Effect of Y2O3 addition on the phase transition and growth of YSZ nanocrystallites prepared by a sol-gel process

The effect of Y₂O₃ addition on the phase transition and growth of yttria-stabilized zirconia (YSZ) nanocrystallites prepared by a sol-gel process with various mixtures of ZrOCl₂ · 8H₂O and Y(NO₃)₃ · 6H₂O ethanol-water solutions at low temperatures has been studied. DTA/TGA, XRD, SEM, TEM and ED have been utilized to characterize the YSZ nanocrystallites. The crystallization temperature of 3YSZ, in which Y₂O₃/(Y₂O₃ + ZrO₂) = 0.03, gel powders estimated by DTA/TG is about 427 °C. When 3YSZ and 5YSZ gels are calcined at 500-700 °C, their crystal structures as composed of coexisting tetragonal and monoclinic ZrO₂, and tetragonal phase decreases with calcination temperature increasing from 500 to 700 °C. Pure cubic ZrO₂ is obtained when added Y₂O₃ is greater than 8 mol%. A nanocrystallite size distribution between 10 and 20 nm is obtained in TEM observations.     

Synthesis, modeling of the structure and kinetic study of the thermal decomposition of La(III) and Nd(III) complexes with 3-hydroxypicolinic acid

Synthesis, spectroscopic studies, prediction of the structure and thermal decomposition of the La(3-OHpic)₃ · 3H₂O and Nd(3-OHpic)₃ · 3H₂O (3-OHpic = 3-hydroxypicolinic acid) complexes are described. Elemental analysis and the IR vibrational data are consistent with the complex formulae. The absorption spectra in ethanol of the La(3-OHpic)₃ · 3H₂O and Nd(3-OHpic)₃ · 3H₂O show maximum absorptions at 214 and 211 nm, respectively, which are shifted to 225 nm in the free ligand. The ab initio method RHF/STO-3G/ECP(MWB52) was used to optimize the geometry and the INDO/S-CI model for calculating the electronic spectra of these complexes. A good agreement between theoretical and experimental UV absorption spectra has been obtained. The thermal decomposition was studied by non-isothermal thermogravimetry. Thermal decomposition reactions of the complexes La(3-OHpic)₃ · 3H₂O and Nd(3-OHpic)₃ · 3H₂O are best described by R2 and R3 kinetic models.     

Preparation and optical properties of samarium doped sol-gel materials

Transparent crack-free glassy monoliths containing up to 0.2 Sm/Si are prepared at room temperature by sol-gel technique. The sol-gel preparation conditions are: acid catalyzed hydrolysis followed by basic catalyzed gelation and controlled drying. The prepared xerogels are characterized by X-ray diffraction, thermogravimetry with Fourier transforming infrared spectroscopy, scanning electron microscopy and optical spectroscopy. The values of the phenomenological Ω-intensity parameters of Sm(III) ions in the gels are (in 10⁻²⁰ cm²) Ω₂ = 76 ± 16.71, Ω₄ = 3.01 ± 0.21, Ω₆ = 2.99 ± 0.41. The oscillator strengths of the Sm(III) ions in the gels are calculated. The results show a linear concentration dependence of Sm(III) in UV/Vis absorption spectra and formation of a Sm(NO₃)₃ · 6H₂O complex at high samarium concentrations.     

Thermal Properties and Phase Transformation of 2 mol% Y2O3-PSZ Nanopowders Prepared by a Co-precipitation Process

Two mol% Y₂O₃-PSZ precursor powders for dental applications were synthesized using ZrOCl₂·8H₂O and Y(NO₃)₃·6H₂O by a co-precipitation process at pH 7 and 348 K for 2 h. The thermal properties and phase transformation of 2Y-PSZ nanocrystallite powder have been investigated using a thermogravimetric and difference scanning calorimeter (TG/DSC), Fourier transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy (TEM), selected area electron diffraction and dilatometric analysis. Two weaker broad exothermic peaks appear at around 618 and 718 K were explored in DSC results. The TG analysis shows that minor weight loss occurs from 298 to 348 K, followed by three major weight losses at 610, 630 and 773 K. Calcinated at 773 and 1273 K, the crystallized phases are composed of the major phase of tetragonal ZrO₂ and minor phase of monoclinic ZrO₂. TEM reveals that the tetragonal ZrO₂ with an average size of less than 20.0 nm is mainly aggregated into the secondary aggregates with a size of small than 30.0 nm. The sintering curve of the compact pellet has a significant shrinkage with a linear rate of 18.5% at about 1341 K. Maximum densification rate happened at 1473 K, demonstrating the good low temperature sinterability for dental applications.     

Preparation of anhydrous dicalcium phosphate, DCPA, through sol-gel process, identification and phase transformation evaluation

Anhydrous dicalcium phosphate, CaHPO₄, DCPA, as a member of the series of calcium phosphates, has considerable biological importance to the biomineralization processes in bones and teeth, and has found practical applications in dental cements and restorative materials. This compound, can reconstruct hard tissues because of high solubility in vivo in comparison with many of the other calcium phosphate compounds. In this work, Ca-deficient DCPA was synthesized through sol-gel process as a new method. Ca(NO₃)₂ · 4H₂O and H₃PO₄ were employed as precursors and identified by XRD, FTIR and SEM spectroscopic techniques. The later technique makes the elemental analysis possible. The measured Ca/P molar ratio suggests, Ca_1−x(H₂PO₄)_2x(H₂PO₄)_1−2x (x = 0.02, 0.04 and 0.07) formula for the synthesized compounds. The effect of aging time and heat treatment (sintering stage) on phase purity and phase transformations of products were systematically studied. The minimum necessary aging time for Ca-deficient DCPA preparation was 24 h. From X-ray patterns of powders sintered at different temperatures, the sintering temperature of Ca-deficient DCPA was confirmed to be 300 °C. According to the experimental results, varying the temperature from 300 to 1000 °C gave different stable phases as products: Ca-deficient DCPA at 300 °C, hydorxyapatite (Ca₅(PO₄)₃OH, HA) at 600 °C and β-tri calcium phosphate (β-Ca₃(PO₄)₂, β-TCP) at 1000 °C.     

Devitrification behavior and structure of Li2O-B2O3-Al2O3 composite gels from metal alkoxides

(30 − x/2)Li₂O·(70 − x/2)B₂O₃·xAl₂O₃(x = 0, 5 and 10) composite gels have been fabricated by the sol-gel method. LiOCH₃, B(OC₄H₉)₃, and Al(OC₄H₉)₃ were used as precursor for Li₂O, B₂O₃, and Al₂O₃, respectively. B(OC₄H₉)₃ and Al(OC₄H₉)₃ were hydrolyzed separately and then mixed. The crystallization behavior and structure of the gels upon thermal treatment temperatures between 150 and 550 °C are characterized on the basis of SEM, XRD and IR analyses. Xerogel with x = 0 exhibits non-crystal features, whereas crystalline phases are found in the xerogels with x = 5 and 10. The crystalline phases are not found with increasing heat treatment temperatures from 150 to 450 °C, but crystalline phases appear present at 550 °C. The xerogel with x = 0, subject to thermal treatment below 450 °C, is found to be still amorphous, and a 550 °C heat treatment leads its structure changing from glassy to crystalline.     

Di-2-pyridylketone semicarbazone as ligand in metal complexes: synthesis and X-ray crystal structure

A series of complexes of di-2-pyridylketone semicarbazone (Hdips) and Mn(II), Co(II), Co(III), Ni(II) and Cu(II) nitrates were synthesized and characterized by means of IR spectroscopy and for cobalt and nickel by X-ray crystal structures. The results are in agreement with the formulae: Mn(Hdips)₂(NO₃)₂·2H₂O, [Co(Hdips)₂](NO₃)₂·H₂O (I), [Ni(Hdips)₂](NO₃)₂·H₂O (II), Cu(Hdips)(NO₃)₂·2H₂O, [Co(dips)₂](NO₃)·2H₂O (III). The structure of I and II are monoclinic, space groupP2₁/c, with, I,a=15.980(4),b=11.531(2),c=16.170(2)Å;=104.20(2)°,Z=4,R=0.032; II,a=16.109(5),b=11.480(3),c=16.135(6)Å;=104.15(2)°,Z=4,R=0.069. Compound III is also monoclinic, space groupP2₁/c witha=12.173(5),b=15.619(5),c=15.338(8)Å;=111.40(4)°,Z=4,R=0.059. In these complexes the ligand is tridentate via carbonylic oxygen, semicarbazone and pyridine nitrogens forming each two five membered chelate rings with the metal in a distorted octahedral geometry.     

CeO2-Bi2O3 nanocomposite: Two step synthesis, microstructure and photocatalytic activity

CeO₂-Bi₂O₃ composite was synthesized via a two-stage process. The precursors were prepared from Ce(NO₃)₃·6H₂O, Bi(NO₃)₃·5H₂O and CO(NH₂)₂ with different molar ratio through the hydrothermal process, and then was completed by carrying out the precursors for 4 h at 600 °C under flowing air atmosphere. Techniques of X-ray diffraction (XRD), transmission electron microscopic (TEM) and diffuse reflectance ultraviolet-vis spectra (UV-DRS) were employed to characterize the as-synthesized materials. The results showed that the microstructure and morphology of CeO₂-Bi₂O₃ composite were similar in spite of different inverse proportion. We also investigated improved photocatalytic activity in the case of CeO₂-Bi₂O₃ composite catalyst compared to the catalytic activity of pure Bi₂O₃ or CeO₂ powder. The suppression of charge recombination in the composite CeO₂-Bi₂O₃ catalyst led to higher catalytic activity for the degradation of RhB. The CeO₂ 10%/Bi₂O₃ photocatalyst exhibited maximum photocatalytic activity. The photocatalytic activity is in close relation with the inverse proportion between reactants.     

Synthesis of Fe-doped nanosized SnO2 powders by chemical co-precipitation method

Fe-doped nanosized SnO₂ powders were prepared by chemical co-precipitation technique using SnCl₄ and FeCl₃ as starting materials and water as a carrier. Experimental results show that the grain size of Fe-doped SnO₂ crystallites is smaller than 5 nm, and the particle size is smaller than 15 nm. When the calcination temperature is below 650 °C, the SnO₂ crystal has tetragonal lattice structure. At higher temperature the particles become a two-phase mixture of tetragonal SnO₂ and hexagonal Fe₂O₃ crystallites. Fe doping can obviously prevent the growth of nanosized SnO₂ crystallites, and a higher Fe-doping concentration is more effective to prevent the growth of nanosized SnO₂ particles when the calcination temperature is below 550 °C.     

Dielectric properties and structural features of barium-iron phosphate glasses

The dielectric constant of barium-iron phosphate glasses with the general composition (40−x)BaO · xFe₂O₃ · (60−x)P₂O₅ has been investigated at two fixed frequencies (100 kHz and 9.0 GHz). The dielectric constant measured using microwave technique, and the ratio O/P of these glasses increase with increasing Fe₂O₃ content. The structure and valence states of the iron ions in these glasses were investigated using Mössbauer spectroscopy, infrared spectroscopy and differential thermal analysis. Both Fe(II) and Fe(III) ions present in these glasses in octahedral coordination act as permanent dipoles, and the increase of the iron concentration increase these permanent dipoles, contributing to the dielectric constant.     

Structural and optical property studies of CdSe crystalline nanorods synthesized by a solvothermal method

CdSe nanorods are synthesized via a simple solvothermal method at a moderate temperature of 180 °C. The influences of introducing hydrazine hydrate (N₂H₄·H₂O) as the reducing agent, and ammonia (NH₃·H₂O) as the complexing agent and also the reaction temperature, on the morphology and size of the obtained CdSe nanorods are investigated and reported. CdSe nanorods with a mean diameter and length of 25 and 82 nm, respectively, are synthesized and the problem of handling the stacking faults present in the long CdSe nanorods is analyzed. The use of increased quantity of hydrazine hydrate and also prolonged reaction time is found to reduce the stacking faults on the synthesized nanorods. The morphology, phase and the optical properties of CdSe nanoparticles are studied using powder X-ray diffraction, TEM and high-resolution transmission electron microscope (HRTEM), UV–visible absorption spectroscopy and photoluminescence (PL) spectroscopy. The low-resolution TEM images confirm the formation of CdSe nanorods, and also the agglomeration of nanoparticles and the presence of few spherical nanoparticles. The strong PL intensity from the CdSe nanorod at 702 nm confirms a blue shift of 14 nm, when compared with the bulk wurtzite CdSe.     

The effect of composition on UV-vis-NIR spectra of iron doped glasses in the systems Na2O/MgO/SiO2 and Na2O/MgO/Al2O3/SiO2

Glasses with the compositions xNa₂O · 10MgO · (90 − x)SiO₂, 10Na₂O · xMgO · (90 − x)SiO₂, 5Na₂O · 15MgO · xAl₂O₃ · (80 − x)SiO₂, xNa₂O · 10MgO · 10Al₂O₃ · (80 − x)SiO₂, 10Na₂O · 10MgO · xAl₂O₃ · (80 − x)SiO₂, 10Na₂O · 5MgO · 10Al₂O₃ · (80 − x)SiO₂ were melted and studied using UV-vis-NIR spectroscopy in the wavenumber range from 5000 to 30 000 cm⁻¹. At [Al₂O₃] > [Na₂O], the UV-cut off is strongly shifted to smaller wavenumbers and the NIR peak at around 10 000 cm⁻¹ attributed to Fe²⁺ in sixfold coordination gets narrower. Furthermore, the intensity of the NIR peak at 5500 cm⁻¹ increases. This is explained by the incorporation of iron in the respective glass structures.     

Synthesis,morphology and phase transition of the zinc molybdates ZnMoO4·0.8H2O/α-ZnMoO4/ZnMoO4 by hydrothermal method

ZnMoO₄ with a rhombus sheet or flower-like structure, α-ZnMoO₄ and needle-like ZnMoO₄·0.8 H₂O were successfully synthesized by simple hydrothermal crystallization processes with citric acid. ZnMoO₄·0.8 H₂O was easily synthesized in a shorter reaction time (2 h) at a higher reactant concentration. It gradually transformed into ZnMoO₄ with a monoclinic wolframite tungstate structure with an increased reaction time, and pure ZnMoO₄ was obtained with a longer reaction time (8 h). Citric acid (CA) played an important role in controlling the morphology of the as-obtained molybdates. The α-ZnMoO₄ and ZnMoO₄ were synthesized by heating ZnMoO₄·0.8 H₂O at 130 °C for 4 h and 8 h, respectively, under hydrothermal conditions. With transforming of ZnMoO₄·0.8 H₂O to α-ZnMoO₄ and further to ZnMoO₄, the needle-like crystals gradually disappeared and were transformed into crystals with rhombus sheet morphology and then further to pentacle or flower-like crystals that can be ascribed to continuous splitting and growing of the rhombus sheets.     

Er photoluminescence enhancement in Ag-doped sol-gel planar waveguides

This paper reports on the study of the effects of silver (Ag^o) nanoparticles on the optical and spectroscopic properties of Er³⁺-doped silica-based gels and glasses, including active bulk materials and planar waveguides for integrated optics. Two different procedures for silver and erbium ion incorporation into the glassy matrices have been investigated: the direct incorporation of a metal salt (AgNO₃ and/or Er(NO₃)₃) into the sol-gel solution, as well as a modified sol-gel process, based on pore-doping of a precursor gel with AgNO₃ and/or Er(NO₃)₃ solutions. The study of the parameters determining the average size and size distribution of the nanoparticles, together with their influence on the sol-gel material densification and Er³⁺ photoluminescence at 1.5 μm, has been performed by means of transmission electron microscopy, plus ultra-violet/visible and photoluminescence spectroscopies. The Ag^o colloidal nanoparticles, obtained by thermal precipitation, were approximately spherical, homogeneously distributed and they exhibited an average size between ∼2 and 15 nm, depending on the silver content and heat treatment performed. They are shown to be responsible for a remarkable enhancement of the Er³⁺ photoluminescence intensity, which is mainly due to the increase of the local electric field around the Er³⁺ ions, due to the surface plasmon resonance of the Ag^o nanoparticles.     

Studies of Er doped germanate-oxyfluoride and tellurium-germanate-oxyfluoride transparent glass-ceramics

An erbium doped germanate-oxyfluoride glass 60GeO₂ · 20PbO · 10PbF₂ · 10CdF₂ (GPOF) and a tellurium-germanate-oxyfluoride glass 30TeO₂ · 30GeO₂ · 20PbO · 10PbF₂ · 10CdF₂ (TGPOF) were prepared in the bulk form. By appropriate heat treatment of the as-prepared glasses above, transparent glass-ceramics were obtained with the formation of β-PbF₂ nanocrystals in the glass matrix confirmed by X-ray diffraction. Optical absorption and photoluminescence measurements were performed on as-prepared glass and glass-ceramics. The luminescence of Er³⁺ ions in transparent glass-ceramics revealed sub-band splitting generally seen in a crystal host. The intensity of red and near infrared luminescence significantly increased in transparent glass-ceramic compared to that in as-prepared glass. Two luminescence bands at 758 nm from ⁴F_7/2 → ⁴I_13/2 and at 817 nm from ²H_11/2 → ⁴I_13/2 transitions were observed from transparent glass-ceramic but cannot be seen from the corresponding as-prepared glass. These results are attributed to the change of ligand field of Er³⁺ ions and the decrease of effective phonon energy when Er³⁺ ions were incorporated into the precipitated β-PbF₂ nanocrystals.     

Scale-up synthesis of zinc borate from the reaction of zinc oxide and boric acid in aqueous medium

Synthesis of zinc borate was conducted in a laboratory and a pilot scale batch reactor to see the influence of process variables on the reaction parameters and the final product, 2ZnO·3B₂O₃·3.5H₂O. Effects of stirring speed, presence of baffles, amount of seed, particle size and purity of zinc oxide, and mole ratio of H₃BO₃:ZnO on the zinc borate formation reaction were examined at a constant temperature of 85 °C in a laboratory (4 L) and a pilot scale (85 L) reactor. Products obtained from the reaction in both reactors were characterized by chemical analysis, X-ray diffraction, particle size distribution analysis, thermal gravimetric analysis and scanning electron microscopy. The kinetic data for the zinc borate production reaction was fit by using the logistic model. The results revealed that the specific reaction rate, a model parameter, decreases with increase in particle size of zinc oxide and the presence of baffles, but increases with increase in stirring speed and purity of zinc oxide; however, it is unaffected with the changes in the amount of seed and reactants ratio. The reaction completion time is unaffected by scaling-up.     

Phase separation and crystallization in the system SiO2-Al2O3-P2O5-B2O3-Na2O glasses

The phase separation and crystallization behavior in the system (80 − X)SiO₂ · X(Al₂O₃ + P₂O₅) · 5B₂O₃ · 15Na₂O (mol%) glasses was investigated. Glasses with X = 20 and 30 phase separated into two phases, one of which is rich in Al₂O₃-P₂O₅-SiO₂ and forms a continuous phase. Glasses containing a larger amount of Al₂O₃-P₂O₅ (X = 40 and 50) readily crystallize and precipitates tridymite type AlPO₄ crystals. It is estimated that the phase separation occurs forming continuous Al₂O₃-P₂O₅-SiO₂ phase at first, and then tridymite type AlPO₄ crystals precipitate and grow in this phase. Highly transparent glass-ceramics comparable to glass can be successfully obtained by controlling heat treatment precisely. The crystal size and percent crystallinity of these transparent glass-ceramics are 20-30 nm and about 50%, respectively.     

Synthesis and structure of [Ca(triethyleneglycol)2](NO3)2·H2O

Crystallization of calcium nitrate from a toluene solution of triethyleneglycol (= 2,2-[1,2-ethanediylbis(oxy)]-bisethanol) resulted in the formation of the 1:2 solvate [Ca(triethyleneglycol)₂](NO₃)₂·H₂O. [Ca(C₆H₁₄O₄)₂](NO₃)₂·H₂O is monoclinic, P2₁/c, a = 15.775(1), b = 8.660(2), c = 16.342(1) Å, = 91.239(7)°, V = 2232.1(6) ų, Z = 4, and D _c = 1.429 g cm^–3. The eight-coordinate calcium has square antiprismatic geometry with two triethyleneglycol molecules straddling the metal center. The nitrate anions and water of crystallization are involved in hydrogen bonding with the alcoholic hydrogen atoms.     

Synthesis and crystal structure of [Y(NO3)3(OH2)3]·(Me2-16-crown-5)·H2O

The complex [Y(NO₃)₃(OH₂)₃]·(Me₂-16-crown-5)·H₂O has been prepared and its crystal and molecular structure determined using single crystal X-ray diffraction. The colorless crystals belong to the monoclinic space group P2₁/n with Z = 4. Lattice parameters are a = 10.420(1), b = 17.257(3), c = 14.646(2) Å, = 96.79(1)°, V = 2615.1(6) ų. The yttrium(III) ion is nine-coordinate, bonded to three bidentate nitrate groups and three water molecules. The average Y–O(nitrate) and Y–O(water) distances are 2.42(3) and 2.33(1) Å, respectively. The average HO–H···O hydrogen bonded separation is 2.767Å.     

Synthesis and structure of bis(2,6-dimethylpyrazine)(THF)copper(II) nitrate

Attempts to crystallize Cu(2,6-dmpz)(NO₃)₂ (2,6-dmpz = 2,6-dimethylpyrazine) by reaction of 2,6-dmpz with Cu(NO₃)₂·3H₂O in THF resulted in the synthesis of Cu(2,6-dmpz)₂(NO₃)₂·THF. The compound crystallized in the monoclinic space group C2/c and exists as isolated molecules with distorted square pyramidal geometry: a = 11.609(4) Å, b = 10.415(3) Å, c = 18.256(6) Å, = 108.332(4)°. The 2,6-dmpz molecules coordinate to the Cu ions through the distal (remote from the methyl) nitrogens. The molecules are arrayed in stacks parallel to the b-axis.