Electrical properties of pulsed laser-deposited SrxBiyTa2O9 thin films on Bi/Sr ratios

The dependence of the electrical properties of Sr_xBi_yTa₂O₉ thin films on the (Bi/Sr ratio 1.6, 2.3, 2.8, 3.4) has been investigated. The Sr_xBi_yTa₂O₉ ferroelectric thin films were synthesized on Pt/Ti/SiO₂/Si substrates using the pulsed laser deposition method. Saturation polarization (P_st) and coercive field (2E_c) depend on the Bi/Sr ratio. P_st increases while E_c decreases with an increase in Bi/Sr ratio. Atomic Force Microscopy images show that the grain size grows with increasing Bi/Sr ratio. It is observed that the impedance behavior in Sr_xBi_yTa₂O₉ thin film, conforms to the Constant Phase Element (CPE) model. It is believed that the diffuse charges at the grain boundary build up a surface polarization because the impedance behavior close to pure capacitor with grain size increased.     

The effect of potential of impedance in the pulsed-laser-deposited SrBi2Ta2O9 thin film

Ferroelectrics SrBi₂Ta₂O₉ (SBTO) thin films were grown on a highly oriented Pt/Ti/SiO₂/Si substrates using the pulsed laser ablation. The ac impedance of SBTO thin films have been measured at room temperature both in the frequency range from 10⁻¹ to 10⁶ Hz and bias voltage range from −6 to 6 V. The ac impedance dispersion was observed at low frequency with increasing bias voltage, which was interpreted based on a blocked charge. We can explain that the blocking interface gives rise to constant phase element (CPE) response, and we give an impedance model function that can fit data along the low frequency range when such a CPE is found. The low frequency dispersion phenomena of SBTO thin film are related to a charge diffusion process at the surface of thin film.     

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.     

Temperature-dependent ferroelectric and dielectric properties of Bi3.25La0.75Ti3O12 thin films

To investigate temperature-dependent ferroelectric and dielectric properties of ferroelectric films, Bi_3.25La_0.75Ti₃O₁₂ (BLT) thin films were prepared on Pt-coated silicon substrates by pulsed laser deposition. The ferroelectric and dielectric behaviors have been studied in a wide temperature range from 80 K to room temperature. The saturated polarization (P_sat) decreases with decreasing temperature and decreasing electric field, whereas remnant polarization (P_r) shows a more complex temperature dependence. These results, which can be well explained based on a temperature-dependent charged defects-domain wall interaction model, might be helpful for further understanding the domain switching behavior. Based on these results, an alternative way to investigate temperature-dependent ferroelectric fatigue is proposed and experimentally carried out. The measured fatigue rate is found to be linearly dependent on temperature, consistent with the report on Pb(Zr,Ti)O₃ films. Temperature-dependent dielectric measurements of the films further confirm the above explanation.     

Relaxor behavior of K0.5La0.5Bi2Ta2O9 ceramics

Potassium lanthanum bismuth tantalate (K_0.5La_0.5Bi₂Ta₂O₉), a new relaxor ferroelectric was synthesized via the solid-state reaction route. X-ray structural studies along with Rietveld refinement confirmed it to be an n=2 member of the Aurivillius family of oxides and the refined lattice parameters are , and . The appearance of 1/2{h00} and 1/2{hk0} type superlattice reflections in the electron diffraction patterns reflected the presence of ordered polar regions. A broad dielectric peak associated with frequency dependent dielectric maximum temperature was observed. The value of the diffuseness parameter γ=1.93, obtained from the fit of a modified Curie-Weiss law established the relaxor nature of the title compound. The dielectric relaxation obeyed the Vogel-Fulcher relation wherein and . The relaxor behavior was attributed to the local polar ordering on A-sites.     

Ti deficiency effect on the dielectric response of CaCu3Ti4O12 ceramics

Single phase ceramics CaCu₃Ti_4.0O₁₂ and CaCu₃Ti_3.9O₁₂ have been prepared using the traditional solid-state reaction method. Compared with the stoichiometric ceramics CaCu₃Ti_4.0O₁₂, Ti-deficient ceramics CaCu₃Ti_3.9O₁₂ have the larger lattice parameter, the higher force constant, and smaller dielectric constant and the lower dissipation factor, although their fundamental characters of dielectric response are similar. Their characteristic relaxation frequencies are not well fitted with the Arrhenius Law but a tentatively supposed relation. With the Cole-Cole Law, the fitted broadened factors of dissipation peaks are 0.5433 and 0.8651 for CaCu₃Ti_3.9O₁₂ and CaCu₃Ti_4.0O₁₂, respectively. All facts mentioned above imply that mutually correlated motion of Ti ions or defects may be expected to be responsible for the giant dielectric constant and high dissipation factor of CaCu₃Ti_4.0O₁₂.     

Maxwell-Wagner characterization of dielectric relaxation in Ni0.8Zn0.2Fe2O4/Sr0.5Ba0.5Nb2O6 composite

Dense composites were prepared through incorporating the dispersed Ni_0.8Zn_0.2Fe₂O₄ ferromagnetic particles into Sr_0.5Ba_0.5Nb₂O₆ ferroelectric matrix. Extrinsic dielectric relaxation and associated high permittivities of the materials are reported in the composites. We used an ideal equivalent circuit to explain electrical responses in impedance formalism. A Debye-like relaxation in the permittivity formalism was also found. Interestingly, real permittivity (ε′) of the sample containing 30% Ni_0.8Zn_0.2Fe₂O₄ shows obvious independence of the temperature at 100 kHz. Dielectric relaxation and high-ε′ properties of the composites are explained in terms of the Maxwell-Wagner (MW) polarization model.     

Observation of giant dielectric constant in CdCu3Ti4O12 ceramics

Although CdCu₃Ti₄O₁₂ is isostructural to CaCu₃Ti₄O₁₂, the room temperature low-frequency dielectric constant of the former compound was reported to be ∼400, only 1/25 of that of the latter material [M.A. Subramanian, et al., J. Solid State Chem. 151 (2000) 323]. In this communication, we report that the dielectric constant of CdCu₃Ti₄O₁₂ can be remarkably increased by elevating the sintering temperature. The room temperature dielectric constant at 100 kHz achieves 9000, almost as much as that of CaCu₃Ti₄O₁₂, for the sample sintered at 1283 K. The appearance of giant dielectric constant in CdCu₃Ti₄O₁₂ is explained in terms of internal barrier layer capacitance (IBLC) effect with the subgrain boundary as the barrier. Our result supplies an approach in searching for new giant-dielectric-constant materials in the CaCu₃Ti₄O₁₂ family.     

Texture control and its impact on the properties of SrBi2Ta2O9 thin films prepared by pulsed laser deposition

SrBi₂Ta₂O₉ (SBT) ferroelectric thin films with different preferred orientations were deposited by pulsed laser deposition (PLD). Several methods have been developed to control the preferred orientation of SBT thin films. For SBT films deposited directly on Pt/TiO₂/SiO₂/Si substrates and in situ crystallized at the deposition temperature, the substrate temperature has a significant impact on the orientation and the remnant polarization (Pr) of the films; a higher substrate temperature benefits the formation of (115) texture and larger grain size. The films deposited on Pt/TiO₂/SiO₂/Si substrates at 830 °C are (115)-oriented and exhibit 2Pr of 6 μC/cm². (115)- and (200)-predominant films can be formed by using a La_0.85Sr_0.15CoO₃ (LSCO) buffer layer or by annealing amorphous SBT films deposited on Pt/TiO₂/SiO₂/Si substrates at 450 °C using rapid thermal annealing (RTA). These films exhibit good electric properties; 2Pr of the films are up to 12 μC/cm² and 17 μC/cm², respectively. The much larger 2Pr of the films deposited on the LSCO buffer layer and of the films obtained by RTA than 2Pr of the films deposited on Pt/TiO₂/SiO₂/Si substrates at 830 °C is attributed to a stronger (200) texture. Received: 30 January 2001 / Accepted: 30 May 2001 / Published online: 25 July 2001     

Bismuth zinc niobate (Bi1.5ZnNb1.5O7) ceramics derived from metallo-organic decomposition precursor solution

The preparation, microstructure development and dielectric properties of Bi_1.5ZnNb_1.5O₇ pyrochlore ceramics by metallo-organic decomposition (MOD) route are reported. Homogeneous precalcined ceramic powders of 13-36 nm crystallite size were obtained at temperatures ranging from 500 to 700 °C. The thermal decomposition/oxidation of the gelled precursor solution was chemically analyzed, TG/DTA, XRD, and SEM, led to the formation of a pure cubic pyrochlore phase with a stoichiometry close to Bi_1.5ZnNb_1.5O₇ which begins to form at 500 °C. The metallo-organic precursor synthesis method, where Bi, Zn and Nb ions are chelated to form metal complexes, allows the control of Bi/Zn/Nb stoichiometric ratio on a molecular scale leading to the rapid formation of bismuth zinc niobate (Bi_1.5ZnNb_1.5O₇) ceramic fine powders with pure pyrochlore structure. The powders were pressed into pellets and can be sintered at temperatures as low as 800-1000 °C. Fine crystalline ceramics with the grain size in the range of 200-500 nm have been obtained at the sintering temperature of 800 °C. The dielectric properties in high frequency to microwave range were measured and discussed.     

Ferroelectric properties of neodymium-doped Sr2Bi4Ti5O18 thin film prepared by solgel route

Sr₂Bi₄Ti₅O₁₈ (SBTi) and Nd-modified SBTi (SBNT) thin films were deposited on Pt/Ti/SiO₂/Si (1 0 0) substrates using a sol-gel method. Structure, morphology and electric properties were investigated systematically. These films were randomly oriented and composed of rod-like grains. The remanent polarization (2P_r) and coercive field (E_c) of SBNT films were 30 μC/cm² and 55 kV/cm, respectively. This value of 2P_r was much higher than the reported value of SBTi prepared by pulsed-laser deposition. More importantly, the SBNT films showed high fatigue resistance against continuous switching up to 3×10⁹ cycles and excellent charge-retaining ability up to 3×10⁴ s.     

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.     

Dielectric relaxations in Tb0.91Yb1.38Bi0.71Fe5O12 ceramics

Dielectric relaxations of Tb_0.91Yb_1.38Bi_0.71Fe₅O₁₂ ceramics were investigated. A Debye-type relaxation was observed in the temperature range of 125-620 K with an activation energy of 0.29 eV. This activation energy agreed well with that of carriers hopping between Fe²⁺ and Fe³⁺, indicating that this relaxation might be a dipolar-type relaxation associated with the hopping carries. A high relaxorlike dielectric peak with a very strong frequency dispersion in the high temperature range of 400-620 K might be originate from the oxygen vacancies related dielectric relaxation.     

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.     

Electric-field dependence of dielectric properties of sol-gel derived Ba(Zr0.2Ti0.8)O3 ceramics

The effect of a dc bias field on the diffuse phase transition and nonlinear dielectric properties of sol-gel derived Ba(Zr_0.2Ti_0.8)O₃ (BZT) ceramics are investigated. Diffuse phase transitions were observed in BZT ceramics and the Curie–Weiss exponent (CWE) was γ∼2.0. The dielectric constant versus temperature characteristics and the γ in the modified Curie–Weiss law, ε ⁻¹=ε _m ⁻¹[1+(T−T _m ) ^γ /C₁](1≤γ≤2), as a function of the dc bias field was obtained for BZT ceramics. The results indicated that γ is a function of dc bias field, and the γ value decreased from 2.04 to 1.73 with dc bias field increasing from 0 to 20 kV/cm. The dielectric constant decreases with increasing dc bias field, indicating a field-induced phase transition. The dc bias field has a strong effect on the position of the dielectric peak and affects the magnitude of the dielectric properties over a rather wide temperature range. The peak temperature of the dielectric loss does not coincide with the dielectric peak and an obvious minimum value for the dielectric loss at the temperature of the dielectric peaks is observed. At room temperature, 300 K, the high tunability (K=80%), the low loss tangent (≈0.01) and the large FOM (74), clearly imply that these ceramics are promising materials for tunable capacitor-device applications.     

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.     

Dependence of high electric-field-induced strain on the composition and orientation of Pb(Mg1/3Nb2/3)O3-PbTiO3 crystals

Electric-field-induced strain behavior of (1−x)Pb(Mg_1/3Nb_2/3)O₃-xPbTiO₃ (PMNT) crystals with different orientations and compositions was investigated for use as electromechanical actuators. Crystallographically, high strains with low hysteresis were achieved for 〈001〉 oriented rhombohedral crystals (29%≤x≤31%) near a morphotropic phase boundary, rather than 〈110〉 and 〈111〉. Domain instability could explain inferior strain levels and large hysteresis for 〈110〉 and 〈111〉 oriented crystals. Ultrahigh strain levels up to 1.8% could be achieved for 〈001〉 oriented PMNT crystals, being related to an E-field induced phase transition. −2 kV/cm negative E-field can be applied to PMNT ferroelectric material with low hysteresis. High strain with low hysteresis makes PMNT crystals promising candidates for high performance solid-state actuators.     

Strain and Size Effects on Ferroelectric Properties of BaTiO3 Nanofilms

The strain and size effects on the ferroelectric properties of BaTiO3 films are studied using the molecular dynamics method based on a shell model. It is found that from microscopic view, these two effects share the same physical nature, i.e., the resulting crystal cell distortions lead to the separation of negative and positive charge eentres. The strain and size effects are therefore coupled, and the critical thicknesses of films would depend on the in-plane strains, which provides a possible interpretation on the discrepancies among the experimental measurements of the critical thicknesses. A polarization map is given to clearly reflect the relations among the size, strain and polarization of the nano films.     

Dielectric and Ferroelectric Properties of La-Doped SrBi2Nb2O9 Ceramics

Sr1-xLa2x/3Bi2Nb20O （0 ≤ x ≤0.2） ceramic samples are prepared by the solid-state reaction method. Their structure, dielectric and ferroelectric properties are investigated. The incorporation of La^3＋ improves the den- sification and decreases the grain size of the ceramics without changing the crystal structure. The remanent polarization 2PT increases with increasing La content and reaches a maximum value of 22.8μC/cm^2 at x = 0.125, which is approximately 60% larger than that of pure SrBi2Nb2O9. The Curie temperature keeps almost unchanged at a value of about 440℃. The relationship between doping and the ferroeleetrie and dielectric properties are discussed.     

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.