgO layer is thicker than 5nm. The MgO layer can mitigate the interdiffusion between BST and Pt, causing the dielectric loss and leakage current of BST thin films to decrease significantly. The dielectric loss, tunability, and the largest figure of merit of BST thin films on 10nm MgO achieve 0.009, 30%, and 33.4, respectively.

Diffused phase transition and multiferroic properties of 0.57(Bi1-xLax)FeO3-0.43PbTiO3 crystalline solutions

Crystalline solutions of 0.57(Bi1−xLax)FeO3−0.43PbTiO3 (BLF-PT) for x=0, 0.1, 0.2, and 0.3 have been fabricated by the solid state reaction method. The dielectric constant of BLF-PT was significantly enhanced by using La substitutions, reaching about 1850 for x=0.3. The ferroelectric-paraelectric phase transition of BLF-PT becomes more diffused with a decreased transition temperature for higher La concentration. BLF-PT of x=0.2 exhibits multiferroic characteristics with the simultaneously enhanced remnant magnetization and polarization of 0.119 emu/g and 33.5 μC/cm2, respectively.

Detection of residual stresses in Pb(Zr0.53Ti0.47)O3 thin films prepared on LaNiO3 buffered metal substrates with Raman spectroscopy

Sol-gel derived Pb(Zr0.53Ti0.47)O3 (PZT) thin films have been prepared on LaNiO3 buffered Si, Ti, NiCr, and stainless steel. Raman scattering was carried out on both PZT thin films and powders. Compared with PZT powders, notable shifts of Raman modes to the lower frequency were observed in the spectra of PZT thin films on metal substrates, whereas to a higher frequency for PZT on Si. The correlation between Raman shifts and thermal stresses agrees well with the Curie-Weiss law, which indicates that the Raman scattering technique provides an effective way to estimate the magnitude and types of residual stresses in the film.

Ferroelectric enhancement in heterostructured ZnO/BiFeO3-PbTiO3 film

The authors have prepared heterostructured ZnO∕BiFeO3-PbTiO3 (BFO-PT) composite film and BFO-PT film on Pt∕Ti∕SiO2∕Si substrates by pulsed-laser deposition. The structure and morphologies of the films were characterized by x-ray diffraction (XRD) and scanning electron microscope. XRD results show that both films are perovskite structured last with different orientations. The leakage current density in the ZnO∕BFO-PT film was found to be nearly two orders of magnitude lower. This could be due to the introduced ZnO layer behaving as a Schottky barrier between the BFO-PT film and top electrodes. The dramatic ferroelectric enhancement in ZnO∕BFO-PT film is mostly ascribed to the improved insulation.

A high temperature piezoelectric ceramic: (1-x)(Bi 0.9 La 0.1 )FeO 3-x PbTiO 3 crystalline solutions

(1-x)(Bi0.9La0.1)FeO3-xPbTiO3 (BLF-PT) crystalline solutions for x = 0.35, 0.37, 0.4, 0.43 and 0.45 have been prepared by the solid-state reaction method. The X-ray diffraction analysis shows that BLF-PT has a single perovskite phase with mixed tetragonal and rhombohedral phases between x = 0.4 and 0.43. The Curie temperature of BLF-PT for x = 0.4 attains 460degC, which is about 80degC higher than that of hard Pb(Zr,Ti)O3 ceramics. The remnant polarization and piezoelectric constant of BLF-PT for x = 0.4 reach 38 muC/cm2 and 112 pC/N, respectively. The planar coupling factor kp of BLF-PT for x = 0.4 remains stable at temperature increases of up to 360degC. The impedance spectroscopy study reveals that the high temperature conduction of BLF-PT may be attributed to the motion of oxygen vacancies within the material. Our results indicate that BLF-PT is a promising candidate for high temperature applications.

Improvement in dielectric and tunable properties of Fe-doped Ba/sub 0.6/Sr/sub 0.4/TiO/sub 3/ thin films grown by pulsed-laser deposition

Fe-doped Ba0.6Sr0.4TiO3 (BST) thin films were prepared on Pt/Si substrates by the pulsed laser deposition method. The concentrations of Fe dopants vary from 0.1 mol% to 1.0 mol%. Our results indicate that a certain amount of Fe dopants can decrease the dielectric loss of BST thin films without causing the significant reduction of the tunability. The leakage current of BST thin films was also reduced by addition of Fe dopants. BST thin films doped with 0.3 mol% Fe ions show a minimum dielectric loss of 0.88 % at 10 Hz, which is 1.7 % for the undoped BST films. Moreover, the 0.3 mol% Fe-doped BST films reveal a maximum figure of merit (FOM) of 51, indicating the improved comprehensive dielectric and tunable properties.

Effects of la concentration on the structural and dielectric properties of 0.57BiFeO/sub 3/-0.43PbTiO/sub 3/ crystalline solutions

Crystalline solutions of 0.57(B1-xLax)FeO3-0.43PbTiO3 (BLF-PT) for x=0, 0.1, 0.2 and 0.3 have been fabricated by traditional solid state reaction method. X-ray diffraction (XRD) analysis reveals that the tetragonal to rhombohedral phase transformation of BLF-PT occurs with the increase of La content. The dielectric and ferroelectric properties of BLF-PT were investigated at room temperature for different La contents. BLF-PT reveals strong ferroelectric characteristics for the lower La composition, which transfers to the relaxor ferroelectrics for x>0.2. The dielectric constant and remanent polarization achieve of 1461 and 33.5 muC/cm respectively for BLF-PT of x=0.2. The dielectric constant and polarization of BLF-PT are enhanced simultaneously with increasing La content. Our results demonstrate that BLF-PT are competitive piezoelectric ceramics.

Improvement in Dielectric and Tunable Properties of Fe-Doped Ba 0.6 Sr 0.4 TiO 3 Thin Films Grown by Pulsed Laser Deposition

Fe-doped Ba0.6Sr0.4TiO3 (BST) thin films were prepared on Pt/Si substrates by the pulsed laser deposition method. The concentrations of Fe dopants vary from 0.1 mol% to 1.0 mol%. Our results indicate that a certain amount of Fe dopants can decrease the dielectric loss of BST thin films without causing the significant reduction of the tunability. The leakage current of BST thin films was also reduced by addition of Fe dopants. BST thin films doped with 0.3 mol% Fe ions show a minimum dielectric loss of 0.88 % at 10 Hz, which is 1.7 % for the undoped BST films. Moreover, the 0.3 mol% Fe-doped BST films reveal a maximum figure of merit (FOM) of 51, indicating the improved comprehensive dielectric and tunable properties.

Structure and electrical properties of PZT/LNO/PT multilayer films on stainless steel substrates

PbZr0.53Ti0.47O3 (PZT) ferroelectric thin films were deposited on LaNiO3 (LNO) by sol-gel method. The PbTiO3 (PT) seed layer was deposited between the LNO buffer layer and stainless steel (SS) substrate, which effectively decreased the annealing temperature of LNO layer from 750 °C to 650 °C. X-ray diffraction (XRD) reveals that LNO layers with PT layer crystallize into a perovskite phase on annealing at 650 °C for 10 min. PZT deposited on LNO buffer layer with PT seed layer exhibits good ferroelectric property.