Internal Bias Electric Field Research Articles

Large piezoelectric property of Bi(Fe0.93Mn0.05Ti0.02)O3 film by constructing internal bias electric field

BiFeO3 (BFO), Mn-doped-BFO (BFMO), Ti-doped-BFO (BFTO), and (Mn,Ti)-codoped-BFO (BFMTO) thin films are fabricated on the Pt/TiO2/SiO2/Si substrates via a sol–gel method combined with spin-coating and the subsequent layer-by-layer annealing technique. Compared with BFO film, the BFMTO film exhibits the lowest leakage current density ([Formula: see text][Formula: see text]A/cm2@290[Formula: see text]kV/cm). Notably, the polarization–electric field (P–E) loop of BFMTO film exhibits a positive displacement along the x-axis due to the existence of internal bias electric field, which is in agreement with the results of the PFM phase and amplitude curves. Especially, a very prominent inverse piezoelectric constant of [Formula: see text][Formula: see text]pm/V was obtained, which overcomes other related thin films. The internal bias electric field of BFMTO film can be caused by the different work functions of the thin film and the bottom electrode, accumulation of oxygen vacancies and the formation of defect dipoles. Besides, the internal bias electric field of BFMTO film has a good stability at the same electric field after experiencing the test cycle from low electric field to high electric field (400–1900[Formula: see text]kV/cm). These results indicate that self-polarized BFMTO film can be integrated to devices without additional polarization process, and have a wide range of application in microelectromechanical systems.

Kinetics of the Domain Structure in Uniform Electric Field in LiNbO3 with Surface Layer Modified by Soft Proton Exchange

The creation of periodic domain structures in lithium niobate crystals makes it possible to realize highly efficient nonlinear optical interactions in optical waveguides. The influence of near‐surface H+ ion concentration gradient on the domain kinetics in uniform electric field in lithium niobate crystals modified by soft proton exchange is studied. The spatial distribution of the H+ ions concentration in the surface layer is obtained by confocal Raman microscopy. The observed anomalous evolution of the domain structure at the surface represents the formation of stripe domains and their anisotropic growth along three directions. The domain imaging in the bulk allows revealing a comb‐like domain shape. The obtained strong influence of the proton exchange duration on the threshold field is attributed to the action of the concentration gradient in the near‐surface layer, which is considered as an analog of the internal bias electric field. It is shown that the internal bias field is proportional to the increase in the concentration gradient in the surface layer. The mechanism of the comb‐like domain formation is proposed. The obtained results can be used for development of domain engineering methods in optical waveguides.

Pinched hysteresis loop and internal bias field in Ba4(La0.2Nd0.2Sm0.2Eu0.2Y0.2)2Ti4Nb6O30 tungsten bronze ceramics

A-site high entropy Ba4(La0.2Nd0.2Sm0.2Eu0.2Y0.2)2Ti4Nb6O30 tungsten bronze ceramics were designed and prepared by a standard solid state sintering process. First-order ferroelectric transition occurs around 240 °C on heating, while around 136 °C on cooling. Pinched and asymmetric P–E hysteresis loops were observed within and below the thermal hysteresis temperature range of the ferroelectric transition. Pinched P–E hysteresis loops were attributed to the coupling between the ferroelectric transition and the commensurate/incommensurate modulation transition. The reason for the asymmetry of the hysteresis loop was the presence of an internal bias electric field. Different measuring procedures were designed to clarify the evolution of hysteresis loop asymmetry. The existence of oxygen vacancy and Eu3+/Eu2+ was identified by x-ray photoemission spectroscopy. The electric field cycling with elevated temperatures caused defect dipoles incline to align along the direction of spontaneous polarization leading to the internal bias electric field. Due to the A-site high entropy effect, dielectric strength of Ba4(La0.2Nd0.2Sm0.2Eu0.2Y0.2)2Ti4Nb6O30 ceramics is up to 300 kV/cm, which is increased by more than 50% than that with the single element in the A1-site.

Secondary phase softening effect in PZT‐based ceramics by introducing the random electric fields

AbstractIn this work, the random electric fields are constructed in the hard PZT ceramics by adding the ZnO particles as a secondary phase to tune the piezoelectric properties and losses. It is found that the internal bias electric field existing in the hard PZT ceramics has been tuned successfully by the random electric fields and its value reduces with the increased ZnO content. As a consequence, the piezoelectric constant d33 reaches up to 483 pC/N in the PZT/0.75 wt%ZnO composite, which is much higher than that of the hard PZT matrix. In the meantime, the electromechanical quality factor Qm, dielectric loss tan δ, and Curie temperature TC for this composite are about 1109, 0.55%, and 279°C, respectively. The promoted d33 is attributed to the small domain size and reduced internal bias electric field, whereas the low losses (large Qm and low tan δ) can be put down to the still existing nonzero internal bias electric field.

Preferences of polarity and chirality in triglycine sulfate crystals by alanine ghost

Triglycine sulfate (NH2CH2COOH)3⋅H2SO4, (TGS) has attracted much attention because it exhibits excellent ferroelectricity below the Curie temperature. Although TGS is composed of glycine and sulfuric acid, which are achiral molecules, it forms chiral crystals below the Curie temperature. Ferroelectric domain observations and polarization-electric field hysteresis loop measurements showed that TGS polarity become preferred after a small amount of doping with enantiomeric alanine. It has been confirmed that the preferred polarity appears when the internal bias electric field, caused by alanine doping, is larger than the coercive field. Furthermore, X-ray crystal structure analysis has revealed that l-alanine-doped TGS (LATGS) and d-alanine-doped TGS (DATGS) with the nominal amount of alanine above 50 mol% exhibited great preferences for either chirality, although the alanine content in the crystal was too low to be detected; alanine was a “ghost”. Correlation between the polarity and chirality, thus the “absolute polarity”, of LATGS and DATGS were identified, and the preferences induced by the alanine ghost were noted. We have found that the chirality of TGS grown from achiral molecules can be preferred using an extremely simple method; doping with a tiny amount of alanine.

Memory Effect in Antiferroelectrics: A Systematic Analysis on Various Electric Hysteresis Loops

Antiferroelectric materials are proposed as a potential solution to achieve multi-state memories, but the fundamental physical mechanism underlying the memory effect still needs to be clarified. Here, we study the memory effect in a typical antiferroelectric ceramic of Pb0.99Nb0.02[(Zr0.6Sn0.4)0.95Ti0.05]0.98O3 by systematically analyzing various hysteresis loops of polarization intensity and current density vs. electric field, where the kinetic behaviors are concerned about for the first time. The parallel pre-poling electric field reduces the critical electric field of antiferroelectric-ferroelectric phase transition, while the antiparallel field increases it. The memory behavior is significantly enhanced with the increasing of pre-poling time, but exhibits a remarkable weakening with the relaxation time increasing. It is a combined effect of electric-field-induced preferentially oriented antiferroelectric domains and internal bias electric field. This work not only improves comprehending in memory effect in antiferroelectric materials, but also enlightens the deeper understanding of other physical properties related to field-induced phase transitions.

Memory effect in antiferroelectrics: A systematic analysis on various electric hysteresis loops

Antiferroelectric materials are proposed as a potential solution to achieve multi-state memories, but the fundamental physical mechanism underlying the memory effect still needs to be clarified. Here, we study the memory effect in a typical antiferroelectric ceramic of Pb0.99Nb0.02[(Zr0.6Sn0.4)0.95Ti0.05]0.98O3 by systematically analyzing various hysteresis loops of polarization intensity and current density vs. electric field, where the kinetic behaviors are concerned about for the first time. The parallel pre-poling electric field reduces the critical electric field of antiferroelectric-ferroelectric phase transition, while the antiparallel field increases it. The memory behavior is significantly enhanced with the increasing of pre-poling time, but exhibits a remarkable weakening with the relaxation time increasing. It is a combined effect of electric-field-induced preferentially oriented antiferroelectric domains and internal bias electric field. This work not only improves comprehending in memory effect in antiferroelectric materials, but also enlightens the deeper understanding of other physical properties related to field-induced phase transitions.

Phase transition, ferroelectric and piezoelectric properties of B-site complex cations (Fe0.5Nb0.5)4+-modified Ba0.70Ca0.30TiO3 ceramics

Ba0.70Ca0.30Ti1-x (Nb0.5Fe0.5)xO3 lead-free ceramics (abbreviated as BCTNFx, x = 0–0.12) were prepared by solid-state reaction method. The influence of B-site (Fe0.5Nb0.5)4+ substitution on phase structure, microstructure, dielectric, ferroelectric and piezoelectric properties of Ba0.70Ca0.30TiO3 ceramics were systematically studied. The BCTNFx ceramics consist of diphasic tetragonal (T) and orthorhombic (O) phases at x = 0–0.04, pseudocubic (PC) and O phases at x = 0.05–0.08, cubic (C) and O phases at 0.08 < x ≤ 0.12. Increase of (Fe0.5Nb0.5)4+ doping improves sinterability, depresses the ferroelectric - paraelectric phase transition temperature (Tm) monotonically from 128 °C at x = 0 to -86 °C at x = 0.12, induces enhanced relaxor behavior and weakens piezoelectric properties. The room temperature relative dielectric constant (εr) and dielectric loss tangent (tanδ) increase with increasing x and reach the maximum values of 4869 and 0.06 respectively at x = 0.06. Whereas the average grain size (abbreviated as AGS), ferroelectric properties and electric field induced strain increase significantly by introducing 2.0 mol% B-site complex cations (Fe0.5Nb0.5)4+ into Ba0.70Ca0.30TiO3 ceramics. The BCTNF0.02 ceramics achieve optimal electrical properties with εr = 1268, tan δ = 0.03, Tm = 102 °C, Pmax = 12.8 μC/cm2, Pr = 6.1 μC/cm2, EC = 6.0 kV/cm, d33 = 117 pC/N, kp% = 0.18%, Qm = 236, bipolar Smax% = 0.20%, unipolar Smax% = 0.16% and d33∗ = 314 pm/V. The variation of electrical properties of BCTNFx ceramics is attributed to the combined action of grain size effect, phase transition, weakness of octahedral distortion, clamping effects of the internal bias electric field Ei on domain wall motion induced by B-site cations (Fe0.5Nb0.5)4+ displacement.

Ferroelectricity temperature characterizes of hardened KNN–CC lead-free piezoceramics

The qualitative and quantitative analyses of ferroelectricity temperature characterizes for (K0.48Na0.52)NbO3–1 mol%CuO–1 mol%Co2O3 (KNN–CC) lead-free piezoceramic has been systematically investigated. KNN–CC ceramic shows an asymmetric P–E loops at various temperatures, and remnant polarization (Pr) reaches the maximum at T ~ 80 °C. Dynamic hysteresis characterizes indicate orthorhombic (O) to monoclinic (M) phase transition occurs round 80 °C. Large internal bias electric field (Ei) is attributed to defect dipoles polarization (PD), which is difficult to orientation because of low migration rate of defects. Moreover, owing to CuO and Co2O3 additives, the space charge cluster at grain boundary confirmed by impedance spectroscopy (IS) analysis result in enlarged Ei with increasing temperature. Mechanical quality factor (Qm ~ 868) of aged KNN–CC ceramic is almost doubled that of unaged one. In short, both defects and phase structure affect the temperature stability of ferroelectricity and macroscopic electrical property for KNN lead-free piezoceramics.

Influence of external electric field on the physical characteristics of lead free BZT- BCT piezoceramic

The electrical poling of piezoceramics is an essential process, to maximize their piezocoefficient prior to applications, which can significantly alter their other physical properties. In this study, the effect of poling on the properties of lead free 0.5Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 exhibiting large piezocoefficient was investigated. The sample revealed octahedral distortion induced structural transformation upon poling. The impedance spectrum displayed the resonance modes in poled state, where maximum power transmission is feasible. The polarization hysteresis loop exhibited an asymmetry with an internal bias electric field of 41 V/mm due to the field induced orientational defect. The strain measurements revealed 50% enhancement in electrostriction for the sample after poling. Additionally, the sample revealed an incremental change in bandgap due to B-site cationic off-centre displacements induced by the octahedral distortion. Importantly, the poling induced large internal bias field and the near UV bandgap of the sample facilitated the observed large photovoltaic response with giant open circuit voltage of 18 V which could open up an additional application in the fields such as photovoltaic and UV detector for this versatile compound.

Effect of Mn on Dielectric and Piezoelectric Properties of 71PMN-29PT [71Pb(Mg1/3Nb2/3)O3-29PbTiO3] Single Crystals and Polycrystalline Ceramics

In order to investigate the effect of Mn on the dielectric and piezoelectric properties of PMN-PT [Pb(Mg1/3Nb2/3)O3-PbTiO3], four different types of 71PMN-29PT samples were prepared using the solid-state single crystal growth (SSCG) method: (1) Undoped single crystals, (2) undoped polycrystalline ceramics, (3) Mn-doped single crystals, and (4) Mn-doped polycrystalline ceramics. In the case of single crystals, the addition of 0.5 mol% Mn to PMN-PT decreased the dielectric constant (K3T), piezoelectric charge constant (d33), and dielectric loss (tan δ) by about 50%, but increased the coercive electric field (EC) by 50% and the electromechanical quality factor (Qm) by 500%, respectively. The addition of Mn to PMN-PT induced an internal bias electric field (EI) and thus specimens changed from piezoelectrically soft-type to piezoelectrically hard-type. This Mn effect was more significant in single crystals than in ceramics. These results demonstrate that Mn-doped 71PMN-29PT single crystals, because they are piezoelectrically hard and simultaneously have high piezoelectric and electromechanical properties, have great potential for application in fields of SONAR transducers, high intensity focused ultrasound (HIFU), and ultrasonic motors. Key words: Piezoelectric, Single Crystal, 71PMN-29PT, Mn Doping, Ultrasonic Transducer

Photocurrent enhancement of chemically synthesized Ag nanoparticle-embedded BiFeO3 thin films

BiFeO3 and Ag nanoparticle-embedded BiFeO3 thin films were prepared on Pt/TiOx/SiO2/Si and MgO(100) substrates using colloidal silver and BiFeO3 metal–organic precursor solutions. Colloidal silver solution was prepared by a chemical reductive method using NaBH4 as a reductant. The prepared Ag nanoparticles exhibited characteristic optical absorption properties based on their surface plasmon resonance related to particle size. The synthesized BiFeO3 and Ag nanoparticle/BiFeO3 thin films demonstrated rapid on/off responses of photocurrent to visible light. The Ag nanoparticle-incorporated BiFeO3 film exhibited a 2–4-fold higher photocurrent than the BiFeO3 film. Optical and ferroelectric properties did not change markedly even when Ag nanoparticles were embedded in the BiFeO3 thin film within the quantities of this study. Furthermore, in the Ag nanoparticle/BiFeO3 composite structure, Ag nanoparticles were introduced in the near-metallic state with maintained their nanometer size. In the Ag nanoparticle-embedded BiFeO3 film, photoinduced charge separation and transport of photoexcited carriers were enhanced by the surface plasmon effect of nanosized Ag particles as well as the internal bias electric field existed in the narrow-bandgap BiFeO3 thin film.

Enhancement of photoinduced electrical properties of Al-doped ZnO/BiFeO3 layered thin films prepared by chemical solution deposition

Polycrystalline BiFeO3 and Al-doped ZnO/BiFeO3 bilayered thin films were prepared on Pt/TiOx/SiO2/Si substrates by chemical solution deposition. Their photoinduced electrical properties under blue light irradiation were characterized. The rapid on/off response of the photocurrent to light in unpoled BiFeO3 (BFO) and Al-doped ZnO/BiFeO3 (AZO/BFO) thin films was demonstrated. The AZO/BFO layered film exhibited an approximately triple-digit larger photocurrent in comparison with a BFO single-layer film. This is attributable to the photoexcited carrier generation effect at the interface between AZO (n-type) and BFO (p-type) films. Furthermore, in the AZO/BFO layered structure, the direction of the internal bias electric field caused by the space charge distribution in the unpoled BFO film is the same as that of the built-in electric field by forming a p–n junction of AZO and BFO layers. Photovoltaic properties were also improved by fabricating such a layered film. On the other hand, when the placement of BFO to AZO was reversed, the photoelectric current decreased to approximately one-tenth of that of the BFO single-layer film. In the BFO/AZO film, the internal electric field at the p–n junction between BFO and AZO is considered to have an orientation opposite to the self-bias field formed in the BFO film.

The hysteretic response of lead zirconate titantate ceramics after mechanical depolarization

The hysteretic response of mechanically depoled polycrystalline PZT specimens was investigated. Results show that the mechanically depoled domains can be repoled to their original state by electric fields much lower than their coercive electric field. Such a phenomenon is attributed to two factors: (i) during mechanical depoling, some energy was stored in the form of domain interactions and these released energy to help domains switch back during repoling; (ii) an internal bias electric field. During the second cycle of unipolar electric field loading, polarizations and longitudinal strains induced by electric fields increased with increasing depolarization stress, indicating that the number of irreversible domains increased in mechanically depoled specimens. During bipolar electric field loading, the hysteresis loops and butterfly curves of the mechanically depoled specimen nearly overlapped with those of an un-depoled one, demonstrating that an internal bias electric field cannot be eliminated by mechanical depolarization.

Photoinduced electrical properties of Mn-doped BiFeO3 thin films prepared by chemical solution deposition

Polycrystalline Mn-doped BiFeO3 thin films with a relatively narrow band gap were prepared on Pt/TiOx/SiO2/Si and MgO(100) substrates by chemical solution deposition. Their photoinduced electrical properties under visible light irradiation (400–700 nm) were characterized. The rapid on/off response of the photocurrent to light in unpoled BiFeO3-based thin films was demonstrated. From the direction of the electric current, the internal bias electric field caused by the space charge distribution in the unpoled film is considered to have an important effect on photocurrent generation and photovoltaic phenomena. Although Mn doping did not greatly affect the band gap and ferroelectric remanent polarization, it had an influence on the photocurrent behavior and photovoltaic properties. The magnitude of the photoinduced current of the film decreased with increasing Mn doping. In this case, the energy level created in BiFeO3 by Mn doping traps carriers generated by photoexcitation. The interfacial state between the thin film and the top or bottom electrode and the electrical resistivity at low applied voltages were also found to be related to the photoinduced behavior of the Mn-doped BiFeO3 thin films.

Photocurrent Properties of BiFeO3 Thin Films Prepared by Chemical Solution Deposition

Polycrystalline BiFeO3 thin films that exhibit a photo-induced current under the irradiation of visible light have been synthesized on Pt/TiO x /SiO2/Si substrates by chemical solution deposition. The quick on/off response of the photocurrent to light in these BiFeO3 thin films is demonstrated. It is also shown that the photo-induced current behavior of the film strongly depends on the wavelength of the irradiated light. This behavior is strongly related to the optical transmittance properties (including band gap energy) of the BiFeO3 thin films. From the direction of the electric current, the internal bias electric field caused by the space charge distribution in the unpoled film is considered to have an important effect on the generation of the photocurrent.

Effect of depletion layers on scaling effect in barium strontium titanate epitaxial film

The influence of different work functions of metal electrodes on (Ba,Sr)TiO3 thin film capacitor was investigated. We fabricated BST film parallel plate capacitor with top electrodes of Pt, Au, Ag, and In. The apparent dielectric permittivity increased depending on the work function of the electrodes. We measured the complex impedance of the capacitors and separated the capacitance of the low permittivity layers from that of BST. We concluded that the scaling effect of the BST films is negligible, and the origin of the low permittivity layer is the internal bias electric field in the interface.

Peculiarities of the pyroelectric effect and of the dielectric properties in Bi-doped Pb(Zr0.95Ti0.05)O3 ceramics

Abstract Unusual behaviour of the pyroelectric effect and some peculiarities of the dielectric characteristics in the vicinity of AFE↔FE phase transitions in Bi-doped Pb(Zr0.95Ti0.05)O3 ceramics are confirmed. Two pyroelectric peaks are found both on heating and cooling through this phase transition. They occur at temperatures, which depend on the strength of the DC field, and on other conditions of the pre-poling procedure. The internal bias electric field associated with the metastable space charge polarisation is considered to be the reason for the observed peculiarities in the pyroelectric effect and dielectric properties.