Characteristics of sol-gel derived PZT thin films with lead oxide cover layers and lead titanate interlayers

The sol-gel derived PbZr_0.53Ti_0.47O₃ (PZT) films were fabricated on the bare Pt/Ti/SiO₂/Si substrates or the same substrates coated by the PbTiO₃ (PT) interlayers. The post-deposition annealing temperature and time were optimized when the PbO cover layers and PbO vapour-containing atmosphere were compared with each other and adopted as the method to diminish the lead-loss problem during the high-temperature post-deposition annealing. The X-ray diffraction patterns, microstructures, and electrical properties such as relative permittivity, _r, remanent polarization, P _r, and coercive electrical field, E _c, were investigated in relation to the annealing conditions. The PZT films deposited on the bare Pt/Ti/SiO₂/Si substrates under the PbO vapour-containing atmosphere showed better electrical properties. This indicates that the PbO vapour-containing atmosphere may be the better method of lead-loss-prevention to process the lead-containing films rather than the PbO cover layer method. The electrical characteristics of the PZT films, _r=1150, a dissipation factor of 0.039, P _r=26 C cm^–2, and E _c=40.5 kV cm^–1 were measured at 1 kHz. When PZT films were deposited on substrates coated by the PT layers, PZT-PT films with single perovskite phase were derived by post-deposition annealing at 500 °C for 1 h. However, the relative electrical properties are very poor, i.e. E _r=160, P _r=2.0 C cm^–2 and E _c=75 kVcm^–1. The optimum combination for preparing PZT-PT films is a 40 nm PbTiO₃ interlayer and annealing conditions of 6 h at 550 °C in a PbO vapour-containing atmosphere; the derived films exhibit electrical properties of E _r=885, P _r=21.5 C cm^–2 and E _c=64 kV cm^–1. The combination of inserting a PT interlayer and annealing in a PbO vapour-containing atmosphere can prevent the formation of electrical short paths. In this case, nearly pin-hole-free PZT films can be grown on the PT (interlayer) /Pt/Ti/SiO₂/Si substrates. It is believed that it is possible to prepare the PZT films with nano-scale uniformity, reproducible quality, which may be worth considering for commercial applications.     

Charge-field hysteresis of BaTiO3: PVDF composites

Hysteresis phenomena in BaTiO₃: PVDF composites with different weight fractions of BaTiO₃ and PVDF were studied in the temperature range 20–180°C. A sinusoidal electric field of up to 100 kV ^–1 at 50 Hz was used. The saturation polarization, P _sat, remanant polarization, P _r, and coercive field, E_c, were observed to increase with increasing ceramic content of the composite samples. An increase of polarization with temperature was observed for all composites up to 80°C. This has been explained on the basis of an increase in the conductivity of the PVDF phase.     

Dielectric and thermal properties of xPbTiO3-(1 − x)SrTiO3 Polycrystals

SrTiO₃ and PbTiO₃ perovskites are combined to form the xPbTiO₃-(1 – x)SrTiO₃ (PST) solid solution. In this work, a study of its dielectric and thermal properties is reported as a function of PbTiO₃ content. The dielectric properties of the xPbTiO₃-(1 – x)SrTiO₃ solid solution are determined through a thermoelectric analysis technique and hysteresis measurements. Such measurements made at room temperature for all compositions show the influence of one component upon the other resulting in a response to the electric field that involves a strained lattice behavior. A limiting case of antiferroelectric-like behavior is observed for x = 0.5. The thermal properties such as the specific heat capacity (c) and thermal diffusivity () were determined using a photoacoustic technique (PA) and the temperature relaxation method (TRM). The thermal conductivity was calculated from the results obtained for c and .     

The influence of defects on ferroelectric and pyroelectric properties of Pb(Mg1/3Nb2/3)O3-0.28PbTiO3 single crystals

Relaxor-based ferroelectric single crystals 0.72Pb(Mg_1/3Nb_2/3)O₃-0.28PbTiO₃ (PMN-0.28PT) were grown by a modified Bridgman technique. The direct current (dc) conductivity was investigated and corresponding conduction mechanisms were discussed. V^″Pb−VO defects are dominant from 245 °C to 650 °C. The ferroelectric properties of [1 1 1]-oriented PMN-0.28PT were systematically investigated, with the coercive field (E_c) of 5.2 kV cm⁻¹ and remnant polarization (P_r) of 37.8 μC cm⁻² at room temperature. Moreover, the dielectric and pyroelectric performances of PMN-0.28PT were measured and the integrated pyroelectric performances greatly enhanced after annealing in oxygen at 500 °C for 20 h. This is due to the decrease of oxygen vacancies in the single crystals when being annealed in the oxygen-rich atmosphere. These make [1 1 1]-oriented PMN-0.28PT crystals a promising candidate for infrared detectors and thermal imagers used at room temperature.     

Upper critical and irreversibility fields in selectively doped YBa2Cu3O7

The electrical resistivity of (Y_1–xPr_x)Ba₂Cu₃O_7–gd and YBa₂(Cu_1–xZn_x)₃O_7– thin films and (Y_1–x. Tb_x)Ba₂Cu₃O_7– thin films and single crystals has been measured as a function of 0xx_crit, 2KT300K and OTH20T. The samples were oriented withc-axis parallel to applied fields. Upper critical field H_c2 and irreversibility field H_irr values have been determined from these measurements. Increased Tb doping appears to shift H_irr to higher temperatures. This coupled with observed twin peaks in magnetization measurements reflects an enhancement of flux pinning. Unlike Tb which does not appear to alterT _c , Pr and Zn doping of this system tends to depress bothT _c and the slope of the mean field normal phase-mixed phase boundary line (dH _c2/dT).     

Temperature-dependent electrical properties of 0.5Pb(Ni1/3Nb2/3)O3–(0.5 − x)PbTiO3–xPbZrO3 piezoceramics near the morphotropic phase boundary

0.5Pb(Ni_1/3Nb_2/3)O₃–(0.5 ? x)PbTiO₃–xPbZrO₃ (x = 0.10–0.20) polycrystalline ceramics were fabricated by solid-state reaction method. The phase structures, microstructure and temperature dependence of the electrical properties were investigated in detail. Both X-ray diffraction and Raman spectroscopy results indicated that the morphotropic phase boundary (MPB) separating tetragonal from rhombohedral phases located around the region with x = 0.14–0.16. Well-saturated ferroelectric P–E loops were obtained for all compositions and the compositions near MPB possessed the relative large remnant polarization P _r  ~ 24 μC/cm² and low coercive field E _c  ~ 5 kV/cm. High performance of electric-induced-strain property with $ d_{33}^{*} $ (S _max /E _max ) up to 1,140 pm/V could be achieved in the composition with x = 0.15. When the content of PbZrO₃ was 14 mol%, the ceramics showed slightly lowered piezoelectric coefficient $ d_{33}^{*} $ of 898 pm/V. But excellent temperature stability of piezoelectric property was exhibited that the $ d_{33}^{*} $ changed <10 % when the temperature increased from room temperature to 120 °C. The piezoelectric property of this solid solution makes it promising for application in multilayer piezoactuators.     

Study on the properties of a nanocrystal and polymer composite PbTiO3/PEK-c film with optical anisotropy

Composite thin films of PbTiO₃ nanocrystals and PEK-c polymer for applications in nonlinear optical devices were prepared by spin coating. The size of PbTiO₃ nanocrystals was estimated to be 30–40 nm. The microstructure of PbTiO₃/PEK-c composite polymer film before and after poling was analyzed by X-ray diffraction, which show that this film is c axis-orientated. The poled composite film displayed the refractive index anisotropy. In this sample the TE- and TM-indices differences are found to be 0.02945 for 633 nm and 0.03915 for 414 nm. The electro-optic coefficient ₃₃ of poled composite film was measured to be 12.89 pm V^–1 at 633 nm by the transmission technique. The dielectric constant of it at 100 KHz under room temperature was determined to be 7.32. The figure of merit F ₂ was estimated to be 492. In addition, a relaxation process was observed in the time range of 28 days and the relaxation time constant was calculated to be 2393 min.     

Effect of La-doping content on the dielectric and ferroelectric properties of 0.88Pb(Mg1/3Nb2/3)O3–0.12PbTiO3 ceramics

Dense relaxor ferroelectric 0.88Pb(Mg_1/3Nb_2/3)O₃–0.12PbTiO₃ (0.88PMN–0.12PT) ceramics with different La-doping contents (0, 1, 2 and 4 at.%) were sintered by using powders synthesized via a solid-state reaction route. The effects of La doping on the microstructures and electric properties of the 0.88PMN–0.12PT ceramics were investigated. It was found that the average grain size, remanent polarization P _r, coercive field E _c, Curie temperature T _c and leakage-current density J of the ferroelectric ceramics decrease significantly with increasing La doping content. The decrease in P _r, E _c and T _c can be understood in term of the fact that the substitution of Pb²⁺ ions by La³⁺ ions suppresses the long-range coupling of BO₆ octahedrons, while the abatement in J can be explained according to the reduction of oxygen vacancies caused by La doping. By fitting the J–E curves, the conduction mechanism of the 0.88PMN–0.12PT ceramics is confirmed to be Ohmic conduction generated from oxygen vacancies. The dielectric and ferroelectric properties of 0.88PMN–0.12PT ceramics are tunable with manipulating the La doping content.     

Fermi Surface Map of the Single-Layer Bi-Cuprate Bi2Sr2 ? xLaxCuO6 + δ at Optimal Doping

A first Fermi surface map of a single-layer high-T _c superconductor is presented. The experiments were carried out on optimally doped Bi₂Sr_{2 – x}La_xCuO_{6 +} (x = 0.40) with synchrotron radiation which allow to discuss in detail the strong polarization dependence of the emissions near the Fermi edge. For the cuprates, only little is known about the impact of the electron–photon matrix element determining the photoelectron intensity. For the example of the model layered superconductor Bi₂Sr_{2 – x}La_xCuO_{6 +} , it will be demonstrated that the polarization geometry has significant influence on the energy distribution curves at E _F, and consequently also for the determination of the topology and character of the Fermi surface (FS) by angle-resolved photoemission. For further clarification also, a FS map of the n = 2 material Bi-2212 has been measured applying a different polarization geometry as previously used by Saini et al. In the context of the current debate on the character of the FS of Bi-cuprates, our results confirm a hole-like FS for n = 1 as well as for n = 2 material, what might be the universal FS for high-T _c superconductors.     

Temperature dependence of dielectric and piezoelectric properties of (1?x)(BiScO3–0.64PbTiO3)–xLiNbO3 high-temperature relaxor ferroelectric ceramics

(1−x)(0.36BiScO₃–0.64PbTiO₃)–xLiNbO₃ (BSPT64–xLN) high-temperature relaxor ferroelectric ceramics near the morphotropic phase boundary (MPB) composition were investigated. X-ray diffraction showed a change in symmetry from MPB phase to rhombohedral phase with LiNbO₃ content increasing. A change from normal ferroelectric features to relaxor ferroelectric features was observed with LiNbO₃ substitution up to x = 0.06, while high-temperature dielectric relaxation was exhibited at T _max ~230 to 383°C for 0.02 ≤ x ≤ 0.06. The BSPT64–xLN ceramics with x = 0.02 LiNbO₃ exhibited good piezoelectric properties compared with BS–0.64PT ceramics: piezoelectric coefficients d ₃₃ = 505pC/N, planar electromechanical coupling factors k _p = 0.47, and remnant polarization P _r = 40 μC/cm², respectively. The annealing temperature dependence of piezoelectric response for BSPT64–xLN ceramics was measured and it was found that the piezoelectric properties decreased slightly before 210°C for x = 0.02 and 0.04, showing excellent thermal stability, which indicated that BSPT64–xLN relaxor ferroelectric ceramics can be used in the range of high temperature compared to Pb-based relaxor ferroelectrics.     

Preparation and characterization of Zn3P2-Cd3P2 solid solutions

Solid solutions of Zn₃P₂-Cd₃P₂ systems of the type (Zn _x Cd_1–x )₃P₂ have been prepared by direct reaction of the constituent elements (Zn, Cd, P) for values of x equal to 0.0, 0.2, 0.4, 0.5, 0.6, 0.8 and 1.0. X-ray diffraction data indicate that all the systems crystallize in tetragonal () phase only, exhibiting preferred orientation along the (220) and (224) directions. The lattice parameters, a and c, and the interplanar spacing, d, vary linearly with x, obeying Vegard's law. The systems show minimum conductivity at room temperature for composition corresponding to x values in the range 0.4–0.6. Electrical conductivity for all systems is measured in the temperature range 100–450 K. In view of the estimated (low) values of the activation energy the conduction process in the different temperature regions has been attributed to the presence of shallow trapping levels in the systems.     

Superconducting Density of States from the Magnetic Penetration Depth of Electron-Doped Cuprates La2−x Ce x CuO4−y and Pr2−x Ce x CuO4−y

From measurements of the magnetic penetration depth, (T), from 1.6 K to T _c in films of electron-doped cuprates La_2–x Ce _x CuO_4–y and Pr_2–x Ce _x CuO_4–y we obtain the normalized density of states, N _s(E) at T=0 by using a simple model. In this framework, the flat behavior of ^–2(T) at low T implies N _s(E) is small, possibly gapped, at low energies. The upward curvature in ^–2(T) near T _c seen in overdoped films implies that superfluid comes from an anomalously small energy band within about 3k _B T _c of the Fermi surface.     

Preparation and Characterization of Epitaxial-Grown Ba0.65Sr0.35TiO3 Thin Films by the Sol-Gel Process on Pt/MgO Substrates

Epitaxial-grown barium-strontium-titanate (BST, Ba_0.65Sr_0.35TiO₃) thin films have been successfully deposited on Pt/MgO (100) substrates using sol-gel techniques. Crack-free 350-nm-thick films were fabricated using a multilayer spinning technique and calcination at 650°C in oxygen for 1 hr. The X-ray diffraction pattern showed that (001) planes of BST films were mainly laid parallel to Pt (100) and MgO (100). The dielectric constant and dissipation factor for BST thin films at a frequency of 10 kHz were 480 and 0.02, respectively. The results of the temperature-dependence of the dielectric constant and dissipation factor showed that sol-gel–derived BST films had Curie temperatures of about 35°C and diffused ferroelectric phase transition characteristics. The leakage current density through the BST films was about 2.75 × 10^–7 A/cm² at an applied voltage of 3 V. The BST films exhibited a well-saturated ferroelectric hysteresis loop with remnant polarization P _r = 2.8 C/cm² and coercive field E _c = 52 kV/cm.     

Morphotropic phase boundary in high temperature ferroelectric xBi(Zn1/2Ti1/2)O3 − yPbZrO3 − zPbTiO3 perovskite ternary solid solution

A bismuth and lead oxide based perovskite ternary solid solution xBi(Zn_1/2Ti_1/2)O₃ − yPbZrO₃ − zPbTiO₃ (xBZT − yPZ − zPT) was investigated as an attempt to develop a high T_C ferroelectric material for piezoelectric sensor and actuator applications. A morphotropic phase boundary (MPB) between rhombohedral and tetragonal phases was determined through an XRD study on a pseudobinary line 0.1BZT − 0.9[xPT − (1 − x)PZ] for composition 0.1Bi(Zn_1/2Ti_1/2)O₃ − 0.5PbZrO₃ − 0.4PbTiO₃. Enhanced piezoelectric and ferroelectric activities were observed for MPB composition with dielectric constant ε_r′ ~ 23,000 at Curie temperature (T_C) ≈ 320 °C, remanent polarization (P_r) = 35 μC/cm², piezoelectric coefficient (d₃₃) = 300 pC/N, unipolar strain = 0.15%, and electromechanical coupling coefficient (k_P) = 0.45.     

Thermal induced transformations in glassy chalcogenides SixTe60−xAs30Ge10

Temperature-induced transformations are considered to be interesting characteristic properties of amorphous materials including the Si _x Te_60–x As₃₀Ge₁₀ system, withx=5, 10, 12 and 20. Density (), X-ray diffraction and differential thermal analysis (DTA) were used to characterize the compositions. DTA traces of each glass composition at different heating rates from 5 to 30° C min^–1 were obtained and interpreted. Fast and slow cooling cycles were used to determine the rate of structure formation. Cycling studies of materials show no memory effect but only ovonic switching action. The compositional dependence of the crystallization activation energy (E) and the coefficient of glass-forming tendency (K _gl) have been calculated. The thermal transition temperatures and associated changes in specific heat have been examined as a function of the Te/Si ratio by differential scanning calorimetry. It was found that andE increase linearly with increasing tellurium content, while the heat capacity (c _p) andK _gl, decrease with increasing tellurium content.E=1.54 eV andc _p=0.246 J g^–1 K^–1 forx=20 whileE=2.74eV andc _p=0.22 J g^–1 K^–1 forx=5.     

Study of ferroelectricity in the PMN-PT system near the morphotropic phase boundary

The ferroelectric properties of tetragonal phase Pb (Mg_1/3Nb_2/3)O₃-PbTiO₃ (PMN-PT) solid solutions have been investigated. The coercivity,E _C, increases monotonically with PT content. The remanent polarization,P _r, on the other hand, decreases rapidly with PT content and reaches a minimum value for a sample containing 0.365 mol % PT. It increases moderately when the PT content is further increased. The deformation parameter, , is used to correlate the composition to ferroelectric characteristics of these materials. A critical deformation parameter, _C=0.008 984, is observed at which the remanent polarization contributed from Mg²⁺ and Nb⁵⁺ cations,P _r ^MN , decreases with value when <_C and vanishes when >_C. The remanent polarization contributed from Ti⁴⁺ cations,P _r ^Ti , on the other hand, increases with value, following the trendP _r ^Ti =k^1/2. The rattling of Mg²⁺ and Nb⁵⁺ cations among off-centred sites in oxygen octahedra is adapted to explain such a phenomenon.     

Structure and dielectric/piezoelectric properties of LiNbO3-doped BiScO3–PbTiO3 ceramics with morphotropic phase boundary composition

0.02LiNbO₃–0.98{(1 − x)BiScO₃–xPbTiO₃} (2LN–BS–xPT) ceramics near the morphotropic phase boundary (MPB) were investigated. MPB region of 2LN–BS–xPT ceramics was identified to be in the composition of 0.62 < x ≤ 0.64. The coexistence of the tetragonal domain structure and a polar microdomain structure was observed by transmission electron microscope for x = 0.64. It is found that 2LN–BS–xPT ceramics (x = 0.64) showed good piezoelectric and ferroelectric properties with piezoelectric constant d ₃₃ about 505 pC/N, planar electromechanical coupling factors k _p about 0.47, and remnant polarization P _r about 40 μC/cm², respectively, while T _max is about ~350–400 °C. The high-temperature relaxation behavior was also studied in 2LN–BS–xPT ceramics. Effects of thermal depoling on the piezoelectric properties of 2LN–BS–xPT ceramics indicated good thermal stability before 300 °C for x = 0.62 and 0.64.     

Comparative investigating the properties of Pb-based multilayer ferroelectric thin films for FeRAM

The PbZr_0.3Ti_0.7O₃(PZT) thin film and multilayer PbZr_0.3Ti_0.7O₃/PbTiO₃(PZT/PT), PbTiO₃/PbZr_0.3Ti_0.7O₃/ PbTiO₃(PT/PZT/PT) thin films were prepared by a Sol-Gel method on the Pt(111)/Ti/SiO₂/Si(100) substrate for FeRAM application. The microstructure, ferroelectric, fatigue, dielectric, and leakage current properties of these thin films were investigated. The results indicate that the multilayer PT/PZT/PT thin film have a better ferroelectric, fatigue, dielectric and leakage current density properties. Its remanent polarization P_r reaches a maximum value of 21.2 μC/cm² and the coercive field E_c gets to a minimum value of 64.2kV/cm. After 10¹⁰ cycles, it still has more than 80% remnant polarization. The PT/PZT/PT thin film exhibits lower dielectric constant and lower dielectric loss, which is beneficial for FeRAM application. It also has the lowest leakage current density. The leakage current mechanism of the PZT, PZT/PT and PT/PZT/PT thin films is correlated to the microstructure and can be modeled in terms of GBLC and SCLC theory. The microstructure and electric properties of these films are correlated. The double-sided PT seed layers enhance not only the microstructure but also the electric properties. It is evident that the PT/PZT/PT multilayer thin film is a promising candidate for FeRAM application.     

The effect of Ti4+ ions on some magnetic properties of lithium ferrite

Some magnetic properties of the spinel structure compound, Li_0.5+0.5x Ti _x Fe_2.5-1.5x O₄, wherex=0–0.5, have been studied by different methods. The initial permeability, _i, was measured as a function of temperature at a constant frequency of 10 kHz. A maximum value was observed for each composition indicating the Curie temperature,T _c , which decreases with increasing titanium concentration. The magnetization,M, and theB-H loop were measured atRT in the range of magnetizing field from 0–1200 Am^–1 and at constant fieldH=205 Am^–1, respectively. The relative permeability, _r, depends on the magnetizing field and composition. It was found from theB-H loop that the remanence induction,B _r, and the apparent loss energy,P _s, depend on the composition but the coercive force,H _c, is independent of composition.     

Optical study of charge dynamics along thec-axis in high-Tc superconductors

Comparing the optical spectra withEc for typical high-T _c superconducting cuprates, we discuss the charge dynamics along thec-axis. The plasma energy or the mass anisotropic factorm _* ^c //m _* ^b is one of the key parameters determining the spectrum forEc. In Bi₂Sr₂CaCu₂O₈ and La_2–x Sr _x CuO₄ with a largem _* ^c /m _* ^b , the plasma energy is smaller than the superconducting gap energy, and thus the supercurrent along thec-axis is a kind of Josephson current flowing through insulating layers such as the BiO layers. On the other hand, in YBa₂Cu₃O₇ with a smallm _* ^c /m _* ^a , it seems that the coherent supercurrent flows along thec-axis. Although the spectrum forEc strongly depends on samples, presumably due to the difference in the hole concentration, a clear anisotropy between theab- and thec-directions is observed in the characteristics energy scales such as the plasma energy as well as the reflectivity knee energy.