Papers by Keyword: Ferroelectric Property

Abstract: Ferroelectric ceramics, Sr_1-xLa_xBi₂Nb_2-x/5O₉ (SLBNO), were prepared using the conventional solid-state reaction method. Effect of lanthanum substitution on dielectric and ferroelectric properties of SrBi₂Nb₂O₉ (SBN) ceramics were investigated. X-ray diffraction analyses (XRD) revealed that all the specimens had a single phase with orthorhombic space group A2₁am. The maximum dielectric permittivity peak broadened gradually with the increase in lanthanum substitution indicated that the phase transition from normal ferroelectrics to relaxor ferroelectrics occurred in SLBNO ceramics. The modified Curie-Weiss (CW) law was used to describe the relaxor behavior of the SLBNO ceramics. The relaxation indication coefficient (γ) was estimated from a quadratic fit of modified CW law and was found to be 1.7 and 2.0 for the SLBN20 and SLBN30 specimens, respectively. Curie temperature (T_c) of the SBN ceramic was decreased gradually with the increase in lanthanum substitution. In addition, the ferroelectric properties of the SBN ceramic were enhanced significantly by the introduction of lanthanum ions and the maximum of remnant polarization (P_r) was found to be 4.35 μC/cm² for the SLCB20 specimen. Nature of relaxor behavior of the SLBNO ceramic is attributed to the cationic disordering at nanoscale on A site by the introduction of lanthanum ions.

Abstract: PZT thin film was fabricated by using RF-sputtering process, and platinum was used as bottom electrodes. The sputtering gases were Ar：O2＝25：0 sccm, Ar：O2＝20：5 sccm, or Ar：O2＝15：10 sccm. After sputtering, the PZT film was annealed for 5 minutes under O2 gas environment and at the temperature of 600 0C, 650 0C, 700 0C or 750 0C. To judge the quality of the deposited PZT film, its physical properties and electric properties were evaluated. The results indicate that the best crystallization temperature of PZT thin film is about 700 0C. Also, the roughness of the PZT thin film becomes larger with the increasing of annealing temperature. By adding more oxygen in the sputtering gas, one could have better crystallization of the PZT film. As for the electrical properties, the leakage current of PZT thin film increases with the increasing of annealing temperature. Furthermore, the ferroelectric property is affected by the crystallization amount of perovskite, the thickness of PZT thin film, and the diffusion situation between the bottom electrode and the PZT film.

Abstract: The Ion Beam Enhanced Deposited (IBED) lithium tantalate (LiTaO₃) thin film samples with Al/LiTaO₃/Pt electrode structure were prepared on the Pt/Ti/SiO₂/Si(100) and SiO₂/Si(100) substrate respectively. The crystallization, surface morphology, ferroelectric property, and fatigue property of the prepared samples with the different annealed processes were investigated. The XRD measured results show that the prepared samples have the polycrystal structure of LiTaO₃ with the preferred orientation of <012> and <104> located at the 2θ of 23.6⁰ and 32.7⁰ respectively. The SEM morphology analysis reveals the prepared film annealed at 550°C is uniform, smooth and crack-free on the surface and cross section. The ferroelectric property measured results show that the remanent polarization Pr of the samples annealed at different temperature almost increase with the electric field intensity stronger. The leakage current makes the hysteresis loop of the samples subjected to a strong measured electric filed difficult to appear the same saturation hysteresis loop as the single-crystal LiTaO₃. The prepared samples annealed at 550°C have a Pr value of 11.5μC/cm² when subjected to the electrical field of 400kV/cm. The breakdown voltage of the 587nm thick thin film sample is high as to 680 kV/cm. The fatigue property measured results show only 15.17% Pr drop of the prepared films annealed at 550°C appear after 5×1010 cycles polarized by the 10MHz sinusoidal signal with the peak-to-peak amplitude of 10 Volt. The ferroelectric properties of the prepared films meet the practical application requirements of charge response measurement of the LiTaO₃ infrared detector owe to the Pr of the prepared films annealed at different temperature large beyond 10μC/cm² when the prepared films subjected to a strong electric filed larger than 400 kV/cm. The experimental results also show that the surface morphology, the ferroelectric and fatigue properties of the IBED LiTaO₃ thin films are significant better than those of the Sol-Gel derived LiTaO₃ thin films.

Abstract: Lead-free piezoelectric ceramics Sr₂Bi_4-xGd_xTi₅O₁₈ were prepared by conventional solid-state reaction method. Pure bismuth layered structural ceramics with uniform gain size were obtained in all samples. The effect of Gd-doping on the dielectric, ferroelectric and piezoelectric properties of Sr₂Bi₄Ti₅O₁₈ ceramics were also investigated. It was found that that Gd³⁺ dopant gradually decreased the Curie temperature (T_c) with the lower dielectric loss (tand) of SBTi ceramics. In addition, Gd-doping with appropriate content improved the ferroelectric and piezoelectric properties of the SBTi ceramics. The piezoelectric constant (d₃₃) of the Sr₂Bi_3.9Gd_0.1Ti₅O₁₈ ceramic reached the maximum value, which is 22 pC/N. The results showed that the Sr₂Bi_4-xGd_xTi₅O₁₈ ceramic was a promising lead-free piezoelectric material.

Abstract: Rare-earth ion La is doped at the bismuth site in BiFeO₃ to produce Bi_0.8La_0.2FeO₃ polycrystalline ceramics via a sol-gel auto-combustion synthesis method. For comparison, the similar experiments are also carried out for the non-doped BiFeO₃ at the same time. It is found that both non-doped and La doped BiFeO₃ are composed of nanoscale crystallites (~50 nm). Furthermore, La doping suppresses the formation of the secondary phase and leads to a structural phase transition from a rhombohedral to an orthorhombic or a pseudotetragonal structure. More importantly, the magnetic and ferroelectric properties in La doped ceramics were both enhanced, as evidenced by the typical electric and magnetic hysteresis loops. These property evolutions can be attributed to the elimination of the secondary phase and the structural distortion caused by La doping.

Abstract: (Pb_1-xBa_x)ZrO₃ (PBZ) ceramics for x = 0.10 were synthesized by the mixed oxide solid state reaction method. Phase transition was investigated by dielectric measurements in the temperature range from 27 to 350 °C at various frequencies. The permittivity of the solids corresponding to (Pb_1-xBa_x) ZrO₃ showed the maximum value of 10220 at x = 0.10 at the phase transition temperature. The maximum permittivity gradually increasing concentration up to x = 0.10. The ferroelectric hysteresis loop of the PBZ ceramics for x = 0.10 is displayed at room temperature and 0.2 Hz.

Abstract: Multiferroic ceramic samples of Bi_1-xGd_xFeO₃ (x = 0, 0.05, 0.1 and 0.15) have been prepared by the rapid liquid phase sintering technique. The effect of Gd substitution on ferroelectric properties of Bi_1-xGd_xFeO₃ ceramics has been investigated. The results of x-ray diffraction (XRD) patterns show that the single-phase BiFeO₃ sample has a rhombohedral structure and Gd³⁺ substitution for Bi³⁺ has not affected the perovskite structure. Experimental results suggest that Gd³⁺ substitution for Bi³⁺ has markedly affected the Raman scattering spectra, and the ferroelectric properties of BiFeO₃ are improved by Gd³⁺ doping. When x = 0.15, saturated ferroelectric hysteresis loop is observed at room temperature with the maximal 2Pr = 1.62 μC/cm².

Abstract: Niobium doped Pb(Zr,Ti)O₃ fiber/epoxy resin 1-3 composites with different ceramic volume fraction of 10-85% were fabricated by filling-casting method. Effects of ceramic volume fraction on electric properties were investigated. For a typical 30% ceramic content composite, the thickness coupling coefficient k_t, mechanical quality factor Q_m, acoustic impedance Z_m and anisotropic property k_t/k_p were 0.67, 0.55, 11.03 MRayl and 2.23, respectively.

Abstract: Bi_3.15Nd_0.85Ti₃O12 (BNT) thin films with different thicknesses (200, 270, 360, 450 and 540 nm) were prepared on Pt/Ti/SiO₂/Si substrates by sol–gel method. The effect of film thickness on the microstructure and ferroelectric properties of BNT thin films was investigated. All BNT thin films were consisted of a single phase of bismuth-layered perovskite structure. With increasing film thickness, grains gradually became larger, the remanent polarization (2P_r) firstly increased and then decreased, and the leakage current density showed opposite trend. The 360 nm-thick BNT film exhibited better electrical properties with 2P_r 26 µC/cm², coercive field (2E_c) 220 kV/cm, dielectric constant 345 (at 1 MHz) and low leakage current density.

Abstract: The Aurivillius phases [Bi2O2][An-1BnO3n+1] are well-known ferroelectrics with high Curie temperatures. Recently this class of compounds attracted significant attention due to possible multiferroic and photocatalytic properties. We have investigated the possibility of the Bi→Ln and Ti→Mn substitution in the double-layered Aurivillius phases Bi3NbTiO9 and Bi3TaTiO9. In both cases substitution appeared to be limited. The Ln-substituted compounds can be obtained only for Ln=La-Gd. The Ti→Mn substitution is possible only if the substitution degree does not exceed 0.2. The formation of the double-layered Aurivillius phases has been investigated by means of the X-ray diffraction and thermal analysis. The limits of substitution have been explained on the basis of the formation mechanism. The stability of the intermediate Bi4Ti3O12-based phase appeared to be crucial for the possibility of obtaining the substituted Aurivillius phase. The temperature dependence of the dielectric and magnetic properties has been investigated. The magnetoelectric coupling is found at low temperatures.