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The CoFe2O4-BaTiO3 core-shell (CFO@BTO) nanocomposites have been synthesized, and a particular volume fraction of 15% CoFe2O4–85% BaTiO3 has been studied for its magnetic, ferroelectric, and magnetoelectric properties. The optimization of synthesis conditions showed that a temperature of at least 800 °C is required to obtain pure phase BaTiO3, whereas for the tetragonality to be visible in the x-ray diffraction (XRD) pattern, BaTiO3 needed to be sintered to at least 1050 °C. Even though the CFO@BTO composite began to react at the interface at 1050 °C and a small amount of the secondary phase was observed in the XRD pattern, the ferroelectric and magnetic properties were found to be not affected. Upon treating the living epithelial cells with either CFO@BTO or BTO nanoparticles, no toxicity was observed for up to 7 days. Together, these results establish the potential for the use of CFO@BTO nanoparticles in biomedical applications. [ABSTRACT FROM AUTHOR]

Eu+3 was incorporated into the lattice of a lead-free ferroelectric Na1/2Bi1/2TiO3 (NBT) as per the nominal formula Na0.5Bi0.5-xEuxTiO3. This system was investigated with regard to the Eu+3 photoluminescence (PL) and structural behaviour as a function of composition and electric field. Electric field was found to irreversibly change the features in the PL spectra and also in the x-ray diffraction patterns below the critical composition x=0.025. Detailed analysis revealed that below the critical composition, electric field irreversibly suppresses the structural heterogeneity inherent of the host matrix NBT and brings about a long range ferroelectric state with rhombohedral (R3c) distortion. It is shown that the structural disorder on the nano-scale opens a new channel for radiative transition which manifests as a new emission line branching off from the main 5D0→7F0 line along with a concomitant change in the relative intensity of the other crystal field induced Stark lines with different J values. The study suggests that Euþ3 luminescence can be used to probe the relative degree of field induced structural ordering in relaxor ferroelectrics and also in high performance piezoelectric alloys where electric field couples very strongly with the lattice and structural degrees of freedom. [ABSTRACT FROM AUTHOR]

A comprehensive global and local structural characterization using X-ray and neutron diffraction, and EXAFS have been performed to investigate the effect of electrical poling on the structure of (1 −x )Na 0.5 Bi 0.5 TiO 3 –( x )K 0.5 Bi 0.5 TiO 3 compositions. While the annealed samples showed definite indication of presence of local displacive disorders in all the compositions studied (0 < x < 0.3), this disorder persisted to some extent even after poling the samples. The tendency of electric field to reduce the local displacive disorder decreased with increasing K 0.5 Bi 0.5 TiO 3 content in the samples. [ABSTRACT FROM AUTHOR]

The complex nature of the structural disorder in the lead-free ferroelectric Na1/2Bi1/2TiO3 has a profound impact on the perceived global structure and polar properties. In this paper, we have investigated the effect of electric field and temperature on the local structure around the Bi and Ti atoms using extended x-ray absorption fine structure. Detailed analysis revealed that poling brings about a noticeable change in the bond distances associated with the Bi-coordination sphere, whereas the Ti coordination remains unaffected. We also observed discontinuity in the Bi-O bond lengths across the depolarization temperature of the poled specimen. These results establish that the disappearance of the monoclinic-like (Cc) global distortion, along with the drastic suppression of the short-ranged in-phase octahedral tilt after poling [B. N. Rao etal., Phys. Rev. B 88, 224103 (2013)] is a result of the readjustment of the A-O bonds by the electric field, so as to be in conformity with the rhombohedral R3e structure. [ABSTRACT FROM AUTHOR]

The complexity associated with local structures continues to pose challenges with regard to the understanding of the structure-property relationship in Na1/2Bi1/2Ti03-based lead-free piezoceramics. (l-x)Na1/2Bi1/2Ti03-(x)BaTi03 is an extensively studied system because of its interesting piezoelectric properties. Recently, a room temperature phase boundary was reported at x = 0.03 in this system [Ma et al., Adv. Funct. Mater. 23, 5261 (2013)]. In the present work we have examined this subtle phase boundary using x-ray diffraction, neutron diffraction, dielectric measurements as a function of composition (x < 0.06), temperature, and electric field. Our results show that this boundary separates an R3c + Cc-like structural state for x < 0.03 from an R3c+ cubiclike structural state for 0.03 ≤ x ≤ 0.05 in the unpoled specimens. This phase boundary is characterized by an anomalous reduction in the depolarization temperature, and a suppression of the tetragonal distortion of the high temperature PAbm phase. Our results also provide the clue to understand the pathway leading to the cubiclike structure of the critical composition x = 0.06, known for its highest piezoelectric response. [ABSTRACT FROM AUTHOR]

Heterophase structures in lead-free perovskite-type ferroelectric solid solutions of (1 − z)(Na0.5Bi0.5)TiO3− zBaTiO3are analysed for a few critical compositions near the morphotropic phase boundary (z = 0.05−0.07). Examples of the phase coexistence and elastic matching of the phases from different symmetry groups are considered to find optimum volume fractions of specific domain types and coexisting phases at the complete stress relief in two-phase samples. Some interrelations between these volume fractions are described using variants of the domain arrangement at changes in the composition and unit-cell parameters. The evaluated room-temperature volume fractions of the ferroelectric monoclinic (Cm symmetry) and tetragonal (P4mm symmetry) phases near the morphotropic phase boundary are in agreement with experimental data. [ABSTRACT FROM AUTHOR]

he highly complex structure-property interrelationship in the lead-free piezoelectric (x)Na1/2Bi1/2TiO3-(1-x)BaTiO3 is a subject of considerable contemporary debate. Using comprehensive x-ray, neutron diffraction, dielectric, and ferroelectric studies, we have shown the existence of a new criticality in this system at x=0.80, i.e., well within the conventional tetragonal phase field. This criticality manifests as a nonmonotonic variation of the tetragonality and coercivity and is shown to be associated with a crossover from a nonmodulated tetragonal phase (for x<0.8) to a long-period modulated tetragonal phase (for x>0.80). It is shown that the stabilization of long-period modulation introduces a characteristic depolarization temperature in the system. While differing qualitatively from the two-phase model often suggested for the critical compositions of this system, our results support the view with regard to the tendency in perovskites to stabilize long-period modulated structures as a result of complex interplay of antiferrodistortive modes [Bellaiche and Iniguez, Phys. Rev. B88, 014104 (2013); Prosandeev, Wang, Ren, Iniguez, ands Bellaiche, Adv. Funct. Mater. 23, 234 (2013)]. [ABSTRACT FROM AUTHOR]

Na0.5Bi0.5TiO3 (NBT) and its derivatives have prompted a great surge in interest owing to their potential as lead-free piezoelectrics. In spite of five decades since its discovery, there is still a lack of clarity on crucial issues such as the origin of significant dielectric relaxation at room temperature, structural factors influencing its depoling, and the status of the recently proposed monoclinic (Cc) structure vis-à-vis the nanosized structural heterogeneities. In this work, these issues are resolved by comparative analysis of local and global structures on poled and unpoled NBT specimens using electron, x-ray, and neutron diffraction in conjunction with first-principles calculation, dielectric, ferroelectric, and piezoelectric measurements. The reported global monoclinic (Cc) distortion is shown not to correspond to the thermodynamic equilibrium state at room temperature. The global monocliniclike appearance rather owes its origin to the presence of local structural and strain heterogeneities. Poling removes the structural inhomogeneities and establishes a long-range rhombohedral distortion. In the process the system gets irreversibly transformed from a nonergodic relaxor to a normal ferroelectric state. The thermal depoling is shown to be associated with the onset of incompatible in-phase tilted octahedral regions in the field-stabilized long range rhombohedral distortion. [ABSTRACT FROM AUTHOR]

Morphotropic phase boundary (MPB) systems are characterized by the coexistence of two ferroelectric phases and are associated with anomalous piezoelectric properties. In general, such coexistence is brought about by composition induced ferroelectric-ferroelectric instability. Here we demonstrate that a pure ferroelectric compound Na1/2Bi1/2TiO3 (NBT) exhibits the coexistence of two ferroelectric phases, rhombohedral (R3c) and monoclinic (Cc), in its equilibrium state at room temperature. This was unravelled by adopting a unique strategy of comparative structural analysis of electrically poled and thermally annealed specimens using high resolution synchrotron x-ray powder diffraction data. The relative fraction of the coexisting phases was found to be highly sensitive to thermal, mechanical, and electrical stimuli. The coexistence of ferroelectric phases in the ground state of the pure compound will have significant bearing on the way MPB is induced in NBT-based lead-free piezoceramics. [ABSTRACT FROM AUTHOR]

The lead free ferroelectric Na1/2Bi1/2TiO3 (NBT) is shown to exhibit electric-field-induced monoclinic (Cc) to rhombohedral (R3c) phase transformation at room temperature. This phenomenon has been analyzed both from the viewpoint of the intrinsic polarization rotation and adaptive phase models. In analogy with the morphotropic phase boundary systems, NBT seems to possess intrinsic competing ferroelectric instabilities near room temperature. [ABSTRACT FROM AUTHOR]

To control the properties of multiferroic materials, substitution of magnetic elements is a useful technique. In this study, we fabricated GaCrxFe1−xO3 and Ga1−yCryFeO3 films by substituting Cr3+ (3d3) ions in GaFeO3 for magnetic Fe3+ (3d5) and nonmagnetic Ga3+ (d10) sites, respectively. The effect of the Cr substitution on the magnetic and dielectric properties was systematically investigated. The obtained GaCrxFe1−xO3 and Ga1−yCryFeO3 films (x ≤ 1/4 and y ≤ 1/2) simultaneously exhibit ferrimagnetism and ferroelectricity. For the GaCrxFe1−xO3 films, the magnetic transition temperature (TC) and magnetic anisotropy decrease with increasing x. On the other hand, for the Ga1−yCryFeO3 films, TC increases with increasing y. Unlike the GaFeO3 film, the Cr-substituted GFO films show a peak in the magnetization versus temperature curves and exhibit a sudden decrease in the coercive field near the peak, probably due to the formation of Fe3+–O–Cr3+ coupling which prefers to form ferromagnetic interactions in the antiferromagnetic Fe3+–O–Fe3+ networks. Furthermore, we found that the Cr-substituted GaFeO3 films show out-of-plane ferroelectricity at room temperature. [ABSTRACT FROM AUTHOR]

A Sol-gel method assisted with spin-coating has been successfully used to grow orthorhombic GaFeO3 epitaxial films on SrTiO3 (111) substrates for the first time. The film with Pna21 crystal structure has been grown along the c-axis. The rocking curve of (004) reflection shows that the Full-Width at Half-Maximum (FWHM) value could be determined to be 0.230°, indicating good single crystallinity and high quality. X-ray Φ scan reveals a three-fold symmetry of the substrate and a six-fold symmetry of the film, respectively. The in-plane domains rotate 60° from each other in the film. Uniform film with dense structure, columnar grains with similar grain size was obtained. The thickness of the film was evaluated to be ~170 nm. The roughness value (RMS) measured by AFM was 4.5 nm, revealing a flat film. The in-plane Magnetization versus Magnetic field (M-H) curve at 5 K performs a typical ferri- or ferromagnetic hysteresis loop with a saturated magnetization (Ms) value of 136 emu/cm3. The Curie temperature could be determined to be 174 K. Compared to Pulsed Laser Deposition (PLD), the sol-gel method can prepare large area films with low cost. These new films show promising applications in multiferroic devices. [ABSTRACT FROM AUTHOR]