Characteristics of PbTiO3 thin films on Pt/Ti/SiO2/Si by continuous cooling process

In order to introduce a new deposition process for ferroelectric thin film, the deposition temperature was continuously cooled down from 580°C to 400°C during the deposition which we call continuous cooling process (CCP). X-ray diffraction patterns showed that the PbTiO₃ thin films deposited by the CCP and at 480°C had polycrystallinity, but at substrate temperatures of 400°C and 580°C had poor crystallinity. Scanning electron microscopy of the CCP-deposited film surface showed larger granular-like micrograins than that of the film deposited at 480°C and smaller than that of the film at 580°C. While there was no other phase formation at the PbTiO₃-Pt interface in the CCP-deposited film, resulting in a sharp interface, there was severe interface reaction at the PbTiO₃-Pt and the Pt-Si in the film deposited at 580°C, resulting in an abrupt interface. Atomic force microscopy under ambient conditions showed smoother surface of the film by the CCP than that of the films at 580°C. Furthermore, the film by the CCP had higher packing density than that of the film at 480°C. Besides enhancement of the structural properties, the CCP deposition appeared to have improved the electrical properties such as dielectric constant, dissipation factor, leak current density and polarization. In the case of the film by the CCP, polarization-electrical field measurement showed the saturation polarization of 27 Ccm^–2, remanent of 14 Ccm^–2 and coercive of 150 kV. These results indicate that the CCP in metalorganic chemical vapour deposition has a possibility for fabrication of PbTiO₃ ferroelectric thin films.     

Crystal Chemistry of Lead Titanate in Relation to Its Electrical Properties

The origin of the discrepancy between the measured average parameter of the perovskite unit cell of PbTiO₃and the unit-cell parameter calculated for an ideal perovskite structure is analyzed with the use of extended x-ray absorption fine structure spectroscopy data, which demonstrate that PbTiO₃contains Pb⁴⁺ions. The amount of Pb⁴⁺depends on the preparation conditions and may attain 6 at. %. Assumption is made that the presence of crystallographic shear planes allows a fraction of the Pb²⁺ions to occupy octahedral sites near the shear planes. The maximum content of Pb²⁺on the B site is 2.5 at. %. The formula proposed for the cation composition of imperfect lead titanate differs from the ideal formula Pb²⁺Ti⁴⁺O₃and indicates that lead titanate can be thought of as an internal solid solution. It is shown that the composition of lead titanate influences its electrical properties: /₀increases with Pb⁴⁺concentration and exceeds that in single crystals by an order of magnitude.     

Interfacial reactions between titanium film and single crystal α-Al2O3

Titanium is commonly used to join metals and ceramics by active metal brazing methods. In this work, titanium was sputter deposited on to single-crystal -Al₂O₃ substrates and the interfacial reactions between the titanium film and the Al₂O₃ substrate were studied. Al₂O₃ was reduced by titanium when samples were annealed at 973 and 1173 K for 300 s in an argon gas flow. Metallic aluminium was produced at the interface, and this diffused from the interface into the titanium film. At 1173 K, the intermetallic compound Ti₃Al and the intermediate titanium oxides, such as Ti₂O and TiO, were formed. The Al⁰ diffusion is important in stimulating interfacial reactions.     

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.     

Piezoelectric properties of sol-gel-derived samarium-dysprosium-modified lead titanate ceramics

Samarium- and dysprosium-modified lead titanate ceramics have been prepared by a sol-gel route to utilize the finer control of the process on homogeneity and microstructure. By varying the sintering schedule (temperature and time) for samarium-modified PbTiO₃, ceramics with grain sizes ranging from submicrometre to 4 m have been prepared. The dielectric and piezoelectric properties of ceramics poled sequentially from 0 to 60 kV cm^–1 are reported. The dependence of the electromechanical properties on grain size and poling conditions is discussed. It is shown that dysprosium behaves very differently to samarium, and the successful insertion of dysprosium into the Pb²⁺ sites to produce true dysprosium-modified PbTiO₃ ceramics was not possible.     

Preparation and characterization of radio-frequency-sputtered Ba2Si2TiO8 thin films

Radio-frequency-sputtered barium titanium silicate (BST, Ba₂Si₂TiO₈) thin films were grown on crystalline Si (100) substrates and were characterized using wavelength-dispersive spectrometry (WDS), X-ray diffraction (XRD), optical microscopy (OM) and scanning electron microscopy (SEM), and diagonal techniques for dielectric properties. The chemical compositions of the films increasingly deviated from stoichiometry with film thickness. At the initial stage of deposition the grain configuration is dependent on the Si substrate texture. XRD analysis indicates that the BST films deposited at an optimum substrate temperature of 845 °C were strongly c-axis oriented, and that the film orientation is manipulated by substrate temperature and supersaturation. The corresponding film-growth rate in the direction normal to the film surface at 845 °C was 1.95 nm min^–1 at the initial stage, and decreased with sputtering time. The as-deposited films have a room-temperature bulk resistivity of 1.8 ×10⁷ m in the direction of thickness and an isotropic surface resistivity of 1.5×10³ m. The high-frequency relative dielectric constant, 0.05 at frequencies higher than 9 MHz, is lower than that of many typical piezoelectric materials. The high-frequency impedance character is typical of piezoelectric materials, giving a minimum impedance frequency of 9.0 MHz and a serial resonant frequency at about 9.5 MHz.     

A parametric study of the deposition of the TiN thin films by laser reactive ablation of titanium targets in nitrogen: the roles of the total gas pressure and the contaminations with oxides

The multipulse excimer laser-reactive ablation of a titanium target in nitrogen has been found to result in a total pressure of the ambient gas in the range 7–70 bar, in the deposition on to a silicon collector surface of high-purity f c c TiN thin films. These films were hard and adherent to substrate. The deposition rate was 0.03–0.05 nm per pulse for an incident laser fluence of 5 J cm^–2. For a lower gas pressure of a few microbars the deposits were amorphized with an excess of titanium. For a nitrogen pressure larger than 100 bar, the layers were contaminated with oxides. The oxides became more abundant with further increase in the gas pressure, and the deposited layer consisted of oxides only when the pressure reached several millibars.     

The growth of oriented ceramic eutectics

Controlled microstructures of the two eutectics in the alumina-titania system have been grown using a special electron beam heating technique. In the aluminium titanate-titania system, the eutectic interlamallar spacing varies with the freezing rate R as =AR ^–n where n=0.5 and the value of the constant A is 8.5×10^–6 cm^3/2sec^–1/2. Primary plate-like dendrites of aluminium titanate in a matrix of discontinuous aluminium titanate-titania eutectic are formed on solidifying a composition TiO₂-20 wt % Al₂O₃. These dendrites appear to deflect cracks in this ceramic. In the alumina-aluminium titanate system, primary rod-like dendrites of alumina were grown in a ribbon-like eutectic of alumina and aluminium titanate on solidifying a composition Al₂O₃–38.5% TiO₂.     

Chemical vapour deposition of PbTiO3 films onto TiO2-Si

Ferroelectric lead titanate thin films were deposited on the TiO₂ coated Si(100) substrate by chemical vapour deposition under atmospheric pressure. We have used Pb powder and tetraethyle-orthotitanate [Ti(C₂H₅O)₄] as the source material of Pb and Ti vapour. We investigated the variations of the phase of deposited films with the Ti(C₂H₅O)₄ input fractions. When the mole fraction was 0.021, PbTiO₃ single phase was obtained. For the other Ti(C₂H₅O)₄ input fractions, we could find PbO solid solutions phase in addition to the PbTiO₃ phase. The results of AES analysis revealed that the TiO₂ layer on the Si substrate acted as diffusion barriers between Si substrate and PbTiO₃ films.     

Coating of hydroxyapatite on various substrates via hydrothermal reactions of Ca(edta)2- and phosphate

Hydroxyapatite was coated on various substrates such as 12 mol % ceria-doped tetragonal zirconia (12Ce-TZP), 3 mol % yttria-doped tetragonal zirconia (3Y-TZP), alumina, monetite coated titanium (Ti/CaHPO₄) and calcium titanate coated titanium (Ti/CaTiO₃) via hydrothermal reactions of Ca(edta)^2- and 0.05 M NaH₂PO₄ at initial pH 6 and 160–200 °C for 0.5–6 h. Rod-like particles of hydroxyapatite precipitated to form film on the substrates above 160 °C. The morphology of the film changed significantly depending on the characteristics of substrate, i.e. hydroxyapatite entirely coated the surfaces of 12Ce-TZP, Ti/CaHPO₄ and Ti/CaTiO₃ plates, but sparsely deposited on 3Y-TZP and Al₂O₃ plates. Film thickness increased with time (ca. 20 and 90 m on 12Ce-TZP plates for 0.5 and 6 h, respectively, at pH 6 and 200 °C). The adhesive strength of the film for the substrate was in the order, 12Ce-TZP/hydroxyapatite(28 MPa) > Ti/CaTiO₃/hydroxyapatite (22 MPa) > Ti/CaHPO₄/hydroxyapatite (9 MPa). © 2001 Kluwer Academic Publishers     

Synthesis of PbTiO3 film on LaNiO3-coated substrate by the spray-ICP technique

In an attempt to utilize LaNiO₃ as a bottom electrode for PbTiO₃ ferroelectric film, PbTiO₃ and LaNiO₃ films were prepared by the spray-ICP technique under atmospheric pressure. The dense LaNiO₃ films crystallized with preferred (1 1 1) and (1 0 0) orientations on sapphire (0 0 1) and MgO (1 0 0), respectively. Resistivities of the LaNiO₃ films deposited above 600 °C were about 4 × 10^–6 m. The PbTiO₃ film with preferred (001) orientation was successfully prepared on LaNiO₃-coated MgO (1 0 0). Its dielectric constant and dissipation factor were about 200 and 0.02, respectively, at 1 kHz. The Curie temperature suggested that PbTiO₃ films were free from contamination by LaNiO₃.     

Oxide-dispersed titanium alloys Ti-Y prepared with the rotating electrode process

This work deals with an evaluation of the range of cooling rates during solidification necessary to obtain rare earth oxide-dispersed titanium alloys, which constitute a potentially interesting alloy system for high temperature use, due to the thermodynamic stability of rare earth oxides in titanium. The results of the microstructural studies on binary Ti-Y alloy powders prepared by the rotating electrode process show that it is possible to obtain e fine and homogeneous dispersion of yttrium oxide Y₂O₃ in a titanium maul with relatively moderate cooling rates ( 10⁴ K sec^–1). The results also indicate that the stability of the dispersion is excellent during hot consolidation but only in the phase temperature region (< 882.5° C). The preliminary mechanical teas performed on consolidated products show u substantial increase in 0.2% Woof stress (about 100 M Pa) up to 55O° C with respect to unalloyed titanium of commercial purity. Above 550° Q this strength increment becomes negligible or disappears. These results imply that the oxide dispersion loses its hardening effect at high temperatures, probably due to the increasing importance of grain-boundary sliding.     

TiCxNy and TiCx-TiN films obtained by CVD in an ultrasonic field

TiC _x N _y mono- and TiC_x-TiN double-layer films with a thickness of 30 to 100 m were prepared on a carbon steel (C: 0.6 to 0.7%) substrate by CVD in an ultrasonic field (ultrasound frequency: 19kHz; power: 10 to 20Wcm^–2). The moderate deposition conditions for obtaining an adherent and thick film of TiC _x N _y were: substrate temperature: 1050° C; H₂, N₂, TiCl₄ and CH₄ flow rates: 6.2, 4.0, 0.9 and 0.26 to 2.0 ml sec^–1, respectively. The growth rate, grain size and degree of 2 2 0 preferred orientation were found to decrease with increase in CH₄ concentration. TiC _x N _y film on carbon steel had a Vickers microhardness of 1800 to 2600 and an adhesion strength to the substrate of more than 120 kg cm^–2. A TiC _x -TiN (x0.5) double-layer film was obtained at 1050° C by a controlled alternative deposition of TiC _x or TiN. Quasiepitaxial growth of crystallites in the double layers was found to prevail in both coatings of TiC _x (220)/TiN (220)/steel and TiN (200)/TiC_x (200)/steel.     

Ferroelectric Films of Ba0.7–0.8Sr0.2–0.3TiO3 Solid Solutions Deposited from Carboxylate Solutions

Ferroelectric films of Ba_0.7–0.8Sr_0.2–0.3TiO₃ solid solutions 2–3 m in thickness were deposited onto platinum substrates from carboxylate solutions and characterized by dielectric measurements at 1000 Hz: t _C = 15–16°C, ₂₀ > 1000, tan = 0.04–0.06 in the range 10–100°C. The controllability coefficient of the films in a dc electric field between 36 and 42°C is 1.6.     

Plastic deformation mode of retainedβ phase inβ-eutectoid Ti-Fe alloys

Plastic deformation mode of-eutectoid Ti-Fe alloys has been investigated at 300 and 77 K in a retained single phase (containing athermal phase). Surface analysis and transmission electron microscopy show that {332}1 1 3 twinning and 1 1 1 slip appear to be dependent on orientation, composition and deformation temperature. The {3 3 2} 1 1 3 twinning appears only in metastable regions adjacent to the M_s curve in good agreement with previous work in-isomorphous alloys. Orientation dependence for occurrence of the preferential {332} 1 1 3 twinning among the twelve equivalent twinning systems can be explained in terms of the Schmid factor and the polarization of twinning shear. It is concluded that the {332} <1 1 3 twinning is common for-titanium alloys and related to the instability of the phase.     

Lead-strontium titanate glass ceramics: I – crystallization and microstructure

The crystallization behaviour of glasses in the system [(Pb Sr ) O·TiO₂]-[2SiO₂· B₂O₃]-[K₂O]-[BaO] (0.2 ≤ x ≤ 0.9) have been studied. Perovskite titanate was found to be the major phase in all the glass ceramic samples investigated. The actual composition of crystalline phases could not be confirmed on the basis of shift in the X-ray diffraction (XRD) peak positions because of similar effects due to solid solution formation and strain due to crystal clamping. Comparison of the observed intensities of various XRD peaks of the perovskite titanate phase with the calculated intensities for (Pb Sr )TiO₃ with same lead/strontium ratio confirmed the formation of lead strontium titanate solid solution. Microstructural characteristics of various glass ceramics are also discussed. The advantages of using K₂O and BaO as additives instead of only K₂O are also discussed.     

Prolonged laser ablation effects of YBCO ceramic targets during thin film deposition: Influence of processing parameters

Cumulative laser irradiation during high-Tc superconducting thin film pulsed laser deposition (PLD) may have a detrimental effect on film characteristics. Initial decrease of deposition rate and gradual shift of the center of the deposited material spot towards the incoming laser beam were registered on cold glass substrates. Their absorbance was used for evaluation of the film thickness distribution over the substrate area. At the initial stage, two components of the spot could be distinguished along its short axis: central (cosⁿ , n1) and peripherial (cos ), while with cumulative irradiation the thickness followed an overall cos^m (m相似文献   

Optical and structural properties of (Ba, Sr)TiO3 thin films grown by radio-frequency magnetron sputtering

We studied the structural and optical properties of (Ba, Sr)TiO₃ (BST) films deposited on the transparent substrates at various temperatures of 350–650°C and annealed at 450–650°C. Improved crystallization can be observed on 650°C annealed film whose substrate temperature is 350°C. The refractive index increased from 2.17 to 2.59 at =410 nm for the BST films deposited at 350–650°C and it varied from 2.17 to 2.25 after annealing up to 650°C. In addition, the refractive-index dispersion data related to the short-range-order structure of BST films obeyed the single-oscillation energy model. The indirect energy gap of the films deposited on Al₂O₃ and quartz substrates was found to be about 3.5 eV. According to the analysis of reflectance data, the optical inhomogeneity of films can be reduced by depositing the films at intermediate temperatures 450–550°C.     

Preparation and characterization of Ce-doped BaTiO3 thin films by r.f. sputtering

Ce-doped BaTiO₃ thin films prepared on silicon-platinium by r.f. sputtering has been investigated. BaTiO₃ doped with 5.5 mol%CeO₂ thin film was deposited at 550°C substrate temperature in an Ar atmosfere. The crystal structure and shape were examined by X-ray diffraction and scanning electron microscopy with EDAX. Analysis by X-ray diffraction patterns show that the crystalline film with a cubic structure of BaTiO₃, was obtained. The surface morphology (roughness, the grain size and the droplet size) of the thin film surface was examined by atomic force microscopy (AFM). The grain size is about 160 nm, the droplet size is about 0.675 m and the roughness is 36.88 nm. EDAX analysis established a composition of the film to be identical with that of the target (BaTiO₃ doped with 5.5 mol%CeO₂). The broad peak in the capacitance versus temperature curve at the Curie point indicate that the r.f. sputtered Ce-doped BaTiO₃ film is ferroelectric. The values of the capacitance of the thin film at 1 KHz were found to be 86 pF and the loss dielectric was tan = 0.0875. The film exibits a dielectric anomaly peak at 23°C showing ferroelectric to paraelectric phase transition.     

Heat transfer in plane film formation

A mathematical model is obtained for the process of cooling with formation of a planar film. The solution obtained is verified experimentally.Notation mean axial velocity gradient - v_x current axial velocity - v_o initial polymer velocity - v₁ sampling velocity - K draw ratio - deformation rate tensor - x, y, z spatial coordinates - X, Y dimensionless coordinates - L() differential operator - T temperature - T_o initial temperature - T_c temperature of surrounding medium - dimensionless temperature - dimensionless temperature averaged over film thickness - thermal-diffusivity coefficient - 2_o initial film thickness - thermal conductivity - heat-transfer coefficient - f(X) distance function - Bi Biot criterion, Bi_o, Biot criterion calculated for initial film thickness - Gz* modified Graetz criterion - V dimensionless velocity - ₁, ₂, ₃ heat-transfer coefficients produced by radiation, free convection, and forced convection - v_c, _c mean velocity and film half-thickness in formation zone - T₁ calculated temperature value - T₂ experimental temperature value - l formation zone length Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 37, No. 5, pp. 854–858, November, 1979.