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A new approach was employed in explaining the weak ferromagnetic behavior of conventionally synthesized Zr4+ modified Bi0.8La0.2FeO3. Rietveld refinement of XRD patterns revealed a polar-tonon-polar R3c → Pnma structural transition in Zr4+substituted samples. Magnetic properties were discovered to be remarkably enhanced, with extracted coercivity and remanence as high as 14 kOe and 0.2 emu/g, respectively. More importantly, an answer to the essential question of the magnetic domain state of the samples has been put forward. Our analysis established, nearly without doubt, the presence of grains consisting of a single magnetic domain. Separated ferromagnetic and anti-ferromagnetic components of the total M-H curves helped to reveal an immense effect of the structural transition on the shape of the hysteresis loops. The orthorhombic magnetocrystalline anisotropy of the Pnma phase has been primarily deemed responsible for the high coercivity and remanence of the Zr4+ modified samples. The effect of the grain size and Fe-O-Fe bond angle on the magnetic properties of the samples has also been discussed. Ferroelectricity was found to be absent in Zr-substituted samples because of their non-polar structure. However, the leakage current was reduced by up to two orders of magnitude compared to Bi0.8La0.2FeO3 upon addition of Zr4+. Dielectric measurements conformed to the ferroelectric and leakage current characteristics, and Zr4+ substitution was again found to be beneficial. [ABSTRACT FROM AUTHOR]

Relaxation behavior was investigated in typical La-based bulk metallic glasses by dynamic mechanical analysis, both in the isochronal and in the isothermal routes. Two relaxations were observed: the main relaxation (α), associated with the glass transition, and a secondary relaxation, at lower temperature or higher frequency. This secondary relaxation corresponds to the well known Johari-Goldstein (JG) β relaxation. Master curves can be obtained. The activation energy Eβ of β relaxation (about 1 eV) is in agreement with the empirical relation Eβ ≈ 26(±2) RTg. The high value of the activation energy Eα of the α relaxation (about 5 eV) indicates that this relaxation corresponds to correlated movements. The mechanism of JG β relaxation in metallic glasses is discussed. [ABSTRACT FROM AUTHOR]

The dielectric relaxation at temperatures ranging from 100 °C to 550 °C in lanthanum-doped barium strontium titanate glass ceramics has been investigated by measurements of both dielectric temperature curve and complex impedance spectroscopy. The temperature dependence of dielectric properties reveals two regimes. In the first regime, at temperatures lower than 350 °C, the charge carrier contributed to interfacial polarization is conduction electrons. In contrast, in the second regime, at temperatures higher than 350 °C, the dielectric relaxation was attributed to the thermally activated movement of oxygen vacancies. Thus, two relaxation mechanisms could be explained on the basis of defect chemistry and impedance analysis. [ABSTRACT FROM AUTHOR]

Well-ordered large-area arrays of ferroelectric La-substituted Bi4Ti3O12 (BLT) nanostructures were prepared by pulsed laser deposition using gold nanotube membranes as shadow masks. By x-ray diffraction and transmission electron microscopy, it was found that well-defined (001)-, (118)/(100)-, and (104)-oriented BLT nanostructures were obtained on (001)-, (011)-, and (111)-oriented SrTiO3 single crystal substrates covered with epitaxial SrRuO3 electrode layers, respectively, through ex situ crystallization at 700 °C. Atomic force microscopy analyses revealed that the epitaxial BLT nanostructures maintain a height of about 100 nm and a lateral size of about 150 nm in spite of the postannealing process. The anisotropic ferroelectric properties of the BLT nanostructures of three different orientations were investigated by scanning force microscopy in piezoresponse mode. The highest effective remanent piezoresponse coefficient (2dzz) of about 38.0 pm/V was observed in (118)/(100)-oriented BLT nanostructures, whereas (001)- and (104)-oriented nanostructures showed smaller 2dzz values of 5.0 pm/V and 1.4 pm/V, respectively. [ABSTRACT FROM AUTHOR]

Lanthanum doped multiferroic DyFeO3 was synthesized by solid state reaction. X-ray diffraction and refinement show that the lattice parameters of Dy1-xLaxFeO3 increase linearly with the La content. Raman spectroscopy reveals that the short-range force constant in Dy1-xLaxFeO3 is decreased by La3+ ion substitution. The spin reorientation phase transition temperature (TSRPT) is observed to decrease along with the doping level. The antiferromagnetic ordering temperature TN of Fe3+ ions is depressed with increasing doping level. Both decreasing TSRPT and decreasing TN indicate that Fe-Dy and Fe-Fe interactions are weakened by La substitution. It is found that the electron configuration of Fe3+ is high spin state and not affected by the La doping in all the samples above TN. [ABSTRACT FROM AUTHOR]

We have probed the role of La substitution on the ferroelectric properties of epitaxial BiFeO3 films on SrTiO3-templated Si. This provides a mechanism to engineer the rhombohedral distortion in the crystal and, thus, control domain structure and switching. With a 10% La substitution, the (Bi0.9La0.1)FeO3 film showed well-saturated ferroelectric hysteresis loops with a remanent polarization of 45 μC/cm2, a converse piezoelectric coefficient d33 of 45 pm/V, and a dielectric constant of 140. Over this range of La substitution, the coercive field systematically decreases such that a coercive voltage of 1 V can been obtained in a 100 nm thick film. These results show promise for the ultimate implementation of this lead-free multiferroic operating at voltages in the range of 2–3 V. [ABSTRACT FROM AUTHOR]

The influence of La doping on the crystal structure and multiferroic properties of BiFeO3 (BFO) thin films was investigated. BFO-based films of pure perovskite phase were deposited on BaPbO3/Pt/TiOx/SiO2/Si substrates by rf-magnetron sputtering. The increased dielectric constant and remanent polarization of the La-doped BFO films were due to the increased lattice parameters and an improved crystallinity. The polarization switching and the fatigue behavior of the BFO films were significantly enhanced by the La doping. The in-plane magnetization-field curves revealed that the room-temperature saturated magnetization of the BFO films increased with La doping. [ABSTRACT FROM AUTHOR]

We report the dielectric response of La1.5Sr0.5NiO4, a system that experiences charge ordering above room temperature (TCO=480 K) and a rearrangement of its charge-order pattern in the temperature region 160–200 K. A careful analysis of the role of the electrical contacts used, sample thickness, and grain size on the experimental data allows us to determine that this material exhibits a high intrinsic dielectric constant. In addition, the temperature dependence of the dielectric constant, that shows a maximum in the region of the rearrangement of the charge-order pattern, points to a link between the two phenomena. [ABSTRACT FROM AUTHOR]