Electronic Structure and Chemical Bonding of Zr Substitution of Ti Site on Pb(Zr1 −xTix)O3 Using DV-Xα Method

Electronic structures were investigated on Pb(Zr_{1 ?x}Ti_x)O₃ (PZT) using the discrete variational Xα cluster method for obtaining the information of dependence on the amount and position of the substituted Zr atoms. Also, we investigated the effect of them on fatigue. The net charge and the overlap population were discussed together with the energy gap, which is related to fatigue. As a result, the net charge was independent on the amount and position of the substituted Zr atoms, and the overlap population wasn't. Furthermore, from the calculated energy gap, we conclude that Zr-rich PZT is less susceptible to fatigue than Ti-rich PZT.     

Filament-assisted pulsed laser deposition of epitaxial PbZrxTi1−xO3 films: Morphological and electrical characterization

Abstract

A modification of the conventional pulsed laser deposition technique was employed, whereby a low energy electron emitting filament was placed between the target and the substrate (-20 V filament/substrate bias) in order to produce reactive species (O_2- and O_?) during deposition. Using this modification, epitaxial thin films of PbZr_xTi_1?xO3 (PZT, 0 ≤ × ≤ 0.6) were prepared in situ on virgin (100) MgO and (100) Pt/(100) MgO substrates at a substrate temperature of 550°C and in an oxygen ambient (0.3 Torr). The topography of films prepared without a filament on virgin MgO were porous and composed of grains of about 1000 Å in diameter. As the emission current was increased from 0 to 400 μA, the grain size decreased to less than 100 Å with a concomitant decrease in the porosity. The nucleation of crystallites of other orientations was observed at emission currents greater than about 500 μA. Trilayer structures (Pt/PZT/Pt/<100>MgO) were fabricated for electrical measurements. Non-filament-assisted PZT cells usually failed because of a high probability of conductive paths through the PZT layer. Filament-assisted films were much less prone to this problem. Typical remanent polarizations and coercive fields were 15–20 μC/cm² and 30–50 kV/cm, respectively.     

Raman Scattering Study of the Pb(Hf x Ti1−x )O3 Ceramics

Raman spectroscopy was used to study the long wavelength vibrations of tetragonal perovskite (space group P4mm) Pb(Hf_xTi_1–x)O₃ (PHT) (0.10 x 0.50) samples at room temperature and at 20 K. For x 0.40, Raman spectra collected from the PHT samples were very similar to the previous spectra collected from the PZT samples with the same value of x, except the mode at around 190 cm^–1, whose frequency was decreasing with increasing x in PHT ceramics. Correspondingly, the latter feature was taken as a sign of the mass effect (Hf versus Zr) while the similarity of the remaining parts of the Raman spectra was assumed to be due to the almost identical ionic radii difference between Ti⁴⁺ and Zr⁴⁺ and between Ti⁴⁺ and Hf⁴⁺ ionic radii. The behaviour of the mode at around 280 cm^–1 revealed that a phase transition occurred once x was changing from 0.40 to 0.50.     

Chemical Solution Deposition of Epitaxial La1−x (Ca, Sr) x MnO3 Thin Films

We report on the epitaxial growth of magnetoresistive La_0.7Ca_0.3MnO₃ and La_0.7Sr_0.3MnO₃ thin films by chemical solution deposition. Thin films were prepared by spin-coating of single-crystal LaAlO₃ (100) substrates with precursor solutions of different concentrations and crystallized at 850°C. The structure of the thin film was found to be influenced by the concentration of the spin-coating solution. The thin film structure and epitaxy was clearly improved by reducing the concentration of the precursor solution. All thin films displayed excellent electrical properties such as a low resistivity and very high metal-insulator transition temperatures T _MI .     

Synthesis and Dielectric Characterization of Pyrochlore-Free Pb1−x Ba x (Zn1/3Nb2/3)O3 Ceramics

The dielectric properties and synthesis of pyrochlore-free lead zinc niobate ceramics with Ba substituting for Pb were investigated. Ba partial substitution for Pb was effective in stabilizing the perovskite structure in PZN ceramics, where the minimum amount of Ba substitution needed was about 20 mol%. The dielectric loss and the temperature coefficient of dielectric constant of PZN were reduced markedly with Ba substitution, while the dielectric constant was greater than 110. Good dielectric properties were obtained for the composition of Pb_0.3Ba_0.7(Zn_1/3Nb_2/3)O₃: = 133.5, tan = 0.0009, = –811 ppm/°C.     

Evaluation of Chemical Solution Deposited Ba x Sr 1−x TiO 3 Thin Films on LaAlO 3 in Tunable Microwave Devices

Epitaxial Ba x Sr 1 m x TiO 3 (BST) films grown on LaAlO 3 by several deposition methods have been tested in coupled microstrip phase shifters (CMPS) at frequencies from 10 to 24 GHz. To date the best performance for the devices has been achieved using Pulsed Laser Deposition (PLD). However, recently chemical solution deposition (CSD) methods such as sol-gel and Metal-Organic Chemical Liquid Deposition (MOCLD) have shown advances in fabricating BST films for tunable microwave applications. CSD processes promise improvements in cost, speed and area covered during BST film deposition. This paper compares over 35 BST films used in identical CMPS circuits. In this study, the highest measured figures of merit of phase shift per dB of loss for PLD, MOCLD and sol-gel CMPS are 49, 47 and 41°/dB respectively. While other phase shifter designs using BST films have surpassed these values, these data base of identical circuits allows us to compare the BST films. X-ray diffraction characterization for many of the BST films is also given.     

Deposition of large-area graded (Pb1−xLax)TiO3 thin films by pulsed laser depesition

Abstract

Thin films of the composition (Pb_1?xLa_x)TiO₃, PLT, with x=0.05, 0.10 and 0.15 were sequentially pulsed laser deposited on Pt(Si) substrates at 200°C, followed by post-annealing at 550–600°C in furnace to result in a film with graded composition. The ferroelectric properties of the graded materials are markedly different from those of the uniform thin PLT films. For down graded materials, which contain PLT5 composition (x=0.05) at the top and PLT 15 composition (x=0.15) at the bottom of the films, the hysteresis loops are slim and the width of the P-E curves increases with voltage cycling, attaining an equilibrium polarization states similar to the P-E properties of PLT 15 thin films. By contrast, the ferroelectric hysteresis properties reaches the same value as those of PLT5 thin films when the composition is up-graded.     

Pb(Mg1/3Nb2/3)O3 and (1 − x)Pb(Mg1/3Nb2/3)O3 − xPbTiO3 Relaxor Ferroelectric Thick Films: Processing and Electrical Characterization

The lead magnesium niobate [Pb(Mg_1/3Nb_2/3)O₃ or PMN], and its solid solutions with lead titanate (PbTiO₃ or PT), are of great interest because of their high electromechanical properties. At large PMN content, these materials exhibit relaxor characteristics with large electrostrictive strains and a large permittivity, while compositions near the morphotropic phase boundary present very interesting piezoelectric properties. So far, properties of these materials in ceramic, thin film and single-crystal form have been investigated. In this paper, we report on preparation and properties of pyrochlore free PMN and 0.65PMN-0.35PT thick films (thickness = 10 to 20 m). The films were prepared from ethyl cellulose ink by screen printing on alumina substrate. The influence of various parameters, such as powder characteristics, inks formulation and films sintering conditions, on films densification are discussed. The dielectric and electromechanical properties of the films were examined. Relaxor-like behaviour was clearly demonstrated in PMN films. The maximum relative permittivity for PMN film was 10000 (at 0.1 kHz), which is lower than in bulk ceramics (17800 at 0.1 kHz) prepared under the same conditions. For 0.65PMN-0.35PT, the maximum relative permittivity was around 15500 against 24000 in the bulk. Several parameters, which might be responsible for the lower permittivity, are discussed. Poled 0.65PMN-0.35PT thick films exhibit relatively large piezoelectric response (d ₃₃ up to 200 pm/V) and unipolar strains approaching 0.1%, making these films of interest for various actuator and transducer applications.     

Properties of CaTi1 − x Fe x O3 − δ Ceramic Membranes

CaCO₃, TiO₂ and Fe₂O₃ were mixed in the appropriate stoichiometric quantities and calcined at 1100C for 10 h. These powder mixtures were uniaxially pressed and sintered at temperatures ranging from 1350 to 1500_C for 2 h in order to obtain dense disk-shaped samples with nominal CaTi_{1 – x}Fe_xO_3– (x = 0.05, 0.15, 0.20, 0.40 and 0.60) compositions. Dilatometry and in situ high temperature powder X-ray diffraction analysis showed a good agreement on the thermal expansion behaviour of these materials between room temperature and 1000_C. The estimated linear thermal expansion coefficient is close to 13× 10^{– 6} K^{– 1} and is little affected by composition. No evidence for surface carbonation was detected in the infrared spectra collected on samples previously annealed in CO₂ atmospheres. The oxygen permeability measured at temperatures ranging from 750 to 1000_C goes through a sharp maximum for x = 0.20. This result is interpreted by structural differences related to change from disordered to ordered oxygen vacancies. The overall performance of CaTi_0.80Fe_0.20O_3– is compared to other mixed conducting materials.     

Ferroelectric Properties of Pb(Zr1 − x,Tix)O3 Prepared by Modified Metallo-Organic-Decomposition Process

Beneficial effect of nano-sized PZT powder incorporation on modifying the characteristics of Pb(Zr_0.52Ti_0.48)O₃, PZT films was demonstrated. The amorphous phase derived from metallo-organic-decomposition (MOD) process started to crystallize at a post-annealing temperature as low as 500°C and can withstand 650°C post-annealing temperature process without inducing the PbO-loss phenomenon. However, 500°C post-annealed PZT films still exhibit paraelectric properties, which can be ascribed to the co-existence of large proportion of amorphous phase, surrounding the crystalline phase. It needs at least 650°C post-annealing process to fully developed the pervoskite structure for PZT films. The remnant polarization (Pr) of the PZT films increases with the proportion of crystalline phase, achieving Pr = 24.9 μC/cm² for 650°C annealed films, with coercive field (Hc) around Ec = 373 kV/cm.     

Piezoelectric and Dielectric Properties of Pb(Zr x Ti1 − x )O3-Pb(Ni1/3Sb1/3Nb1/3)O3 Piezoelectric Ceramics

In this paper, piezoelectric and dielectric properties of 0.9PbZr_xTi_1–xO₃-0.1PbNi_1/3Sb_1/3Nb_1/3O₃ were studied as a function of Zr/Ti mole ratio(x) for application to piezoelectric actuator. Also, microstructure and crystalline phase are investigated by using SEM and XRD, respectively. As a results, the substitution of Sb5+ to B-site increases the piezoelectric and dielectric properties, and when Zr/Ti mole ratio is 49/51 and ternary mole ration is 0.1(0.9PbZr_0.49Ti_0.51O₃-0.1PbNi_1/3Sb_1/3Nb_1/3O₃), the corresponding composition were found belonging to the Morphotropic Phase Boundary region with electromechanical coupling coefficient(k_p), mechanical quality factor (Q_m), permittivity(_r) and piezoelectric strain constant(d₃₃) equaled to 63%, 360, 2000 and 470 pC/N, respectively. Sintering temperature was about 1150_C and Curie temperature was determined around 290_C.     

A comparative study of tunable Ba1−x Sr x TiO3 thin film capacitors prepared by rf-sputtering and liquid-phase deposition

Abstract

Ba_1?x Sr _x TiO₃ thin film capacitors have been successfully prepared using rf-sputtering and a metal organic deposition (MOD) method. The structure, microstructure and composition of the BSTO films are presented. Films grown on lanthanum aluminate LAO(100) showed c-axis preferred growth orientation. Broad paraelectric-to-ferroelectric transitions were observed in films prepared by both methods. The tunability of the capacitance by means of an appplied electric field is examined using various capacitor geometries. A decrease in the capacitance exceeding 75% at 77 K was obtained from the MOD deposited films under an electric field strength of 0.3 MV/cm. On the other hand, the tunability of the capacitance in the rf-sputtered films ranged from 5 to 10% at 77 K and at 20 kV/cm, while it exceeds 50% in some films. The results are compared with the predictions of Devonshire's phenomenological theory.     

DIELECTRIC AND PIEZOELECTRIC CHARACTERISTICS OF 0.07Pb (Mn1/3Nb2/3) O3 −0.10Pb (Ni1/3Nb2/3) O3− 0.83Pb(Zr0.48Ti0.52) O3 CERAMICS ACCORDING TO THE HEATING RATE

ABSTRACT

In this study, in order to develop the composition ceramics for low loss multilayer piezoelectric actuator, 0.07Pb (Mn_1/3Nb_2/3) O₃ ?0.10Pb (Ni_1/3Nb_2/3) O₃? 0.83Pb(Zr_0.48Ti_0.52) O₃ (abbreviated as PMN-PNN-PZT) ceramics were fabricated using Li₂CO₃, Bi₂O₃ and CuO as sintering aids and according to variation of heating rate. And also, their dielectric and piezoelectric properties were investigated. At the heating rate of 700°C/h and sintering temperature of 900°C, density, electromechanical coupling coefficient (kp), mechanical quality factor (Qm), dielectric constant (ε _r ) and piezoelectric constant (d₃₃) of PMN-PNN-PZT ceramics showed the excellent values of 7.67 g/cm³, 0.58, 1199, 1560 and 380 pC/N, respectively for low loss multilayer piezoelectric actuator application.     

Defect Chemical Modeling of (La, Sr)(Co, Fe)O3 − δ

Different defect chemical models for calculation of ionic and electronic defect concentrations are discussed regarding their applicability to transition metal perovskite-type oxides (ABO_{3 –} ) with large ranges of oxygen non-stoichiometry. A point defect model, which allows simultaneous consideration of three different B-site species concentrations as a function of the oxygen partial pressure is compared to a simple point defect model, considering only two different B-site species. Additionally, a model assuming electrons/holes as negative resp. positive electronic charge carriers is presented. Further, models involving association of point defects in different complexes are discussed. Examples are given for fits of experimental data of La_{1 – x}Sr_xBO_{3 –} (x = 0.6, B = Fe, Co) to selected models in the temperature range 700–900_C and oxygen partial pressures 10^{– 5} < pO₂/atm < 1.     

Microwave Dielectric Properties of Ferroelectric Pb(Zr1 − x Ti x )O3 Thin Films Using Interdigital Capacitors

Ferroelectric Pb(Zr_{1 ? x} Ti _x )O₃ (PZT) films were deposited on (001) MgO single crystals using sol-gel method. Structural properties and surface morphologies of PZT films were investigated using an X-ray diffractometer and a scanning electron microscopy, respectively. The dielectric properties of PZT films were investigated with the dc bias field of 0–135 kV/cm using interdigitated capacitors (IDC) which were fabricated on PZT films using a thick metal layer by photolithography and etching process. The small signal dielectric properties of PZT films were calculated by a modified conformal mapping method with low and high frequency data, such as capacitance measured by an impedance gain/phase analyzer at 100 kHz and reflection coefficient (S-parameter) measured by a HP 8510C vector network analyzer at 1–20 GHz. The IDC on PZT films exhibited about 67% of capacitance change with an electric field of 135 kV/cm at 10 GHz. These PZT thin films can be applied to tunable microwave devices such as phase shifters, tunable resonators and tunable filters.     

Development of ferroelectric Pb(ZrxTi1−x)O3 thin films by metallo-organic decomposition process and rapid thermal annealing

Polycrystalline Pb(Zr_0.5Ti_0.5)O₃ thin films with good ferroelectric properties have been prepared by metallo-organic decomposition (MOD) process, using acetate-based precursors, and followed by two different kinds of annealing process, independently, including oven annealing and rapid thermal annealing (RTA). The experimental procedures were described for the films deposited on Pt-coated silicon substrates. There were distinct differences between oven annealing and RTA process, in terms of structures, morphologies, and electrical properties of the films. The films with RTA process showed denser and smoother surface, finer grain sizes, and much higher dielectric constant (1200–1400), remnant polarization of 30–35 μC/cm² and lower coercive field of 65–85 kv/cm in the entire annealing temperature range of this study. At an annealing temperature of 550°C, RTA processed films showed identical XRD patterns of perovskite phase and clear ferroelectricity; however, it was not possible to realize the perovskite structure and ferroelectricity in the films oven-annealed at that temperature. These acetate-derived PZT films with RTA process were reproducible, showed high quality in uniformity and homogeneity.     

Piezoelectric characteristics of low temperature sintering Pb(Ni1/3Nb2/3)O3–Pb(Zr1/2Ti1/2)O3 ceramics as a function of Pb(Mn1/3Sb2/3)O3 substitution

In this study, in order to develop the composition ceramics for multilayer ceramic for ultrasonic nozzle and ultrasonic actuator application, Pb(Mn_1/3Sb_2/3)O₃ (abbreviated as PMS) substituted Pb(Ni_1/3Nb_2/3)O₃–Pb(Zr,Ti)O₃ (abbreviated as PNN-PZT) ceramics were fabricated using two-stage calcinations method and Li₂CO₃, Na₂CO₃ and ZnO as sintering aids, and their piezoelectric and dielectric characteristics were investigated. With the increase of the amount of PMS substitution, electromechanical coupling factor (k _p), and mechanical quality factor (Q _m) of specimens showed the maximum value at 3 mol% substituted specimen while dielectric constant (? _r) was decreased. At the sintering temperature of 900 °C, the density, ? _r, k _p, and Q _m of 3 mol% PMS substituted PNN-PZT composition ceramics showed the optimal values of 7.92 [g/cm³], 959, 0.584, and 1003, respectively, for low loss multilayer piezoelectric actuator application.     

Perovskite phase formation in sol-gel derived Pb(ZrxTi1−x)O3 thin films

Abstract

Thin films of lead zirconate titanate having the composition Pb_1.05(Zr_0.53Ti_0.47)O₃ were deposited by a solgel method on a set of crystalline and amorphous substrates. The thickness of the film was varied by controlling the sol concentration or by repeated coatings. Factors controlling phase formation in the films such as nature of the substrate material, film thickness, chemical composition of the film, heating rate and gaseous atmosphere during the heat treatment were studied. On glass substrates the pyrochlore phase was obtained in thin (0.4 um) films and the perovskite phase in thicker (>1.5 um) films. Crystalline substrates (except Si and stainless steel) yielded a perovskite phase in 0.6 um thick film. Low Zr/Ti ratio, rapid heating and introduction of nitrogen in the later stage of heat treatment also favoured the formation of the perovskite phase. It is shown that Pb deficiency in the film caused by diffusion of Pb into amorphous substrates or by other mechanisms is primarily responsible for inhibiting the pyrochlore to perovskite transformation. The initial crystallisation of the amorphous film into pyrochlore rather than a perovskite phase (as in powders) is proposed to be due to higher strain energy barrier which exists for the amorphous to perovskite transformation in the film.     

Luminescence and photocatalytic performance of Ca1−xTiO3:Pr3+ material

Abstract

Luminescent perovskite photocatalysts activated by Pr³⁺ were prepared by combustion. The structural phase, morphology, and chemical composition of the as-prepared photocatalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) analysis, and ultraviolet–visible (UV–vis) diffuse reflectance spectroscopy. The photocatalytic activities of the synthesized samples were investigated on the basis of the degradation of methylene blue (MB) under UV light irradiation. CaTiO₃:Pr³⁺ was obtained in high purity and good crystallinity with a perovskite structure. The degradation of the photocatalyst was fitted with pseudo-first-order kinetics according to the Langmuir–Hinshelwood model. Compared to CaTiO₃:Pr³⁺, Ca_1–xTiO₃:Pr³⁺ (x?=?0–0.3) multifunctional materials exhibit higher luminescence intensity and photocatalytic activity toward the degradation of MB. Ca_0.8TiO₃:0.1%Pr³⁺ exhibited the best performance.     

Influence of ion beam bombardment on characteristic of InGaN/GaN single quantum well grown by metal–organic chemical vapor deposition

The influence of ion beam bombardment on sapphire substrate was investigated on the electrical and optical characteristics of Indium–Gallium–Nitride/Gallium–Nitride (InGaN/GaN) single quantum well (SQW) structure. Ion bombardment of N⁺, He⁺, H⁺ ions were made on single crystal substrate of sapphire with dose of 1?×?10^14–17 ions/cm². The InGaN/GaN SQW was fabricated on the ion beam bombarded sapphire substrate in two-flow Metal Organic Chemical Vapor Deposition (MOCVD) equipment. The thickness of InGaN/GaN SQW was about 20 nm and the composition of InGaN/GaN SQW was found to be In_0.1Ga_0.9N. In PL spectra, it is found that InGaN/GaN SQW was emitted from 441.1 to 446.6 nm (2.8–2.7 eV). The highest mobility value of 118 cm²/V–S and the lowest carrier concentration of 3.41?×?10¹⁷/cm² was found for N of 10¹⁶ ions/cm² ion beam bombarded sample. The optimal condition for InGaN/GaN SQW on sapphire substrate of ion beam bombardment was deduced to be N⁺ ion dose of 10¹⁶ ions/cm².