Ferroelectric Barium Titanate Research Articles

Diffuse phase transitions, electrical conduction, and low temperature dielectric properties of sol–gel derived ferroelectric barium titanate thin films

Ferroelectric thin films of barium titanate were fabricated by sol–gel technique on platinum substrates. The processing temperature was 700 °C. The films obtained with a thickness of 1.5 μm were dense, transparent, and showed ferroelectricity. Scanning electron microscopy and x-ray diffraction were used for studying the surface morphology and crystallographic structure of the film. Films in the metal–ferroelectric–metal configuration (MFM) were used for the electrical measurements. Dielectric constant and loss tangent were found to be 430 and 0.015, respectively, at 10 kHz under ambient conditions. The ε′(T) curve shows broad peak centered around 120 °C as in the case of diffuse phase transition. The ac conductivity is proportional to ω0.9 in the low frequency region and ω1.8 in the high frequency region. The dc conductivity versus temperature curve showed a change in the slope around 125 °C, corresponding to the phase transition. To study the low temperature phase transitions, dielectric parameters on the films were measured to a temperature down to about 10 K. Remanent polarization (Pr) and coercive field (Ec) obtained from the hysteresis loop at room temperature are ∼2.0 μC/cm2 and ∼27 kV/cm, respectively. Capacitance–voltage studies performed on the MFM structures showed butterfly loop at 135 °C.

Microstructure and dielectric parameters of epitaxial SrRuO3/BaTiO3/SrRuO3 heterostructures

Epitaxial films of ferroelectric barium titanate are desirable in a number of applications but their properties are inferior to those of bulk material. Relations between microstructure and dielectric properties may give better understanding of limitations. Trilayer heterostructures SrRuO3/BaTiO3/SrRuO3 were grown by laser ablation on (100)LaAlO3 and (100)MgO substrates. The BaTiO3 layer was granular in structure. When grown on (100)SrRuO3/(100)LaAlO3, it was preferentially a-axis oriented due to tensile mechanical stress. Using (100)MgO as a substrate, on the other hand, produced a mixture of about equal value of a-axis and c-axis oriented grains of BaTiO3. The dielectric permittivity, ε, of the BaTiO3 layer was almost twice as large, at T>200 K and f=100 kHz, for the LaAlO3 substrate as compared to the MgO one. Its maximum value (ε/ε0≈6200) depended on temperature of growth, grain size, and electric field and compares well with optimal values commonly used for ceramic material. The maximum in the ε(T) shifted from about 370 to 320 K when the grain size in the BaTiO3 film decreased from 100 to 40 nm. At T<300 K, hysteresis loops in polarization versus electric field were roughly symmetric. The BaTiO3 films grown on (100)SrRuO3/(100)MgO exhibit the largest remnant polarizations and coercive fields in the temperature range 100–380 K.

Silver Selectively Deposited on Ferroelectric Barium Titanate Domains Enable Creation of Metallic Patterns with Submicron Features

Silver Selectively Deposited on Ferroelectric Barium Titanate Domains Enable Creation of Metallic Patterns with Submicron Features

Spatially Selective Photochemical Reduction of Silver on the Surface of Ferroelectric Barium Titanate

When BaTiO3 is immersed in an aqueous AgNO3 solution and illuminated by UV light, silver metal deposits on the surface in patterns determined by the ferroelectric domain structure. Because the photochemical reduction of Ag occurs preferentially on the positive ends of the dipoles, metal patterns with submicron dimensions are produced. The static dipolar field in certain domains is thought to promote the transport of photogenerated electrons to the solid−liquid interface where they reduce silver cations.

Switching current measurements in Pb(Zn1/3 Nb2/3)O3-PbTiO3 relaxor ferroelectric single crystals

Switching current measurements have been carried out on relaxor ferroelectric single crystal-PZN, and the solid solution 0.86PZN-0.04PT and 0.91PZN-0.09PT for crystallographic directions [001] and [111]. The experiments showed the presence of two maximum points in the switching current for 0.86PZN-0.04PT and 0.91PZN-0.09PT that can be attributed to the co-existence of two phases. The switching time inverse shows a two-fold linear dependence on applied field for both [001] and [111]. This suggests that the polarization reversal in the relaxor systems is related to the mobility of the domains. The switching time in relaxor ferroelectric is long (millisecs) compared to the reported data on normal ferroelectric Barium titanate (microsecs). The switching time is dependent on the composition of the crystal along both [001] and [111]. Along [111], the switching time decreases as the PT component increases in the crystal while along [001], the switching time increases as the PT increases.

Surface modification and characterization of functional oxide ceramics using CO 2 laser

Surface of powder-sintered oxides such as superconductor and ferroelectric barium titanate ceramics were recrystallized using scanned CO 2 laser irradiation. Conventionally, the ceramic is sintered at high temperature, to increase adhesive forces between powdered ceramic grain. During such process, however, many micro-pores and -cracks are produced owing to large shrinkage of fine aggregate grains into the surface layer. Superconductor surface does not allow the flow of superconductor current uniformly and the flow is concentrated on the surface. Thus properties of superconductor are so sensitive to their surface condition that some substantial modifications of the material are necessary. To clarify this issues, both sample of the powder-sintered superconductor YBa x Sr 2− x Cu 3O 7− y and the BaTiO 3 ceramic film were modified by laser irradiation to recrystallize only the surface layer. Their microstructural features in the surface, the characteristic of superconducting and ferroelectric have been investigated. Thus laser-scanning process appears to be suited to generating large grains with preferred orientation by changing of irradiation condition.

Hydrothermal synthesis of ferroelectric barium and strontium titanate extremely fine particles

BaTiO3, SrTiO3 and (Ba1− xSrx)TiO3 fine particles were synthesized from amorphous TiO2 fine particles by a hydrothermal method. The relationship between the specific dielectric constant of the sintered disk and the mean size of composing particles has been investigated. The specific dielectric constants of the sintered disks of BaTiO3 and SrTiO3 particles attain values exceeding 6000 in the range of the particle size of 0.10–0.17 μm. The specific dielectric constant for the sintered disk of (Ba1− xSrx)TiO3 particles synthesized at various atomic fractions of Sr (x) attains maximum values at both atomic fractions of 0.08 and 0.95. It has been suggested that the size of particles composing the disk should considerably affect the specific dielectric constant of the sintered disk.

Influence of the electric field on vickers indentation crack growth in BaTiO 3

In this study, the Vickers indentation method was used to determine the crack growth of ferroelectric barium titanate (BaTiO 3) ceramic under the influence of electric fields. It was verified that an applied electric field induces distinct anisotropic crack growth parallel and perpendicular to the poling direction which is mainly interpreted as an anisotropy in fracture toughness. The curve of the measured crack lengths as a function of the applied electric field shows similarity with the strain hysteresis. Curves of cracks parallel and perpendicular to the electric field direction are symmetric to each other. Stress-induced ferroelastic domain switching is used to explain the observed crack lengths anisotropy and change in fracture toughness.

Physico-chemical modification effects of nanoparticles in radiation-cured polymeric composites

For studying nanoglobular modification effects in radiation-cured polymeric composites, we prepared polymerisation-active metallo-organic cerium(IV) sorbate (CeSo) and ferroelectric barium titanate (BaTiO 3) nanoparticles. Through electron beam curing (EBC) of nanopowder/acrylate dispersion films the latter particles can impart ferroelectricity on thin polymeric nanocomposite foils which are of potential importance in piezo- and pyrosensorics. The CeSo nanoparticles, through the high redox potential of the metal ions, can undergo pronounced radiation-induced solid-state polymerisation. In radiation-cured polymeric nanocomposites the CeSo nanoparticles form crosslinks, thus efficiently modifying the viscoelastic properties. In the event, quite analogous silico-organic nanoparticles were used to apply this modification scheme to novel scratch and abrasion resistant coatings.

Ferroelectric domain characterisation and manipulation : A challenge for scanning probe microscopy

Domain writing and reading on the nanometer scale is addressed with scanning force microscopy (SFM) Compared to other scanning probe methods, SFM provides broad possibilities for the on-line data controlling. i.e. three-dimensional mapping of polarisation distribution, differentiation between polarisation and topography, nanoscale domain switching of domains with a 60 nm diameter, recording of nanoscale hysteresis loops, phase transition mapping. domain wall imaging with 9 nm resolution, atomic resolution of ferroelectric surfaces, etc. All these issues are reported in this paper. The challenging result of such a concerted investigation is the possibility of using SFM for nanoscale domain writing and reading with nanometer resolution. Fig. 1 illustrates such an example where line shaped c – domains are purposely written into a ferroelectric Barium-Titanate single crystal with a 400 nm line-width. With this figure we highly appreciate and honour the work of Bob Newnham passing our best nano-wishes for his future.

Nanoscale reconstruction of surface crystallography from three-dimensional polarization distribution in ferroelectric barium–titanate ceramics

The three-dimensional orientation of polarization vectors at the surface of ferroelectric barium–titanate (BaTiO3) ceramics is evaluated using voltage-modulated scanning force microscopy (SFM). By applying an ac voltage to the conductive SFM tip, we measure the relative amount of the three orthogonal components Px, Py, and Pz, of the polarization vector at any surface point. The measured polarization orientation together with the actual domain-wall orientation allows a precise reconstruction of the crystallographic orientation of the investigated grains down to a 40 nm resolution. Excellent agreement is obtained when comparing this orientation with the crystallographic reconstruction revealed by etch patterns from the sample surface topography. We show that the surface topography manifests a domain structure, which was present in the past, while the actual ferroelectric domain configuration is revealed by the modulation technique.

Displacement Charge Patterns and Ferroelectric Domain Wall Dynamics Studied by In-Situ Tem

AbstractWe have observed the growth of domains in ferroelectric barium titanate and potassium niobate using a transmission electron microscope. When domains move in response to electric fields we see a scaling effect where the fine scale domain structure is activated first, followed by larger length-scale patterns. Curvature and tilting of domain walls leads to local uncompensated displacement charge and external fields can interact with these charged walls. In this paper, we posit that the presence of displacement charge on domain walls is important for polarization switching. Charge-neutral domain configurations are in a lower energy state and are harder to switch. We argue that the number of charge-neutral, low energy domain configurations can increase with time. This mechanism provides an intrinsic contribution to ferroelectric fatigue.

Fatigue in sol-gel derived barium titanate films

The effect of fatigue on the electrical properties of sol-gel derived ferroelectric barium titanate (BaTiO3) thin films have been investigated. At room temperature, the resistivity, breakdown field, dielectric constant (ε), and loss tangent (tan δ) decreases after fatigue while the coercive field increases. Fatigue also influences the dielectric properties of the film at high temperatures. The sharpness and magnitude of the peak in the dielectric constant at the transition temperature decreases after fatigue. The loss tangent of the virgin film showed a peak at the transition temperature while it is absent in the case of the fatigue film. The phenomena are explained in terms of (i) the accumulation of point charge defect, (ii) the pinning of domain wall mobility, and (iii) the space charge layer models of fatigue.

Landau theory-based analysis of grain-size dependence of ferroelectric-to-paraelectric phase transition and its thermal hysteresis in barium titanate ceramics

Ferroelectric barium titanate ceramics with grain sizes in the range (0.5, 20) µm were used for a comparative study of grain-size influence on the ferro-para phase transition and its thermal hysteresis. The investigations were performed by recording the temperature dependence of the dielectric constant, heat capacity and pyrocharge. The experimental results have been analysed in the framework of Landau-Devonshire theory. The grain-size dependent Landau coefficients of the free energy have been derived from our experimental data and used to compute the grain-size dependence of the theoretical transition interval related to the thermal hysteresis. The good qualitative agreement between theory and experiment recommends the size dependent Landau coefficients as a way to improve the modelling of the size dependent ferro-para phase transition in ceramics.

Electrical properties of sol-gel processed barium titanate films

The sol-gel technique has been used to prepare ferroelectric barium titanate (BaTiO3) films. The electrical properties of the films have been investigated systematically. The room temperature dielectric constant (ϵ) and loss tangent (tanδ) at 1 kHz were respectively found to be 370 and 0.012. Both ϵ and tanδ showed anomaly peaks at 125°C. The room temperature remanant polarization (Pr) and coercive field (Ec) were found to be 3.2 μC/cm2 and 30 kV/cm, respectively. The capacitance–voltage (C–V) and conductance–voltage (G–V) characteristics also showed hysteresis effect. The temperature variation of C–V and G–V characteristics also confirms the ferroelectric to paraelectric phase transition at 125°C.

Sol-gel processed barium titanate ceramics and thin films

Ferroelectric barium titanate (BaTiO3) ceramics and thin films have been prepared from barium acetate (Ba(CH3COO)2) and titanium (IV) isopropoxied (Ti((CH3)2CHO)4) precursors by a sol–gel technique. The as-grown powder and thin films were found to be amorphous, which crystallized to the tetragonal phase after annealing at 700°C in air for 1 h. Both the ceramics and thin films showed well-saturated polarization–field (P–E) hysteresis loops at room temperature. The value of the spontaneous polarization, PS, remnant polarization, Pr, and coercive field, Ec, of the ceramics and thin films determined from the P–E hysteresis loop were found to be 19.0 and 12.6; 14.0 and 3.2 μG cm−2, and 30 and 53 kV cm−1, respectively. The coercive field of the film determined from the capacitance–voltage, C–V, characteristics is slightly lower than that determined from the P–E hysteresis loop (43 kV cm−1). The room-temperature dielectric constant, e, of the ceramics and films was found to be 1135 and 370, respectively. Both the films and ceramics showed dielectric anomaly peaks at 125 °C, showing ferroelectric to paraelectric phase transition. © 1998 Kluwer Academic Publishers

The effect of grain and particle size on the microwave properties of barium titanate (BaTiO3)

The use of ferroelectric ceramics and thin films in microwave devices requires that they possess frequency-stable, low-loss dielectric properties. At microwave frequencies, ferroelectric polycrystalline ceramic materials typically exhibit a large dielectric relaxation, characterized by a decrease in the relative permittivity (εr) and a peak in the dielectric loss (tan δ). Mechanisms attributed to the relaxation phenomenon include piezoelectric resonance of grains and domains, inertia to domain wall movement, and the emission of gigahertz shear waves from ferroelastic domain walls. As a result, the relaxation phenomenon appears to be intimately linked to the domain state of the ferroelectric. The domain state of a ferroelectric is, in part, dependent upon its microstructure. In this study, the microwave dielectric properties of ferroelectric barium titanate were measured as a function of grain and particle size. Polycrystalline ceramic ferroelectric BaTiO3 (having average grain sizes of 14.4, 2.14, and 0.26 μm) and BaTiO3 powder-polymer matrix composites (possessing average particle sizes of 1.33 μm, 0.19 μm, and ∼66 nm) were employed. The composite samples were used to decouple resonances between adjacent grains as well as reduce the three dimensional clamping experienced by grains in ceramic. Characterization studies were performed to determine the effects of grain size and particle size on the crystal structure and degree of tetragonality. Microwave dielectric measurements through 6 GHz were carried out using lumped impedance, cavity perturbation, and post resonance experiments. All samples exhibited evidence of relaxation or resonance phenomena in their dielectric spectra. Except for the 0.26 μm grain size ceramics and the 66 nm particle size composites, all other samples exhibited relaxation in their dielectric spectra. The 0.26 μm ceramic and 66 nm composite showed evidence of resonance in their dielectric spectra. This work clearly shows the potential to tune the microwave properties of ferroelectrics through control of grain/particle size and the domain state. In general, relaxation frequencies increased and loss tangents decreased with decreasing grain/particle size. The relaxation mechanisms were identified and correlated with the material characterization results and theoretical models. Relaxation frequencies were generally governed by the smallest resonant width, i.e., the domain width.

The role of interfaces on an apparent grain size effect on the dielectric properties for ferroelectric barium titanate ceramics

We report the effect of interfaces (and thus internal surface area effects) on the value of dielectric constant (K′) calculated from capacitance and geometry data for sub-micron barium titanate (BaTiO3) ceramics prepared with decreasing grain size (and grain volumes). A series model is proposed to explain the decreasing values of apparent K′ obtained for grain sizes below 0.5 μm. A distinction is made between the true dielectric constant (K′) and the apparent dielectric constant (K′) calculated from experimental data. The progressive suppression in K′ is explained in terms of ferroelectric grains of constant dielectric constant (K′1) separated by a lower-K 2 boundary region (i.e., grain boundary) of constant thickness (d 2). The problem is one of an increasing interfacial surface area to grain volume ratio in fine-grain dielectrics. We begin by reporting original dielectric data for high pressure-densified ultrafine-grain BaTiO3 ceramics. Chemically prepared BaTiO3 powder was consolidated at high pressure (8GPa) and low temperature to prepare ultrafine grain microstructures. Specimens pressed at 700°C were substantially dense (≥98% of theoretical density) with an average grain size of 70 nm. Subsequent heat treatment at increasing temperatures (and atmospheric pressure) yielded a series of specimens with increasing grain sizes up to 20 μm. High-pressure consolidation at room temperature, followed by heat treatment at 800°C (and atmospheric pressure), yielded a finer-grain (40 nm) and less dense (≈90%th) microstructure. The temperature dependence of K′ was determined for ceramics ranging in grain size from 40 nm to 20 μm. Curie-Weiss analysis of the dielectric data clearly suggests a series dilution of the composite K′ by the interfacial grainboundary regions. We were able to model the dielectric measurements by considering grain boundary regions of relaxed thickness d 2 = 8 Å and dielectric constant K′2 = 130. Polarization reversal and Curie-Weiss characteristics were observed for all BaTiO3 ceramics studied in this investigation. Thus, the conclusions are made that if a critical grain size exists for ferroelectricity it is less than 40 nm for polycrystalline BaTiO3, and the role of interfaces is extremely important on the calculated values of K′ for fine-grain ceramics below 0.5 μm.

In-Situ TEM Study of Domain Propagation in Ferroelectric Barium Titanate, and Its Role in Fatigue

AbstractWe have conducted in-situ transmission electron microscopy (TEM) experiments on thinned single crystal barium titanate in order to study the effects of applied electric field, temperature, electron beam irradiation and UV irradiation on domain nucleation and propagation. We observe two basic modes of domain wall motion; (i) a lateral motion which uniformly widens or narrows the total domain width; (ii) a “zipping” motion in which one end of a domain narrows to a point, which then propagates lengthwise, widening (or narrowing) the domain behind it. Both domain creation and destruction can occur by this latter process. When cooling from above Tc, domain growth usually occurs by the “zipping” motion. We believe that both the lateral and “zipping” modes of motion are related. The “zipping” mode tends to occur in the presence of inhomogeneous long-range strain fields, or when trapped charges are present locally. In some instances, the trapped charge is strong enough to show significant image contrast in bright-field. Domain motion, initiated by heat, electric fields or UV irradiation, moves such charges. A model of domain motion is presented which shows how displacement charge can be injected into the ferroelectric, and which may contribute to the fatigue of these materials.

Phase transition in Sol-Gel processed barium titanate ceramics

Ferroelectric barium titanate (BaTiO3) ceramics have been prepared from barium acetate [Ba(CH3COO)2] and titanium isopropoxide [Ti(CH3)2CHO)4] precursors by sol-gel technique The as-grown powder was found to be amorphous which crystallized to tetragonal phase after annealing at 700°C in air for one hour. The ceramics showed well saturated polarization-field (P-E) hysteresis loops at room temperature. The values of spontaneous polarization(Ps), remanent polarization (Pr) and coercive field (Ec) of the ceramics were found to be19.0, 12.66μC-cm−2 and 30KVcm−1 respectively. The room temperature dielectric constant (ε) and loss tangent (tanδ) of the ceramics were found to be 1135 and 0.012 respectively. The dielectric constant and tanδ showed anomaly peaks at 125°C showing ferroelectric to paraelectric phase transition. The polarization parameters also vanish at 125°C confirming the phase transition.