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.     

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.     

Electron spin resonance and magnetic studies on CaO-SiO2-P2O5-Na2O-Fe2O3 glasses

Room temperature electron spin resonance (ESR) spectra and temperature dependent magnetic susceptibility measurements have been performed to investigate the effect of iron ions in 41CaO · (52 − x)SiO₂ · 4P₂O₅ · xFe₂O₃ · 3Na₂O (2 ? x ? 10 mol%) glasses. The ESR spectra of the glass exhibited the absorptions centered at g ≈ 2.1 and g ≈ 4.3. The variation of the intensity and linewidth of these absorption lines with composition has been interpreted in terms of variation in the concentration of the Fe²⁺ and Fe³⁺ in the glass and the interaction between the iron ions. The magnetic susceptibility data were used to obtain information on the relative concentration and interaction between the iron ions in the glass.     

Dielectric analysis of tungsten-phosphoniobate 20A2O-30WO3 -10Nb2O5 -40P2O5 (A = Li, Na) glass-ceramics

New phosphate glasses of the quaternary system A₂O-Nb₂O₅-WO₃-P₂O₅, where X = Li and Na were prepared by the melt-quenching method. The introduction of WO₃ in the glass composition was based on the proposal of analysing the effect of the diminishing of the molar amount of the alkaline oxide and thus decreasing the molar ratio between network modifiers and network formers (M/F).In the present work we present the preparation of 20A₂O-30WO₃-10Nb₂O₅-40P₂O₅ (A = Li, Na) transparent glasses. These glasses were heat-treated in air, at 550 °C and 650 °C for 4 h. The structure of the obtained samples was studied by X-ray powder diffraction (XRD) and Raman spectroscopy and the morphology by scanning electron microscopy (SEM). The dc (σ_dc), ac (σ_ac) conductivity and dielectric spectroscopy measurements were performed in the function of the temperature and were related with the structural changes of the glass structures.     

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.     

The effect of alumina on the Sn/Sn redox equilibrium and the incorporation of tin in Na2O/Al2O3/SiO2 melts

Glasses with the basic compositions 10Na₂O · 10CaO · xAl₂O₃ · (80 − x)SiO₂ (x=0, 5, 15, 25) and 16Na₂O · 10CaO · xAl₂O₃ · (74 − x)SiO₂ (x=0, 5, 10, 15, 20) doped with 0.25-0.5 mol% SnO₂ were studied using square-wave-voltammetry at temperatures in the range from 1000 to 1600 °C. The voltammograms exhibit a maximum which increases linearly with increasing temperature. With increasing alumina concentration and decreasing Na₂O concentration the peak potentials get more negative. Mössbauer spectra showed two signals attributed to Sn²⁺ and Sn⁴⁺. Increasing alumina concentrations did not affect the isomer shift of Sn²⁺; however, they led to increasing quadrupole splitting, while in the case of Sn⁴⁺ both isomer shift and quadrupole splitting increased. A structural model is proposed which explains the effect of the composition on both the peak potentials and the Mössbauer parameters.     

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.     

Structure and non-linear optical performance of TeO2-Nb2O5-ZnO glasses

The non-linear optical performance and structure of TeO₂-Nb₂O₅-ZnO glasses was investigated as a function of ZnO content. The third-order non-linear optical susceptibility (χ⁽³⁾) as measured by a Degenerate Four Wave Mixing (DFWM) method, initially increased with increasing ZnO content to about 8.2 × 10⁻¹³ esu for a glass containing 2.5 wt% ZnO, and then decreased to 5.9 × 10⁻¹³ esu as the ZnO content increased to 10 wt%. There was no noticeable change as the ZnO content increased from 10 to 15 wt%. The non-linear optical response time, which caused electron cloud deformation, was from 450 to 500 fs. The structure of these glasses as analyzed by Raman spectroscopy and FT-IR spectra, was affected by the addition of ZnO up to 5 wt%, when, it is believed, the Zn²⁺ ions occupied the interstitial positions in the glass network by replacing the Nb⁵⁺ ions. The replaced Nb⁵⁺ ions occupied the network forming positions as the Te⁴⁺ ions. Increasing ZnO > 5 wt% did not have any further effect on the glass structure.     

Synthesis and structural characterization of amorphous nano-sized SiBONC ceramic powders via polymer pyrolysis

SiBONC ceramic powders have been prepared via a polymer pyrolysis route using silicon tetrachloride (SiCl₄), benzaldehyde (PhCHO), boron trichloride (BCl₃) and aniline (PhNH₂) as starting materials. Fourier transform infrared spectra (FT-IR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and transmission electron microscopy (TEM) were performed to investigate the structural characteristics of the polymer precursor and the ceramic powders. The SiBONC ceramic powders in spherical shape with a mean diameter of 50 nm are amorphous and composed of B-N, Si-O, Si-C, and SiON_x groups. The SiBONC ceramic powders were sintered at 1700 °C to a dense material which still remained amorphous.     

Non-isothermal crystallization kinetics of La2CaB10O19 from glass

The non-isothermal crystallization kinetics of La₂CaB₁₀O₁₉ (LCB) from a La₂O₃-CaO-B₂O₃ glass was studied. Differential thermal analysis methods were performed on three glass powders to obtain the kinetic parameters of LCB crystallization mechanism. The activation energies for overall crystallization (E), obtained by the methods of Kissinger and Ozawa, were in the range of 479-569 kJ/mol. Multiple (five) analysis methods were used to estimate the Avrami exponent (n), which could consequently be reduced into the single value of n = 3.1 ± 0.3. The growth morphology index (m) of LCB was corroborated by microscopy (optical and electron) images, which revealed a three dimensional growth. Energy dispersive spectroscopy confirmed that LCB is the crystallizing phase from the glass by an interface controlled mechanism. The parameters of the Johnson-Mehl-Avrami kinetic model for the analysis of LCB crystallization from glass were found to be n = m = 3.     

EPR study of RLi2O.V2O5, RNa2O.V2O5, RCaO.V2O5, and RBaO.V2O5 modified vanadate glass systems

Experimental EPR spectra in several modified vanadate glass systems reveal hyperfine structure (hfs) lines whose widths vary with the molar ratio of modifier to vanadium pentoxide, R. In the RNa₂O.V₂O₅ system, for example, hfs lines show no resolution at low R values (near 0.1); by contrast, these lines exhibit dramatic narrowing as R approaches 0.5. In the model proposed here, this narrowing is due to an increase in hopping time for small polarons associated with V⁴⁺ ions in these systems. Increases in polaron hopping times are accompanied by increases in electron spin-spin relaxation times T₂'s, and, an associated narrowing of EPR linewidths. Experiments confirm that spectral widths are limited by electron T₂'s due to the fact that EPR linewidths do not vary with temperature down to 4.2 K. Resolved spectra in RNa₂O.V₂O₅ at R = 0.5 reveal a hyperfine coupling parameter of 0.0177 ± 0.0008 T, corresponding to an upper-limit polaron hopping frequency of 487 ± 20 MHz. By similar analyses, the systems of RCaO.V₂O₅, RBaO.V₂O₅, and RLi₂O.V₂O₅ exhibit comparable polaron hopping frequencies limits of 480 ± 20 MHz, 469 ± 20 MHz, and 468 ± 20 MHz, respectively, when R is near 1.0. In addition to the relaxation effects discussed here, results of modeling of resolved spectra to obtain hyperfine coupling constants A_|| and A_┴, and g_┴ values g_|| and g_┴ are presented and discussed.     

Electrical conductivity of NbN-SiO2 films obtained by ammonolysis of Nb2O5-SiO2 sol-gel derived coatings

The studies of electrical conductivity of NbN-SiO₂ films are reported. To obtain these films, sol-gel derived xNb₂O₅-(100 − x)SiO₂ (where x = 100, 90, 80, 70, 60, 50 mol%) coatings were nitrided at 1200 °C. The nitridation process leads to the formation of some disordered structures, with NbN metallic grains dispersed in insulating SiO₂ matrix. The structure of the samples was studied using X-ray diffraction (XRD) and atomic force microscopy (AFM). The electrical conductivity was measured with the conventional four-terminal method in the temperature range from 5 to 280 K. The superconducting transition was not observed even for the sample that does not contain silica. All the samples exhibit negative temperature coefficient of resistivity. The results of conductivity versus temperature may be described on the grounds of a model proposed for a weakly disordered system.     

Effects of Nb2O5 Replacement by Er2O3 on elastic and structural properties of 75TeO2-(10 − x)Nb2O5-15ZnO-(x)Er2O3 glass

Tellurite 75TeO₂-(10 − x)Nb₂O₅-15ZnO-(x)Er₂O₃; (x = 0.0-2.5 mol%) glass system with concurrent reduction of Nb₂O₅ and Er₂O₃ addition have been prepared by melt-quenching method. Elastic properties together with structural properties of the glasses were investigated by measuring both longitudinal and shear velocities using the pulse-echo-overlap technique at 5 MHz and Fourier Transform Infrared (FTIR) spectroscopy, respectively. Shear velocity, shear modulus, Young's modulus and Debye temperature were observed to initially decrease at x = 0.5 mol% but remained constant between x = 1.0 mol% to x = 2.0 mol%, before increasing back with Er₂O₃ addition at x = 2.5 mol%. The initial drop in shear velocity and related elastic moduli observed at x = 0.5 mol% were suggested to be due to weakening of glass network rigidity as a result of increase in non-bridging oxygen (NBO) ions as a consequence of Nb₂O₅ reduction. The near constant values of shear velocity, elastic moduli, Debye temperature, hardness and Poisson's ratio between x = 0.5 mol% to x = 2.0 mol% were suggested to be due to competition between bridging oxygen (BO) and NBO ions in the glass network as Er₂O₃ gradually compensated for Nb₂O₅. Further addition of Er₂O₃ (x > 2.0 mol%) seems to further reduce NBO leading to improved rigidity of the glass network causing a large increase of ultrasonic velocity (v_L and v_S) and related elastic moduli at x = 2.5 mol%. FTIR analysis on NbO₆ octahedral, TeO₄ trigonal bipyramid (tbp) and TeO₃ trigonal pyramid (tp) absorption peaks confirmed the initial formation of NBO ions at x = 0.5 mol% followed by NBO/BO competition at x = 0.5-2.0 mol%. Appearance of ZnO₄ tetrahedra and increase in intensity of TeO₄ tbp absorption peaks at x = 2.0 mol% and x = 2.5 mol% indicate increase in formation of BO.     

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.     

Growth and shape control of orthorhombic Fe5(PO4)4(OH)3·2H2O single crystalline dendrites

Orthorhombic Fe₅(PO₄)₄(OH)₃·2H₂O single crystalline dendritic nanostructures have been synthesized by a facile and reproducible hydrothermal method without the aid of any surfactants. The influences of synthetic parameters, such as reaction time, temperature, the amount of H₂O₂ solution, pH values, and types of iron precursors, on the crystal structures and morphologies of the resulting products have been investigated. The formation process of Fe₅(PO₄)₄(OH)₃·2H₂O dendritic nanostructures is time dependent: amorphous FePO₄·nH₂O nanoparticles are formed firstly, and then Fe₅(PO₄)₄(OH)₃·2H₂O dendrites are assembled via a crystallization-orientation attachment process, accompanying a color change from yellow to green. The shapes and sizes of Fe₅(PO₄)₄(OH)₃·2H₂O products can be controlled by adjusting the amount of H₂O₂ solution, pH values, and types of iron precursors in the reaction system.     

Structure and crystallization of potassium titanium phosphate glasses containing B2O3 and SiO2

Transparent glasses composition of which can be expressed by the formula: (100−x) · (K₂O · 2TiO₂ · P₂O₅) · x(K₂O · 2B₂O₃ · 7SiO₂), where x=5, 10, 15 and 20 mol% (KTP-xKBS), were obtained by melt quenching technique. The structure and crystallization behavior of these glasses have been examined by Fourier transform infrared spectroscopy, differential thermal analysis and X-ray diffraction. In spite of their nominal composition, the studied glasses exhibit a similar oxygen polyhedra distribution. However, significant differences were found in the trigonal BO₃ units amount. During DTA runs all the examined glasses devitrify in two steps. In the former, very small crystals of an unknown crystalline phase are produced. In KTP-5KBS and KTP-10KBS glasses anatase phase was also detected. Attempts were made in order to identify the unknown phase (UTP) for which a AB₃(XO₄)₂(OH)₆ Crandallite-type structure was proposed where the A, B and X sites were occupied by K, Ti and/or Al, and P, respectively. In the second devitrification step the crystallization of the KTiOPO₄ phase occurs while the UTP phase previously formed disappears. Isothermal heat treatments performed at temperature just above T_g have allowed one to obtain transparent crystal-glass nanocomposites, formed by crystalline nanostructure of the UTP phase uniformly dispersed in the amorphous matrix.     

Structural and electrical properties of lead-free perovskite ceramic: Ba(In1/2Nb1/2)O3

Lead-free perovskite Ba(In_1/2Nb_1/2)O₃ was prepared by conventional ceramic fabrication technique at 1350 °C/5 h in air atmosphere. The crystal symmetry, space group and unit cell dimensions were determined from Rietveld analysis using FullProf software whereas crystallite size and lattice strain were estimated from Williamson-Hall approach. XRD analysis of the compound indicated the formation of a single-phase cubic structure with the space group Pm3m. EDAX and SEM studies were carried out in order to evaluate the quality and purity of the compound. Complex impedance as well as electric modulus analyses suggested the dielectric relaxation to be of non-Debye type. The correlated barrier hopping (CBH) model was employed to successfully explain the mechanism of charge transport in Ba(In_1/2Nb_1/2)O₃.     

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 and characterization of calcium phosphate based bioactive quaternary P2O5-CaO-Na2O-K2O glasses

Calcium phosphate based bioactive quaternary glass systems P₂O₅-CaO-Na₂O-K₂O were prepared by melt growth technique. Glasses were prepared in five different compositions by fixing P₂O₅ at 47 mol% and CaO at 30.5 mol% and by varying the K₂O and Na₂O concentrations. The structural properties of the glasses are analyzed using X-ray diffraction (XRD) studies and scanning electron microscopy (SEM) studies; and the composition of the glasses are studied using energy dispersive X-ray spectrum (EDS). The microhardness of the glass systems are studied by Vickers hardness measurements and the bioactivity of the glasses are studied using in vitro study. The thermal properties have been examined by means of thermogravimetric analysis (TGA) and differential thermal analysis (DTA). The ultrasonic velocity measurements show that the addition of K₂O contents produces non-bridging oxygen ion and hence weaken of the glass structure. The weakening of the glass structure reduces the ultrasonic velocity and hence an increase in attenuation.     

1H-1,2,3-triazole,a promising precursor for chemical vapor deposition of hydrogenated carbon nitride

Well-crystallized hydrogenated carbon nitride thin films have been prepared by microwave plasma enhanced chemical vapor deposition (MWPECVD). 1H-1,2,3-triazole+N₂ and Si (1 0 0) were used as precursor and substrate, respectively. Substrate temperature during the deposition was recorded to be 850 °C. The synthesized samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photo-electron spectroscopy (XPS) analyses. The plasma compositions were checked by optical emission spectroscopy (OES). XRD observation strongly suggests that the films contain polycrystalline carbon nitride with graphitic structure of (1 0 0), (0 0 2), (2 0 0) and (0 0 4). XPS peak quantification reveals that the atomic ratio of the materials C:N:O:Si is 32:41:18:9. X-ray photo-electron peak deconvolution shows that the most dominant peak of C (1s) and N (1s) narrow scans correspond to sp² hybrid structure of C₃N₄. These observations indicate that 1H-1,2,3-triazole favors the formation of hydrogenated carbon nitride with graphitic phase by CVD method and thus is in good agreement with XRD results. SEM of surface and OES of plasma also support the formation of polycrystalline carbon nitride films from 1H-1,2,3-triazole+N₂ by CVD.