Synthesis of KTiOPO4 (KTP) Thin Films Using Metallo-organics

Crack-free and highly transparent KTiOPO₄ (KTP) thin films were synthesized by the sol-gel method using a homogeneous precursor solution prepared from ("BuO)₂-P(O)(OH), Ti(OEt)₄, and KOEt in EtOH. Precipitated powders from the solution crystallized directly to KTP above 550°C. Polycrystalline KTP thin films were obtained at 600°C on various substrates. On NdAlO₃(100) substrates, KTP films with (101) and (240) preferred orientations were formed at 600°C. KTP films on glass substrates showed a refractive index of 1.75 and an absorption edge of 350 nm. KTP films exhibited the second harmonic generation of the 532 nm light on irradiaton with 1064 nm light.     

Destabilization of Zirconia Thermal Barriers in the Presence of V2O5

Impurities, such as vanadium, degrade the operating performance of yttria-stabilized zirconia thermal-barrier coatings. V₂O₅ reacts preferentially with Y₂O₃, forms YVO₄, and leads to the destabilization of zirconia thermal-barrier material. A model experiment has been designed to monitor the destabilization of zirconia thermal barriers by directly exposing thin films of yttria-stabilized zirconia to V₂O₅ vapor. The growth of YVO₄ from yttria-stabilized zirconia and the destabilization of cubic yttria-stabilized zirconia into tetragonal and/or monoclinic zirconia polymorphs are monitored by selected-area diffraction and energy-dispersive X-ray spectroscopy in the transmission electron microscope. A special crystallographic orientation relation between YVO₄ and cubic zirconia is discussed.     

Alkoxy-Derived KTiOPO4 (KTP) Fibers

Crack-free and dense KTiOPO₄ (KTP) fibers could be successfully synthesized through metallo-organics. A homogeneous, drawable KTP precursor solution was prepared from the reaction of (ⁿBuO)₂P(O)(OH), Ti(OEt)₄, and KOEt. KTP precursor fibers crystallized to a single-phase KTP at 650°C for 0.5 h. KTP fibers were a few centimeters in length and 10–150 μm in diameter. The density of the KTP fibers was higher than 2.97 g/cm³ (>98% of theoretical density).     

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.     

Synthesis of Lead Barium Niobate Powders and Thin Films by the Sol-Gel Method

Crack-free, dense, and transparent Pb_0.6Ba_0.4Nb₂O₆ (PBN60) thin films have been prepared by a sol-gel method with metal alkoxides and metal acetate. A homogeneous and stable precursor solution was obtained from Ba metal, Pb(CH₃COO)₂, and Nb(OEt)₅ in 2-methoxyethanol. PBN60 powder crystallized to the hexagonal phase at 600°C and then completely transformed to the orthorhombic phase of the tungsten bronze structure at 1250°C. The hexagonal phase was formed on SiO₂ glass, MgO(lOO), and sapphire(R) substrate at 600°C, while the orthorhombic phase was only on a sapphire(C) substrate. Orthorhombic PBN60 films with c -axis preferred orientation were successfully synthesized on sapphire(C) substrates at 600°C.     

Hydrolytic Condensation of Tin(IV) Alkoxide Compounds to Form Particles with Well-Defined Morphology

The sol-gel-type condensation of tin(IV) ethoxide [Sn(OEt)₄] n (where OEt is ethoxide) under basic conditions produced spherical, submicrometer-sized tin(IV) oxide (cassiterite) particles. Transmission electron microscopy and powder X-ray diffraction data indicated that the grain size was approximately 20 to 30 Å (2 to 3 nm). The mixed-metal alkoxide compound [ZnSn(OEt)₆] was hydrolyzed under analogous conditions to give either spherical or octahedral submicrometer-sized crystalline particles of ZnSn(OH)₆ depending on the solvents used. These data demonstrated that the stoichiometry of the mixed-metal alkoxide precursor was retained during condensation. Thermal treatment of ZnSn(OH)₆ resulted in crystallization of ZnSnO₃ at approximately 676°C. At neutral pH, hydrolysis of [ZnSn(OEt)₆] resulted in formation of a high surface area (261 m²/g) amorphous powder.     

Metalorganic Chemical Vapor Deposition of Ferroelectric Pb(Zr,Ti)O3 Thin Films

Ferroelectric Pb(Zr_xT_1–x)O₃, films were successfully and reproducibly deposited by both hot–wall metalorganic chemical vapor deposition (MOCVD) and cold-wall MOCVD. One of the important problems associated with the MOCVD techniques is the selection of ideal precursors. After an intensive investigation for the most suitable precursors for MOCVD PZT films, the safe and stable precursors, namely lead tetramethylheptadione [Pb(thd)₂], zirconium tetramethylheptadione [Zr(thd)₄], and titanium ethoxide [Ti(OEt)₄], were chosen. The films were deposited at temperatures as low as 550°C and were single-phase perovskite in the as-deposited state. Also, the films were smooth, specular, crack-free, and uniform, and adhered well to the substrates. The stoichiometry of the films can be easily controlled by varying the individual precursor temperature and/or the flow rate of the carrier gas. Auger electron spectroscopic (AES) depth profile showed good compositional uniformity through the thickness of the films. The AES spectra also showed no carbon contamination in the bulk of the films. As-deposited films were dense and showed uniform and fine grains (≅0.1 μm).The optical properties of the films on the sapphire disks showed high refractive index ( n = 2.413) and low extinction coeflicient ( k = 0.0008) at a wavelength of 632.8 nm. The PZT (82/18) film annealed at 600°C showed a spontaneous polarization of 23.3 μC/cm² and a coercive field of 64.5 kV/cm.     

Preparation and Phase Separation Behavior of (Co,Fe)3O4 Films

(Co,Fe)₃O₄ films were synthesized by the sol–gel method through metalorganic compounds. The (Co,Fe)₃O₄ films (Co:Fe = 2:1) showed the characteristic behavior of the spinodal decomposition by heat treatments within the miscibility gap. The coercive force of the spinodally decomposed films increased from 0.9 kOe for a solid solution to 2.0 kOe for films that underwent the spinodal decomposition. The nonmagnetic phase (rich in Co) formed by the spinodal decomposition contributes to the pinning of the movement of magnetic domain walls. On the other hand, the (Co,Fe)₃O₄ films (Co:Fe = 1:1) showed the typical feature of binodal decomposition during heat treatment within the miscibility gap. The binodally decomposed films showed a slight increase in the coercive force depending upon the evolution of the magnetic region.     

Synthesis of ZrO2 and Y2O3-Doped ZrO2 Thin Films Using Self-Assembled Monolayers

Undoped or Y₂O₃-doped ZrO₂ thin films were deposited on self-assembled monolayers (SAMs) with either sulfonate or methyl terminal functionalities on single-crystal silicon substrates. The undoped films were formed by enhanced hydrolysis of zirconium sulfate (Zr(SO₄)·4H₄O) solutions in the presence of HCl at 70°C. Typically, these films were a mixture of two phases: nanocrystalline tetragonal- ( t -) ZrO₂ and an amorphous basic zirconium sulfate. However, films with little or no amorphous material could be produced. The mechanism of film formation and the growth kinetics have been explained through a coagulation model involving homogeneous nucleation, particle adhesion, and aggregation onto the substrate. Annealing of these films at 500°C led to complete crystallization to t -ZrO₂. Amorphous Y₂O₃-containing ZrO₂ films were prepared from a precursor solution containing zirconium sulfate, yttrium sulfate (Y₂(SO₄)₃8·H₂O), and urea (NH₂CONH₂) at pH 2.2–3.0 at 80°C. These films also were fully crystalline after annealing at 500°C.     

Chemical Solution Deposition of (Pb1−xCax)TiO3 Thin Films with x∼0.5 as New Dielectrics for Tunable Components and Dynamic Random Access Memories

Calcium lead titanate ((Pb,Ca)TiO₃) thin films, with calcium contents of ∼50 at.%, have been prepared by chemical solution deposition (CSD). Different synthetic sol–gel methods have been used for the preparation of the precursor solutions. 1,3-propanediol, OH(CH₂)₃OH, and water, H₂O, were used as solvents. Lead (II) acetate trihydrate, Pb(OCOCH₃)₂·3H₂O, and titanium di-isopropoxide bis(acetylacetonate), Ti(OC₃H₇)₂(CH₃COCHCOCH₃)₂, were used as reagents of lead and titanium, respectively. Calcium was incorporated into the solutions as calcium acetate hydrate, Ca(OCOCH₃)₂· x H₂O, or as calcium acetylacetonate hydrate, Ca(CH₃COCHCOCH₃)₂· x H₂O. Only the use of calcium acetate led to precipitate-free solutions. Pb(II)–Ti(IV)–Ca(II) sols were obtained when calcium acetate was refluxed with the lead and titanium reagents in a diol–water solvent. These sols led to films with a homogeneous compositional profile. Solutions obtained by mixing a water solution of calcium acetate with a Pb(II)–Ti(IV) sol led to films with a heterogeneous compositional profile in which an interface between the film and the Pt bottom electrode is formed. The films derived from the Pb(II)–Ti(IV)–Ca(II) sols have values of dielectric constant at room temperature of ∼500, which, together with their low leakage currents, low dielectric losses, and tunability, make these films promising for dynamic random access memories and tunable devices.     

Preparation of Porous Glass-Ceramics with a Skeleton of NASICON-Type Crystal CuTi2(PO4)3

A novel porous glass-ceramic with a skeleton of CuTi₂(PO₄)₃ was prepared by controlled crystallization of a glass and subsequent chemical leaching of the resulting dense glass-ceramic. A volume-crystallized dense glass-ceramic composed of CuTi₂(PO₄)₃ and Cu₃(PO₄)₂ whose surface was covered by a CuO thin layer was prepared by reheating a glass with a nominal composition of 50CuO·20TiO₂30P₂O₅ (in mol%) glass in air. When the resultant glass-ceramic was leached with dilute H₂SO₄, Cu₃(PO₄)₂ and CuO phases were dissolved out selectively, leaving a crystalline CuTi₂(PO₄)₃ skeleton. The specific surface area and the average pore radius of the porous glass-ceramic obtained were approximately 45 m₂g_-1 and 9 nm, respectively. The porous glass-ceramic showed catalytic activity in the conversion reaction of propene into acrolein.     

Effect of the Atomic Ratio of Ba to Ti on Optical Properties of Gold-Dispersed BaTiO3 Thin Films

Gold-dispersed BaTiO, thin films were prepared by the rf magnetron sputtering method. The atomic ratio of Ba to Ti in the films was varied and the effects on the linear and nonlinear optical properties were investigated. As the atomic ratio increased, the value of χ⁽³⁾/α₅₃₂ for the gold-dispersed BaTiO₃ thin films slightly increased. It was found that the increase in the value of χ⁽³⁾/α₅₃₂ is due mainly to a change in the crystalline state of the BaTiO₃ matrix. However, it was also found that the atomic ratio had a smaller effect on the value of χ⁽³⁾/α₅₃₂ than did the refractive index of the matrix.     

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.     

Physical Properties and Structure of Rf-Sputtered Amorphous Films in the System Ti02-Si02

Amorphous films in the system Ti0₂-Si0₂ were prepared by rf sputtering and their density, refractive index, and thermal expansion were measured. Also, the silicon Kα and titanium Kβ band emission spectra were obtained by X-ray emission spectroscopy in order to determine the coordination state of silicon and titanium ions in these amorphous films. The density and refractive index increased, but not proportionally, with increasing Ti0₂ content. On the other hand, a minimum was observed in the thermal expansion coefficient at =15 mol% Ti0₂. The coordination state of silicon ions in the amorphous films did not change with Ti0₂ content. However, the coordination number of titanium ions changed from 4 to 6, depending on Ti0₂ content. These results indicate that, in amorphous films in the system Ti0₂-Si0₂, the change of the coordination state of titanium ions has an important effect on physical properties, such as volume, molar refractivity, and thermal expansion.     

REVISION OF CRYSTALLINE PHASES IN THE SYSTEM ZRO2-P2O5

Crystalline phases in the system ZrO₂-P₂O_s were reexamined. Samples of varied composition were prepared by the sol-gel route and calcining, as well as by reacting mixtures ofZrO₂ and NH4H2PO4, at temperatures from 200° to 1400°C. Confusion regarding compositions and structures was clarified, and the phase Zr₃(PO₄)₄ was confirmed. The latter can be written Zro.₂sZr₂(PO₄)₃ and is iso-structural withNaZr₂P₃O₁₂. The role of mineralizers and the influence of zirconium salts can now be understood.     

Preparation of Composite Particles by Pulsed Nd-YAG Laser Decomposition of [(CH3)2N]4Ti to TiN-Coat TiO2, Al2O3, or Si3N4 Powders

Irradiation of Ti[N(CH₃)₂]₄ by the 1.064-μm line of a pulsed Nd: YAG laser in the presence of TiO₂, Al₂O₃, or Si₃N₄ particles has been found to form amorphous deposits on the oxide particles. The resulting materials can be processed into TiN/TiO₂, TiN/Al₂O₃, or TiN/Si₃N₄ composites with the TiN component on the surface of the particles. The powders have been characterized by Raman spectroscopy and X-ray powder diffraction studies. The surface analysis of the composites by X-ray photoelectron spectroscopy and high-resolution electron microscopy is presented.     

Preparation and Aging Behavior of Chemical-Solution-Deposited (Pb(Mg1/3Nb2/3)O3)1-x–(PbTiO3)x Thin Films without Seeding Layers

The aging behavior of the solid-solution series (Pb(Mg_1/3Nb_2/3)O₃)_{1− x} –(PbTiO₃) _x (PMN_{1− x} −PT _x ) prepared by chemical-solution deposition without seeding layers was investigated. A strong influence of the rapid thermal annealing step on the film density was determined. The best nucleation and density of the thin films occurred when each deposited layer was separately pyrolyzed and crystallized. The thin-film microstructure was investigated using scanning electron microscopy. Conventional capacitance-voltage and hysteresis measurements were performed. For the first time, investigations on the fatigue performance and the leakage current for alternating-current and direct-current voltage were executed, which are important for the reliability in device applications.     

Characterization of the Piezoelectric Properties of Pb0.98Ba0.02(Mg1/3Nb2/3)O3–PbTiO3 Epitaxial Thin Films

Pb(Mg_1/3Nb_2/3)O₃–PbTiO₃ (PMN–PT) (70/30) thin films were deposited by pulsed laser deposition using two growth strategies: adsorption controlled deposition from lead-rich targets (∼25–30 mass%) and lower-temperature deposition ( T _d≤600°C) from targets containing a small amount of excess lead oxide (≤3 mass %). The substrates used were (001) SrRuO₃/LaAlO₃. Typical remanent polarization values ranged between 12 and 14 μC/cm² for these films. The longitudinal piezoelectric coefficient ( d _33,f) was measured using in situ four-circle X-ray diffraction, and the transverse coefficient ( d _31,f or e _31,f) was measured using the wafer flexure method. d _33,f and e _31,f coefficients of ∼300–350 pm/V and ∼−11 C/m² were calculated, respectively. In general, the piezoelectric coefficients and aging rates were strongly asymmetric, suggesting the presence of a polarization bias. The large, extremely stable piezoelectric response that results from poling parallel to the preferred polarization direction is attractive for miniaturized sensors and actuators.     

A- and B Site Cosubstituted Ba6−3xSm8+2xTi18O54Microwave Dielectric Ceramics

Tin (Sn) substitution into the B-site and Nd/Sn cosubstitution into the A- and B-sites were investigated in a Ba _{6−3 x} Sm_{8+2 x} Ti₁₈O₅₄solid solution ( x = 2/3). A small amount of tin substitution for titanium improved the temperature coefficient of resonant frequency (τ_f) but led to a decrease of the relative dielectric constant (ɛ) and the quality factor ( Qf ). The Ba_{6−3 x} Sm_{8+2 x} (Ti_{1− z} Sn_z)₁₈O₅₄-based tungsten-bronze phase became unstable for compositions with a tin content of ≥10 mol%, where BaSm₂O₄and Sm₂(Sn,Ti)₂O₇appeared, and finally, these phases became the major phases. On the other hand, Nd/Sn cosubstitution led to a good combination of high ɛ, high Qf , and near-zero τ_f. Excellent microwave dielectric properties were achieved in Ba_{6−3 x} (Sm_{1− y} Nd _y )_{8+2 x} (Ti_{1− z} Sn _z )₁₈O₅₄ceramics with y = 0.8 and z = 0.05 sintered at 1360°C for 3 h: ɛ= 82, Qf = 10 000 GHz, and calculated τ_f=+17 ppm/°C. The tolerance factor and electronegativity difference exhibited important effects on the microwave dielectric properties, especially the Qf value. A large tolerance factor and high electronegativity difference generally led to a higher Qf value.     

Porous Glass-Ceramics with a Skeleton of the Fast-Lithium-Conducting Crystal Li1+xTi2−xAlx(PO4)3

Porous glass-ceramics with a skeleton of the fast-lithium-conducting crystal Li_{1+ x} Ti_{2− x} Al _x (PO₄)₃ (where x = 0.3–0.5) were prepared by crystallization of glasses in the Li₂O─CaO─TiO₂─Al₂O₃–P₂O₅ system and subsequent acid leaching of the resulting dense glass-ceramics composed of the interlocking of Li_{1+ x} Ti_{2− x} Al _x (PO₄)₃ and β-Ca₃(PO₄)₂ phases. The median pore diameter and surface area of the resulting porous Li_{1+ x} Ti_{2− x} Al _x (PO₄)₃ glass-ceramics were approximately 0.2 μm and 50 m²/g, respectively. The electrical conductivity of the porous glass-ceramics after heating in LiNO₃ aqueous solution was 8 × 10⁻⁵ S/cm at 300 K or 2 × 10⁻² S/cm at 600 K.