For obtaining optimal properties of both materials and products, a very careful control of changes of primarily morphological, microstructural and other characteristics is necessary. This is the reason why the investigation of the process... more
For obtaining optimal properties of both materials and products, a very careful control of changes of primarily morphological, microstructural and other characteristics is necessary. This is the reason why the investigation of the process of mechanical activation, which is very often used in powder technology, is of both scientifically and practically interest1,2.
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Mechanical activation (MA) is used extensively as a relatively no expensive method for the modification of physico-chemical properties of dispersed systems in technologies for obtaining powders and ceramics. Different processes that occur... more
Mechanical activation (MA) is used extensively as a relatively no expensive method for the modification of physico-chemical properties of dispersed systems in technologies for obtaining powders and ceramics. Different processes that occur during MA of powders lead to the formation of specific structures that promote and accelerate solid-state reactions, as well as densification during sintering. Changes of particle size and structure during MA of the ceramic parent material are the sources of the morphological and structural metastability of the starting powders and they can affect the sintering process, positively or negatively. Many properties of final polycrystalline ceramics strongly depend on a green body microstructure and on conditions under which the green body is sintered. From the other side green body microstructure depend on a powders characteristics such as morphology, particle and pore size distributions. Regarding above mentioned activation and sintering must therefore be carried out under strictly controlled conditions in order to avoid influences that might cause a deterioration of the final properties of the ceramic materials. The present study is focused on the processes of sintering that occurred in mechanically activated single and multiphase oxide powders.
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Two tomato genotypes with constitutively different ABA level, flacca mutant and wild type of Ailsa Craig cv. (WT), were subjected to three repeated drought cycles, with the aim to reveal the role of the abscisic acid (ABA) threshold in... more
Two tomato genotypes with constitutively different ABA level, flacca mutant and wild type of Ailsa Craig cv. (WT), were subjected to three repeated drought cycles, with the aim to reveal the role of the abscisic acid (ABA) threshold in developing drought tolerance. Differential responses to drought of two genotypes were obtained: more pronounced stomatal closure, ABA biosynthesis and proline accumulation in WT compared to the mutant were compensated by dry weight accumulation accompanied by transient redox disbalance in flacca. Fourier-transform infrared (FTIR) spectra analysis of isolated cell wall material and morphological parameter measurements on tomato leaves indicated changes in dry weight accumulation and carbon re-allocation to cell wall constituents in flacca, but not in WT. A higher proportion of cellulose, pectin and lignin in isolated cell walls from flacca leaves further increased with repeated drought cycles. Different ABA-dependent stomatal closure between drought cy...
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AbstractMesoporous anatase nanopowders were doped with 0.05−0.5 mol% of W6+, in order to obtain more efficient photocatalyst than TiO2 Degussa P25 in the degradation of amitriptyline (AMI) under simulated solar irradiation (SSI). Dominant... more
AbstractMesoporous anatase nanopowders were doped with 0.05−0.5 mol% of W6+, in order to obtain more efficient photocatalyst than TiO2 Degussa P25 in the degradation of amitriptyline (AMI) under simulated solar irradiation (SSI). Dominant XRPD peaks were ascribed to anatase phase, with additional peaks which could correspond to brookite, TiO2 bronze and sodium titanate, Na2Ti9O19. The Raman scattering measurements have confirmed anatase as dominant phase, with broad Raman feature at ~270 cm−1 possibly related to Ti–O–Na stretching vibration. All W-doped nanopowders have shown enhanced adsorption and higher efficiency in photodegradation of AMI in comparison to TiO2 Degussa P25 under the same conditions. The catalyst doped with 0.4 mol% of W6+, which has shown the highest efficiency in degradation of AMI under SSI, has also been tested in degradation of alprazolam (ALP). The effect of substrate type (AMI and ALP), catalyst loading, and initial substrate concentration on photocatalytic degradation using SSI was examined. The identification of the species responsible for the photocatalytic degradation of AMI and ALP by the catalyst doped with 0.4 mol% of W6+ was performed in the presence of various scavengers under SSI. The major role in degradation of AMI may be attributed to hydroxyl radicals, whereas superoxide anion radicals, singlet molecular oxygen and hydroxyl radicals contribute to degradation of ALP. HighlightsInfluence of W and Na content on the properties of TiO2 catalysts synthesized by sol-gel method.Powders characterized by XRPD, SEM, EDS, BET, Raman, and UV-vis spectroscopy.Adsorption and photodegradation of amitriptyline and alprazolam under simulated solar irradiation.Optimal synthesis and W-doping conditions for photocatalytic degradation of amitriptyline found.Various scavengers used to identify mechanisms of photodegradation of amitriptyline and alprazolam.
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Ceramic materials obtained on the basis of BaTiO3 and its related compounds are of great importance for their fundamental and model aspects. In order to investigate the influence of heating rate on sintering process of BaTiO3 ceramics,... more
Ceramic materials obtained on the basis of BaTiO3 and its related compounds are of great importance for their fundamental and model aspects. In order to investigate the influence of heating rate on sintering process of BaTiO3 ceramics, tribophisicaly activated powders of 50mol% BaCO3 and 50mol% TiO2, were pressed, calcinated and sintered with different heating rates (4°C/min., 10°C/min. and 30°C/min.) up to 1300°C for 2h. Heating process was studied using dilatometer. The samples were analyzed by X-ray diffraction. Changes of dielectric properties were correlated with changes at different structural levels.
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Phyllostachis bissetti was introduced to urban areas in Belgrade with the aim to improve the quality of air polluted by heavy traffic. Dust released from fuel combustion adsorbed on the leaves reaching up to 10% of leaf dry weight.... more
Phyllostachis bissetti was introduced to urban areas in Belgrade with the aim to improve the quality of air polluted by heavy traffic. Dust released from fuel combustion adsorbed on the leaves reaching up to 10% of leaf dry weight. Adsorbed dust was analyzed for its morphological structure, chemical content and prooxidant activity. SEM analysis of dust indicated the presence of particulate matter fractions PM10 and PM2.5. Determination of peroxidase levels (POD, EC 1.11.1.7), ascorbate concentration and total antioxidant capacity in the leaves showed that, overall, P. bissetii had high antioxidative potential to cope with oxidative stress under urban environmental conditions. Leaf protein and chlorophyll content accompanied by high growth rate of seedlings planted at different locations indicated excellent acclimatization capacity of P. bissetti to the heavily polluted urban areas.
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Donor-doped barium titanate based systems are widely used semi-conducting materials. It is well known that different tehnological processes distinctly influence the microstructure and electrical parameters governing the characteristic... more
Donor-doped barium titanate based systems are widely used semi-conducting materials. It is well known that different tehnological processes distinctly influence the microstructure and electrical parameters governing the characteristic increase of resistivity above Curie temperature - PTCR effect. Having this in mind, in the present investigation the identical mixed-oxides route for powder preparation and two-steps firing for various systems was used. High purity BaCO3, TiO2, PbO, A12O3, SiO2 oxide powders as raw materials and Sb2O3, MnSO4-H2O, and ZnO as dopants, were homogenized in three steps to obtain a mixture with the desired composition. After calcination, milling and pressing, the samples were sintered at various temperature for two hours. Studies of phase compositions and crystallographic data, after calcination and sintering, using X-ray powder diffraction were done. Possible variation of stoichiometry, caused due to volatilization of lead during firing processes and influence of stoichiometry on PTCR effect was examined. The resistivity temperature profile with characteristic values of resistivity, Curie temperature and temperature coefficient were shown.
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Commercial zinc oxide powder was mechanically treated by grinding in a high-energy vibro-mill in a continual regime in air up to 300 minutes. Original and modified ZnO samples were characterized by Raman, photoluminescence (PL) and... more
Commercial zinc oxide powder was mechanically treated by grinding in a high-energy vibro-mill in a continual regime in air up to 300 minutes. Original and modified ZnO samples were characterized by Raman, photoluminescence (PL) and infrared (IR) spectroscopy. This study confirms that change in defect structure of ZnO crystal lattice introduced by mechanical activation greatly affects the optical properties of
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The modified polymeric precursor method (Pechini method) was successfully used for the preparation of epitaxial and polycrystalline ferroelectric Pb(Zr0.52Ti0.48)O3 (PZT) thin films. Films were deposited on LaNiO3 (LNO) – coated silicium... more
The modified polymeric precursor method (Pechini method) was successfully used for the preparation of epitaxial and polycrystalline ferroelectric Pb(Zr0.52Ti0.48)O3 (PZT) thin films. Films were deposited on LaNiO3 (LNO) – coated silicium (1 0 0) and platinum substrates (Pt (1 1 1)/Ti/SiO2/Si) by spin coating technique. LNO electrodes were also prepared by the Pechini method and treated under different thermal treatment conditions to obtain films with different structural and microstructural properties. Investigation of PZT microstructure was performed as a function of orientation and morphology of the bottom electrode, as well as of thermal treatment conditions. Grain size and morphology were analyzed by AFM, while the quality and orientation of PZT films were determined by GIXRD analysis. It has been found that the proposed thermal treatment on a hot plate, with slow heating rate and long annealing time, can result in the formation of epitaxial PZT films on Si and LNO-coated Si sub...
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Research Interests: Materials Engineering, Physics, Condensed Matter Physics, Raman Spectroscopy, Scanning Electron Microscopy, and 10 moreNanotechnology, Zinc Oxide, Theoretical Condensed Matter Physics, First-Order Logic, Lattice Parameter, X ray diffraction, Single Crystal, Thermal Treatment, First Order Logic, and Raman Spectra
We investigated metal accumulation in bamboo leaves during three seasons at three urban locations differing in pollution levels. The higher content of Cu, Pb, and Zn in the leaves was in correlation with the highest bioavailable content... more
We investigated metal accumulation in bamboo leaves during three seasons at three urban locations differing in pollution levels. The higher content of Cu, Pb, and Zn in the leaves was in correlation with the highest bioavailable content of these elements in the soil at the most polluted location. The content of leaf trace elements was higher in summer and autumn compared to spring. Scanning electron microscopy with energy dispersive X-ray spectroscopy showed that Si accumulation in bamboo leaves was the highest in epidermis and vascular tissue, and was co-localized with trace metals. Analysis of phytoliths showed co-deposition of Al, C, and Si, implying the involvement of Si in metal detoxification. Compared to a common urban tree, linden, bamboo showed better capacity to maintain cellular redox homeostasis under deteriorated environmental conditions. The results suggest that bamboo can be efficiently used for biomonitoring of air and soil metal pollution and remediation in urban ar...
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Mechanical activation was used as a method for modification of the structural and optical properties of commercial ZnO powder. For this purpose zinc oxide powder was mechanically treated by grinding in a high-energy vibro-mill in a... more
Mechanical activation was used as a method for modification of the structural and optical properties of commercial ZnO powder. For this purpose zinc oxide powder was mechanically treated by grinding in a high-energy vibro-mill in a continual regime in air up to 300 minutes. Starting and modified ZnO samples were characterized using XRD, BET and TEM measurements. Optical properties of these samples were investigated by Raman and photoluminescence (PL) spectroscopy. The color of commercial ZnO powder was white while mechanically activated ZnO powder was dark yellow, indicating the presence of nonstoichiometry. In the Raman spectra of non-activated sample Raman modes of bulk ZnO were observed, while the spectra of modified samples point out structural and stoichiometric changes. The PL spectra of modified samples excited by 325 and 442 nm lines of a He-Cd laser show great difference with respect to the spectra of the original sample. This study confirms that change in the defect struct...
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The synthesis of calcium titanate, CaTiO3, was performed by mechanical activation and thermal treatment. Milling for up to 360 minutes in a planetary ball mill mechanically activated an equimolar mixture of CaCO3 and TiO2 powders. A small... more
The synthesis of calcium titanate, CaTiO3, was performed by mechanical activation and thermal treatment. Milling for up to 360 minutes in a planetary ball mill mechanically activated an equimolar mixture of CaCO3 and TiO2 powders. A small amount of mechanically activated mixtures was pressed into briquettes and calcined at 850°C for two hours. The effect of mechanical activation on the solid-state reaction was studied using X-ray powder diffraction and differential thermal analysis. The change of morphology and size of powder particles due to milling, were determined by SEM, while BET analysis was used to determine the specific surface area of the powder. The sintering process was followed by a dilatometer during thermal treatment up to 1300C. The main conclusion of the analysis of conducted investigations is that CaTiO3 ceramics can be obtained from an activated mixture at a much lower temperature than reported in the literature owing to acceleration of the chemical reaction and sintering.
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The process of macro- and microstructural transformations of zinc-oxide powders, which were tribophysically activated by grinding in a vibro-mill was investigated using methods of transmission electron microscopy, infrared spectroscopy... more
The process of macro- and microstructural transformations of zinc-oxide powders, which were tribophysically activated by grinding in a vibro-mill was investigated using methods of transmission electron microscopy, infrared spectroscopy and X-ray. It is shown that tribophysical activation contributes to a gradual modification of the fine defect structure of zinc-oxide powders. In the starting stage agglomerates and bigger, longer particles are destroyed first of all. As a result of the formation of both volume and surface defects and changes of the character of interparticles interactions the plate-like polycrystal particles are created. They actually present sets of coherent scattering region.
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Mixtures of ZnO and SnO2 powders, with molar ratio of 2:1, were mechanically activated for 40, 80 and 160 minutes in a planetary ball mill. The resulting powders were compacted into pellets and non-isothermally sintered up to 1200?C with... more
Mixtures of ZnO and SnO2 powders, with molar ratio of 2:1, were mechanically activated for 40, 80 and 160 minutes in a planetary ball mill. The resulting powders were compacted into pellets and non-isothermally sintered up to 1200?C with a heating rate of 5?C/min. X-ray diffraction analysis of obtained powders and sintered samples was performed in order to investigate changes of the phase composition. The microstructure of sintered samples was examined by scanning electron microscopy. The photoacoustic phase and amplitude spectra of sintered samples were measured as a function of the laser beam modulating frequency using a transmission detection configuration. Fitting of experimental data enabled determination of photoacoustic properties including thermal diffusivity. Based on the results obtained a correlation between thermal diffusivity and experimental conditions as well the samples microstructure characteristics was discussed. .
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The development of advanced materials eventually leads to an expansion of new methods for the synthesis. Freeze-drying as a cryochemical method for the synthesis of high purity oxide powders with specific microstructures was presented.... more
The development of advanced materials eventually leads to an expansion of new methods for the synthesis. Freeze-drying as a cryochemical method for the synthesis of high purity oxide powders with specific microstructures was presented. ZnO powders derived by this technique were characterized by X-ray powder diffraction analysis and scanning electron microscopy method. Consolidated submicronic ZnO powders were thermally treated under nonisothermal conditions at different heating rates using dilatometer. An analysis of densification and microstructural evolution was performed. The obtained results were discussed in order to establish a correlation in the triad synthesis-structure-properties.
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In this paper, results of an investigation of the influence of mechanical activation of a raw material mixture on processes of synthesis and reaction sintering of Portland cement clinker are given. Activation was performed in a vibro mill... more
In this paper, results of an investigation of the influence of mechanical activation of a raw material mixture on processes of synthesis and reaction sintering of Portland cement clinker are given. Activation was performed in a vibro mill with rings for 30 minutes in a continual regime in air. It has been established that mechanical activation of the starting raw material mixture increases general activity, which is mostly reflected in reduction of temperatures at which relevant chemical reactions and sintering occur. This is very significant from the viewpoint of the increasingly necessary efficiency and cheaper production, i.e. energy savings during synthesis of Portland cement clinker and indicates that further investigation of the influence of mechanical activation is more than justified.
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The influence of tribophysical activation on Zn2TiO4 synthesis along with the changes in powders during tribophysical treatment was observed. Mixtures of ZnO and TiO2 powders were mechanically activated using a high-energy ball mill at... more
The influence of tribophysical activation on Zn2TiO4 synthesis along with the changes in powders during tribophysical treatment was observed. Mixtures of ZnO and TiO2 powders were mechanically activated using a high-energy ball mill at different time intervals from 0 to 300 minutes. XRD was performed in order to obtain information about phase composition variations. Microstructure parameters were revealed from an approximation method. Particle size distribution along with scanning electron microscopy gave very useful information about powder morphology.
Mechanical activation and sintering are used for obtaining zinc titanate, Zn2TiO4. Starting powder mixtures of ZnO and TiO2, in the molar ratio that is in accordance with the stoichiometry of zinc titanate Zn2TiO4, were mechanically... more
Mechanical activation and sintering are used for obtaining zinc titanate, Zn2TiO4. Starting powder mixtures of ZnO and TiO2, in the molar ratio that is in accordance with the stoichiometry of zinc titanate Zn2TiO4, were mechanically activated using a planetary mill during different time intervals from 0 to180 minutes. Scanning electron microscopy was employed to probe the powders microstructure. Progress of the solid-state reaction from the starting powders and evolution of the phases were followed using X-ray powder diffraction. Sintering kinetics was investigated during isothermal heating at 1100 o C from 0 to 120 minutes. The main conclusion based on the analysis made is that Zn2TiO4 ceramics could be obtained by mechanical activation after a certain time without additional thermal treatment. Also, shorter activation times together with calcination at 900 o C show that the required sintering temperature and sintering time could be lower than those reported in literature.
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Sintering kinetics of the mechanically activated ZnO-TiO2 system was studied. Mixtures of ZnO and TiO2 powders were mechanically activated using a high-energy ball mill for different time intervals from 0 to 300 minutes. Formal... more
Sintering kinetics of the mechanically activated ZnO-TiO2 system was studied. Mixtures of ZnO and TiO2 powders were mechanically activated using a high-energy ball mill for different time intervals from 0 to 300 minutes. Formal phenomenological analyses were performed in order to describe the specimen?s behavior during isothermal sintering at 1100oC. Non-isothermal sintering was investigated by dilatometer measurements up to 1100oC with a constant heating rate. The Dorn method was applied in order to give information on the activation energy. .
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... Soc. 76: 1217 (1995) 3. W. Vogel, W. Holand, Angew. Chem. Int. Ed. Engi 26: 527 (1987) 4. A.Maroua, S. Saiello, F. Branda, A. Buri, Thermochim. Acta 46: 123 (1981) 5. XJ Xu, CS Ray, DE Day, J. Am. Ceram. Soc. 74: 909 (1991) 6. T.... more
... Soc. 76: 1217 (1995) 3. W. Vogel, W. Holand, Angew. Chem. Int. Ed. Engi 26: 527 (1987) 4. A.Maroua, S. Saiello, F. Branda, A. Buri, Thermochim. Acta 46: 123 (1981) 5. XJ Xu, CS Ray, DE Day, J. Am. Ceram. Soc. 74: 909 (1991) 6. T. Ozawa, Polymer 12: 150 (1971) 340
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We report on the differences in the defect structure of ZnO particles that take place at the grinding of powders of pure ZnO and mixture ZnO–SnO2. The defect structure formed was studied by electron paramagnetic resonance (EPR). The... more
We report on the differences in the defect structure of ZnO particles that take place at the grinding of powders of pure ZnO and mixture ZnO–SnO2. The defect structure formed was studied by electron paramagnetic resonance (EPR). The results demonstrate that a sequential two-stage thermal process contributes to the defect structure during prolonged mechanical treatment (MT). In the first stage
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Research Interests: Materials Engineering, Materials Science, Microstructure, Manufacturing, Scanning Electron Microscopy, and 14 moreRietveld refinement, Quantitative analysis, Fabrication, X ray diffraction, Powder, Titanium Oxides, Microstructures, Quantitative Analysis, Solid State Reaction, Chemical Synthesis, Phase Analysis, Electrical And Electronic Engineering, High energy, and Calcium titanate
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ABSTRACT Raman scattering spectroscopy has been used for the characterization of zinc oxide nanoparticles obtained by mechanical activation in a high-energy vibro-mill and planetary ball mill. Raman modes observed in spectra of... more
ABSTRACT Raman scattering spectroscopy has been used for the characterization of zinc oxide nanoparticles obtained by mechanical activation in a high-energy vibro-mill and planetary ball mill. Raman modes observed in spectra of nonactivated sample are assigned to Raman spectra of the ZnO monocrystal, while the spectra of mechanically activated samples point out to the structural and stoichiometric changes, depending on the milling time and the choice of equipment. Observed redshift and peak broadening of the E2high and E1 (LO) first-order Raman modes are attributed to increased disorder induced by mechanical milling, followed by the effects of phonon confinement due to correlation length decrease. The additional modes identified in Raman spectra of activated ZnO samples are related to the surface optical phonon modes, due to the intrinsic surface defects and presence of ZrO2as extrinsic defects introduced by milling in zirconia vials. Copyright © 2009 John Wiley & Sons, Ltd.
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In this paper, changes of microstructural characteristics of disperse systems during mechanical activation of zinc oxide (ZnO) have been investigated. ZnO powder was activated by grinding in a planetary ball mill in a continuous regime in... more
In this paper, changes of microstructural characteristics of disperse systems during mechanical activation of zinc oxide (ZnO) have been investigated. ZnO powder was activated by grinding in a planetary ball mill in a continuous regime in air during 300 min at the basic disc rotation speed of 320 rpm and rotation speed of bowls of 400 rpm but with various balls-to-powder mass ratios. During ball milling in a planetary ball mill, initial ZnO powder suffered high-energy impacts. These impacts are very strong, and large amounts of microstructural and structural defects were introduced in the milled powders. The morphology and dispersivity of particles and agglomerates of all powders were investigated by scanning electron microscopy and scanning transmission electron microscopy. The specific surface area of initial ZnO powder was determined as 3.60 m(2) g(-1) and it increased to 4.42 m(2) g(-1) in mechanically activated powders. An increase of the ball-to-powder mass ratio led to a decrease of particle dimensions as well as increased the tendency for joining into quite compact agglomerates, that is aggregates, compared with the very loose, soft initial agglomerates. The obtained results pointed out that activation of ZnO powders produces a highly disperse, nano-scaled mixture of small particles, that is crystallites with sizes in the range of 10-40 nm. Most of these particles are in the form of aggregates with dimensions of 0.3-0.1 mum. The crystallite and aggregate size strongly depend on milling conditions, that is ball-to-powder mass ratio, as shown in this investigation.
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Structural disorder of ZnO nanopowders with mean crystallite size down to 15 nm, produced by mechanical activation in high energy mills, has been analyzed by x-ray diffraction and Raman spectroscopy. The influence of such disorder on... more
Structural disorder of ZnO nanopowders with mean crystallite size down to 15 nm, produced by mechanical activation in high energy mills, has been analyzed by x-ray diffraction and Raman spectroscopy. The influence of such disorder on optical and electronic properties of ...
Research Interests: Engineering, Applied Physics, Raman Spectroscopy, Mathematical Sciences, Applied, and 14 moreresonance Raman, Solid State electronic devices, Physical sciences, Band Gap, Zinc, Electronic properties, Second Order, Crystallite Size, X ray diffraction, Spectroscopic Ellipsometry, Raman Scattering, Raman Spectra, High energy, and Electron-phonon interaction
ABSTRACT BaTiO3 is usually doped to achieve the temperature stability required bydevice applications, as well as to obtain a large positive temperature coefficient anomaly of resistivity (PTCR). Uniform distribution of dopants among the... more
ABSTRACT BaTiO3 is usually doped to achieve the temperature stability required bydevice applications, as well as to obtain a large positive temperature coefficient anomaly of resistivity (PTCR). Uniform distribution of dopants among the submicron dielectric particles is the key for optimal control of grain size and microstructure to maintain a high reliability. The system Ba0.84Pb0.16TiO3 was synthesized from high purity BaCO3, TiO2, PbO oxide powders as raw materials. Sb2O3, MnSO4 and ZnO were used as dopantsand Al2O3, TiO2 and SiO2 as grain growth controllers. Phase composition was analyzed by using XRD and the microstructure was investigated by SEM. EDS attached to SEM was used to analyze phase composition specially related to abnormal grain growth. Electrical resistivities were measured as a function of temperature and the PTCR effect characterized by an abrupt increase on resistivity.
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