Ferroelectric properties of sol-gel derived Nd-doped SrBi_4Ti_4O_(15) thin films

Neodymium-doped strontium bismuth titanate （SrBi4-xNdxTi4O15） ferroelectric thin films were fabricated using the sol-gel method on Pt/Ti/SiO2/Si substrates. The influence of Nd content on the microstructure and ferroelectric properties of SrBi4-xNdxTi4O15 thin films were systematically studied. The results indicated that the SrBi3.88Nd0.12Ti4O15 （SBNT0.12） thin films had better ferroelectric properties, with a remanent polarization of （2Pr） of 34.3 μC/cm^2 and a coercive field （2Ec） of 220 kV/cm. This could be attributed to the fact that SBNT0.12 ferroelectric thin films consisted of more and larger ball-like grains, approximately 150-200 nm, with structure distortion, which greatly contributed to the improvement of the ferroelectric properties of the films. Furthermore, the film exhibited a good fatigue resistant property. The value of 2Pr after 10^10 switching cycles did not change significantly. The SrBi3.88Nd0.12Ti4O15 films were promising candidates for the application of FeRAMs.

Effect of Pb Substitution on the Microstructure and Ferroelectric Properties of Ba_(0.7)Sr_(0.3)TiO_3 Ceramic

Ferroelectric Ba0.7Sr0.3TiO3（BST） and partially Pb^2＋ substituted for Ba^2＋ ceramics （Ba0.7-xPbx）Sr0.3TiO3 （x=0.1-0.4, BPST） were prepared by using conventional solid-reaction method. XRD analysis shows that the samples microstructure changes from cubic phase to tetragonal one with the Pb^2＋ content increasing. ESEM analysis shows that the Pb^2＋ substituted samples have a denser and more uniform surface morphology than that of pure BST. Measured electrical properties suggest that the Pb^2＋ substitution for Ba^2＋ in the BST system enhances the ferroelectric performance obviously when x=0.2. In addition, the substitution increases the samples Curie temperature （To） r （Ba0.5Pb0.2）Sr0.3TiO3 ceramic has good ferroelectric properties measured at a maximal electric field of 30 kV/cm under the condition of room temperature. The corresponding saturated polarization （Ps）, remnant polarization （Pr） and coercive field （Ec） is respectively 15.687 μC/cm^2, 8.100 μ C/cm^2 and 6.611 kV/cm. The measured Tc of （Ba0.5Pb0.2）Sr0.3TiO3 is 117 ℃.

Effect of annealing process on structures and ferroelectric properties of Ca_(0.4)Sr_(0.6)Bi_(3.95)Nd_(0.05)Ti_4O_(15) thin films

Ca0.4Sr0.6Bi3.95Nd0.05Ti4O15 （C0.4S0.6BNT） ferroelectric thin films were prepared on Pt/Ti/SiO2/Si substrates by sol-gel method. Effect of annealing process （time and temperature） on structures and ferroelectric properties of C0.4S0.6BNT thin film was investigated. The relative intensity of （200） peak increased first then decreased with annealing temperature and became predominant at 800 ℃. In contrast, no evident change could be observed in the （001） peak. The remnant polarization （Pr） and coercive field （Ec） for C0.4S0.6BNT film annealed at 800℃ for 5 min were 21.6μC/cm2 and 68.3 kV/cm, respectively.

Piezoelectric and ferroelectric properties of Na_(0.5)Bi_(4.5)Ti_(4)O_(15)-BaTiO_(3) composite ceramics with Mg doping

As one of the representatives of lead-free NBT ceramics,Na_(0.5)Bi_(4.5)Ti_(4)O_(15) has still attracted much attention due to its excellent dielectric properties and has become the focus of research.However,its piezoelectric properties are far from satisfactory.In order to improve the piezoelectric properties of Na_(0.5)Bi_(4.5)Ti_(4)O_(15),Na_(0.5)Bi_(4.5)Ti_(4-x)Mg_(x)O_(y)–BaTiO_(3)(NBTM–BT)composite ceramics were synthesized by a conventional mixed oxide route and sintered at 1040℃ through two-step method.We optimized the electrical properties of NBTM–BT by changing the stoichiometric ratio of Mg content and studied its microscopic mechanism.The piezoelectric coefficient(d33)is stable at about 20 pC/N.Moreover,the maximum remanent polarization(2Pr)of the ceramic is 3.08
C/cm^(2) with the coercive field of 18.01 kV/cm.The dielectric constant and dielectric loss for Na_(0.5)Bi_(4.5)Ti_(3.96)Mg_(0.04)–BT composite ceramic were found to be 486 and 0.17 at 10 kHz,respectively.The characteristic peaks of BT and Na_(0.5)Bi_(4.5)Ti_(4)O_(15) can be observed clearly from the X-ray diffraction analysis.SEM analysis showed that all samples were well crystallized.Consequently,the piezoelectric and ferroelectric properties of Na_(0.5)Bi_(4.5)Ti_(4)O_(15)–BT composite ceramic will be enhanced much by Mg doping,which means it has a wider range of applications in electronic devices such as piezoelectric devices.

Influence of the sintering temperature on ferroelectric properties of potassium-sodium niobate piezoelectric ceramics

The effect of sintering condition on structure,microstructure,and ferroelectric properties of(K_(0.44)Na_(0.52)Li_(0.04))(Nb_(0.86)Ta_(0.10)Sb_(0.04))-O_(3)(KNL-NTS)has been investigated.Ceramic powders have been synthesized by the solid-state reaction method and sintered at different temperatures(1115℃,1125℃,and 1140℃).Then,samples were characterized by thermogravimetric analysis,X-ray diffraction,scanning electron microscopy,and impedance spectroscopy.Through XRD results,the perovskite structure and small peaks corresponding to a secondary phase were detected.Ceramics processed at the highest temperatures showed higher densities and good piezoelectric properties(d_(33),K_(p),and K_(t)),particularly specimens sintered at 1125℃ presented the highest piezoelectric performance.

Influences of Ho Doping on Structure,Ferroelectric,Energy Storage and Optical Properties of KNN-SYbN Transparent Ceramics

Ho doping 0.825K_(0.5)Na_(0.5)NbO_(3)-0.175Sr(Yb_(0.5)Nb_(0.5))_(O3)(KNN-SYbN-x%Ho)transparent ceramics were prepared by solid-state sintering method.The structure,ferroelectric,energy storage,and optical properties of KNN-SYbN-x%Ho were explored.With the addition of Ho,under the excitation of a 980 nm laser,the ceramics exhibit up-conversion luminescence properties with wavelengths of 550 nm and 670 nm,however,the ceramics change from pseudo-cubic phase to triphase-orthorhombic phase and the light transmittance decreases.The addition of Ho significantly enhances the ferroelectric properties and the energy storage performance of KNN-SYbN-x%Ho ceramics.When x=0.15,the residual polarization P_(r)=9.11μC/cm^(2),while x=0.20,the maximum energy storage density W_(rec) reaches 0.26 J/cm^(3),and the energy storage efficiencyηreaches 87.1%.

Microstructure and Ferroelectric Properties of (Bi_(0.9)Ho_(0.1))_(3.999)Ti_(2.997)V_(0.003)O_(12) Thin Films Prepared by Sol-gel Method for Nonvolatile Memory

The （Bi0.9Ho0.1）3.999Ti2.997V0.003012 （BHTV） films have been prepared on Pt/Ti/SiO2/Si substrates by solgel method. The microstructure and ferroelectric properties of the BHTV films were investigated. The BHTV films show a single phase of Bi-layered Aurivillius structure and dense microstructure. The Ho3＋/V5＋ cosubstitution can effectively improve the ferroelectric properties. The BHTV film exhibits good ferroelectric properties with 2Pr of 47.6℃/cm2, 2Ec of 265 kV/cm （at applied field of 420 kV/cm）, dielectric constant of 305, dielectric loss of 0.031 （at 1 MHz）, good insulting behavior, as well as the fatigue-free behavior.

Effect of Cl doping amount on the microstructure,photovoltaic properties and ferroelectric properties of Bi-based lead-free perovskite

Organic-inorganic hybrid perovskites with 3D perovskite structure have gained much attention as light harvesting materials in thinfilm photovoltaics.This is because of their outstanding light-absorption characteristics,charge-transport dynamics and their simple processability using lab-scale solution and vapor phase deposition techniques.However,the inherent instability and lead toxicity of lead-based PSCs are the major problems at present.Recent studies have shown that the(CH_(3)NH_(3)T_(3)Bi_(2)I_(9)(MBI)0D bismuth-based compound can be used as an optical absorption layer in solar cells.In this paper,the(CH_(3)NH_(3)T_(3)Bi_(2)I_(9)was doped with Cl
and a series of(CH_(3)NH_(3)T_(3)Bi_(2)I_(9-x)Cl_(x)films were prepared.The effects of different doping amounts on the microstructure,photovoltaic properties and ferroelectric properties were systematically investigated.Scanning electron microscope(SEM)and Atomic force microscope(AFM)analysis showed that with the increase of doping content,the density of the films increased and the roughness decreased.The photoelectric conversion efficiency of(CH_(3)NH_(3)T_(3)Bi_(2)I_(9-x)Cl_(x)raises with the increase of doping content.For example,the photoelectric conversion efficiency of(C_(H)3NH_(3)T_(3)Bi_(2)I_(3)Cl_(6)is 0.473%.We find that the leakage current descends into the increase in doping content,which may be due to the increase in the film density and the decrease of porosity.These research results have a positive effect on the development of Bi-based lead-free perovskite.

Ferroelectric properties of Bi_4Zr_(0.5)Ti_(2.5)O_(12) thin films prepared on LaNiO_3 bottom electrode by sol-gel method

The Bi4Zr0.5Ti2.5O12 (BZT) thin films were fabricated on the LaNiO3 bottom electrode using sol-gel method. The structure and morphology of the films were character-ized using X-ray diffraction, AFM and SEM. The results show that the films have a perovskite phase and dense microstructure. The 2Pr and 2Vc of the Pt/BZT/LaNiO3 capacitor are 28.2 μC/cm2 and 14.7 V respectively at an applied voltage of 25 V. After the switching of 1×1010 cycles, the Pr value decreases to 87% of its pre-fatigue val-ues. The dielectric constant (ε) and the dissipation factor (tanδ) of the BZT thin films are about 204 and 0.029 at 1 kHz, respectively. The films show good insulating behavior according to the test of leakage current. The clockwise C-V hysteresis curve observed shows that the Pt/BZT/LaNiO3 structure has a memory effect be-cause of the BZT film’s ferroelectric polarization.

DIELECTRIC AND FERROELECTRIC PROPERTIES OF(1-x)Pb(Mg_(1/3)Nb_(2/3))O_(3)-xPbZrO_(3)CERAMICS WITH CATION ORDER

Electrical properties and the B-site cation order were investigated in the(1-x)Pb(Mg_(1/3)Nb_(2/3))O_(3)-xPbZrO_(3)(0≤x≤0.25)solid solution ceramics.It was found that long range 1.1 B-site cation order can be developed through slow cooling during sintering in the solid solution with compositions around x=0.10.The observed long range cation order is in sharp contrast to previous studies where a disordered structure was invariably resulted in the(1-x)PbeMg_(1/3)Nb_(2/3)TO_(3)-xPbZrO_(3)solid solution.The ceramics with cation order display dielectric and ferroelectric properties similar to those disordered ceramics reported in literature.The dielectric properties were also compared in detail to our previous PbeMg_(1/3)Zr_(2x/3)Nb_(2)(1-x)/3TO_(3-x)/3 ceramics where Zr^(4+)is designed to substitute Nb^(5+)only.The results were discussed on the basis of the relationships between cation order and electric dipole order.

Effects of dwell time during sintering on electrical properties of 0.98(K_(0.5)Na_(0.5))NbO_3-0.02LaFeO_3 ceramics

The effects of dwell time on the phase structure, microstructure, and electrical properties were investigated for the 0.98（K0.sNa0.5）NbO3-0.02LaFeO3 ceramics （abbreviated as 0.98KNN-0.02LF）. All the ceramics sintered for different dwell time are of pure phase and the peak intensity of the 0.98KNN-0.02LF ceramics becomes stronger with a longer dwell time. Denser microstructures with larger grain size are developed for the sample with a longer dwell time. The maximum dielectric permittivity decreases with increasing the dwell time, and the deteriorative dielectric properties are due to the increasing grain size and the domain wall motion. Ferroelectric properties results indicate that 2Pr value slightly decreases with increasing the dwell time, while the 2Ec value increases. Consequently, the 0.98KNN-0.02LF ceramic sintered at 1150 ℃ for 2 h shows optimum dielectric properties （er=2253 and tan fi〈5%） and ferroelectric properties （2Pr=34.51 gC/cm2 and 2Ec=5.07 kV/mm）.

Structural and electrical properties of Nd ion modified lead zirconate titanate nanopowders and ceramics

A modified sol-gel method is used for synthesizing Nd ion doped lead zirconate titanate nanopowders Pb1-3x/2^NdxZr0.52Ti0.48O3 （PNZT） in an ethylene glycol system with zirconium nitrate as zirconium source. The results show that it is critical to add lead acetate after the reaction of zirconium nitrate with tetrabutyl titanate in the ethylene glycol system for preparing PNZT with an exact fraction of titanium content. It has been observed that the dopant of excess Nd ions can effectively improve the sintered densification and activity of the PNZT ceramics. Piezoelectric, dielectric and ferroelectric properties of the PNZT ceramics are remarkably enhanced as compared with those of monolithic lead zirconate titanate （PZT）. Especially, the supreme values of piezoelectric constant （d33） and dielectric constant （ε） for the PNZT are both about two times that of the monolithic PZT and moreover, the remnant polarization （Pr） also increases by 30%. According to the analysis of the structures and properties, we attribute the improvement in electrical properties to the lead vacancies caused by the doping of Nd ions.

Multiferroic properties and exchange bias in Bi_(1-x)Sr_xFeO_3(x=0–0.6) ceramics

Multiferroic properties and exchange bias （EB） in Bi1-xSrxFeO3 （x = 0-0.6） ceramics synthesized by a modified Pechini method are investigated. Sr concentration dependence of structure distorting, ferroelectric properties, and dielectric properties were studied at room temperature. Appropriate Sr doping （x = 0.05-0.2） has been found to decrease the conductivity, enhance ferroelectric properties and give rise to high dielectric constant. Compared with antiferromagnetic BiFeO3 compound, BSFO-x （O≤x ≤0.4） ceramics show weak ferromagnetism at room temperature, and their exchange bias field and vertical magnetization shift are observed and exhibit a strong dependence on the content of Sr. This observed EB effect which keeps stable in BSFO ceramics at 10 K tend to vanish at room temperature with Sr concentration over 0.4.

Effect of La Doping on Microstructure and Ferroelectric Prop-erties of Bi_4Ti_3O_(12) Thin Films Prepared by Sol-gel Method

The Bi4Ti3Oi2 and Bi3.25La0.75Ti3O12 thin films were prepared on the Pt/Ti/SiO2/Si substrate using the sol-gel method. The effect of La doping on the microstructure and ferroelectric properties of Bi4Ti3O12 films were investigated. Both the Bi4Ti3O12 and Bi3.25La0.75Ti3O12 thin films exhibited typical bismuth layered perovskite structure. The 2Pr （remanent polarization） value of Bi3.25La0.75Ti3O12 thin films is 18.6 μC/cm^2, which is much larger than that of Bi4Ti3O12 thin films. And the Bi3.2eLa0.75Ti3O12 films show fatigue-free behavior, while the Bi4Ti3O12 thin films exhibit the fatigue problem. The mechanism of improvement of La doping was discussed.

Crystallization and Electrical Properties of (Ba_(0.4)Pb_(0.3))Sr_(0.3)TiO_3 Thin Film by Pulsed Laser Deposition

（Ba0.4Pb0.3）Sr0.3TiO3 thin films were fabricated via pulsed laser deposition （PLD） technique on Pt/TiO2/SiO2/Si substrate. The crystallization of the films was characterized by XRD and FSEM, and the experimental results suggested deposition parameters, especially the deposition temperature was the key factor in forming the perovskite structure. The dielectric properties of the film deposited with optimized parameters were studied by an Agilent 4294A impedance analyzer at 1 MHz. The dielectric constant was 772, and the loss tangent was 0.006. In addition, the well-shaped hysteresis loop also showed that the film had a well performance in ferroelectric. The saturated polarization P, remnant polarization Pr and coercive field E were about 4.6 μC/cm2, 2.5 μC/cm2 and 23 kV/cm （the coercive voltage is 0.7 V）, respectively. It is suggested the film should be a promising candidate for microwave applications and nonvolatile ferroelectric random access memories （NvFeRAMs）.

Potts-Ising model for simulation of polarization switching in polycrystalline ferroelectrics

This paper proposes a scheme based on the Potts and Ising models for simulating polarization switching of polycrystalline ferroelectrics using the Monte Carlo method. The polycrystalline texture with different average grain size is produced from the Potts model. Then Ising model is implemented in the polycrystalline texture to produce the domain pattern and hysteresis loop. The domain patterns and hysteresis loops have been obtained for polycrystalline texture with different average grain size. From the results of domain pattern evolution process under an applied electric field using this scheme, an extended domain, which covers more than one grain with polarization aligned roughly in the same direction, has been observed during the polarization reversal. This scheme can well reproduce the basic properties of polycrystalline ferroelectrics and is a valuable tool for exploring the physical properties of polycrystalline ferroelectrics.

Enhanced ferroelectricity and ferromagnetism in Bi_(0.9)Ba_(0.1)FeO_3/La_(2/3)Sr_(1/3)MnO_3 heterostructure grown by pulsed laser deposition

Bi0.9Ba0.lFeO3 （BBFO）/La2/3Srl/3MnO3 （LSMO） heterostructures are fabricated on LaA103 （100） substrates by pulsed laser deposition. Giant remnant polarization value （~ 85 μC/cm2） and large saturated magnetization value （~ 12.4 emu/cm3） for BBFO/LSMO heterostructures are demonstrated at room temperature. Mixed ferroelectric domain structures and low leakage current are observed and in favor of enhanced ferroelectrie properties in the BBFO/LSMO het- erostructures. The magnetic field-dependent magnetization measurements reveal the enhancement in the magnetic moment and improved magnetic hysteresis loop originating from the BBFO/LSMO interface. The heterostructure is proved to be effective in enhancing the ferroelectric and ferromagnetic performances in multiferroic BFO films at room temperature.

Structure and Properties of Mg-doped SrBi_4Ti_4O_(15) Bi-layered Compounds

The structure and properties of Mg-doped SrBi4Ti4O15（SBT） were dicussed. Mg substitution into SBT had two possibilities states with the dopant amount variety. Mg cation substituted mostly into Sr^2＋ and the amount proportion was 68.11%.Mg ion will substitute into Ti ion site in perovskite layer when the doping amount increases. Polarization increases sharply when x=0.1 and then decreases becauses of the domain pinning. The Curie temperature of Mg-doped SBT is about 300 ℃ and there is a broad diffuse phase transition near Tc with a flat peak near the Ta of SBT.

Enhanced electrical properties in bilayered ferroelectric thin films

Sr2Bi4Ti5O18(SBTi) single layered and Sr2Bi4Ti5O18 /Pb(Zr0.53Ti0.47)O3(SBTi/PZT) bilayered thin films have been prepared on Pt/TiO2/SiO2/Si substrates by pulsed-laser deposition(PLD).The related structural characterizations and electrical properties have been comparatively investigated.X-ray diffraction reveals that both films have crystallized into perovskite phases and scanning electron microscopy shows the sharp interfaces.Both films show well-saturated ferroelectric hysteresis loops,however,compared with the single layered SBTi films,the SBTi/PZT bilayered films have significantly increased remnant polarization(Pr) and decreased coercive field(Ec),with the applied field of 260 kV/cm.The measured Pr and Ec of SBTi and SBTi/PZT films were 7.9 C/cm 2,88.1 kV/cm and 13.0 C/cm 2,51.2 kV/cm,respectively.In addition,both films showed good fatigue-free characteristics,the switchable polarization decreased by 9% and 11% of the initial values after 2.2 10 9 switching cycles for the SBTi single layered films and the SBTi/PZT bilayered films,respectively.Our results may provide some guidelines for further optimization of multilayered ferroelectric thin films.

Improved ferroelectric and piezoelectric properties of(Na_(0.5)K_(0.5))NbO_(3)ceramics via sintering in low oxygen partial pressure atmosphere and adding LiF

Dense(Na_(0.5)K_(0.5))NbO_(3)lead-free ceramics with the simple composition were prepared via sintering in low oxygen partial pressure(pO_(2),~10^(−12) atm)atmosphere and adding LiF.All the ceramics have pure orthorhombic structure.Compared to the LiF-added(Na_(0.5)K_(0.5))NbO_(3)ceramics sintered in air and the low pO_(2)-sintered pure(Na_(0.5)K_(0.5))NbO_(3)ceramics without LiF addition,the present ceramics exhibit improved piezoelectric and ferroelectric properties.The piezoelectric constant d33 is 125 pC/N,and the converse piezoelectric constant d_(33)^(*)is 186 pm/V.The dielectric constant and dielectric loss of the ceramics at room temperature and 1 kHz are 451 and 0.03,respectively.Under the measured electric field of 70 kV/cm,the remanent polarization is 25.9μC/cm^(2)and the coercive field is 13.9 kV/cm.Furthermore,if the base metals such as Cu and Ni powders were mixed into the green pellets and sintered in the low pO_(2)atmosphere,the base metals cannot be oxidized,suggesting possibility of using base metals as electrodes.