Crystallization behaviour of PZT in multilayer heterostructures

Microstructural and electrical properties of PZT (lead zirconate titanate) thin films prepared by sol-gel techniques at annealing temperatures in the range from 550°C to 900°C are studied. Perovskite (Pe) grain nucleation in PZT film starts but not completes at 550°C. Along with formation of round Pe (111) grains on the Pt (111) interface, the film contains small Pe and pyrochlore (Py) grains. Films annealed at the temperatures higher than 600°C demonstrate column structure of Pe grains, the amount of Py inclusions reduces with the annealing temperature and practically disappears at 700°C. An increase of annealing temperature leads to enhancement of (100) Pe orientation as a result of Ti diffusion on the Pt surface. Polarization decreases with the annealing temperature (maximum at 600°C), whereas permittivity increases up to the annealing temperature of 750°C.     

Effects of Annealing on Microstructure and Optical Properties of TiO2 Sculptured Thin Films

The evolution of microstructure and optical properties of TiO2 sculptured thin films under thermal annealing is reported. XRD, field emission SEM, UV-Vis-NIR spectra are employed to characterize the microstructural and optical properties. It is found that the optimum annealing temperature for linear birefringence is 500℃. The maximum of transmission difference for linear birefringence is up to 18%, which is more than twice of that in as-deposited thin films. In addition, the sample annealed at 500℃ has a minimum of column angle about 12℃. The competitive process between the microstructural and optical properties is discussed in detail. Post-annealing is a useful method to improve the linear birefringence in sculptured thin films for practical applications.     

Preparation and Thermal Properties of Boron-Containing o-Cresol-Formaldehyde Resin/Octa(aminophenyl)-POSS Nanocomposites

The boron-containing o-cresol-formaldehyde resin (BoCFR) and octa(aminophenyl) polyhedral oligomeric silsesquioxane (OAP-POSS) were synthesized, and the BoCFR/OAP-POSS nanocomposite prepared via an in-situ method. The curing process of the resin was characterized by Fourier transform infrared (FTIR). The thermal properties and dynamic mechanical properties of the nanocomposites were investigated. The results show that the maximal mechanical loss temperature (T_p) increased with increasing OAP-POSS content. When the content of OAP-POSS was 10 wt% the T_p was over 200°C, 27°C higher than the pure BoCFR. The BoCFR/OAP-POSS nanocomposite had better thermal stablitity than the pure BoCFR. The residual weight of the o-cresol-formaldehyde resin was only 6.13 wt% at 600°C. But the residual weight of the pure BoCFR was 55.73 wt% at 600°C, and the residual weights of the BoCFR nanocomposites were all higher than pure BoCFR. The residual weight of the BoCFR nanocomposite was 63.2 wt% at 600°C and 21.83 wt% at 900°C when the OAP-POSS content was 10 wt%. The weight loss of BoCFR/OAP-POSS nanocomposite can be divided primarily into two temperature stages, from 430°C to 550°C and from 550°C to 900°C. The main thermal degradation reaction follows first order kinetics.     

Crystal microstructure of annealed nanocrystalline Chromium studied by synchrotron radiation diffraction

The microstructure of electrodeposited nanocrystalline chromium (n-Cr) was studied by using synchrotron radiation (SR) diffraction, SEM, TEM, and EDX techniques. The as-prepared n-Cr samples show the standard bcc crystal structure of Cr with volume-averaged column lengths varying from 25 to 30 nm. The grain growth kinetics and the oxidation kinetics were studied by time resolved SR diffraction measurements with n-Cr samples annealed at 400, 600, and 800 °C. The grain growth process is relatively fast and it occurs within the first 10 min of annealing. The final crystallite size depends only on the annealing temperature and not on the initial grain size or on the oxygen content. The final volume-averaged column lengths observed after 50 min annealing are 40(4), 80(1), and 120(2) nm for temperatures 400, 600, and 800 °C, respectively. It is shown that annealing ex situ of n-Cr at 800 °C both under vacuum and in air gives a grain growth process with the same final crystallite sizes. The formation of the Cr₂O₃ and CrH phases is observed during annealing.     

Accelerated formation of an ultrafine-grained structure in a two-phase Ti alloy during compression with decreasing temperatures

ABSTRACT

Ultrafine-grained (UFG) structure is beneficial for overcoming the strength-ductility trade-off and enhancing the superplasticity of two-phase Ti alloys. Recently, it has been demonstrated that compression with decreasing temperatures is effective for producing UFG two-phase Ti alloys initially with lamellar microstructures. However, the effect of lamellar thickness on the microstructural evolution during this process has not yet been fully elucidated. In this study, Ti-6Al-4V alloys with different lamellar thicknesses were compressed while the processing temperature was decreased from 800°C to 600°C. The thinner lamellar microstructure was preferable for preventing void/crack formation, while accelerating the continuous dynamic recrystallisation, thus providing a fully UFG structure at a relatively low strain of 1.4. In addition, the origin of different plastic flows in each sample was analysed in detail by analysing the microstructural evolution. These findings demonstrate that the processing method is effective for reducing the grain size of a two-phase Ti alloy without severe plastic deformation techniques, which require large strain (≥4). A reduction in the strain required to achieve the UFG structure would be beneficial because conventional metal-forming processes, i.e. rolling, extrusion, or forging, which are suitable for mass production, could be used.     

Effects of thermally induced anatase-to-rutile phase transition in MOCVD-grown TiO2 films on structural and optical properties

Titanium dioxide (TiO₂) films with a thickness of 550 nm were deposited on quartz glass at 300 °C by metalorganic chemical vapor deposition. The effects of post-annealing between 600 °C and 1000 °C were investigated on the structural and optical properties of the films. X-ray diffraction patterns revealed that the anatase phase of as-grown TiO₂ films began to be transformed into rutile at the annealing temperature of 900 °C. The TiO₂ films were entirely changed to the rutile phase at 1000 °C. From scanning electron spectroscopy and atomic force microscopy images, it was confirmed that the microstructure of as-deposited films changed from narrow columnar grains into wide columnar ones. The surface composition of the TiO₂ films, which was analyzed by X-ray photoelectron spectroscopy data, was nearly constant although the films were annealed at different temperatures. When the annealing temperature increased, the transmittance of the films decreased, whereas the refractive index and the extinction coefficient calculated by the envelope method increased at high temperature. The values of optical band gap decreased from 3.5 eV to 3.25 eV at 900 °C. This abrupt decrease was consistent with the anatase-to-rutile phase transition. Received: 4 October 2000 / Accepted: 4 December 2000 / Published online: 23 May 2001     

Mechanism of texture and microstructure evolution during warm rolling of Ti–6Al–4V alloy

Ti–6Al–4V (Ti64) plates were subjected to rolling at 600°C and 800°C, respectively, for reductions up to 90% reduction in thickness. The mechanism of texture and microstructure evolution during rolling was studied in the present study. Extension twins of coherent nature were observed in the samples rolled up to 50% of reduction. The deformation was relatively inhomogeneous in the samples rolled at 600°C compared to that at 800°C. Visco-plastic self-consistent (VPSC) simulation showed that relative activity of pyramidal <c+a> slip was higher during rolling at 800°C compared to that at 600°C. The average activity of slip systems per grain was less than five for the samples rolled at 600°C and this might be responsible for the strain heterogeneity in the large grains. Further, twinning activity was found to be limited to a true strain of 0.5, as supported by the microstructural observation. VPSC simulation also showed the presence of contraction twins in the samples which was further supported by X-ray texture measurement. Dominant basal texture was observed in the samples irrespective of the temperature of rolling.     

Characterization of Laves phase in Crofer 22 H stainless steel

This study investigated the effect of annealing temperature on the precipitation behavior of Crofer^® 22 H at 600 °C, 700 °C, and 800 °C. The grain size distribution, precipitate phase identification, and microstructure were analyzed using electron backscatter diffraction (EBSD) and energy dispersive X-ray spectroscopy (EDS). The morphology of Laves phase (Fe,Cr,Si)₂(Nb,W) precipitates having the Cr₂Nb structure changed from strip-like to needle-shaped as the annealing temperature was increased. The precipitates of the Laves phase also shifted from the grain boundaries to the grain interiors when the temperature was increased. However, the average grain size (150 μm) of the ferritic matrix did not significantly change at 600 °C, 700 °C, and 800 °C for 10 h.     

Temperature dependent surface and spectral modifications of nano V<Subscript>2</Subscript>O<Subscript>5</Subscript> films

Nanocrystalline V₂O₅ films have been deposited on glass substrates at 300°C substrate temperature using thermal evaporation technique and were subjected to thermal annealing at different temperatures 350, 400, and 550°C. X-ray diffraction (XRD) spectra exhibit sharper and broader characteristic peaks respectively indicating the rearrangement of nanocrystallite phases with annealing temperatures. Other phases of vanadium oxides started emerging with the rise in annealing temperature and the sample converted completely to VO₂ (B) phase at 550°C annealing. FESEM images showed an increase in crystallite size with 350 and 400°C annealing temperatures followed by a decrease in crystallite size for the sample annealed at 550°C. Transmission spectra showed an initial redshift of the fundamental band edge with 350 and 400°C while a blue shift for the sample annealed at 550°C, which was in agreement with XRD and SEM results. The films exhibited smart window properties as well as nanorod growth at specific annealing temperatures. Apart from showing the PL and defect related peaks, PL studies also supported the observations made in the transmission spectra.     

Influence of Annealing Temperature on the Microstructure and Morphology of TiN Films Synthesized by Dual Magnetron Sputtering

TiN films synthesized on leucosapphire substrates by dual magnetron sputtering have been annealed in vacuum at 600, 700, 800, and 900°C for 2 min. The microstructure and morphology of the films have been studied by X-ray diffraction and scanning electron microscopy at different temperatures. It has been found that annealing changes the microstructure, texture, grain size, and surface roughness of the TiN films.     

A study on the influence of impurities on the recovery and recrystallisation behaviour of cold rolled Ni above room temperature by means of positron annihilation

The recovery and recrystallisation behaviour of cold rolled Ni of different purity such as Ni doped with Sb, Ti and B between room temperature and 550°C was studied by measurement of the peak counting rate of 2γ-angular correlation during annealing with constant heating rate. The results indicate a strong dependence of the annealing behaviour on type and concentration of impurity atoms. For Ni of purity 99.8% and especially for NiSb the peak counting rate shows a large increment in the temperature region 200–400°C which is explained to be caused by the formation of vacancy clusters.     

Deformation and annealing behaviour of a low carbon high Mn TWIP steel microalloyed with Ti

ABSTRACT

A low carbon high Mn, Ti microalloyed dual phase TWIP steel has been processed through cold rolling and annealing. X-ray diffraction reveals the maximum austenite (≈92%) in HRACST sample whereas, the 50CD sample shows 29% ferrite. The microstructure of HRAC and HRACST samples reveal austenite grains with annealing twins and deformation induced ferrite (DIF). The higher amount of DIF along with deformation twins form during cold deformation. Annealing at 500°C shows recovery, whereas at 700°C shows partial recrystallisation and at 900°C reveals almost full recrystallisation. TEM microstructures of the 900°C for 30?min samples reveal annealing twins with TiC particle. Strong Brass {110}<112> and Goss{110}<001> texture components are observed in HRAC, HRACST and 50CD samples. Goss Twin (GT) {113}<332> and Copper Twin (Cu-T) {552}<115> components are observed in 50CD sample. Addition of Ti results in an average grain size of 20?μm. Maximum YS (1176?MPa) and UTS (1283?MPa) values with the lowest ductility of 11% have been obtained for the 50CD sample which is related to the formation of extensive deformation twin and a higher fraction of DIF. 700°C-30?min and 700°C-60?min samples show an increase in ductility (23% and 34%, respectively) with a marginal decrease in tensile strength (1054?MPa). Annealing at 900°C shows ductility restoration up to 60% with higher tensile strength compared to HRACST sample. Ductile fracture of HRAC and HRACST samples transform to brittle fracture in the 50CD sample. Annealing at 900°C for 30?min shows ductile fracture with some (Fe, Mn)S and TiC particles.     

Peculiar Features of Thermal Aging and Degradation of Rapidly Quenched Stainless Steels under High-Temperature Exposures

This article presents the results of comparative studies of mechanical properties and microstructure of nuclear fuel tubes and semifinished stainless steel items fabricated by consolidation of rapidly quenched powders and by conventional technology after high-temperature exposures at 600 and 700°C. Tensile tests of nuclear fuel tube ring specimens of stainless austenitic steel of grade AISI 316 and ferritic–martensitic steel are performed at room temperature. The microstructure and distribution of carbon and boron are analyzed by metallography and autoradiography in nuclear fuel tubes and semifinished items. Rapidly quenched powders of the considered steels are obtained by the plasma rotating electrode process. Positive influence of consolidation of rapidly quenched powders on mechanical properties after high-temperature aging is confirmed. The correlation between homogeneous distribution of carbon and boron and mechanical properties of the considered steel is determined. The effects of thermal aging and degradation of the considered steels are determined at 600°C and 700°C, respectively.     

Thermoluminescent dosimetric characteristics of annealed quartz

In the given present study, the effect of pre-irradiation heat treatment at 500 and 600 ^°C on the glow peaks of synthetic quartz was examined as a function of annealing time to obtain an optimum annealing procedure. It was observed that the annealing time is not a strongly sensitive parameter to change the intensities of glow peaks. On the other hand, the intensities of glow peaks between room temperature (RT) and 200 ^°C were continuously increased during successive readings after heat treatments. Moreover, the intensities of glow peaks above 250 ^°C have good stabilities. The obtained repeatability of a glow peak at ～320 ^°C over 10 cycles is within 5% after the application of annealing at 600 ^°C for 1 h. The general thermoluminescent dosimetric characteristics of synthetic quartz, such as the dose–response, signal fading as a function of storage time, and reusability were also tested using the annealing condition at 600 ^°C for 1 h. It was observed that dose-response behaviours of all glow peaks are similar to each other. They first follow linear part and then saturated at different dose levels. Peak 1 completely disappeared after 1 month storage in the dark room at RT. On the other hand, the intensity of peaks 2+3 was approximately reduced to 15% of its original value whereas the other peaks (P4–P5) were not sufficiently affected during this period.     

Evolution of phase purity and texture on annealing of BiFeO3 thin film prepared by sol-gel technique

We report preparation of phase pure BiFeO₃ thin films on glass, ITO and Si(100) substrates through chemical route using spin coating technique. Sol-gel process was adopted to prepare the films using bismuth nitrate and iron nitrate as precursors. X-Ray diffraction and Raman spectroscopy studies revealed amorphous nature of the as deposited films. Rhombohedral crystalline phase of BiFeO₃ evolved on annealing the films at 500°C, but with Bi₂Fe₄O₉ and Bi₂₄Fe₂O₃₉ as impurity phases. Increasing the annealing temperature to 550°C caused a drastic reduction of the impurity phases and at 600°C, the films were phase-pure BiFeO₃. Micro Raman spectra showed features consistent with the reported characteristic peaks of BiFeO₃ crystalline phase for films annealed at 500 and 550°C. Crystallite size obtained from X-ray diffraction line width analysis are within 30 to 40 nm. Atomic force microscopy (AFM) however showed grain size of ∼192 nm, indicating polycrystalline nature of the grains.      

Effect of annealing treatment on the uniformity of CeO2/TiO2 bilayer resistive switching memory devices

Bilayer CeO₂/TiO₂ films with high-k dielectric property were prepared by rf magnetron sputtering technique at room temperature. Effect of annealing treatment on resistive switching (RS) properties of bilayer CeO₂/TiO₂ films in O₂ ambient at different temperature in the range of 350–550 °C was investigated. Our results revealed that the bilayer films had good interfacial property at 500 °C and this annealing temperature is optimum for different RS characteristics. Results showed that bilayer CeO₂/TiO₂ film perform better uniformity and reliability in resistive switching at intermediate temperature (i.e. 450 °C and 500 °C) instead of low and high annealing temperature (i.e. 350 °C and 550 °C) at which it exhibits poor crystalline structure with more amorphous background. Less Gibbs free energy of TiO₂ as compared to CeO₂ results in an easier re-oxidation of the filament through the oxygen exchange with TaN electrode. However, the excellent endurance property (>2500 cycles), data retentions (10⁵ s) and good cycle-to-cycle uniformity is observed only in 500 °C annealed devices. The plots of cumulative probability, essential memory parameter, show a good distribution of Set/Reset voltage.     

Effect of thermomechanical processing on microstructural evolution and deformation behaviour of polycrystalline magnesium under quasi-static and high strain rate conditions

Abstract

The effect of thermomechanical processing on microstructure evolution and room temperature flow behaviour of polycrystalline magnesium in compression at strain rates of ~10^?2 and ~10³ s^?1 was investigated. Different initial microstructures were produced by optimising rolling and annealing cycles. Prior to annealing for 1 h at 350 °C, Mg samples were processed by two different treatments such as (i) hot rolling at 350 °C and (ii) hot rolling at 350 °C plus cold rolling at room temperature. Introduction of cold working step led to an increased fraction of hard oriented grains with a marginal grain size difference in post-annealed samples. A profound effect of thermomechanical processing on strain hardening rate as well as rate-sensitive flow behaviour of Mg was observed. The influence of prior processing history and strain rate on flow behaviour of Mg was clearly reflected in terms of texture strengthening/weakening phenomena and formation of microstructural deformation bands.     

Secondary defects in low-energy As-implanted Si

14 /cm² dose of As ions followed by both isochronal and isothermal annealing. The elementary defects generated first during solid-phase epitaxial recovery of implantation-induced amorphous layers at temperatures of 550 °C and/or 600 °C are {311} defects 2–3 nm long. They are considered to be transformed into {111} and {100} defects after annealing at temperatures higher than 750 °C. These secondary defects show the opposite annealing behavior to the dissolution and growth by the difference of their depth positions at 800 °C. This phenomenon is explained by the diffusion of self-interstitials contained in defects. With regard to the formation and dissolution of defects, there is no significant difference between the effects of rapid thermal annealing (950 °C for 10 s) and furnace annealing (800 °C for 10 min). Received: 14 November 1997/Accepted: 16 November 1997