On the synthesis of AlPO4-21 molecular sieve by vapor phase transport method and its phase transformation to AlPO4-15 molecular sieve

An experimental design was applied to the synthesis of AlPO₄-21 molecular sieve (AWO structure) by vapor phase transport (VPT) method, using tetramethylguanidine (TMG) as the template. In this study, the effects of crystallization time, crystallization temperature, phosphor content, template content and water content in the synthesis gel were investigated. The materials obtained were characterized by X-ray diffraction, scanning electron microscopy and fourier transform infrared spectroscopy (FT-IR). Microstructural analysis of the crystal growth in vapor synthetic conditions revealed a revised crystal growth route from zeolite AlPO₄-21 to AlPO₄-15 in the presence of the TMG. Homogenous hexagonal prism AlPO₄-21 crystals with size of 7 × 3 μm were synthesized at a lower temperature (120 °C), which were completely different from the typical tabular parallelogram crystallization microstructure of AlPO₄-21 phase. The crystals were transformed into AlPO₄-21 phase with higher crystallization temperature, longer crystallization time, higher P₂O₅/Al₂O₃ ratio and higher TMG/Al₂O₃ ratio.     

Synthesis and characterization of highly textured Pt–Bi thin films

Pt–Bi films were synthesized on glass and thermally oxidized silicon substrates by e-beam evaporation and annealing. The structures were characterized using X-ray diffraction (XRD) and transmission electron microscopy/selected area electron diffraction (TEM/SAED) techniques. Single-phase PtBi was obtained at an annealing temperature of 300°C, whereas a higher annealing temperature of 400°C was required to obtain the highly textured γ-PtBi₂ phase. TEM/SAED analysis showed that the films annealed at 400°C contain a dominant γ-PtBi₂ phase with a small amount of β-PtBi₂ and α-PtBi₂ phases. Both the PtBi and γ-PtBi₂ phases are highly textured in these two kinds of film: the c-axis of the hexagonal PtBi phase is mostly in the film plane, whereas the c-axis of the trigonal γ-PtBi₂ phase is perpendicular to the film plane. The electrical resistivity of the film with the γ-PtBi₂ phase was smaller by one order of magnitude than that of the film with the PtBi phase.     

Synthesis and Raman characterization of mono-sized single-wall carbon nanotubes in one-dimensional channels of AlPO4-5 crystals

Mono-sized single-wall carbon nanotubes were formed in one-dimensional channels of AlPO₄-5 single crystal (AFI) by pyrolysis of tripropylamine (TPA). Raman spectra have been measured for the TPA-AFI crystals thermally processed at different conditions. TPA molecules are carbonized at 400 °C, and carbon nanotubes were formed at 500 °C or above. The radial-breathing mode, which is special for carbon nanotube geometry, was observed. Three Raman-active modes with symmetry A _1g, E _1g, and E _2g were identified by detailed symmetrical analysis for the polarized-Raman spectra. Received: 29 October 1998 / Accepted: 29 March 1999 / Published online: 24 June 1999     

Phase transitions in liquid crystal 6O.4 (p-<Emphasis Type="Italic">n</Emphasis>-hexyloxybenzylidine-p′-<Emphasis Type="Italic">n</Emphasis>-butylaniline)

DSC measurements on p-n-hexyloxybenzylidine-p′-n-butylaniline (6O.4) showed that the crystalline to liquid crystalline (K-S _H) transition at 33.7°C observed in the heating cycle does not revert even when the sample is cooled down to −100°C. Hence it is inferred that a physically stable supercooled liquid crystalline phase is formed on cooling 6O.4. To investigate the K-S _H transition further the techniques of polarized microscopy and X-ray diffraction were used which concurred with the DSC results. Quasielastic neutron scattering measurements carried out to study the re-orientational motions in the ordered phases of 6O.4 (K and S _H) show that while in the crystalline phase (at RT) the re-orientational motion is found to involve only the core of the molecule, in the S _H phase (at 45°C) the dynamics involves the whole molecule and this motion is found to persist even when the sample cools back to room temperature corroborating the results of the DSC, microscopy and X-ray diffraction.      

Investigation of the ε phase in the Fe–Al system by high-temperature neutron diffraction

In the central part of the Fe–Al system between about 58 and 65 at.% Al, a high-temperature phase denoted as ε occurs with a hitherto unknown crystallographic structure. The phase is stable between 1231°C and 1095°C. In order to study the crystallographic structure of the ε phase, in situ high-temperature neutron time-of-flight diffraction experiments have been performed at the HIPPO instrument at the Los Alamos Neutron Science Center (LANSCE). The ε phase was found to have the formula Fe₅Al₈ with a body-centred cubic structure of the Hume–Rothery Cu₅Zn₈ type (I $\bar{4}3In the central part of the Fe–Al system between about 58 and 65 at.% Al, a high-temperature phase denoted as ε occurs with a hitherto unknown crystallographic structure. The phase is stable between 1231°C and 1095°C. In order to study the crystallographic structure of the ε phase, in situ high-temperature neutron time-of-flight diffraction experiments have been performed at the HIPPO instrument at the Los Alamos Neutron Science Center (LANSCE). The ε phase was found to have the formula Fe₅Al₈ with a body-centred cubic structure of the Hume–Rothery Cu₅Zn₈ type (I[`4]3\bar{4}3m (No. 217), Z=4, cI52) and 52 atoms in the unit cell. Its lattice parameter is a=8.9756(2) ? at 1120°C, which is 3.02 times that of cubic FeAl (B2) at the same temperature. We report here the evolution of the crystallographic parameters over the temperature range between 1080°C and 1120°C.     

Phase stability of Crn+ 1GaCn MAX phases from first principles and Cr2GaC thin‐film synthesis using magnetron sputtering from elemental targets

Ab‐initio calculations have been used to investigate the phase stability and magnetic state of Cr_{n+ 1}GaC_n MAX phase. Cr₂GaC (n = 1) was predicted to be stable, with a ground state corresponding to an antiferromagnetic spin configuration. Thin‐film synthesis by magnetron sputtering from elemental targets, including liquid Ga, shows the formation of Cr₂GaC, previously only attained from bulk synthesis methods. The films were deposited at 650 °C on MgO(111) substrates. X‐ray diffraction and high‐resolution transmission electron microscopy show epitaxial growth of (000?) MAX phase. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

In situ electron microscopy investigations of solid-state synthesis in Al/Au thin bilayer films

In situ transmission electron microscopy investigations of solid-state synthesis in Al/Au thin bilayer films are conducted. The samples are heated in the column of a transmission electron microscope. The heating temperature is changed from room temperature to 300°C with a heating rate of up to 120°C min^?1. It is found that solid-phase synthesis starts at ≈100°C. At 140 ± 5°C, two crystal phases, Al₂Au (Fm3m) and AlAu₂ (I4/mmm), are simultaneously observed, while at 235 ± 5°C and higher (up to 300°C) only Al₂Au phase is detected.     

Suppression of structural degradation of LiNi0.9Co0.1O2 cathode at 90 °C by AlPO4-nanoparticle coating

This study examined the electrochemical and structural stability of ∼1.5 wt.% AlPO₄-coated LiNi_0.9Co_0.1O₂. The AlPO₄-coated LiNi_0.9Co_0.1O₂ retained ∼60% of the original capacity after 50 cycles, compared with the ∼30% capacity retention of the bare LiNi_0.9Co_0.1O₂. The discharge profiles and cyclic voltammograms from 4.5 V at 90 °C for 4 h showed enhanced structural stability. Scanning electron microscopy and X-ray diffraction revealed that the AlPO₄-coated LiNi_0.9Co_0.1O₂ had less degradation than the bare LiNi_0.9Co_0.1O₂.     

Dielectric properties of Bi4Ti3O12–SrBi4Ti4O15 intergrowth ceramics synthesized by a modified oxalate route

In this study, Bi₄Ti₃O₁₂–SrBi₄Ti₄O₁₅ (BIT–SBTi) intergrowth ferroelectric ceramics was synthesized by a modified oxalate route. The phase formation behaviour, structure, morphology and electrical properties of the intergrowth ceramics were also investigated. The phase formation takes place through intermediate phases like SrBi₂O₄ and Bi₁₂TiO₂₀. The precursor mostly changes to Bi₄Ti₃O₁₂ at 600°C and to BIT–SBTi intergrowth at 800°C. Rietveld analysis of the X-ray diffraction pattern showed that the structure of the intergrowth compound was orthorhombic with lattice parameters a = 5.4408(3), b = 5.4505(1) and c = 74.0851(4) Å. The intergrowth ferroelectrics showed a phase transition at 610°C and a frequency-stable permittivity and dielectric loss behaviour. The intergrowth ferroelectrics also showed a larger 2P_r than their constituents BIT and SBTi.     

Effect of phase transformation on optical and dielectric properties of zirconium oxide nanoparticles

Zirconium oxide nanoparticle (ZrO₂) is synthesized by the hydrothermal method at different calcination temperatures. The structural analysis is carried out by X-ray diffraction and Raman spectra. The sample prepared at 400 °C and 1100 °C showed the cubic and monoclinic phase, respectively, and the sample calcined at 600 °C and 800 °C showed the mixed phase with co-existence of cubic and monoclinic phases. Furthermore, the morphology and particle size of these samples were investigated by scanning electron microscope (SEM) and transmission electron microscope (TEM) analysis. The band gap estimated from UV–Vis spectra of ZrO₂ (zirconia) nanocrystalline materials calcined at different temperatures from 400 °C to 1100 °C was in the range of 2.6–4.2 eV. The frequency dependence of dielectric constant and dielectric loss was investigated at room temperature. The low frequency region of dielectric constant is attributed to space charge effects.     

Structural evolution of ZrO2–mullite nanocomposites from the Si–Al–Zr–O amorphous bulk

ZrO₂–mullite nanocomposites were fabricated by in-situ-controlled crystallization of Si–Al–Zr–O amorphous bulk at 800–1250°C. The structural evolution of the Si–Al–Zr–O amorphous, annealed at different temperatures, was studied by X-ray diffraction, infrared, Laser Raman spectroscopy, field emission scanning electron microscopy, and high-resolution transmission electron microscopy. The materials consisted of an amorphous phase up to 920°C at which phase separation of Si-rich and Al, Zr-rich clusters occurred. The crystalline phases of t-ZrO₂ and mullite were observed at 950°C and 1000°C, respectively. Mullite with a tetragonal structure, formed by the reaction between Al–Si spinel and amorphous silica at low temperature, changed into an orthorhombic structure with the increase of temperature. It was the phase segregation that improved crystallization of the Si–Al–Zr–O amorphous bulk. The anisotropic growth of mullite was observed and the phase transformation from t-ZrO₂ to m-ZrO₂ occurred when the temperature was higher than 1100°C.     

Dielectric and calorimetric studies on 1BC1EPOPB feroelectric liquid crystal having a large spontaneous polarization

Experimental investigations on the ferroelectric liquid crystal, R-4′(1-butoxycarbonyl-1-ethoxy) phenyl 4-(4-octyloxy phenyl) benzoate (1BC1EPOPB) of large spontaneous polarization (P _S(+) = 240?nC?cm^?2), using dielectric and calorimetric techniques, are reported. The temperature range of 25.0–125.0°C has been chosen for dielectric measurements. Dielectric dispersion studies are carried out in the temperature range 45.0–75.0°C and in the frequency range 2?Hz to 2?MHz for the smectic A, smectic C* and smectic X phases. A new phase called ‘smectic X’ has been found around 56.3°C. The transition temperatures identified by the dielectric dispersion studies for different phases and those given by DSC techniques are in close agreement.     

The microstructure of SiO thin films: from nanoclusters to nanocrystals

The microstructure and electronic structure of silicon-rich oxide (SRO) films were investigated using transmission electron microscopy and electron energy loss spectroscopy as the main analytical techniques. The as-deposited SRO film was found to be a single phase SiO_1.0, as suggested by its electronic structure characteristics determined by the valence electron energy loss spectrum. This single phase undergoes a continuous but incomplete phase decomposition to Si and SiO₂ for films annealed between 300 and 1100°C. The resulting Si phase first appears as ～2?nm-diameter amorphous clusters which grow to larger sizes at higher annealing temperatures, but only crystallize at a critical temperature between 800 and 900°C. This cluster/matrix configuration of the SRO films is consistent with the appearance of the interface plasmon and its oscillator strength as a function of the nanoparticle size. Three separate stages were identified in the sequence of annealed films that were characterized by the presence of single-phase SiO, amorphous silicon nanoclusters, and silicon nanocrystals, respectively. The presence of amorphous silicon nanoclusters in the intermediate stage, the mean size of which can be controlled via annealing, may offer an alternative to silicon nanocrystal composites for optical applications.     

Microstructure,dielectric, and piezoelectric properties of Ce‐modified Na0.5Bi4.5Ti4O15 high temperature piezoceramics

The cerium modified sodium bismuth titanate (Na_0.5Bi_4.5Ti₄O₁₅, NBT) piezoelectric ceramics have been prepared by using the conventional mixed oxide method. X‐ray diffraction analysis revealed that the cerium modified NBT ceramics have a pure four‐layer Aurivillius phase structure. The piezoelectric activity of NBT ceramics was found significantly improved by the modification of cerium. The Curie temperature T_c, and piezoelectric coefficient d₃₃ for the NBT ceramics with 0.50 wt% cerium modification were found to be 655 °C, and 28 pC/N respectively. The Curie temperature gradually decreased from 668 °C to 653 °C with the increase of cerium modification. The dielectric spectroscopy showed that the samples possess stable piezoelectric properties, demonstrating practical potential that for high temperature applications. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Interfacial reactions of rf-sputtered TiNi thin films on (100) silicon with a SiN diffusion barrier

Silicon nitride (SiN) with a 50?nm thickness on Si(100) as a thermal barrier was obtained by plasma-enhanced chemical vapour deposition (PECVD). TiNi thin films were rf sputtered on a SiN/Si substrate and then annealed at 400–700°C for 30?min. Their interfacial reactions were studied using transmission electron microscopy, X-ray diffraction and Auger electron spectroscopy analyses. Experimental results show that the thickness of reaction layer in TiNi/SiN/Si specimens is clearly reduced, compared with that in TiNi/Si specimens under the same annealing conditions. The significant effect of the SiN layer as a diffusion barrier in TiNi/SiN/Si can be recognized. N and Si atoms diffuse from the SiN layer to react with TiNi films at 500°C and 600°C respectively. The TiN_{1 ? x} phase is formed in specimens annealed at 500°C, and mixed Ti₂Ni₃Si and Ti₄Ni₂O compounds are found at 600°C. In the specimen annealed at 700°C, the reaction layer has sublayers in the sequence TiNi/Ti₄Ni₂O/Ti₂Ni₃Si/TiN_{1 ? x} /SiN/Si. The SiN thermal barrier obtained by PECVD caused quite different diffusion species to cross the interfaces between TiNi/SiN/Si and TiNi/Si specimens during the annealing.     

Synthesis of SmAlO<Subscript>3</Subscript> nanocrystalline powders by polymeric precursor method

SmAlO₃ nanocrystalline powders were successfully synthesized by the polymeric precursor method using ethylenediaminetetraacetic acid as a chelating agent. The precursor and the derived powders were characterized by thermogravimetry analysis (TG) and differential scanning calorimetry analysis (DSC), infrared spectroscopy (IR), X-ray diffractometry (XRD) and transmission electron microscopy (TEM). The results showed that pure SmAlO₃ powder with orthorhombic perovskite structure could be synthesized at 800°C for 2 h without formation of any intermediate phase. The average particle size of the powder synthesized at 900°C was as low as 28 nm. Subsequently, the bulk SmAlO₃ ceramics were prepared at various sintering temperatures using the synthesized powders calcined at 900°C for 2 h as starting materials. The sintering experiments indicated that the sample sintered at 1550°C for 2 h exhibited the highest relative density of 97.2% and possessed the best microwave dielectric properties of ε _r=20.94, Q×f=78600 GHz and τ _f=−71.8 ppm/°C.     

Thermostimulated surface autosegregation in bismuth ferrite single crystals

The chemical and phase composition and morphological features of the surface nanostructure have been studied by the methods of high-resolution scanning electron microscopy, X-ray microprobe analysis, and atomic force microscopy in bismuth ferrite single crystals. This structure was formed as a result of the thermostimulated surface segregation after annealing in air or vacuum at the pressure of 10⁻⁴ Pa. It has been experimentally found that, at temperatures less than 500°C, Bi₂F₄O₉ nanoparticles were formed due to the selective diffusion of iron atoms to the surface. Starting from 300°C in vacuum and 450°C in air, the segregating atom type changed and nanophases with high bismuth concentration (sillenites Bi_{26 − x} Fe _x O₃₉ and Bi₂O₃ appeared in some regions. The partial orientation of new phases has been observed in some surface regions. A probable mechanism of the described phenomenon that represents a combination of selective intrinsic mass-transport of atoms from the bulk to the surface and their thermal evaporation has been discussed.     

Superficial Mullite Reinforcement from Silica Coating on Alumina: Influence of Y2O3 Addition

In the present work the sol–gel process is used to obtain mullite (3Al₂O₃·2SiO₂) from silica (SiO₂) deposition on alumina (Al₂O₃) cylindrical pieces. The influence of different percentages of yttria (Y₂O₃) on this superficial reaction is also studied. The alumina matrix is constituted by commercial γ-alumina of 99.99% purity with very high porosity. The cylinders are 3 mm in diameter and 4–6 mm in length. SiO₂ is deposited on the cylinders by sol–gel process, from TEOS (tetraethyl orthosilicate, Si(OCH₂CH₃)₄) in ethanol solution. The yttrium oxide is suspended in this solution and then the alumina cylinders constituting the support material are added. Silica is produced by the hydrolysis reaction of the mentioned alkoxide. The molar ratio TEOS/ETOH/H₂O is strictly controlled to be 2/4/4. The hydrolysis is carried out in basic medium adding 0.3 ml NH₄OH, and at 40°C. The basic medium is used to accelerate the steps of the sol–gel process. The resulting pH before the hydrolysis starts is 9.8. Samples with 2%, 4% and 6% yttria addition were prepared and then heat treated at 1300°C and 1500°C for two hours. For comparative purposes samples without yttria were prepared and treated in the same way. The obtained products were characterized by optical and scanning electron microscopies, electron diffraction analysis X-ray and X-ray diffraction, among other techniques.     

Observation of insulating–insulating monoclinic structural transition in macro‐sized VO2 single crystals

VO₂ single crystals with unprecedented quality, exhibiting a first‐order metal–insulator transition (MIT) at 67.8 °C and an insulator –insulator transition (IIT) at ～49 °C, are grown using a self‐flux evaporation method. Using synchrotron‐based X‐ray microdiffraction analysis, it is shown that the IIT is related to a structural phase transition (SPT) from the monoclinic M2 phase to the M1 phase upon heating while the MIT occurs together with a SPT of M1 to the rutile R phase. All previous reports have shown that VO₂ exists in the M1 phase at room temperature in contrast to the M2 phase observed in this work. We suggest that internal strain inside single crystal VO₂ may generate the previously unobserved IIT and the unusual room temperature structure. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Calibration of berlinite (AlPO4) as Raman spectroscopic pressure sensor for diamond‐anvil cell experiments at elevated temperatures

Changes in the band position of the 462 and the 1111 cm^–1 A₁ modes of berlinite (AlPO₄) with temperature and pressure were determined in situ to 500°C and to 10 GPa using Raman spectroscopy and diamond‐anvil cells. These bands shift in opposite directions with pressure and, likewise, with temperature. At a known temperature, the relative difference of both band positions (Δν)_P,T can therefore be used as a pressure gauge that does not require calibration of the spectrometer. At ambient pressure, the observed temperature dependence of this relative difference of the line positions is very close to linear and can be described by (Δν)_{T, 0.1 MPa} (cm^–1) = 0.0181 T – 0.46 where 23 ≤ T (°C) ≤ 500. Along the 23°C isotherm to 10 GPa, pressure and relative wavenumber difference (Δν)_{P, 23°C} are related by the equation P (GPa) = 0.00083 [(Δν)_{P, 23°C}]² – 0.062 (Δν)_{P, 23°C}. Both equations can be combined to determine pressures at higher temperatures under the assumption that the change in (Δν)_P,T with pressure is insensitive to temperature. Copyright © 2011 John Wiley & Sons, Ltd.