Preparation of PZT Thick Films by an Interfacial Polymerization Method

Pb(Zr_0.53Ti_0.47)O₃ (PZT) films of 10 to 50 m in thickness were prepared by a new sol-gel process using an interfacial polymerization technique. The interfacial polymerization process is that an alkoxide precursor solution is poured on the surface of water in a container to form a gel film at the interface between the two immiscible liquids. The precursor solution was prepared by adding PZT alkoxide solution, PZT powders coated with Pb₅Ge₃O₁₁ (PG), and a surfactant into hexane solvent. After the polymerization at the interface, the gel films were gently placed on a silicon substrate by draining the water in the container. The gel films containing PZT powders were sintered at 950°C for 10 min to obtain crystallized PZT films. The remanent polarization of a PZT thick film was 33.1 C/cm². The piezoelectric d ₃₃ constant measured with a Mach-Zehnder interferometer was 225 pm/V and was independent of frequency from 0.2 to 3 kHz.     

Microstructure and ferroelectric properties of r.f. magnetron sputtering derived PZT thin films deposited on interlayer (PbO/TiO2)

Lead zirconate titanate (PZT) thin films were deposited on Pt/Ti/SiO₂/Si and interlayer/Pt/Ti/SiO₂/Si substrate by radio frequency (r.f.) magnetron sputtering with a Pb_1.1Zr_0.53Ti_0.47O₃ target. The crystallization of the PZT thin films was formed only by substrate temperature. When interlayer (PbO/TiO₂) was inserted between the PZT thin film and the Pt electrode, the grain growth and processing temperature of the PZT thin films were considerably improved. Compared to PZT/Pt structure, the dielectric constant and polarization properties of the PZT/interlayer/Pt structure were fairly improved. In particular, PZT/interlayer/Pt at the substrate temperature of 400 °C showed prevalent ferroelectric properties (_r=475.97, tanδ=0.0591, P_r=23 μC/cm²). As a result of an X-ray photoelectron spectroscopy (XPS) depth-profile analysis, it was found that PZT/interlayer/Pt deposited only by substrate temperature without the post-annealing process via r.f. magnetron sputtering method remained independent of each other regardless of substrate temperatures.     

Preparation and characterization of thin TiO2-films on gold/mica

Flat and highly (111) oriented gold and silver films were prepared by physical vapour deposition (PVD) using optimized deposition parameters. On these films, which were characterized with atomic force microscopy (AFM), scanning tunneling microscopy (STM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), titanium dioxide films were deposited by electron beam evaporation and dip coating. Dip coating from titanium tetraisopropoxide solutions resulted in films with different morphology and coverage depending on the alkoxide concentration (0.009 mol/L – 0.60 mol/L) and the post-treatment. Scanning electron microscopy (SEM) and AFM revealed that the deposited TiO₂ consists of amorphous, highly porous islands when the applied alkoxide concentration is high (0.05 mol/L – 0.6 mol/L). At higher temperatures these amorphous TiO₂ islands sintered significantly and crystallized to anatase. In contrast, transparent TiO₂ films were obtained from low concentrated alkoxide solutions (< 0.01 mol/L) which covered the whole substrate, similar to electron beam evaporated thin films. Sputter profiles with ion scattering spectroscopy (ISS) indicated that the film thickness is in the range of 2 nm when alkoxide solutions with a concentration of 9 mmol/L are used. The deposition of TiO₂ by electron beam evaporation normally resulted in significantly reduced TiO₂ films, completely oxidized ones were obtained when deposition was performed at elevated oxygen partial pressures (p(O₂) > 2 × 10^–5 mbar).     

Microstructure and properties of sol-gel derived Pb(Zr<Subscript>0.3</Subscript>Ti<Subscript>0.7</Subscript>)O<Subscript>3</Subscript> thin films on GaN/sapphire for nanoelectromechanical systems

Highly (111) oriented, phase-pure perovskite Pb(Zr_0.3Ti_0.7)O₃ (or PZT 30/70) thin films were deposited on single-crystal, (0001) wurtzite GaN/sapphire substrates using the sol-gel process and rapid thermal annealing. The phase, crystallinity, and stoichiometry of annealed PZT films were evaluated by X-ray diffraction and Rutherford backscattering spectroscopy. The atomic force microscopy revealed a smooth PZT surface (rms roughness ∼1.5 nm) with striations and undulations possibly influenced by the nature of the underlying GaN surface. The cross-sectional field-emission scanning electron microscopic images indicated a sharper PZT/GaN interface compared to that of sol-gel derived PZT on (111) Pt/TiO₂/SiO₂/(100) Si substrates. The capacitance-voltage (C-V) characteristics for PZT in the Pt/PZT/GaN (metal-ferroelectric-semiconductor or MFS) configuration were evaluated as a function of annealing temperature and applied voltage. The observed C-V hysteresis stemmed from trapped charge at defect sites within PZT. Also, the lower capacitance density (C/A = 0.35 μF/cm², where A is the area of an electrode) and remnant polarization (P _r ∼ 4 μC/cm²) for PZT in the MFS configuration, compared to the values for PZT in the MFM configuration (Pt/PZT/Pt), were attributed to the high depolarization field within PZT.     

Synthesis of titanium dioxide nanocrystalline layers using hexaprismatic shaped μ-oxo Ti(IV) alkoxo carboxylates as precursors

The reaction between Ti(OR)₄ (R = ⁿBu, ⁱBu, SiMe₃) and 2,2-dimethylpropionic acid lead to the formation of hexanuclear μ-oxo titanium(IV) alkoxo carboxylato complexes of the general formula [Ti₆O₆(OR)₆(OOC^tBu)₆]. Thermal decomposition pathways of these compounds and their potential application in the preparation of TiO₂ nanolayers using chemical vapor deposition (CVD) methods have been discussed. The type of the alkoxide ligands causes differences in the thermolysis pathway, and the type of the volatile decomposition products. Among the examined complexes only [Ti₆O₆(OR)₆(OOC^tBu)₆] (R = ⁱBu, SiMe₃) show promising properties for their application as precursors in CVD methods. The TiO₂ films were grown in a wide range of substrate temperatures (653–873 °K), under the total reactor pressure 2.0–3.0 mbar. The crystallinity and the composition of layers were analyzed by X-ray diffraction (XRD). It was found that the formation of TiO₂ amorphous, anatase or rutile films depends on the deposition temperature and gas phase composition.     

Preparation and Optical Characterization of Sol-Gel Deposited Pb(Zr0.45Ti0.55)O3 Films

Homogeneous crack-free lead zirconate titanate (Pb(Zr_0.45Ti_0.55)O₃: PZT 45/55) films were prepared by a chemically modified sol-gel process using lead acetate trihydrate, zirconium n-propoxide, and titanium isopropoxide precursors. The coating solutions were modified by the addition of diethanolamine. Single and multilayer films were deposited with a 2000 rpm spin rate on fused silica and MgO(100) substrates. Multiple spin coating with an intermediate heat treatment in air at 400°C for 3 min between coatings was performed to obtain films up to 2 m in thickness. The formation of the tetragonal perovskite structure was found to depend on the intermediate firing temperature, final annealing temperature, and annealing time. A 650°C rapid thermal annealing treatment in oxygen was required to crystallize the PZT film into the perovskite structure. The films were characterized using optical spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and thermo-gravimetry and differential scanning calorimetry (TG-DSC). The optical constants of the PZT films were evaluated from spectral transmittance and reflectance measurements. Optical constants are presented over the visible and near infrared region.     

Spinnability and rheological properties of sols derived from Si(OC2H5)4 and Zr(O-nC3H7)4 solutions

The shape of the polymers in the mixed alkoxide solutions of Si(OC₂H₅)₄ and Zr(n-OC₃H₇)₄ with various water contents (1, 2, 4, and 8 in molar ratio to alkoxide, r) and catalysts was examined by rheological measurements, and its relation with fiber drawing behavior of the solutions was described. It was found that fibers could be drawn in the viscosity range 1–100 P from the acid-catalyzed solutions with lower water contents of the molar ratio H₂O/alkoxide, r2. On the other hand, no fiber could be drawn from the acid-catalyzed solutions including a large amount of water (r4) and the base-catalyzed solutions.The relation between the intrinsic viscosity [] and the number average molecular weight M_n, namely []=KM _n ^a , has shown that the acid-catalyzed spinnable solutions (r=1 and 2) have linear polymers where the exponent a's are about 0.56 and 0.81, whereas non-spinnable solutions (r=4 and 8) have three dimensional network polymers or spherical particles where the exponent a's are 0.41–0.51 and 0.35.     

Effect of Niobium Modifications to PZT (53/47) Thin Films Made by a Sol-Gel Route

Niobium-modified lead zirconate titanate thin films (PNZT) with nominal compositions, Pb_(1–0.5x) (Zr_0.53 Ti_0.47)_1–x Nb _x O₃:x = 0.02–0.07, have been prepared using a diol based sol-gel route. Single-layer (0.5 m) films were fabricated on platinised silicon substrates by spin-coating. The effect of niobium additions with regard to phase development, microstructure, and ferroelectric and dielectric properties were investigated for different annealing temperatures. For comparison, unmodified PZT films were also prepared. Niobium substitution increased the crystallisation temperatures for perovskite PNZT phase formation. The values of remanent polarisation P _r and dielectric constant _r were found to decrease with the introduction of Nb. For example, in films heated at 700°C for 15 min, the P _r value of an unmodified PZT film was 31 C cm^–2, compared to 17 C cm^–2 for an x = 0.05 PNZT film, whilst respective relative permittivity values fell from 1190 to 600. The highest Nb concentration film, x = 0.07, did not display any switchable polarisation characteristics, which is consistent with high levels of intermediate pyrochlore phase.     

Single-step sol-gel deposition and dielectric properties of 0.4 μm thick, (001) oriented Pb(Zr,Ti)O<Subscript>3</Subscript> thin films

Single-step sol–gel deposition was attempted for realizing submicron thick, (001) oriented Pb(Zr_0.53Ti_0.47)O₃ (PZT) thin films, using an alkoxide solution containing polyvinylpyrrolidone (PVP). A solution of molar composition, Pb(NO₃)₂:Zr(OC₃H₇ ⁿ)₄:Ti(OC₃H₇ ⁱ)₄:PVP:H₂O:CH₃COCH₂COCH₃:CH₃OC₂H₄OH:C₃H₇ ⁿOH = 1.1:0.53:0.47:0.5:5:0.5:22:0.98, was prepared as a coating solution. Gel films were prepared on Pt(111)/TiO₂/SiO₂/Si(100) substrates by spin-coating, and calcined at 350 °C and annealed at 650 °C either in an electric furnace or in a near-infrared (IR) furnace. When calcined in the near-IR furnace, the films became (001) oriented on annealing. When calcined in the electric furnace, on the other hand, the films became randomly oriented on annealing. These observations indicate that the heating the gel films from the substrate side in the calcination step at 350 °C induces crystallographic orientation in the annealing step at 650 °C. The effects of the heating methods on the thermal decomposition of the gel films, and the microstructure and dielectric properties of the fired films were studied. Finally 0.4 μm thick, (001) oriented PZT films could be successfully prepared by non-repetitive, single-step deposition. The oriented film thus obtained had the remnant polarization 2P _r of 39 μC/cm² and the dielectric constant ε′ of 960 ± 169.     

Preparation and Characterization of a Sol-Gel Prepared Ferroelectric Sandwich Structure

A novel silicon-based PbTiO₃/Pb(Zr,Ti)O₃/PbTiO₃ (PT/PZT/PT) sandwich structure has been prepared using a sol-gel method. The annealing temperature is greatly reduced compared with those structures without PT layers. Capacitance-voltage (C-V), leakage current-voltage (I-V), polarization-field (P-E), dielectric-frequency response and polarization fatigue of the sandwich structure are examined. The relative dielectric constant, the coercive field and the remanent polarization of the PZT films are measured to be about 900, 18 kV/cm and 16 C/cm² respectively. The current density is less than 5 × 10^–9 A/cm² below 200 kV/cm. The dielectric constant of the structure remains constant at low frequency, and decreases to some degree at high frequency. The retained polarization does not change significantly after 8 × 10⁹ read/write cycles. The PZT films are proved to have very good dielectric and ferroelectric properties. The new PT/PZT/PT sandwich structure can be valuable for memory devices and other applications.     

Formation of perovskite phase mixed metal oxides via thermal decomposition of metal-organic complexes with bifunctional ligands

Single-source metal precursors designed to form crystalline perovskite phase mixed metal oxides at low temperatures have been synthesized using -hydroxycarboxylates and alkoxides as ligands. Divalent salts of Ba, Sr, Ca and Pb, [A(O₂CCR₂OH)₂], R = H, Me, were formed from the reaction between ACO₃ and HO₂CCR₂OH in which the hydroxyl group is free to react with metal alkoxide compounds B(OR)₄ where B=Ti, Zr, Sn. These compounds react to eliminate two equivalents of alcohol producing precursors with fixed stoichiometry as shown by the equation: A(O₂CCR₂OH)₂+B(OR)₄ A(O₂CCR₂O)₂B(OR)₂+2HOR. The reaction product is only slightly soluble in pyridine, however upon hydrolysis these compounds form clear solutions from which yellow powders can be isolated by removal of the solvent. Thermolysis of these powders in the temperature range 300–350°C yields perovskite ABO₃. Aqueous solutions of these powders can also be used to form sub-micron sized particles of ABO₃ materials via aerosol processing techniques. In control experiments it was shown that Pb(O₂CCH₂OPh)₂ does not react with metal alkoxide compounds. As a result perovskite PbTiO₃ is not formed below 550°C. Solutions for spin coating thin films can be formed by dissolution of the powder in ethanol, but the crystallization behavior is quite different compared to the bulk powders.     

Electrical Properties of Transparent Doped Oxide Films

In the present study n-type and p-type transparent conductive TiO₂ films were prepared by using sol-gel method. The n-type TiO₂ films were obtained by using Ti(OC₃H ₇ ⁱ )₄ solutions co-doped with Ru and Ta. The films were uniform and transparent in all the conditions, and their crystalline phases were anatase when HCl or HNO₃ was used as a catalyst. The resistivity decreased with increasing Ta content and increased with increasing Ru content. Most of the films showed resistivity minima at a heat-treatment temperature of 700°C. The lowest resistivity of 10¹ 10² cm was attained. The p-type TiO₂ films were obtained by using Ti(OC₃H ₇ ⁱ )₄ solutions co-doped with Co and Nb (Sb). The films were also uniform and transparent when AcAc was used, while samples heat-treated at 800°C became opaque when HCl was added. Rutile single phase appeared when the films were heat-treated at 700°C. Logarithmic resistivity of films co-doped with Co and Nb was directly proportional to the reciprocal absolute temperature. On the other hand, the slopes for films co-doped with Co and Sb were different below and above 200°–220°C. The activation energy at the low-temperature region is as low as 0.17 eV, and the resistivity at room temperature is 10⁴ 10⁵ cm.     

Effects of niobium doping on lead zirconate titanate films deposited by a sol–gel route

Niobium (Nb)-doped lead zirconate titanate (PZT) films have been prepared on platinized silicon substrates using a sol–gel method. The Zr/Ti ratios of the films are 53/47 and 40/60, and the Nb doping level ranges from 0 mol% to 3 mol%. Similar to the cases in bulk ceramics, after the doping with Nb, the remanent polarization P_r, effective transverse piezoelectric coefficients e_31,c and pyroelectric coefficient p of the PZT films increase; but the longitudinal effective piezoelectric coefficient d_33,c remains roughly unchanged. At the optimum Nb doping levels, the observed P_r, −e_31,c and p reach a maximum value of 30 μC/cm², 18 C/m² and 350 μC/m² K, respectively, for the PZT (53/47) films, and 37 μC/cm², 7.9 c/m² and 370 μC/m² K for the PZT (40/60) films. Our results also reveal that there exist linear relations between p, e_31,c/ε_r and P_r.     

Chemical solution processing and characterization of Ba(Zr,Ti)O<Subscript>3</Subscript>/LaNiO<Subscript>3</Subscript> layered thin films

Ba(Zr,Ti)O₃/LaNiO₃ layered thin films have been synthesized by chemical solution deposition (CSD) using metal-organic precursor solutions. Ba(Zr,Ti)O₃ thin films with smooth surface morphology and excellent dielectric properties were prepared on Pt/TiO _x /SiO₂/Si substrates by controlling the Zr/Ti ratios in Ba(Zr,Ti)O₃. Chemically derived LaNiO₃ thin films crystallized into the perovskite single phase and their conductivity was sufficiently high as a thin-film electrode. Ba(Zr,Ti)O₃/LaNiO₃ layered thin films of single phase perovskite were fabricated on SiO₂/Si and fused silica substrates. The dielectric constant of a Ba(Zr_0.2Ti_0.8)O₃ thin film prepared at 700°C on a LaNiO₃/fused silica substrate was found to be approximately 830 with a dielectric loss of 5% at 1 kHz and room temperature. Although the Ba(Zr_0.2Ti_0.8)O₃ thin film on the LaNiO₃/fused silica substrate showed a smaller dielectric constant than the Ba(Zr_0.2Ti_0.8)O₃ thin film on Pt/TiO _x /SiO₂/Si, small temperature dependence of dielectric constant was achieved over a wide temperature range. Furthermore, the fabrication of the Ba(Zr,Ti)O₃/LaNiO₃ films in alternate thin layers similar to a multilayer capacitor structure was performed by the same solution deposition process.     

Ferroelectric Properties of New Chemical Solution Derived SBT Thin Films for Non-Volatile Memory Devices

Ferroelectric SBT (Sr/Bi/Ta = 0.8/2.3/2) thin films on Pt/ZrO₂/SiO₂/Si were successfully prepared by using an alkanolamine modified chemical solution deposition method. Acetic acid as a solvent led to the formation of water in the solution, which might continuously induce the hydrolysis and condensation of the precursors, leading to reducing the stability of the solution with aging time. It was observed that alkanolamine provided the stability to the SBT solution by retarding the hydrolysis and condensation rates. This solution could be used as long as up to 30 days without any appreciable change of the solution properties. The typical hysteresis loop of SBT thin films was obtained at 2 V, and it was fully saturated even below an applied voltage of 3 V (2P_r 16 C/cm²). The measured 2P_r value of the SBT thin film at 5 V was almost 20 C/cm². Fatigue and breakdown characteristics of the films, measured at 5 V, showed a stable behavior, and negligible degradation was observed up to 10¹⁰ cycles.     

Synthesis of Calcium Phosphates by PO(OH)x(OBut)3−x and CaO2C2H4

In this work, an alkoxide solution route to synthesize Ca phosphates was developed. For the precursors, a CaO₂C₂H₄ solution was prepared by dissolving Ca metal powder into ethylene glycol, and a PO(OH)_x(OBut)_3–x solution was prepared by dissolving P₂O₅ inton -butanol under reflux conditions. In order to obtain a mixed solution of the two precursors, acetic acid was used as an additive. The experimental results show that (1) -2CaO · P₂O₅, -3CaO · P₂O₅, and hydroxyapatite can be easily synthesized by converting the corresponding mixed solutions to powder products in a hot plate, and calcining the as prepared products at 1100°C; (2) acetic acid behaves as a good agent for controlling the reactions between the two precursors by modifying the CaO₂C₂H₄ species in solution and decreasing the reactivity of the PO(OH)_x(OBut)_3–x species.     

Preparation of BaCe0.8Gd0.2O3−δ by the citrate method and its application in the synthesis of ammonia at atmospheric pressure

BaCe_0.8Gd_0.2O_3– is a kind of high-temperature proton conductor. A precursor of BaCe_0.8Gd_0.2O_3– solid electrolyte was synthesized by the citrate method and characterized by thermal analysis (thermogravimetric analysis–differential thermal analysis), X-ray diffraction and scanning electron microscopy. Using the sintered samples as a solid electrolyte and silver–palladium alloy as electrodes, we synthesized ammonia from nitrogen and hydrogen at atmospheric pressure in the solid-state proton-conducting-cell reactor. The rate of evolution of ammonia was up to 3.09×10^–9 mol s^–1 cm^–2.     

Preparation of La0.75Sr0.25MnO3 Nano-Phase Powders and Films from Alkoxide Precursors

The first purely alkoxide-based sol-gel route to nano-phase powders and thin films of perovskite La_0.75Sr_0.25MnO₃ is described. The phase and microstructure evolution on heat treatment of free gel films to form the target nano-phase oxide were investigated by TGA, IR spectroscopy, powder XRD, SEM and TEM-EDS. The xerogel consisted of a hydrated oxo-carbonate, without remaining alkoxo groups or solvent. Heating at 5°C·min^–1 decomposed the carbonate groups and yielded the pure perovskite La_0.75Sr_0.25MnO₃ at 760°C. The cell dimensions were virtually unchanged from the first observation of perovskite at 680°C, to 1000°C, 4 h. The monoclinic cell of La_0.75Sr_0.25MnO₃ obtained at 1000°C, 4 h, had the dimensions a = 5.475(1), b = 5.504(2), c = 7.771(1) Å, = 90.50(2), fitting the literature data quite well. Crack-free, homogenous, 150 nm thick La_0.75Sr_0.25MnO₃ films were prepared by spin-coating Si/SiO₂/TiO₂/Pt and polycrystalline -Al₂O₃ substrates with a 0.6 M alkoxide solution, followed by heating at 5°C·min^–1 to 800°C, 30 min.     

The Sol-Gel Chemistry of Ferroelectric SrBi2Ta2O9 Thin Layers

A characterization of sol-gel precursors of SrBi₂Ta₂O₉ (SBT) has been carried out. Each molecular precursor, [SrBi_2+x Ta₂(OCH₂CH₂OCH₃)₁₈] _n (1) (x = 0.0, 0.2, and 0.4) and [SrTa₂(OEt)(O ⁱ Pr)₁₁( ⁱ PrOH)₂] (2) was prepared from the mixtures of Bi(OR)₃, Sr(OR)₂, and Ta(OR)₅ (R = Et, ⁱ Pr, and CH₂CH₂OCH₃), respectively. ¹H and ¹³C NMR spectroscopy and powder X-ray diffractometry have been used to characterize precursor molecules and their oxides, respectively. Especially, X-ray single crystal studies of complex 2 show that the molecule is made up of three octahedra; the central [SrO₆] octahedron is sharing two neighboring edges with the peripheral [TaO₆] ones. The SBT film derived from the precursor 1 presents outstanding ferroelectric properties (P _r = 9 C/cm²; E _c = 0.8 V).     

Transport and electrocatalytic properties of La0.3Sr0.7Co0.8Ga0.2O3−δ membranes

Incorporation of gallium into the perovskite lattice of La_0.3Sr_0.7CoO_3– leads to increasing unit cell volume and to decreasing thermal expansion, total conductivity and oxygen permeability. At 973–1223 K, the oxygen permeation fluxes through La_0.3Sr_0.7Co_0.8Ga_0.2O_3– ceramics with 96.5% density are determined by the bulk ionic conduction and surface exchange rates. The total conductivity of La_0.3Sr_0.7Co_0.8Ga_0.2O_3–, predominantly p-type electronic, exhibits an apparent pseudometallic behavior due to oxygen losses on heating, whereas the p(O₂) dependencies of the conductivity and Seebeck coefficient suggest a small-polaron mechanism of hole transport. The average thermal expansion coefficients in air are 15.9×10^–6 K^–1 at 360–710 K and 27.9×10^–6 K^–1 at 710–1030 K. On decreasing oxygen pressure down to 4–30 Pa at 973–1223 K, perovskite-type La_0.3Sr_0.7Co_0.8Ga_0.2O_3– transforms into a brownmillerite-like modification, whose electrical properties are essentially p(O₂) independent. Further reduction results in the decomposition of the brownmillerite into a multiphase oxide mixture at p(O₂)=8×10^–10–3×10^–4 Pa, and then in the segregation of metallic cobalt. Due to surface-limited oxygen transport, La_0.3Sr_0.7Co_0.8Ga_0.2O_3– membranes are, however, kinetically stable under an air/CH₄ gradient up to 1223 K. The conversion of dry methane in model membrane reactors increases with oxygen permeation flux and temperature, but yields high CO₂ concentrations (>90%), indicating a dominant role of complete CH₄ oxidation on the membrane surface.