Processing of Oriented K(Ta,Nb)O3 Films Using Chemical Solution Deposition

K(Ta,Nb)O₃ (KTN) thin films have been prepared by the chemical solution deposition method. KTN precursors consisted of a uniform mixture of K[Ta(OC₂H₅)₆] and K[Nb(OC₂H₅)₆] with interaction at the molecular level. Perovskite KTN thin films with the desired composition (Ta/Nb = 65/35, 50/50, and 35/65) were synthesized from the precursor solutions by the dip coating method. KTN thin films with (100) preferred orientation were successfully synthesized on MgO(100) and Pt(100)/MgO(100) substrates. X-ray pole figure measurements showed that grains of KTN films had a prominent three-dimensional regularity on MgO(100) and Pt(100)/MgO(100) surfaces. The Curie temperatures of KTN films decreased with increasing Ta/Nb ratio. Typical P-E hysteresis loops were observed for KTN thin films of three compositions on Pt(100)/MgO(100) substrates. The values of remanent polarization ( P _r) of KTN films increased as the Ta/Nb ratio changed from 65/35 to 35/65.     

Preparation of Potassium Tantalate Niobate by Sol–Gel Method

Perovskite potassium tantalate niobate (KTN) powders and thin films were synthesized from a metal alkoxide solution. Homogeneous KTN coating solutions were prepared from KOC₂H₅, Ta(OC₂H₅)₅, and Nb(OC₂H₅)₅ in absolute ethanol. The precursor crystallized to pyrochlore at ∼ 650°C, and then to perovskite at ∼ 750°C, depending upon Ta:Nb ratio. H₂O vapor during calcination was found to play a prominent role in the direct and predominant crystallization of perovskite films with preferred orientation. Highly oriented KTN films of perovskite structure were successfully prepared on MgO (100) substrates at 675°C.     

Synthesis of Ba2NaNb5O15 Powders and Thin Films Using Metal Alkoxides

Transparent and highly oriented Ba₂NaNb₅O₁₅ (BNN) thin films have been prepared by using metal alkoxides. A homogeneous precursor solution was prepared by the controlled reaction of NaOC₂H₅, Nb(OC₂H₅)₅, and barium metal. The BNN precursor included a molecular-level mixture of NaNb(OC₂H₅)₆ and Ba[Nb(OC₂H₅)₆]₂ in ethanol. The alkoxy-derived powder crystallized to a low-temperature phase, and then transformed to orthorhombic BNN (tungsten bronze) at 600°C. BNN precursor films on substrates crystallized to orthorhombic BNN at 800°C via the low-temperature phase. Highly (002) oriented BNN films of tungsten bronze structure were successfully prepared on MgO (100) substrates at 700°C by using BNN underlayer.     

Fabrication and Characterization of a (100) Three-Axis-Oriented Single-Crystal (Ba0.7Sr0.3)TiO3 Thin Film Prepared by the Chemical Solution Deposition Method

Epitaxially grown single-crystal perovskite (100) three-axis-oriented (Ba_0.7Sr_0.3)TiO₃ thin films were prepared on a (100) platinum-coated (100) magnesium oxide (MgO) single-crystal substrate by the chemical solution deposition method using a solution derived from Ba(CH₃COO)₂, Sr(CH₃COO)₂, and Ti(O- i -C₃H₇)₄.
The growth of the film was found to depend on the annealing condition. A (Ba,Sr)TiO₃ thin film annealed at 1073 K was found to be a single crystal by transmission electron microscope. The single-crystal film exhibited a (100) three-axis orientation that followed the (100) orientation of the Pt substrate, as observed from an X-ray pole figure measurement and selected area electron diffraction patterns.     

Synthesis of 0.4Pb(Mg1/3Nb2/3)O3–0.3Pb(Mg1/2W1/2)O3–0.3PbTiO3 Ceramics by Metal Alkoxide Method, and Its Dielectric Properties

0.4Pb(Mg_1/3Nb_2/3)O₃–0.3Pb(Mg_1/2W_1/2)O₃–0.3PbTiO₃+ x MgO ( x = 0 to 0.04) were prepared by a metal alkoxide method. The percent of perovskite phase of the calcined powders increased with increased calcination temperatures. About 89% of perovskite phase was obtained at 1050°C. The dielectric constant of the pellets fired at 1100°C was increased by the addition of 10 wt% excess Mg(OC₂H₅)₂ and had a maximum value of 7532 at 1 kHz.     

Modified Sol-Gel Process for the Production of Lead Titanate Films

A modified sol-gel process has been developed for the production of thin films of PbTiO₃. The new route uses the mixed ligand complex titanium diisopropoxide bis(acetylacetonate), Ti(OC₃H₇)₂(CH₃COCHCOCH₃)₂, in place of titanium tetraisopropoxide, Ti(OC₃H₇)₄. For base-catalyzed conditions, the maximum thickness of crack-free PbTiO₃ films after one high-temperature firing cycle is 1 μm. This value represents a twofold increase in thickness over that obtained using existing sol-gel routes based on Ti(OC₃H₇)₄.     

Synthesis of Potassium Niobate from Metal Alkoxides

Preparation of potassium niobate from metal alkoxides was investigated. Potassium-niobium ethoxide, KNb(OC₂H₅)₆, and potassium-niobium propoxide, KNb(OC₃H₇)₆, were synthesized and subsequently hydrolyzed using several water concentrations (0.75 to 6.0 mol of water/(mol of alkoxide)). Rapid precipitation of potassium-deficient particles occurred when higher concentrations of water were used. This resulted in the formation of a multiphase material after calcination, as X-ray diffraction showed the presence of both KNbO₃ and potassium-deficient oxide phases(s). Single-phase KNbO₃ could be prepared by two methods: (1) hydrolysis of KNb(OC₃H₇)₆/propanol solutions using 1 mol of water (per mole of propoxide) added as a water/propanol solution and (2) hydrolysis of KNb(OC₂H₅)₆/ethanol solutions using 1 mol of water (per mole of ethoxide) added as a water/methanol solution. The latter method provided advantages of low calcination temperature for the formation of single-phase KNbO₃ and low weight loss after calcination.     

Proton Conductivity in Zr4+-Ion-Doped P2O5–SiO2 Porous Glasses

The effect of zirconium ions on glass structure and proton conductivity was investigated for sol-gel-derived P₂O₅–SiO₂ glasses. Porous glasses were prepared through hydrolysis of PO(OCH₃)₃, Zr(OC₄H₉)₄, and Si(OC₂H₅)₄. Chemical bonding of the P⁵⁺ ions was characterized using ³¹P-NMR spectra. The phosphorous ions, occurring as PO(OH)₃ in the ZrO₂-free glass, were polymerized with one or two bridging oxygen ions per PO₄ unit with increased ZrO₂ content. The chemical stability of these glasses was increased significantly on the addition of ZrO₂, but the conductivity gradually decreased from 26 to 12 mS/cm at room temperature for 10P₂O₅·7ZrO₂·83SiO₂ glass. A fuel cell was constructed using 10P₂O₅·5ZrO₂·85SiO₂ glass as the electrolyte; a power of ∼4.5 mW/cm² was attained.     

Effect of Low-Energy Accelerated Ion Bombardment on the Properties of Metal-Organic Decomposition Derived SrBi2(Ta,Nb)2O9 Thin Films Processed at Low Temperature

Ferroelectric SrBi₂(Ta,Nb)₂O₉ (SBTN) thin films were deposited on Pt (200 nm)/TiO _x (40 nm)/SiO₂ (100 nm)/Si substrates by metal-organic decomposition. The effects of bombardment from accelerated argon and oxygen ions on the properties of SBTN thin films were investigated. It was found that the argon ion bombardment could decrease the crystallization temperature owing to the increase of internal energy of the films. Also, the oxygen vacancies at the interface between the SBTN film and platinum bottom electrode or at grain boundaries in the film were passivated through the oxygen ion treatment, resulting in the improved electrical properties. By optimizing the process parameters and using bombardment of accelerated argon and oxygen ions, SBTN films with good ferroelectric and electrical properties could be obtained, at a temperature as low as 650°C.     

Structural Investigations of Prehydrolyzed Precursors Used in the Sol-Gel Processing of Lead Titanate

A variety of titanate gels were prepared from lead acetate and titanium isopropoxide in methoxyethanol. In the present study, ¹H and ¹³C Fourier transform-nuclear magnetic resonance and mass spectroscopic techniques were used to identify the structure of the lead and titanium precursors formed from lead acetate and titanium isopropoxide, respectively, when refluxed in methoxyethanol. The lead and titanium precursors were determined to be Pb(OOCCH₃) (OC₂H₄OCH₃). x H₂O, where x < 0.5, and Ti₂(OC₂H₄OCH₃)₈, respectively. Similar spectroscopic procedures were applied to identify the lead titanium complex formed from the reaction between lead and titanium precursors.     

Fine Patterning and Characterization of Gel Films Derived from Methyltriethoxysilane and Tetraethoxysilane

Pregrooves of 1.6 µm pitch for optical data storage have been embossed successfully by pressing a stamper against x CH₃Si(OC₂H₅)₃(100 - x )Si(OC₂H₅)₄-derived gel films (60 ≤ x ≤ 100 mol%) on glass-disk substrates of 130 mm diameter. When x is <40 mol%, the resultant films are too hard to emboss patterns uniformly. The shrinkage of the patterns is ∼4% for all the films when 60 lessthan equal to x lessthan equal to 100 mol%, even after heat treatment at 350°C, so that the nearly net negative shape of the stamper is preserved. The methyl groups in the films decompose at temperatures from 500° to 600°C.     

Compositional Inhomogeneity in Li- and Ta-Modified (K, Na)NbO3 Ceramics

Compositional inhomogeneity is examined in Li- and Ta-modified potassium sodium niobate (K,Na)NbO₃ perovskite ceramics. The inhomogeneous distribution of the A-site (K and Na) and B-site (Nb and Ta) cations is found to be correlative. The inhomogeneity could not be eliminated by prolonged high-temperature annealing in samples prepared by direct mixing of alkaline carbonates and Ta and Nb oxides. In contrast, the precursor method, where a (Nb _x Ta_{1− x} )₂O₅ solid solution was first formed, led to a considerably improved compositional homogeneity and appreciably enhanced dielectric, ferroelectric, and piezoelectric properties. Our results suggest that more attention needs to be paid toward controlling the compositional fluctuation of this complex solid solution system.     

Synthesis of Oriented Ba2NaNb5O15 (BNN) Thin Films from an Alkoxy-derived Precursor

Ba₂NaNb₅O₁₅ (BNN) thin films with a tungsten bronze structure were fabricated using a precursor solution that was synthesized from barium, sodium, and niobium alkoxides. Highly (002)-oriented BNN films were prepared successfully on Pt(100)/MgO(100) substrates at 700°C, using a BNN underlayer. X-ray pole-figure measurement showed that the BNN films that crystallized on Pt(100)/MgO(100) substrates had two in-plane orientations. The remanent polarization and coercive field of the BNN film (thickness of 1.0 µm) that was crystallized at 700°C were 12.3 µC/cm² and 101 kV/cm, respectively, at –150°C (123 K). BNN films on fused silica substrates exhibited second harmonic generation upon irradiation with 1064 nm light.     

Synthesis and Properties of Dielectric Ceramics from Metallo-Organic Precursors through the Solid-State Reaction of Mixed Gels

A perovskite structure of 0.4Pb(Mg_1/3Nb_2/3)O₃·0.3Pb(Mg_1/2W_1/2)O₃·0.3PbTiO₃ was prepared from metallo-organic precursors through the solid-state reaction of the mixed gels. Three types of mixed gels were crystallized to obtain PbTiO₃, MgNb₂O₆, and MgWO₄ powders. These powders were calcined at 900°C after mixing with a stoichiometric amount of Pb(CH₃COO)₂·3H₂O. The dielectric constant of the ceramic fired at 900°C was improved by adding an excess of 10 mol% Mg(OC₂H₅)₂, and the ceramic achieved X7T specification of the Electric Industries Association standard. The dielectric loss was reduced by adding an excess of 5 mol% Pb(CH₃COO)₂·3H₂O.     

Ink Jet Printing of Microdot Arrays of Mesostructured Silica

We report a process for preparing microdot arrays of SiO₂ from a tetraethoxysilane precursor containing either a cationic (CTAB) or non-ionic surfactant. Controlling the ink jet deposition parameters and precursor hydrolysis made it possible to obtain mesoporous silica with a Pm 3 n cubic structure, using CTAB, or an Fmmm orthorhombic structure, using a non-ionic surfactant. The addition of hydrophobic organosilane F₃C(CF₂)₅CH₂CH₂Si(OC₂H₅)₃ leads to the most regular and best-defined three-dimensional microdot array with a constant diameter of 155 μm and a regular space of 250 μm.     

Chemical Processing of Potassium-Substituted Strontium Barium Niobate Thin Films through Metallo-organics

Transparent and highly oriented K _x (Sr_0.5Ba_0.5)_{1− x /2}Nb₂O₆ ( x = 0.2, 0.4) (KSBN) thin films have been synthesized by a chemical solution deposition method. A homogeneous and stable KSBN precursor solution was prepared by controlling the reaction of metallo-organics. K_0.4Sr_0.4Ba_0.4Nb₂O₆ ( x = 0.4, K_0.4SBN50) and K_0.2Sr_0.45Ba_0.45Nb₂O₆ ( x = 0.2, K_0.2SBN50) powders and thin films directly crystallized to the tetragonal tungsten bronze phase above 600°C. The thin films were crystallized on MgO(100) and Pt(100)/MgO(100) with c -axis preferred orientation. Two crystal lattice planes of K_0.4SBN50 and K_0.2SBN50 were intergrown at an orientation of 18.5° on MgO(100) and Pt(100)/MgO(100). K_0.4SBN50 thin film on Pt(100)/MgO(100) showed the typical hysteresis loop ( P _r= 22 µC/cm², E _c= 99 kV/cm at −190°C). The change in remnant polarization with temperature is strongly related to the diffuse phase transition of the epsilon- T curves.     

Preparation of Amorphous Silicas Doped with Organic Molecules by the Sol-Gel Process

Molecular dispersions of amorphous siliceous materials doped with organic molecules were prepared by a sol-gel process in which Si(OC₂H₅)₄ was hydrolyzed in neutral or acidic solution. An amorphous silica which was doped with quinizarin on the order of 5×10⁻⁵ mol/mol SiO₂ showed photochemical hole burning at ∼4 K.     

Formation and Structural Characterization of 1:1 Ordered Perovskites in the Ba(Zn1/3Ta2/3)O3–BaZrO3 System

The phase stabilities in the(1−x)Ba(Zn_1/3Ta_2/3)O₃ (BZT)-xBaZrO₃(BZ)system have been investigated using samples prepared by the mixed oxide method. The substitution of Zr⁴⁺destabilizes the 1:2 cation ordering in BZT and pro-motes the formation of a cubic, 1:1 ordered structure with a doubled perovskite repeat. The homogeneity range of the 1:1 phase extends from x = 0.04 to approximately x = 0.25; substitutions beyond this range stabilize a disordered perovskite. The limits of stability of the 1:1 ordering coin-cide with compositions previously found to exhibit anoma-lies in their dielectric loss. The range of homogeneity is consistent with a "random layer" model for the 1:1 ordered "Ba{β';_1/2β^1/2}O₃" structure. In this model the B× positions are assumed to be occupied exclusively by Ta⁵⁺, and the b× sites by a random distribution of Zn₂₊, Zr₄₊, and the remaining Ta 5+ cations. The validity of the model, where the ordered solid solutions can be represented by Ba{[Zn_{2− y /3}Ta_{(1−2 y )/3}Zr y ]_1/2[Ta]_1/2}O₃(y =2x)was con-firmed by Rietveld refinements conducted using data col-lected with a synchrotron X-ray source.     

Preparation of TiO2-Coated Al2O3 Particles by Chemical Vapor Deposition in a Rotary Reactor

A process of coating Al₂O₃ particles with TiO₂ by hydrolysis of Ti(OC₄H₉)₄ using chemical vapor deposition in a rotary reactor has been developed. The process resulted in (1) a coating film of TiO₂ which was compact and uniform with the fraction of TiO₂ being 0.1%–10.0% and (2) an amorphous TiO₂ coating at a low reaction temperature converted to anatase at a reaction temperature higher than 673 K.     

Single-Step Dip Coating of Crack-Free BaTiO3 Films >1 μm Thick: Effect of Poly(vinylpyrrolidone) on Critical Thickness

BaTiO₃ coating films were prepared from Ba(CH₃COO)₂–Ti(OC₃H₇ⁱ)₄–H₂O–CH₃COOH–C₃H₇ⁱOH solutions containing poly(vinylpyrrolidone) (PVP) via single-step, nonrepetitive dip coating. The critical thickness—i.e., the maximum film thickness achieved without crack formation via nonrepetitive dip coating—was successfully increased by incorporation of PVP in the precursor solution. Relatively dense, crack-free BaTiO₃ films >1 μm in thickness were achieved via single-step deposition using a solution containing PVP of average molecular weight of 630 000. Incorporation of an excess amount of PVP, however, led to a decrease in the critical thickness. Higher-molecular-weight PVP was more effective in increasing the critical thickness, whereas N-vinyl-2-pyrrolidone monomers did not affect the critical thickness. Stepwise heating of the gel films resulted in increased optical transmittance of the films, accompanied by film densification.