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We fabricate BaTi0.85Sn0.15O3 thin films with various Ca doping contents on Pt(100)/Ti/SiO2/Si substrates by a sol-gel and spin-coating method to investigate the effects on dielectric tunable properties. The results show that the greater tunability under a low bias electric field can be achieved compared with undoped BaTi0.85Sn0.15O3 thin films. In particular, the 0.1 mol. % Ca-doped BaTi0.85Sn0.15O3 thin films achieve the highest tunability of 50.9% and the highest FOM value of 23.1 at 16 kV/mm, surpassing most values reported previously for the dielectric tunability of BTS thin films. The use of a low bias electric field avoids the need for a high voltage, thus reducing safety hazards. These outstanding properties are attributed to the broadening of the Curie peak near room temperature, which indicates the existence of diffuse ferroelectric phase transition behavior, a larger grain size, and the suppression of electron hopping between Sn2+ and Sn4+. The results show the great potential of Ca-doped BaTi0.85Sn0.15O3 thin films for dielectric tunable applications.

In this letter, we report on significant flexoelectric fatigue in lead-free (K,Na,Li)(Nb,Sb)O3 (KNNLS) ceramics. In the ferroelectric phase of KNNLS, the observed effective transverse flexoelectric coefficient, which is initially as high as 1 μC/m, decreases nonlinearly with increasing cycles of strain gradient, and the fatigue regulation is well reproduced by a stretched exponential function. By comparing the time dependence of dielectric permittivity and ferroelectricity in KNNLS ceramics, we conclude that large flexoelectric and flexocoupling coefficients in the ferroelectric phase originate mainly from ferroelectricity and that the related flexoelectric fatigue is likely due to the pinning effect of ferroelectric domains.

Flexoelectricity couples strain gradient to polarization and usually exhibits a large coefficient in the paraelectric phase of the ferroelectric perovskites. In this study, we employed the relaxor 0.3Pb(In1/2Nb1/2)O3-0.35Pb(Mg1/3Nb2/3)O3-0.35PbTiO3 (PIN-PMN-PT) single crystals to study the relationship between flexoelectric coefficients and the crystal structure. The flexoelectric coefficients in PIN-PMN-PT single crystal are found to vary from 57 μC/m at orthorhombic/monoclinic phase to 135 μC/m at tetragonal phase, and decreases to less than 27 μC/m in the temperature above Tm. This result discloses that ferroelectricity can significantly enhance the flexoelectricity in this kind of perovskite.

SrTiO3/nano-Al2O3 composite films have been prepared using a sol-gel spin-coating method. When external electric fields were previously applied to the films with Al electrodes, the dielectric properties were strongly correlated with the applied field: both the dielectric constant and the dielectric loss decreased gradually with an increase in the previously applied voltage. For the films with Al electrodes, a superior dielectric strength of 507 MV/m was achieved; more importantly, the leakage current remained on the same order, i.e., microamperes; the results were ascribed to the Al electrode/film interface-reactions. The interface-reactions were experimentally confirmed by the cross-sectional transmission electron microscopy images and theoretically determined by Faraday's laws. The anodic oxidation reactions dominate the interface-reactions. The newly generated aluminum oxide originating from the interface-reactions contributes to the electric properties of the films.

Ba(Zr0.35Ti0.65)O3 (BZT) thin films were deposited via a sol-gel process on Pt-coated silicon substrates. The BZT films were in the perovskite phase and had polycrystalline structure. Temperature-dependent dielectric measurements revealed that the thin films have relaxor behavior and diffuse phase transition characteristics. The tunability K of the dielectric constant (at 600 kV/cm) is about 40% in the temperature range of 179–293 K. The improved temperature stability from this BZT thin film is beneficial to applications requiring a wide range of operating temperatures, thereby eliminating the need for environmental controls. Although the K value is not extraordinarily large compared to (Ba,Sr)TiO3, the low dielectric constant of BZT is attractive for microwave frequency applications. This provides an additional possibility in balancing K and dielectric constant through materials engineering for optimum device performance.

A kind of slow relaxation of field-induced piezoelectric resonance is observed in paraelectric barium stannate titanate ceramics. The piezoelectric resonance peaks vanish in several minutes when bias field is either applied or removed. These phenomena may be universal for dielectrics and can be explained by a model of slow dipoles composed of injected homocharges. With this model, the authors predict a negative piezoelectric modulus of d33 when just the bias field is removed, and verify it by experimental results.

Via incorporation of Sr2+ into (Pb,La)(Zr,Sn,Ti)O3, high recoverable energy density (Ure) is achieved in (Pb,Sr,La)(Zr,Sn,Ti)O3 (PSLZST) ceramics. All Sr2+ modified ceramics exhibit orthorhombic antiferroelectric (AFE) characteristics, and have higher ferroelectric-AFE phase switching electric field (EA, proportional to Ure) than the base composition with a tetragonal AFE phase. By properly adjusting the Sr2+ content, the Ure of PSLZST ceramics is greatly improved. This is attributed to the substitution of Pb2+ by Sr2+ with a smaller ion radius, which decreases the tolerance factor leading to enhanced AFE phase stability and thus increased EA. The best energy storage properties are achieved in the PSLZST ceramic with a Sr2+ content of 0.015. It exhibits a maximum room-temperature Ure of 5.56 J/cm3, the highest value achieved so far for dielectric ceramics prepared by a conventional sintering technique, and very small energy density variation ( 4.9 J/cm3) over ...

SrTiO3/nano Al 2O3 inorganic nanocomposites were prepared by using a conventional sol-gel spin coating process. For comparison, SrTiO3 films doped by equivalent amount of sol-Al2O3 have also been investigated. Aluminum deposited by using vacuum evaporation was used as the top electrode. The nanocomposites exhibited a significantly enhanced dielectric strength of 506.9 MV/m, which was increased by 97.4% as compared with the SrTiO3 films doped with sol-Al2O3. The leakage current maintained of the same order of microampere until the ultimate breakdown of the nanocomposites. The excellent electrical performances are ascribed to the anodic oxidation reaction in origin, which can repair the internal and/or surface defects of the films.

Ge nanoparticles with different sizes in silica glasses were prepared by a sol–gel method using Cl3–Ge–C2H4–COOH as a Ge source. The size of the Ge nanoparticles decreases with a reduction in the content of Ge in the starting materials, and thus the optical absorption edge shifts to a higher energy. Silica gel glasses doped with Ge nanoparticles showed a strong room-temperature photoluminescence with peaks at 568, 607, 672, 722, and 775 nm. The peak position of photoluminescence spectrum scarcely depends on the Ge/Si ratio. However, the photoluminescence intensity increases sharply as the Ge/Si ratio is reduced. The photoluminescence arises from the Ge clusters of diameter of

Band-gap energies of sol-gel-derived SrTiO3 thin films were studied in terms of annealing temperature and film thickness. The band-gap energies of highly crystallized films were comparable to those of single crystals reported, whereas for poor-crystallized films, their band-gap energy values were much larger than those of single crystals. The larger band-gap energy shift was believed to be mainly due to both quantum size effect and existence of amorphous phase in thin films. The band-gap energies also showed a strong dependence on film thickness. There was a critical film thickness (∼200 nm), above which the films had band-gap energies close to those of crystals or bulks, but below that, the values shifted largely, which can be attributed to the influence of crystallinity of thin films. Such a thickness effect of band-gap energy should be of high interest in optical device applications.

Homogeneous LaNiO3 thin films were grown on thermally oxidized silicon (SiO2/Si) substrates by a sol-gel technique, for the subsequent sol-gel deposition of (Pb, La)TiO3 thin films, under the assumption that the structural and compositional compatibility between ferroelectric films and bottom electrodes could lead to enhanced electrical properties of ferroelectric thin films. In this work, the LaNiO3 films served three functions: the first was used as bottom electrodes for the fabrication of integrated ferroelectric devices on Si due to their low resistivity; the second was used as a seeding layer, promoting perovskite phase formation due to their structural compatibility with ferroelectric films; and the third was to suppress the composition diffusion between ferroelectric films and bottom electrodes due to their composition compatibility. The experimental results demonstrated that (Pb, La)TiO3 films prepared on the LaNiO3/SiO2/Si substrates had excellent electrical properties. The dielectric constant an...

Compositionally graded (Pb, Ca)TiO3 thin films were prepared on platinum-coated silicon substrates by a monoethanolamine-modified sol–gel technique. The crystalline orientation and surface morphology of the graded films were related to the deposition sequence of the film layer. The dielectric constants, for up-graded and down-graded films annealed at 600 °C for 60 min were found to be 504 and 399, respectively. Both were larger than those reported for conventional (Pb, Ca)TiO3 thin films. The compositionally graded films had large polarization offsets in hysteresis loops when driven by an alternating electric field. The magnitude of polarization offsets displayed a power-law dependence on the electric field, and the direction of the offsets depended on the direction of the composition gradient with respect to the substrate. The offset, 120 μC/cm2 at 300 kV/cm driving electric field, was obtained. These results showed that compositionally graded (Pb, Ca)TiO3 thin films had enhanced dielectric properties an...

Compositionally step-varied (Pb, Ca)TiO3 thin films were prepared on platinum-coated silicon substrates by a monoethanolamine-modified sol-gel technique. The dielectric constant and dissipation factor were found to be 342 and 0.019, respectively, for thin films of 0.6μm in thickness annealed at 550 °C for 60 min. The remanent polarization and coercive field were 37.7 μC/cm2 and 60.4 kV/cm, respectively. The leakage current was 1.31×10−7 A/cm2 at the voltage of 5 V. The compositionally step-varied (Pb, Ca)TiO3 thin films had enhanced dielectric and ferroelectric properties which were suitable for various device applications.

Lead-free (1 − x)BaTiO3-x(Na0.5Er0.5)TiO3 (0 ≤ x ≤ 0.15) ceramics were prepared by a solid state reaction method. Their structure and electric properties were analyzed. Rietveld refinements suggested that the ceramics crystallized in the tetragonal perovskite space group P4 mm at room temperature. With increasing x from 0 to 0.05, Na+/Er3+ co-substitution at Ba-site in BaTiO3 leads to the decrease of lattice parameters and unit cell volume. While minor secondary phase, Er2Ti2O7 and (TiO1.2)0.787, appears at x = 0.10 or above. A great enhancement of piezoelectric properties and other electric parameters was obtained in this system by properly moderating the compositions. For example, in the ceramics with composition x = 0.05, a large piezoelectric coefficient d33 (333 pm/V), a high remnant polarization Pr (14.3 μC/cm2), a good planar electromechanical coupling factor kp (0.391), a mechanical quality factor Qm (97.3), and a high Curie temperature (TC = 134 °C) (higher than that of pure BaTiO3) were achieved...

In this paper, we presented a combined piezoelectric effect between perpendicular faces of the piezoelectric unimorph with polarization along the thickness direction, which was decomposed into shear and transverse piezoelectric effects in analytical model. Nine types of output electrode configurations based on perpendicular electrodes were designed for the combined piezoelectric effect. In the prototype, compared with traditional transverse piezoelectric effect, the superimposed piezoelectric effect can produce 1.5 times open circuit voltage and 3.9 times power for energy harvesting.

The effect of the top electrode material on electrical characteristics of Al2O3 thin film capacitors has been investigated. Compared to devices with Pt top electrodes, devices using Al as the top electrode material exhibit a significantly reduced leakage current and a much higher breakdown strength. These electrical characteristics are linked to the anodic oxidation reaction, which makes the capacitors have the capability of self-repairing the defects in a high electric field.

The converse flexoelectric effect, referred as the electric field gradient induced strain, widely exists in dielectric materials, but its experimental studies have been reported by few research groups so far. In this Letter, we report our studies on the converse flexoelectric behavior of (Ba0.67Sr0.33)TiO3 ceramics and present the measured value of its flexoelectric coefficient f1212. In the experiments, the electric field gradient was generated by applying an electric field across the two lateral sides of trapezoid (Ba0.67Sr0.33)TiO3 samples. The shear displacement was measured using a laser vibrometer. The converse flexoelectric coefficient f1212 was found to be 124 ± 14 μC/m at room temperature. This result was in good agreement with the theoretical prediction of the flexoelectricity of the (Ba, Sr)TiO3 ceramics.

Pb0.97Ln0.02(Zr0.63Sn0.26Ti0.11)O3 ceramics with large electrically induced strain were fabricated by doping the base composition with rare earth ions. The enhancement of strain was because the substitution of rare earth ions for Pb2+ could decrease the tolerance factor of the ceramics and improve the stability of antiferroelectric phase. In addition, it was found that the electrically induced strain increased as the measuring frequency decreased; this was attributed to more complete domain reversal at the low frequency. The maximum electrically induced strain of 0.66% was obtained in Pb0.97Sm0.02(Zr0.63Sn0.26Ti0.11)O3 ceramics at the frequency 1 Hz.

Enhanced direct flexoelectricity has been observed in paraelectric phase of Ba(Ti0.87Sn0.13)O3 ceramics by using a quasi-static cantilever beam system. The transverse flexoelectric coefficient was found to be about 53 μC/m near the Curie temperature. Temperature-dependence of the transverse flexoelectric coefficient was studied, exhibiting a nonlinear relationship with dielectric constant.

The polarization of polar domain in ferroelectric materials is orientated and reversed with the alternating electric field, and the hysteresis loops of polarization-electric field (P-E) and strain-electric field (S-E) are observed. For electrocaloric (EC) effect, the temperature change with the application and removal of electric field is also attributed to the change of polarization with the applied field. In most reports about EC, the temperature change is shown as an abrupt jump or slump due to the applied electric field that is a pulsed wave. Obviously, it is impossible to observe the hysteresis loop of EC. In our research, both sine wave and pulsed wave electric field are applied to samples in direct measurement, and temperature-electric field hysteresis loop (T-E) is observed only in measurement of sine wave. The T-E hysteresis loop displays a shape of butterfly, just like the shape of S-E. The electric field dependence of EC is also given. The obtained results will be helpful for us to know the electrocaloric effect further.

(Pb0.832Ba0.138La0.02)(Zr0.7Ti0.05Sn0.25)O3 ceramics with stable antiferroelectric phase at room temperature were fabricated by Mn doping. The enhancement of antiferroelectric phase is attributed that the substitution of Mn ion into the B site decreased tolerance factor of the ceramics. The largest pyroelectric figure of merit of 25 × 10−5 Pa−0.5 was obtained in (Pb0.832Ba0.138La0.02)(Zr0.7Ti0.05Sn0.25)O3 antiferroelectric ceramics with 0.2 mol. % Mn doping, which is far higher than that of convention phase transition materials. The increase of the pyroelectric response was attributed to the improvement in dc field-induced dielectric enhancement effect and the reduction in dielectric loss.

Percolative properties in dielectric (DE) tunability were observed in three ferroelectric (FE)-DE composite ceramics as follows: xBa0.5Sr0.5TiO3–MgO, xBa0.4Sr0.6TiO3–Mg2TiO4, and xBa0.5Sr0.5TiO3–Mg3B2O6. Dielectric constants of the composites increased monotonously with increasing volume fractions of FE component. Comparatively, their DE tunabilities exhibited a weak dependence on FE concentrations over a wide range. However, their tunabilities started to decrease substantially below a critical concentration of FE. The critical concentrations were 40 vol % for Ba0.5Sr0.5TiO3–MgO, 38 vol % for Ba0.4Sr0.6TiO3–Mg2TiO4, and 33 vol % for Ba0.5Sr0.5TiO3–Mg3B2O6. These results could be used as a guide to tailor the properties of FE-DE composites for tunable device applications.

Mn-doped K0.5Na0.5NbO3 (KNN) thin films derived from chemical solution deposition have been investigated. 2 mol % manganese acetate was introduced into the polyvinylpyrrolidone-modified KNN precursor solution to prepare the KNN thin films. It was found that Mn doping can increase the dielectric constant and decrease the dielectric loss, as well as significantly decrease the leakage current. The leakage current density of Mn-doped KNN film is about 3×10−6 A/cm2 at an electric field of 50 kV/cm, which is 104 times lower than that of the undoped film (about 3×10−2 A/cm2). These are attributed to the decrease in the concentration in oxygen vacancies and free carrier-holes by increasing the valence of Mn during thermal treatment. As a result, well saturated polarization-electric field hysteresis loops were obtained in the Mn-doped KNN thin films.

Ba(Sn0.15Ti0.85)O3 thin films were grown on the LaNiO3 buffered LaAlO3, SrTiO3, MgO, and Al2O3 single crystal substrates, respectively. These substrates provide a systematic change in the stress while maintaining the same film microstructure. The stress in the thin film induces an obvious change in the dielectric behavior. The reduction in the ferroelectric transition temperature with increasing biaxial tensile stress is attributed to the suppression of in-plane polarization due to the small lateral grain size in the films. The in-plane tensile stress in this study reduces the unit cell along electric field in the parallel plate capacitor structure and decreases the tunability.

The polarization and depolarization of antiferroelectric Pb(Nb,Zr,Sn,Ti)O3 (PNZST) ceramics under a dc bias were studied in a hydraulic pressure from 0to250MPa. It is found that the antiferroelectric ceramic can be induced to a metastable ferroelectric state and that the ceramic at this ferroelectric state can be switched to the antiferroelectric state using hydraulic pressure. The hydraulic pressure to induce the transition from the ferroelectric to the antiferroelectric states increases with the positive and decreases with the negative dc bias. Based on the results, the pressure–electric field phase diagram for polarized PNZST ceramics was established.

The Ba0.6Sr0.4TiO3 (BST)/poly(methyl methacrylate) (PMMA) tunable composites in 1-3-type structure consisting of BST rods in low-permittivity PMMA matrix are fabricated by dice and fill technique. For the composite containing 41.6vol% BST, the permittivity and the loss tangent of the composite are 1212 and 0.026 at 10kHz, respectively, while the dielectric tunability is about 36% under the 16kV∕cm dc bias flied. The theoretical tunability and permittivity are in agreement with the experimental data. The 1-3-type BST/PMMA composites can meet the device requirement for tunable dielectrics with high dielectric tunability and low permittivity.

Ba0.5Sr0.5TiO3–Mg2TiO4 composite ceramics are fabricated via the conventional solid-state reaction method. The microstructures, dielectric tunability, and microwave properties of composite ceramics are investigated. The dielectric constant is tailored from 335 to 35 by manipulating the addition of Mg2TiO4 from 50% to 80% weight ratio and the tunability is 10.8% measured at 10kHz for the 80% Mg2TiO4 addition. The composite ceramics with high Q value (>200) at L band are useful for potential tunable microwave device applications in the wireless communication system.

A systemic study was performed on bismuth strontium titanate (Sr1−1.5xBixTiO3, 0.04⩽x⩽0.25) ceramics. Dielectric properties were measured from 83to373K at different frequencies. A transformation from relaxor ferroelectrics to relaxor behavior was observed when x>0.10. Both diffuseness and relaxation degree increase as x rises. Tunability was found to increase with increasing x value until 0.07, and then decrease when Bi3+ content increases. Meanwhile, their figures of merit (defined as tunability/loss) shows a maximum at x=0.12. The change from relaxor ferroelectrics into relaxor behavior has a positive impact on the tunability of bismuth strontium titanate system.

Phase transformation from β-BiNbO4 to α-BiNbO4 in BiNbO4 bulk samples was studied. From x-ray diffraction patterns, the transformation from β to α phase of BiNbO4 could be observed by heating the bulk samples of β-BiNbO4 from low temperatures to 700–1030°C. Such a transformation did not occur in powder samples and in the cooling course. This phenomenon might be related with associated activation of stress and heat energy in the heating course. Differential thermal analysis, shrinkage, and dielectric properties as a function of temperature were carried out, and all the results confirmed the transformation from β to α phase of BiNbO4.

Barium titanate (BT) thin films have been prepared on Pt∕Ti∕SiO2∕Si substrates through the use of a low temperature process. This technique combines the conventional sol-gel process and hydrothermal methods. X-ray diffraction analysis showed that the BT thin films had a pure perovskite structure. Au∕BT∕Pt capacitors have been fabricated and the dielectric properties have been discussed for SGHT-prepared BT films treated at 180 and 500°C, respectively. It was found that the BT films annealed at 500°C had much better ferroelectric properties. This improvement of ferroelectric properties through a heat treatment is probably associated with the change of density of hydroxyl groups in the films.

Pyrochlore type systems with generic formula (Bi1.5Zn0.5)(Nb0.5M1.5)O7 (M=Ti, Sn, Zr, and Ce) have been synthesized to investigate the influence of M on the dielectric properties. It was found that the incorporation of Sn or Ce resulted in a reasonably reduced dielectric constant. The incorporation of Zr and Ce has led to an appreciable increase in dc conductivity in high temperature. The dc conductivity diminishes as the size of M grows. Dielectric constants, temperature coefficient, and dc conductivity of series ceramics were studied and the relationships among composition, crystal structure, and properties were discussed.

The isothermal time dependences of the dielectric constant and the discharging current of barium stannate titanate ceramics after application or removal of a step field were investigated in both ferroelectric and paraelectric temperature regions. The experimental results exhibited a substantial difference for these two phases. For the ferroelectric phase, the relaxation of the dielectric constant is weak and the discharging current obeys Hammon’s model. While for the paraelectric phase, the relaxation is relatively strong and the discharging current obeys the complex exponential decay model. The relaxation of the field-induced piezoelectric resonance indicated the first relaxation observed in a paraelectric phase sample corresponding to homocharges. The authors proposed that the transportation of homocharges is the microscopic origin of the strong relaxation observed in the paraelectric phase.

An abnormal resonance behavior was observed from the transient current in the time domain for both ferroelectric ceramics and single crystals excited with a stepwise electric field. The phenomenon can be accounted for as piezoelectric resonance. Corresponding resonant peaks in the frequency spectrum of impedance verified the piezoelectric origin of the abnormal resonance. Using a RLC series equivalent circuit of the piezoelectric resonance model, the resonance behavior of the transient current can be calculated and well fitted with experiments.

(Bi2−xCax)(Zn1∕3Ta2∕3)2O7 (0⩽x⩽1) ceramic were prepared by using a solid-state reaction technique. (Bi1.2Ca0.8)(Zn1∕3Ta2∕3)2O7 was found to have cubic pyrochlore structure, while (Bi1.9Ca0.1)(Zn1∕3Ta2∕3)2O7 was shown to have a monoclinic zirconolite structures. cubic pyrochlore (Bi1.2Ca0.8)(Zn1∕3Ta2∕3)2O7, not monoclinic zirconolite (Bi1.9Ca0.1)(Zn1∕3Ta2∕3)2O7, was found to show relaxation behavior at room temperature. Dielectric constant and dielectric loss were measured as functions of electric field and temperature. The results show a maximum tunability of 12% under a bias 60 KV∕cm in cubic-pyrochlore-structure (Bi1.2Ca0.8)(Zn1∕3Ta2∕3)2O7 ceramics.

Lanthanum doped lead titanate (PLT) thin films with good surface morphology and perovskite structure were fabricated by the metalo‐organic decomposition process. Their nonlinear optical property was investigated by Z‐scan technique. PLT30 thin films on the quartz substrate display strong nonlinear optical effects. A nonlinear refractive index as high as 3.0×10−7 esu was obtained for the thin film. All the results show that PLT ferroelectric thin films are promising materials for nonlinear optics.

We report structural, dielectric, and ferroelectric properties of compositionally graded (Pb,La)TiO3 thin films on LaNiO3/SiO2/Si substrates, where all the films were prepared by the sol-gel technique. The crystalline orientation and surface morphology of the graded films were closely related to the deposition sequence of film layer. Upgraded film exhibited (100) preferentially oriented growth, whereas downgraded film showed a randomly oriented growth, where the films with La content increasing or decreasing gradually along film thickness from the substrate to the top surface are called “upgraded” or “downgraded” films, respectively. The dielectric constants, for upgraded and downgraded films annealed at 650 °C for 60 min, were found to be 659 and 641, respectively. The thin films had large polarization offsets in hysteresis loops when driven by an alternating electric field. The magnitude of the offsets displayed a power law dependence on the electric field, and the direction of the offsets depended on t...