Dielectric and Piezoelectric Properties of Sodium Bismuth Titanate Ceramics with KCe Substitution

The piezoelectric properties of the (KCe)-substituted sodium bismuth titanate (Na_0.5Bi_4.5Ti₄O₁₅, NBT) piezoelectric ceramics are investigated. The piezoelectric properties of NBT ceramics are significantly enhanced by (KCe) substitution. The Curie temperature Tc, and piezoelectric coefficient d₃₃ for the (KCe)-substituted NBT are found to be 663ºC, and 27pC/N, respectively. Dielectric and annealing spectroscopy resent that the (KCe) co-substituted NBT piezoelectric ceramics possess stable piezoelectric properties.     

Ac behaviour and phase transition in PLZT 6/80/20 ferroelectric ceramics

The Ac behaviour of PLZT 6/80/20 ferroelectric ceramics was analyzed around and above the phase transition. Two relaxation processes are identified, showing that the so-called ‘universal relaxation law’ holds for the ceramics. A critical point in the values of the Ac conductivity, around the temperature corresponding to the maximum of the dielectric losses, is observed below the transition temperature due to the relaxor behaviour. The frequency dependence of the Ac conductivity at various temperatures and the hysteresis loops show classical relaxor behaviour with a diffuse phase transition.     

Bi-fluctuation in Na0.5Bi0.5TiO3 ferroelectric ceramics with abnormal relaxor behaviour

ABSTRACT

The existence of Bi-fluctuation dispersing in Na_0.5Bi_0.5TiO₃ (NBT) relaxor ferroelectric is hinted in other recent studies. However, this fluctuation has not been directly observed yet. We introduce the Bi-rich nano-regions with different sizes in a series of NBT ceramics by the slight excess of Bi³⁺ content. The crystal symmetries of the Bi-rich nano-regions and the NBT matrix are rhombohedral. The lattice parameters of the nano-regions are larger than those of the matrix in NBT ceramics, which were confirmed by the X-ray diffraction Rietveld refinement, TEM techniques and first-principles calculation. Also, the disorder-induced nano-regions appearing as Bi-fluctuation are associated with the complex phase transitions and the high-frequency relaxor behaviour of NBT suggested by the dielectric measurements and Raman spectra.     

Relaxor behavior of (Ba,Sr)(Zr,Ti)O3 ferroelectric ceramics

We examine the ferroelectric-relaxor behavior of (Ba_0.65Sr_0.35)(Zr_0.35Ti_0.65)O₃ (BSZT) ceramics in the temperature range from 80 to 380 K. A broad dielectric maximum, which shifts to higher temperature with increasing frequency, signifies the relaxor-type behavior of these ceramics. The value of the relaxation parameter γ∼2 estimated from the linear fit of the modified Curie-Weiss law, indicates the relaxor nature of the BSZT ceramics. The dielectric relaxation rate follows the Vogel-Fulcher relation with T_VF=107 K, E_a=0.121 eV, and ν₀=6.83×10¹⁴ Hz, further supports such relaxor nature. The slim P-E hysteresis loop and ‘butterfly’ shape dc bias field dependence of permittivity at T>T_m (T_m, the temperature of permittivity maximum) clearly signifies the occurrence of nanopolar clusters, which is the typical characteristic of ferroelectric relaxor. At 300 K and 10 kHz, the dielectric constant and loss tan δ are ∼1100 and 0.0015, respectively. The high tunability (∼25%) and figure of merit (∼130) at room temperature show that the BSZT ceramics could be a promising candidate for tunable capacitor applications.     

Effects of uniaxial stress on dielectric properties of lithium modified potassium sodium niobate ceramics

In this work, the solid solution of ((K_0.5Na_0.5)_1−xLi_x)NbO₃ ceramics with x=0.03, 0.04, 0.05, 0.06 and 0.07 was prepared by a conventional mixed-oxide and solid-state sintering method. The structural phase formation and microstructure were characterized by X-ray diffraction technique and scanning electron microscopy. The ceramics were identified by XRD as a single-phase perovskite structure with symmetry gradually changing from orthorhombic to tetragonal. The grain size and the optimum density of the sintered ceramics were noticeably compositional-dependent. The dielectric properties of the ((K_0.5Na_0.5)_1−xLi_x)NbO₃ ceramics under the uniaxial compressive stress were observed at stress up to 180 MPa. The results showed that the dielectric constant and the dielectric loss tangent increased with applied stress. The change in the dielectric properties with stress was seen to depend on the composition and grain size. The observations were interpreted in terms of the intrinsic and extrinsic contributions to the changes in dielectric properties upon the applied compressive stress.     

Simulation on dielectric susceptibility and domain evolution of relaxor ferroelectrics

Dielectric susceptibility and domain evolution of the relaxor ferroelectrics have been simulated using the Monte Carlo method upon the Potts-Ising model. The grain size effect and the applied ac field frequency effect on the dielectric susceptibility were theoretically investigated. We found that the dielectric susceptibility increases and the T_m (the temperature at which the dielectric susceptibility reaches the maximum) shifts to lower temperature with increasing average grain size or decreasing frequency. In addition, we obtained the value of the relaxation parameter γ estimated from the linear fit of the modified Curie-Weiss law; its changing trend with increasing average grain size or increasing frequency was well consistent with the experimental observation. From the results of the domain pattern evolution process, we observed the differences between relaxor ferroelectrics and normal ferroelectrics subjected to an applied ac field.     

Characterization of lead free (K0.5Na0.5)NbO3-LiSbO3 piezoceramic

(K_0.5Na_0.5)NbO₃ (KNN) based lead free ceramics have been fabricated by a solid state reaction. In this work, LiSbO₃ (LS) modified KNN based ceramics were sintered at atmospheric pressure and high density (>96% theoretical) was obtained. The detailed elastic, dielectric, piezoelectric and electromechanical properties were characterized by using the resonance technique combined with the ultrasonic method. The full set of material constants for the obtained polycrystalline ceramics were determined and compared to the pure hot pressed KNN counterpart. KNN-LS polycrystalline ceramic was found to have higher elastic compliance, dielectric permittivity and piezoelectric strain coefficients, but lower mechanical quality factor, when compared to pure KNN, exhibiting a “softening” behavior. However, a high coercive field (∼17 kV/cm) was found for the LS modified KNN material. The properties as a function of temperature were determined in the range of −50-250 ^°C, showing a polymorphic phase transition near room temperature, giving rise to improved piezoelectric behavior.     

Microstructure,dielectric, and piezoelectric properties of Ce‐modified Na0.5Bi4.5Ti4O15 high temperature piezoceramics

The cerium modified sodium bismuth titanate (Na_0.5Bi_4.5Ti₄O₁₅, NBT) piezoelectric ceramics have been prepared by using the conventional mixed oxide method. X‐ray diffraction analysis revealed that the cerium modified NBT ceramics have a pure four‐layer Aurivillius phase structure. The piezoelectric activity of NBT ceramics was found significantly improved by the modification of cerium. The Curie temperature T_c, and piezoelectric coefficient d₃₃ for the NBT ceramics with 0.50 wt% cerium modification were found to be 655 °C, and 28 pC/N respectively. The Curie temperature gradually decreased from 668 °C to 653 °C with the increase of cerium modification. The dielectric spectroscopy showed that the samples possess stable piezoelectric properties, demonstrating practical potential that for high temperature applications. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Investigations of structural, dielectric and ferroelectric behavior of europium substituted SrBi2Ta2O9 ferroelectric ceramics

Europium substituted samples of the compositions Sr_1−xEu_xBi₂Ta₂O₉ (x=0.0,0.025,0.050,0.10 and 0.20) were synthesized by solid state reaction method and studied for their structural, dielectric and ferroelectric properties. The X-ray diffractograms confirmed the formation of single phase layered perovskite structure in all the samples. The temperature variation of dielectric constant shows that the Curie temperature (T_c) decreases on increasing concentration of europium. The dielectric loss reduces significantly with europium addition. The P-E studies of the Eu-substituted SBT ceramics show that the remanent polarization increases with increasing concentration of europium.     

Relaxor Behaviour and Ferroelectric Properties of （Li0.12Na0.88） （Nb0.9-xWa0.10Sbx）O3 Lead-Free Ceramics

New lead-free ceramics （Lio.12Na0.88） （Nbo.9-x Ta0.10 Sbx） 03 （0.01 × 0.06） are synthesized by solid-state reaction method. The dielectric, piezoelectric and ferroelectric properties of the ceramics are studied. The dielectric constant dependence with temperature and frequency of the ceramic specimen with x = 0.04 shows typical characteristics of relaxor ferroelectrics, and the Vogel-Fulcher relationship is fulfilled. The dielectric behaviour and its relation to the phase transition phenomena are discussed. The polarization hysteresis loops at room temperature are also measured.     

Effect of strontium addition on ferroelectric phase transition of PZT thin films prepared by chemical route

The dependence of ferroelectric phase transition temperature as a function of strontium substitution in lead titanate zirconate thin films (referred here as PSZT) on platinum-coated silicon substrates was investigated. The dielectric study reveals that the material undergoes a diffuse type ferroelectric phase transition that depends on the substitution of Sr for Pb in PZT. At 100 kHz, the phase transition temperatures were 633, 613 and 516 K for PSZT10, PSZT20 and PSZT30 thin films, respectively. On the other hand, the results showed that the dependence of the dielectric constant upon the frequency does not reveal any relaxor behavior. The diffusivity increases with increasing Sr contents in the studied composition range. The experimental data obtained from measurements of the dielectric constant as a function of temperature and frequencies showed a classical behavior of ferroelectric phase transition in PSZT thin films, rather than a relaxor ferroelectric phase transition. The transition temperature decreases with increasing Sr contents due to the decrease in grain size, lattice decrease and local structural disorder.     

Enhanced piezoelectric properties of sodium bismuth titanate (Na0.5Bi4.5Ti4O15) ceramics with B‐site cobalt modification

The piezoelectric properties of the cobalt‐modified sodium bismuth titanate (Na_0.5Bi_4.5Ti₄O₁₅, NBT) piezoelectric ceramics were investigated. The piezoelectric properties of NBT ceramics were significantly enhanced by cobalt modification. The Curie temperature T_C and piezoelectric constant d₃₃ for the 0.3 wt% cobalt‐modified NBT ceramics (NBT‐C3) were found to be 663 °C and 30 pC/N, respectively. Thermal annealing studies presented that the cobalt‐modified NBT ceramics possess stable piezoelectric properties, demonstrating that the cobalt‐modified NBT‐based ceramics are promising candidates for high temperature piezoelectric applications. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effects of composition on phase structure and electrical properties of (K0.5Na0.5)0.90Li0.06Sr0.02Nb(1−x)SbxO3 ceramics

Lead-free (K_0.5Na_0.5)_0.90Li_0.06Sr_0.02Nb_(1−x)Sb_xO₃ (KNLSN-Sb_x) ceramics were synthesized by ordinary sintering technique. The compositional dependence of phase structure and electrical properties of the ceramics was systematically investigated. All samples possessed pure perovskite structure, showing room temperature symmetries of orthorhombic at x<0.01, coexistence of orthorhombic and tetragonal phases at x=0.01, and tetragonal at 0.02≤x≤0.05. The temperature of the polymorphic phase transition (PPT) was shifted to lower temperature and dielectric relaxor behavior was induced by increasing Sb content. The samples near the coexistence region (x=0.01) exhibited enhanced electrical properties: d₃₃∼145 pC/N, k_p∼38% and P_r∼20.4 μC/cm².     

Sub-coercive field dynamic hysteresis in morphotropic phase boundary composition of Pb(Zr1/2Ti1/2)O3-Pb(Zn1/3Nb2/3)O3 ceramic and its scaling behavior

Sub-coercive field dynamic ferroelectric hysteresis of a morphotropic phase boundary composition of the PZT-PZN ceramic was investigated under influence of the compressive stress. The scaling relation of hysteresis area 〈A〉 against frequency f, field amplitude E₀, and stress σ took a form of , which is not different significantly to that of other PZT-PZN compositions with pure tetragonal or rhombohedral structure, as well as to that of soft and hard PZT bulk ceramics. This study suggested that the domain structures, not ceramic compositions, played a key role in controlling dynamic hysteresis behavior of ferroelectric materials.     

Dielectric properties Ca-substituted barium strontium titanate ferroelectric ceramics

The dielectric and ferroelectric properties of Ba_1−xSr_xTiO₃ (BST) (x=0.10,0.20,0.30,0.40 and 0.60) ceramics and Ba_1−2xSr_xCa_xTiO₃ (BSCT) (x=0.10,0.20,0.30) ceramics have been investigated. The low temperature phase transitions of BST ceramics vanish after Ca²⁺ substitution while the high temperature transition is diffused and relaxed, which becomes more obvious with increasing x. Ca²⁺ substitution obviously decreases the dielectric constant maximum, K_m, of BST ceramics and changes the temperature of dielectric constant maximum, T_m, of BST ceramics. The shift of T_m in BST is attributed mainly to the Sr²⁺ and Ba²⁺ concentration. BST ceramics exhibit almost normal ferroelectric characteristics, while a typical relaxor behavior was observed in BSCT ceramics. The relaxor behavior observations may be understood by a random electric field induced domain state.     

Properties of the ferroelectric ceramics PbSc<Subscript>0.5</Subscript>Ta<Subscript>0.5</Subscript>O<Subscript>3</Subscript> fabricated from an ultradispersed powder

The relaxor ceramics PbSc_0.5Ta_0.5O₃ produced from an ultradispersed powder is studied by X-ray diffraction and dielectric measurements. Before sintering, the powder was subjected to treatment in Bridgman anvils in combination with shear deformation. This method is shown to affect the order parameter and dielectric properties of the ceramics without using long-term high-temperature annealing.     

钛酸铋钡陶瓷的介电性、铁电性及对晶格结构的依赖性

采用溶胶-凝胶工艺成功制备出BaBi₄Ti₄O₁₅微细粉料，并利用此微粉烧结出成瓷良好的BaBi₄Ti₄O₁₅陶瓷.研究了BaBi₄Ti₄O₁₅陶瓷的铁电 顺电相 变，测定了BaBi₄Ti₄O₁₅的介 电特性和饱和状态下的铁电特性.所作测量表明B 关键词： 铁电性 介电性 晶格结构 溶胶 凝胶法     

The effect of CuO and NiO doping on dielectric and ferroelectric properties of Na0.5Bi0.5TiO3 lead-free ceramics

In the present work, lead-free piezoelectric ceramics (Na_0.5Bi_0.5)TiO₃ –xCuO–yNiO (for x = 0.0, 0.02, 0.04 and 0.06) have been prepared by a conventional solid-state reaction method. An investigation of CuO and NiO doping in bismuth sodium titanate (BNT) and a study of the structure, morphology, and dielectric and ferroelectric properties of the NBT–CuNi system have been conducted. Phase and microstructural analysis of the (Na_0.5Bi_0.5)TiO₃ (NBT) based ceramics has been carried out using X-ray diffraction and scanning electron microscopy (SEM) techniques. Field emission scanning electron microscopy (FE-SEM) images showed that inhibition of grain growth takes place with increasing Cu and Ni concentration. The results indicate that the co-doping of NiO and CuO is effective in improving the dielectric and ferroelectric properties of NBT ceramics. Temperature-dependent dielectric studies have also been carried out at room temperature to 400 °C at different frequencies. The NBT ceramics co-doped with x = 0.06 and y = 0.06 exhibited an excellent dielectric constant ?_r = 1514. The study suggests that there is enormous scope of application of such materials in the future for actuators, ultrasonic transducers and high-frequency piezoelectric devices.     

Investigation of microwave dielectric relaxation process in the antiferroelectric phase of NaNbO3 ceramics

This letter reports microwave dielectric measurements performed in the antiferroelectric phase of NaNbO₃ ceramics from 100 to 450 K. Remarkable dielectric relaxation was found within the antiferroelectric phase and in the vicinity of the ferroelectric-antiferroelectric phase transition. Such dielectric relaxation process was associated with relaxations of polar nanoregions with strong relaxor-like characteristic. In addition, the microwave dielectric measurements also revealed an unexpected and unusual anomaly in the relaxation strength, which was related to a disruption of the antiferroelectric order induced by a possible AFE-AFE phase transition.     

Dielectric properties of PIN–PT ceramics under compressive stress

Lead indium niobate, Pb(In_1/2Nb_1/2)O₃ or (PIN), is an interesting ferroelectric material, because it can be changed from a disordered state to ordered state by long-time thermal annealing. However, the temperature related to the maximum dielectric constant (T_max) of PIN in relaxor phase is low (at 1 kHz, T_max = 66 °C). In this study, to increasing T_max of PIN, lead titanate, PbTiO₃(PT) was thus added to PIN with compositions (1 − x)PIN–xPT (for x = 0.1–0.5). The influence of stress on the dielectric properties of (1 − x)PIN–xPT ceramics was then investigated. The dielectric properties were measured under various uniaxial compressive stress up to 400 MPa. The results showed that the superimposed compression load reduced the dielectric constant in 0.9PIN–0.1PT. For the other compositions, the dielectric constants first increased with the compressive stress, and then decreased when the stress was further increased up to 400 MPa. The dielectric loss tangent of all composition was found to decrease with increasing compressive stress.