BiFeO3 xPbTiO3 Research Articles

Model-based analysis of the ferroelectric response of multiferroic (1-x)BiFeO3-xPbTiO3 solid solution thin films around morphotropic phase boundary

It is a challenging task to deposit single phase multiferroic (1-x)BiFeO3-xPbTiO3 (BF-xPT) solid solution thin films on Fluorine-doped tin oxide (FTO) coated glass substrate due to its high crystallization temperature. This study presents the preparation of BF-xPT solid solution thin films covering the morphotropic phase boundary (MPB) region. Films were prepared in ambient conditions via solution processing method on FTO coated glass substrate. Optical absorption in the visible region has been observed for intermediate compositions, promising for optoelectronic applications. The presence of multiple phases, strain, and finite-size effects results in structural complexities that have been discussed in detail. In addition to that, due to the presence of defects such as grain boundaries and porosity, considerable leakage in hysteresis loops has been observed. Linear capacitive and ferroelectric responses have also been observed, indicating that the films are composed of induced dipoles and ferroelectric domains, respectively. The origin of each mechanism has been discussed in detail. Model-based analysis was carried out to separate intrinsic ferroelectric switching by identifying MPB compositions exhibiting optimum results. Based on the intrinsic response MPB compositions are found to lie in the 0.35 < x < 0.45.

Solution processing of morphotropic phase boundary BiFeO3‐PbTiO3 thin films with reduced conductivity for high room temperature switchable polarization

AbstractThe (1 – x)BiFeO3‐xPbTiO3 (BFO‐PTO) perovskite solid solution has great potential for being used in practical devices, as it exhibits significant ferroelectric response at its morphotropic phase boundary (MPB). However, the significant conduction, particularly high electrical leakage currents that BFO‐PTO films show at room temperature, deteriorates their functionality. This is mainly associated with the presence of multivalent iron along with A‐site and oxygen vacancies. Here, solution‐derived BFO‐PTO thin films have been crystallized at low temperature on Pt/TiO2/SiO2/Si substrates, by a rapid thermal annealing process to minimize Bi and Pb volatilization. X‐ray analyses have revealed that textured films are obtained with a pseudocubic perovskite structure and without the formation of detectable second phases. Microstructural studies indicated a columnar growth of the films with grain size well above the nanometric range, which, therefore, should not produce an appreciable reduction of the ferroelectric response due to size effects. Because of the relatively low content of charged defects produced in these BFO‐PTO films during processing, ferroelectric hysteresis loops can be measured at room temperature. The highest value of remnant polarizations (2PR = 58 μC/cm2) was obtained for the 0.65BiFeO3‐0.35PbTiO3 (65BFO‐35PTO) films, which suggests that this film composition lies in the proximity of the MPB where the coexistence of a highly textured &lt;100&gt; tetragonal phase and a rhombohedral one seems to occur.

High‐temperature BiFeO3–PbTiO3‐Ba(Zr,Ti)O3 ternary ceramics with excellent piezoelectricity

AbstractTernary ceramics of (0.87−x)BiFeO3–xPbTiO3–0.13Ba(Zr0.5Ti0.5)O3 (BF–xPT–0.13BZT, 0.27 ≤ x ≤ 0.37) were prepared by the traditional solid state reaction methods. X‐ray diffraction results display that BF‐xPT‐0.13BZT ternary ceramics of x ≥ 0.29 exhibit the perovskite structure with dominant tetragonal (T) phases mixed with a small amount of rhombohedral (R) phases. Scanning electron microscopy (SEM) images reveal that the average grain size of BF‐xPT‐0.13BZT ternary ceramics is in a range of 10–11 μm, increasing first and then decreasing with the increase of PbTiO3 (PT) content. The low tanδ of about 0.015 and high Curie temperature Tc of above 450°C were obtained for BF‐xPT‐0.13BZT ternary ceramics. Moreover, the fluctuation of piezoelectric coefficient d33 is less than ±10% over a broad temperature range of 30°C–400°C. BF‐xPT‐0.13BZT ternary ceramics for x = 0.33 possess the maximum Tc and d33 of 470°C and 320 pC/N respectively, with the room temperature resistivity of about 1011 Ω·cm. These results indicate that BF‐xPT‐0.13BZT ternary ceramics for x = 0.33 with both excellent piezoelectric properties and high Curie temperature have promising applications in high‐temperature piezoelectric devices.

Improved ferroelectric response of pulsed laser deposited BiFeO3-PbTiO3 thin films around morphotropic phase boundary with interfacial PbTiO3 buffer layer

(1 − x)BiFeO3-xPbTiO3 (BF-xPT) is an interesting material for sensing and actuating devices with large polarization near the morphotropic phase boundary (MPB) (x = 0.30) in the bulk form. However, pulsed laser deposition (PLD) grown (BF-xPT) thin films usually show high electrical leakage and, hence, saturated ferroelectric hysteresis loops are only obtained at subzero temperatures. In this article, we report on high room temperature ferroelectric polarization with saturated hysteresis loops in pulsed laser deposited (BF-xPT) polycrystalline thin films of compositions near the MPB with the use of a thin buffer layer of PbTiO3 (PT). The thin films possessed a perovskite structure with excellent crystallinity and exhibit the presence of a monoclinic (Cm) phase (MA-type) for x = 0.20–0.25 and a mixture of a monoclinic (Cm) phase and a tetragonal (P4mm) phase for x = 0.30–0.35 compositions. The thin films with composition x = 0.25 exhibit a monoclinic phase and yield very large room temperature ferroelectric polarization (2Pr &amp;gt; 80μC/cm2), perhaps the highest room temperature ferroelectric polarization and excellent piezoelectric properties in PLD deposited (BF-xPT) thin films of near-MPB composition. Furthermore, the evolution of ferroelectricity with PT content, studied using room temperature Raman spectroscopy, reveals a correlation with lattice dynamics and stereochemical activity of Bi. Piezoforce domain analysis of the thin films reveals that ferroelectric polarization and electrical leakage in the thin films are intricately related to the type of domains present in the samples, viz., 180°, 109°, 90°, and 71° due to differences in the nature of the domain walls.

Magnetically driven robust polarization in (1 − x)BiFeO3–xPbTiO3 multiferroic composites

In this letter, we demonstrate an apparent magnetically activated electric polarization reorientation at room temperature through magneto-electric coupling in (1 − x)BiFeO3–xPbTiO3 (x = 0.0, 0.1, 0.2, 0.3, 0.4 and 0.5) composites. A change in magnetic field causes variation in electric polarization, attributed to the destruction of space modulated spin antiferromagnetic structure with the PbTiO3 addition. This behavior also results in the increase in magnetic parameters as the coercive field of the composites increases with the increase in PbTiO3 contents. The analysis demonstrates that the magneto-electric coupling in the prepared ferromagnetic/ferroelectric composites is dominant at room temperature, quite feasible for modern day devices.

Magnetic controlled voltage in the pseudo-ternary multiferroic BiFeO3–PbTiO3–BaTiO3

We have investigated the magnetoelectric coupling in multiferroic system (0.9 − x)BiFeO3–xPbTiO3–0.1BaTiO3 with x = 0.21, 0.23 and 0.25, synthesized by conventional solid state reaction. X-ray diffraction study revealed the coexistence of monoclinic (Cc) and tetragonal (P4mm) symmetries, suggesting these compositions to be at the morphotropic phase boundary (MPB) of this alloy system. We found a systematic increase in polarization with increasing PbTiO3 content. These compositions also exhibit weak ferromagnetism at room temperature. These MPB compositions are shown to exhibit high values of the dynamic magnetoelectric coupling coefficient (αE), viz. 3.6, 11.4 and 15.45 mV/cmOe, respectively, for x = 0.21, 0.23 and 0.25.

Structure and dielectric characteristics of (1 – x)BiFeO3–xPbTiO3 solid solutions

Undoped (1 – x)BiFeO3–xPbTiO3 binary solid solutions (0 ≤ x ≤ 0.50, Δx = 0.1) are obtained via a solid-state reaction combined with sintering in accordance with conventional ceramic technology. Features of their crystal structure formation and dielectric properties are studied in a wide range of temperatures and frequencies.

Structural, optical and magnetic properties of multiferroic (1−x)BiFeO3[sbnd]xPbTiO3 nanoparticles

We report structural, optical and magnetic properties of single-crystalline (1−x)BiFeO3xPbTiO3 (BF-xPT) solid solution nanoparticles synthesized by a facile sol–gel method in the compositional range of 0.1 ≤ x ≤ 0.5. It was observed that the substitution of PbTiO3 (PT) in BiFeO3 (BF) not only suppresses the impurity phases but it also improves the structure stability of perovskite phase. X-ray diffraction (XRD) and transmission electron microscopy (TEM) characterization confirmed the high purity of the nanoparticles and the structural transformation from rhombohedral (space group: R3c) to tetragonal structure (space group: P4mm) with increasing x. The average particle size was estimated to be around 29–47 nm from TEM and XRD analysis and size decreases with increasing x. The optical study shows that the band gap of BF-xPT nanoparticles, as measured from UV–visible absorption profiles, increases 1.81–2.69 eV as x increases from 0.1 to 0.5, indicating their usefulness as the photovoltaic material and photocatalyst. The magnetic measurements exhibited the improved magnetic behavior with the remnant magnetization values of Mr ≤ 0.025 emu/g, indicating the suppression of the cycloid spin structure of BiFeO3.

Spin phonon interactions and magnetodielectric effects in multiferroic BiFeO3–PbTiO3

Here, we report the observation of magneto-dielectric and magneto-structural coupling in (1 − x)BiFeO3–xPbTiO3 i.e.(1 − x)BF–xPT) solid solutions with compositions in the vicinity of morphotropic phase boundary, as manifested by a combination of temperature dependent magnetic, Raman and dielectric measurements. Whilst x-ray diffraction and Raman spectroscopy suggest absence of any structural phase transition between 90–300 K, temperature dependent magnetic studies reveal magnetic anomalies in the solid solutions. These results are complemented by identical observations in the dielectric measurements at similar temperatures indicating a coupling between magnetic and electric order parameters. Further, Raman studies on rhombohedral i.e. x = 0.20 samples reveal a coupling between the magnetic structure and the lattice, causing spin-phonon interactions that are possibly responsible for observed magneto-dielectric effects. Our results illustrate that the phase transitions in BiFeO3–PbTiO3 system are fewer than expected and are attributed to a spatial averaging in an inhomogeneous albeit single-phase material due to clustering of Fe- or Ti-ions on different length scales.

Extraordinary enhancement of Néel transition temperature in nanoparticles of multiferroic tetragonal compositions of (1 − x)BiFeO3-xPbTiO3 solid solutions

The Néel temperature (TN) in conventional antiferromagnets (AFM) decreases with decreasing particle size. In contrast, we present here evidence for an exotic facet of multiferroicity, whereby one can raise the TN by more than 200 K by decreasing the particle size. We illustrate this by taking the example of a tetragonal composition with x = 0.5 in the solid solutions of (1 − x)BiFeO3-xPbTiO3 (BF-xPT). We attribute it to the increase in the strength of the superexchange interaction via a decrease in the ferroelectric distortion in nanocrystalline powder of BF-0.5PT. The BF-0.5PT nanoparticles also exhibit exchange bias effect due to AFM core-FM shell type magnetic nanostructure.

Local polar structure and multiferroic properties of (1−x)Bi0.9Dy0.1FeO3−xPbTiO3 solid solution

The multiferroic (1–x)[0.9BiFeO3–0.1DyFeO3]–xPbTiO3 (BDF–xPT) solid solution with compositions around the morphotropic phase boundary (x = 0.25, 0.28, 0.31, 0.34, and 0.37) has been synthesized in the form of ceramics. The phase symmetry, microstructure, ferroelectricity, piezoresponse, and ferromagnetic properties have been characterized by various techniques. It is found that, with increasing content of lead titanate from x = 0.25 to x = 0.37, the grain size increases and the ferroelectric property is improved. The ferroelectric performance is further enhanced by the introduction of an excess amount (2%) of TiO2 or by sintering in oxygen atmosphere, which reduces the leakage. The local polar structure is imaged by piezoresponse force microscopy. Both the out-of-plane and in-plane images reveal distinct ferroelectric domain structures, with the amplitude and the average domain size decreasing with the increase of lead titanate amount. Compared with the (1–x)BiFeO3–xPbTiO3 binary solid solution of about the same concentration of PT, the magnetic properties are enhanced in BDF–xPT due to the presence of dysprosium, as demonstrated by the ferromagnetic hysteresis loops displayed at room temperature and at 10 K, but the remnant magnetization decreases with increasing PT content. The simultaneous presence of ferroelectricity and ferromagnetism entitles the BDF–xPT solid solution a room-temperature multiferroic material.

Simultaneous changes of nuclear and magnetic structures across the morphotropic phase boundary in (1−x)BiFeO3−xPbTiO3

We present here the results of a powder neutron diffraction study on the (1−x)BiFeO3–xPbTiO3 (BF-xPT) system, which reveal an abrupt change in magnetic structure from a noncollinear antiferromagnetic one to a collinear G-type antiferromagnetic as the nuclear structure of the ferroelectric phase changes from monoclinic in Cc space group for x≤0.27 to tetragonal in P4mm space group for x≥0.31 across the morphotropic phase boundary (MPB). This reflects the multiferroic character of the MPB in the BF-xPT system.

Effect of tetragonal distortion on ferroelectric domain switching: A case study on La-doped BiFeO3–PbTiO3 ceramics

The ferroelectric and piezoelectric properties of (1−x)BiFeO3–xPbTiO3 (BF-PT) ceramics were investigated as a function of tetragonal distortion. The latter was adjusted by employing La-doping (0–30 at %) while keeping the material near the morphotropic phase boundary by varying x between 0.35 and 0.46. This allows changing the c/a ratio of tetragonal BF-PT in the range from 1.10–1.01 and consequently alters the level of compatibility stresses. It was found that the c/a ratio has a significant influence on domain switching as inferred from electric field induced polarization, strain hysteresis, and Rayleigh measurements. Specifically, a threshold c/a ratio of about 1.045 was identified below which the electric field induced domain mobility increases sharply.

Stability of the various crystallographic phases of the multiferroic (1−x)BiFeO3–xPbTiO3 system as a function of composition and temperature

In this report, we have studied the stability of various crystallographic phases of (1−x)BiFeO3–xPbTiO3 as a function of composition and temperature. The structure of BF-xPT is reconfirmed to be tetragonal and monoclinic in the P4mm and Cc space groups for x&amp;gt;0.31 and 0.10≤x≤0.27, whereas the two phases coexist in the morphotropic phase boundary (MPB) region 0.27&amp;lt;x&amp;lt;0.31. A recent proposition of an orthorhombic phase in the MPB region has been ruled out comprehensively. From the high temperature powder x-ray diffraction (XRD) data it is shown that the MPB in this system is tilted towards the tetragonal side, a unique feature among the family of PbTiO3 based MPB systems. We have established accurately the room temperature phase diagram for this solid solution. By comparing the observed bond lengths between oxygen and other cations, obtained from Rietveld analysis of the room temperature powder XRD data with expected ionic bond lengths, we have shown that the very high c/a ratio in the tetragonal phase of this system is linked with the covalency effects for bonding between both A and B site cations with oxygen.

Structural changes and ferroelectric properties of BiFeO3–PbTiO3 thin films grown via a chemical multilayer deposition method

Thin films of (1−x)BiFeO3–xPbTiO3 (BF-xPT) with x≈0.60 were fabricated on Pt/Si substrates by chemical solution deposition of precursor BF and PT layers alternately in three different multilayer configurations. These multilayer deposited precursor films upon annealing at 700 °C in nitrogen show pure perovskite phase formation. In contrast with the equilibrium tetragonal structure for the overall molar composition of BF:PT::40:60, we find monoclinic structured BF-xPT phase of MA type. Piezoforce microscopy confirmed ferroelectric switching in the films and revealed different normal and lateral domain distributions in the samples. Room temperature electrical measurements show good quality ferroelectric hysteresis loops with remanent polarization Pr of up to 18 μC/cm2 and leakage currents as low as 10−7 A/cm2.

Ferroelectric properties of chemically synthesized perovskite BiFeO3–PbTiO3 thin films

Ferroelectric BiFeO3–PbTiO3 thin films with near morphotropic phase boundary composition were synthesized on Pt/TiOx/SiO2/Si substrates by chemical solution deposition. Perovskite BiFeO3–PbTiO3 single-phase thin films were successfully fabricated at 600 °C by optimizing several processing conditions, such as the PbTiO3 content. Typical ferroelectric polarization-electric field (P-E) hysteresis loops were observed for (1−x)BiFeO3–xPbTiO3 (x=0.2, 0.3, 0.4, 0.5) thin films, which contained some leakage current components at room temperature. In the low temperature region, the BiFeO3–PbTiO3 thin films demonstrated improved insulating resistance and exhibited relatively saturated P-E hysteresis loops. Among these films, 0.7BiFeO3-0.3PbTiO3 thin films exhibited the largest remanent polarization, and the remanent polarization (Pr) and coercive field (Ec) at −190 °C were approximately 60 μC/cm2 and 230 kV/cm, respectively. Furthermore, Mn doping of the BiFeO3–PbTiO3 thin films was effective in changing the dominant leakage current factors and improving the ferroelectric properties of the resultant thin films at room temperature. The Pr and Ec values of 5 mol % Mn-doped 0.7BiFeO3-0.3PbTiO3 films at room temperature were approximately 40 μC/cm2 and 100 kV/cm, respectively. Potentially large remanent polarization (∼90 μC/cm2) was also demonstrated by the BF-PT thin films.

Growth and characterization of tetragonal bismuth ferrite–lead titanate thin films

Thin films of tetragonal bismuth ferrite–lead titanate (1−x)BiFeO3–xPbTiO3 with x=0.9–0.7 were prepared by pulsed laser deposition (PLD). The films exhibit a dense columnar grain growth. XRD analysis reveals that the films have a perovskite structure and exhibit a preferred (111) texture. The film microstructure was studied using SEM. The ferroelectric properties of the films are discussed in the light of polarization-field hysteresis behaviour and impedance spectroscopy. The remanent polarization values ranged between 2Pr∼45 and ∼60μCcm−2 at a field amplitude of 500kVcm−1 and −10°C, while the dielectric permittivity of the films ranged between 375 and 1096 at a frequency of 2kHz.

Structure and properties of multiferroic (1 − x)BiFeO3–xPbTiO3 single crystals

Single crystals of the multiferroic (1 − x)BiFeO3–xPbTiO3 (BF–PT) solid solution with a nominal morphotropic phase boundary (MPB) composition were grown from flux. Structural characterization by x-ray diffraction shows the simultaneous existence of a tetragonal, an orthorhombic, and a rhombohedral perovskite phase in the crystals. A high ferroelectric Curie point of 660 °C was found in the BF–PT crystals by dielectric measurements. The variation of the magnetic moment as a function of temperature of the BF–PT crystals measured under zero field cooling mode reveals three anomalies with the highest one around 440 K, corresponding to the antiferromagnetic ordering temperatures of the rhombohedral, orthorhombic, and tetragonal phases, respectively. These results demonstrate the intrinsic relations between the MPB phase components and the macroscopic ferroic properties.

Morphotropic phase boundary in (1−x)BiFeO3–xPbTiO3: phase coexistence region and unusually large tetragonality

It is shown that the tetragonal (T) and rhombohedral (R) structures of (1−x)BiFeO3–xPbTiO3 are stable for xT⩾0.31 and xR⩽0.27, respectively, giving the narrowest width of 0.03, reported so far, for the morphotropic phase boundary region in this system. The Rietveld refined structure of the T phase for x=0.31 reveals partial covalent character of the Ti∕Fe–O and Pb∕Bi–O bonds which may be responsible for the unusually large tetragonality.

Large remanent polarization in ferroelectric BiFeO3–PbTiO3 thin films on Pt∕Si substrates

Bismuth ferrite–lead titanate thin films in the region of the morphotropic phase boundary, with compositions of (1−x)BiFeO3–xPbTiO3 (0.3&amp;lt;x&amp;lt;0.5), were prepared by pulsed laser deposition on Pt∕Si substrates. X-ray diffraction confirmed the formation of pure perovskite phase at a substrate temperature of 565°C under 75mTorr of oxygen. The films exhibit remanent polarizations with 2Pr up to 100μCcm−2 for a field amplitude of 820kVcm−1 and switchable polarization up to 80μCcm−2.