Cubic Phase Crystallization Research Articles

Structural and optical properties of erbium doped ceria nanoparticles synthesized by hydrothermal method

The lanthanide compound nanoparticles were prepared by the hydrothermal method. They were characterized by x-ray diffractometer, scanning electron microscopy, ultraviolet-visible spectrophotometry and photoluminescence. The x-ray diffractometer patterns of all samples indicated crystallization of pure ceria fluorite cubic phase. The optical properties of cerium oxide nanoparticles have changed with the increase of erbium ion in initial reactants. Two peaks at 739 and 780 nm are observed in photoluminescence spectra at 200 nm excitation in the range of 400–800 nm. The lanthanide compound nanoparticles with strongest luminescence were identified in the samples.

Yttrium-dopants-induced phase-controllable and luminescence-tunable lanthanide-doped α/β-NaYbF4 nanocrystals in glass for laser-driven upconverted lighting

In-situ glass crystallization is an effective way to integrate lanthanide-doped upconversion nanocrystals into amorphous glass, producing bulky nanocomposites for specific applications. However, the precipitation of hexagonal NaYbF4 nanocrystals from glass is rarely reported owing to the preferred crystallization of cubic phase. Herein, phase-controllable in-situ crystallization of cubic/hexagonal NaYbF4 nanocrystals in glass is achieved via Y3+ doping. A series of structural and spectroscopic characterizations evidence the formation of Na(Yb/Y)F4 solid-solution nanocrystals in glass and the incorporation of lanthanide emitting centers (Er3+, Tm3+, Eu3+) into the crystalline lattice. Introducing high-content Y3+ dopants is beneficial to induce the crystallization of hexagonal NaYbF4 phase in glass and enables elaborated tunability of Er3+ upconversion emissive colors. Finally, a prototype upconverted solid-state-lighting device is constructed by coupling 980 nm laser with the as-prepared Er/Tm doped monolithic glasses containing Na(Yb/Y)F4 nanocrystals, producing bright upconversion white-light with luminous efficiency of 1 lm/W and energy efficiency of 0.5%.

Characterization of 3 mol% Fe from Different Source Doped 8YSZ Ceramics

Pure 8 mol% yttria stabilized zirconia (YSZ) and 3mol % of Fe-doped YSZ electrolyte from different source of Fe (p)in oxide form (pure iron oxide powders, Fe2O3) and Fe(s) source from salt (iron nitrate, Fe(NO3)3) were prepared and sintered at 1550°C for 2 hours. The effect of Fe dopant from different source of Fe to the crystal structure and ionic conductivity of 8YSZ samples were investigated. The addition of 3 mol % Fe from iron nitrate source (sample 3Fe(s)YSZ) greatly enhanced the growth of monoclinic phase as compared to 8YSZ sintered samples while the addition of 3 mol % Fe from pure iron oxide powder source (sample 3Fe(s)YSZ) enhanced the crystallization of cubic phase and decrease the monoclinic phase. The addition of Fe significantly enhanced the ionic conductivity of 8YSZ sample for both source of Fe. However, 3Fe(p)8YSZ has smaller grain resistivity and thus has higher conductivity compared to 3Fe(s)YSZ.

Crystallization kinetics of new heavy metal oxide glasses within the Sb2O3-Na2O-WO3-PbO system

Crystallization kinetic studies of new quaternary antimonite glasses within the Sb2O3-Na2O-WO3-PbO system were performed by non-isothermal methods using differential scanning calorimetry (DSC), X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. The kinetic parameters n and m which determine crystallization reaction mechanism in glasses were obtained using experimental values of the crystallized volume fraction, χ, by applying Ozawa method. Values of n and m were found as 1 indicating surface crystallization which was confirmed by SEM investigations. The values of crystallization activation energy were calculated in the range of 234–272kJ/mol by using seven different theoretical models. The calculated crystallization activation energy values were associated with the crystallization of cubic crystalline senarmontite phase of Sb2O3.

Microwave assisted synthesis of cubic Zirconia nanoparticles and study of optical and photoluminescence properties

Synthesis of pure ZrO2 nanoparticles in its cubic phase is a challenging task for the researchers. ZrO2 is a promising material and has received considerable attention recently due to superior properties that provide significant advantages in various applications like display systems and lighting. This paper discusses a better method of synthesis of pure ZrO2 nano crystals in cubic phase, free from impurities that alter the luminescence emissions. Studies on structural, optical and photoluminescence properties are reported. The structural studies show that as formed ZrO2 nanoparticles are in cubic phase. The crystallinity and phase formation of the samples were studied by XRD, the crystallinity increases as the calcination temperature increases. The samples are mesoporous and pore size decreases with increase in the calcination temperature as studied by BET. The optical energy band gap (Eg) was calculated and found to be 5.21eV for the as formed sample. As calcination temperature increases the increase in the optical band gap is observed. The PL spectra show an intense violet emission band peak centered at 387nm, due to the presence of the oxygen vacancies in the ZrO2 matrix. The crystallinity, particle size and the phase formation was further confirmed by HRTEM.

Single crystallization of an inverse bicontinuous cubic phase of a lipid.

We report a simple method to produce a single crystal region of an inverse bicontinuous cubic (QII) phase of a lipid, 1-monoolein. By starting with the lipid of the sponge (L3) phase in the presence of 1,4-butanediol, we can obtain a single crystal region of the double-diamond QII phase in 1 week by controlled dilution of 1,4-butanediol. The length of the single crystal region in a 0.5 mm diameter capillary was on the order of millimeters. X-ray diffraction images of the region showed diffraction "spots", but not "rings" as in powder diffraction. The diffraction images also changed rotation angle dependently. We could assign Miller indices to all of the distinguishable diffraction spots from the region. This method would bring benefits to the basic and applied research areas of the Q phases.

Visualization of membrane protein crystals in lipid cubic phase using X-ray imaging.

The focus in macromolecular crystallography is moving towards even more challenging target proteins that often crystallize on much smaller scales and are frequently mounted in opaque or highly refractive materials. It is therefore essential that X-ray beamline technology develops in parallel to accommodate such difficult samples. In this paper, the use of X-ray microradiography and microtomography is reported as a tool for crystal visualization, location and characterization on the macromolecular crystallography beamlines at the Diamond Light Source. The technique is particularly useful for microcrystals and for crystals mounted in opaque materials such as lipid cubic phase. X-ray diffraction raster scanning can be used in combination with radiography to allow informed decision-making at the beamline prior to diffraction data collection. It is demonstrated that the X-ray dose required for a full tomography measurement is similar to that for a diffraction grid-scan, but for sample location and shape estimation alone just a few radiographic projections may be required.

The improvement of dispersibility of YIG precursor prepared via chemical coprecipitation

To prevent YIG (Y3Fe5O12) precursor from agglomeration in the chemical coprecipitation process, the relationship between YIG precursor’s surface electric charge and its dispersibility was studied through the combination of electrophoresis and SEM test. The thermochemical characteristics of YIG precursor with improved dispersibility were also investigated. The results showed: when the coprecipitation pH is smaller than 10.5, the YIG precursor is positively charged which is in favor of YIG precursor’s good dispersibility. The YIG precursor coprecipitated at pH of 9.5 has the least agglomeration due to its most positive surface electric charge. The effect of three typical surfactants viz., SDS (anionic surfactant), CATB (cationic surfactant) and p123 (non-ionic surfactant) on the surface electric charge of YIG precursor was studied. The CATB surfactant is found to be superior to the other two surfactants in the aspect of improving YIG precursor’s dispersibility. The YIG precursor with improved dispersibility has superior homogeneity. The crystallization of cubic YIG phase can be initiated directly from amorphous YIG precursor just below 758°C and completed above 758°C, without the formation of other intermediate phase and tetragonal YIG phase, which are often involved in the preparation of YIG or doped-YIG by applying chemical coprecipitation method.

Mid-infrared spectroscopic study of crystallization of cubic spinel phase from metakaolin

The structural changes during thermal conversion of metakaolinite into cubic spinel phase that was in literature considered as Al–Si spinel or γ-Al 2O 3 were investigated by mid-infrared spectroscopy (FT-IR) and differential scanning calorimetry (DSC) using medium ordered kaolin with high content of kaolinite. Spectrum features were studied in the mid-infrared region from 4000 to 400 cm −1 as function of fractional conversion that resulted from DSC experiments. The increasing contends of Al–O bonds in the octahedral position (AlO 6) was observed during thermal transformation. The high ratio of antisymmetric stretching of Si–O–Al and Si–O–Si bands and bands belonging to stretching of Al–O bonds in the (AlO 4) tetrahedra and (AlO 6) octahedra decreases exponentially with fractional conversion. The antisymmetric stretching band of Si–O–Si bond in the (SiO 4) tetrahedra becomes more expressive due to formation of amorphous SiO 2 phase.

Structural characterization of CdS nanoparticles grown in polystyrene matrix by thermolytic synthesis

Cadmium sulfide nanoparticles embedded in a polystyrene matrix (CdS/PS) were successfully prepared by in situ thermolysis of a cadmium thiolate precursor dispersed in the polymer. The heat-induced formation of cadmium sulfide was studied by thermogravimetric analysis and differential thermal analysis, while the chemistry of the reaction forming the CdS/PS compound was investigated by nuclear magnetic resonance and X-ray photoelectron spectroscopy. The structural characterization was performed by X-ray diffraction and transmission electron microscopy. The CdS nanocrystals are single crystals of cubic phase (zincblende structure) of spherical shape. The average diameter of the nanocrystals embedded in the polystyrene matrix achieved by our synthesis process is as small as 2.5±0.5 nm. Room temperature UV–VIS absorption spectra exhibit a shoulder at 412 nm that is consistent with the presence of CdS nanocrystals of ∅≈2 nm. The role of the polymer on the nanoparticle growth was also discussed.

Simulating Pyroelectric Curves of TGS Series Crystals by Pseudo Thermodynamic Model

The thermodynamic theory of Triglycine sulfate crystal (TGS) series pyroelectric crystals is studied in this paper. The state of pyroelectric crystals in cubic phase to be considered is assumed to approach the state of the single crystal at absolute zero. When the cubic phase transits into the tetragonal phase with temperature decreasing, the entropy and spontaneous polarization will change. Based on the Landau thermodynamic theory, pyroelectric equation of pseudo thermodynamics model is established when the classical oscillation equation is modified, and the simulating curves described by pseudo thermodynamics model are in accordance with that of the experimental results of TGS series pyroelectric crystals.

Lyotropic bicontinuous cubic phase single crystals investigated using high-resolved X-ray scattering

Single crystals of an Ia d bicontinuous direct cubic phase formed by a non-ionic surfactant in water are investigated using high-resolved X-ray diffraction. The shape of the Bragg peaks confirms the existence of a 3D long-range order inside the cubic phase. A weak diffuse scattered intensity signal is measured very near the Bragg peaks. We attribute this signal to thermal diffuse scattering (TDS) and we give an estimation of the contribution of elastic waves to this TDS.

Flux synthesis of cubic potassium antimonate

Although the compound KSbO 3 has been reported to occur in a high temperature cubic polymorph, only the rhombohedral ilmenite phase was obtained in this study for pure material at ambient pressure and temperatures up to about 1350°C in open Pt crucibles or sealed Pt tubes. With the addition of about 2 mole percent SiO 2, B 2O 3 or other oxides of small cations a primitive cubic phase was found with a⋍9.578 A . Small single crystals of a body centered cubic phase (a=9.605A) were easily synthesized by a flux evaporation technique at about 1000°C in an open Pt crucible from a composition of about 5 mole % Sb 2O 4:95 mole % KF. The exact composition and structure of this phase (presumably K 1−xSbO 3−xF x, 0<x≤0.5) is now under investigation.