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The influence of dopant concentration and sintering parameters on properties of Sb-doped BaSnO3 ceramics
Get PDFThe influence of dopant concentration and sintering parameters on properties of Sb-doped BaSnO3 ceramics
Jelena Mitrović1, Milica Počuča-Nešić1, Zorica Branković1, Goran Branković1
1Institute for Institute for Multidisciplinary Research, University of Belgrade, Belgrade, Serbia
In recent years, the modern industry and technology development has focused on non-magnetic, non-inductive, and electroconductive materials that can be used in conditions unfavorable for metals and alloys, such as constant high voltage, current and energy, with a particular emphasis on operating in acidic and humid environments. These conditions could be satisfied using chemically inert and thermally stable ceramic resistors with linear current-voltage (I-U) characteristic and low and almost constant electrical resistivity in the wide temperature range. Barium stannate (BaSnO3, BSO) is perovskite-type oxide with almost ideal cubic crystal structure, good thermal and chemical stability. Undoped BSO exhibits semiconductor behviour, but doping with an appropriate concentration of antimony can lead to changes in the electrical properties of BSO, making its metallic-like conductor.
In this study, we investigate the influence of antimony concentration and sintering parameters on properties of antimony-doped barium stannate, BaSn1-xSbxO3 (BSSO, x = 0,00; 0,04; 0,06; 0,08 and 0,10) to obtain conductive electroceramic samples with linear current-voltage (I-U) characteristic and constant electrical resistivity in the temperature range of 25 °C to 150 °C. Ceramic samples were obtained by three different sintering techniques conventional, spark plasma and cold sintering.
XRD analysis confirmed the existence of single-phase cubic BaSnO3 in all conventionally sintered samples at 1600 °C for 3 h, and also in spark plasma sintered samples at 1100 °C for 5 min. However, the spark plasma sintering at 1200 °C for 5 min led to the formation of secondary phase, tetragonal Ba2SnO4 in BSSO samples, whose content is significantly decreased by Sb doping. On the other hand, XRD analysis revealed the presence of unreacted starting components, SnO2 and BaCO3 in cold sintered BaSn0.92Sb0.08O3 sample (310 °C for 5 min, 20 wt.% 1 M acetic acid). The presence of low angle grain boundaries (LAGBs) was observed in conventionally (1600 °C for 3 h) and spark plasma sintered (1200 °C for 5 min) samples with x = 0.08. The results of DC (I-U characteristic) and AC (Impedance spectroscopy) measurements confirmed the semiconducting properties of all BSSO sample, except the spark plasma sintered BaSn0.92Sb0.08O3 (1200 °C for 5 min) sample. Metallic-like behavior of this sample is manifested through the linear I-U characteristic and low electrical resistivity, which remained almost constant in the investigated temperature range, due to the loss of potential barriers at the grain boundary region as a consequence of LAGBs present in BaSn0.92Sb0.08O3 ceramic sample
Energy Harvesting Potential of Polymer Composites
Get PDFEnergy is available all around us in different forms and shapes such as from sun, wind, waves, vibrations etc. The enormous amount of mechanical energy released in everyday life by human walking, transportation movement, sound waves and other, represent renewable and safe energy source. Piezoelectric generators exhibit a great potential for powering up low-power portable devices and self-powered electronic systems by extraction of mechanical energy. Employment of lead-free piezoelectric materials will be a breakthrough of a completely new type of safe and harmless production of energy for daily life. Recent challenge in electronics is also utilization of flexible electronics with the ability to bend into diverse shapes which expands the applications of modern electronic devices in different areas.Polymer PVDF/piezoelectric ceramics, flexible composite films were prepared by hot pressing method. The influence of hot pressing method on the formation of electroactive PVDF phases in the polymer was proven by FTIR analysis. DSC analysis have shown the change of PVDF crystallinity degree in the flexible films with addition of ceramics filler particles. The dielectric permittivity value increased with the addition of filler in the polymer matrix while the relaxation processes were governed mostly by the PVDF matrix. Polarization of flexible films enhanced the formation of PVDF electroactive β- phase in the samples. Energy harvesting potential was studied by measuring of voltage output under the impulse hammer load
Lead Free (BaZr0.2Ti0.8O3) and Lead Based (PbZr0.52Ti0.48O3) Flexible Thick Films: Structural Properties and Potential Use as Energy Storage and Energy Harvesting Systems
Get PDFIn the last year energy harvesters based on piezoelectricity from mechanical vibration has emerged as the very promising devices that are explored extensively for its functionality in energy technologies. In this paper a series of flexible lead- free BZT/PVDF and lead based PZT/PVDF piezocomposites with variable filler content up to 50 vol. % have been prepared by hot pressing method. Structure and morphology of BZT and PZT powders as well as distribution of piezo-active filler in obtained flexible films were characterized by XRD and SEM analysis. Total amoun of electro active phase (% FEA) of PVDF is higher in PZT-based films in comparison with BZT based ones but the contribution of more desirable β- phase is higher in BZT-PVDF films. In both composite dielectric permittivity's was increased in contrast to their polymer PVDF host matrix, but also displayed decreased breakdown strenght and raised energy loss. In addition, the remnant polarization (Pr) and leakage current were also investigated to evaluate the breakdown strength in both types of flexible films. Calculations of storage energies and output voltage obtained for the investigated materials revealed an increasing trend with increasing amount of BZT and PZT active phase. The maximum storage energy of 0.42 J/cm3 at 390 kV/cm3 was obtained for PZT-PVDF (40-60) films while the maximum output voltage of about 10 V was obtained for PZT-PVDF (50-50) flexible film. In addition, comparisons between properties of lead based and lead free flexible films as well as potential use of those films as energy storage and energy harvesting systems were considered
Maternal Subclinical and Clinical Hypothyroidism Effects on Rat Offspring: A Story of the Skin and its Derivatives
Get PDFEpidermis stem cells have a crucial role through the processes of proliferation and
differentiation, to replace cells that are constantly lost during tissue turnover or
following injury. On the other hand, thyroid hormones regulate the proliferation and
differentiation of epidermal cells and thus significantly influence the homeostasis
of the skin. It is well known that maternal hypothyroidism during pregnancy leads
to impaired development of many organ systems in their offspring. However, there
is a lack of data about the influence of maternal subclinical hypothyroidism during
pregnancy and lactation on the development of the skin and its derivatives in the litter.
The aim of this study was to investigate the effects of maternal thyroid dysfunction on
the development of the skin and its derivatives in their offspring in the early postnatal
period. Antithyroid substance 6-n-propyl-2-thiouracil was added into the drinking water
to female Albino Oxfords rats from the beginning of pregnancy and during lactation,
with the aim to induce subclinical and overt form of hypothyroidism. Skin samples
were taken from male pups within twenty-four hours and seven days after birth. The
main findings of this investigation were that both forms of maternal hypothyroidism
lead to serious damage of the epidermis in pups in terms of pronounced hyperkeratosis
and reduction of the germinal layer along with a reduced number of hair follicles and
their delayed morphogenesis. Epidermal impairments were more pronounced in pups
with the overt form of hypothyroidism while offspring with the subclinical form had
impairments that were less pronounced and delayed in occurrence
LENGTH-WEIGHT RELATIONSHIP AND CONDITION FACTOR OF THE WHITE BREAM (Blicca bjoerkna) IN THE DANUBE RIVER NEAR BELGRADE (1168-1170 RKM)
Get PDFWhite bream is an important species in commercial and sport fishing that is caught in nets throughout the year. The analyzed samples of white bream (n = 377) came from commercial catches carried out between December 2014 and May 2015 at two locations in the Danube near Belgrade, Jojkića Dunavac (JD) – an armlet of the Danube, with slow water flow and Veliko ratno ostrvo (VRO) – the main channel of the Danube, with fast water flow. Total body length (TL, cm) and body weight (BW, g) of each fish were measured, and Fulton's condition factor (K = W/L3 x 100) was calculated.
Average TL of the fish samples from the JD and VRO were 23.1±1.7 and 23.8±2.4, respectively, and average BW were 164.4±42.2 and 201.0±73.0, respectively. In general, fish from VRO were in better condition (K=1.44±0.16) compared to sample from JD (K=1.31±0.11). Individuals in the sample from JD had a negative allometric growth (a = -1.79, b = 2.93, r² = 0.85), while those from VRO have a positive allometric growth (a = -2.22, b = 3.28, r² = 0.89). Based on the results of this study, positive allometric growth (b > 3) and fish condition indicated that individuals from VRO increased body mass more than body length. The source of food, its availability, and better habitat conditions at VRO could be the reason for the differences in the growth and condition of the fish from the investigated locations
Magnetic, redox and structural properties of Mn-O-Ca cluster, synthesized by the green microalga Chlorella sorokiniana
Get PDFMetabolism of metals in microalgae, as well as their adaptation to metal excess, are of significant environmental importance. We have found previously that the green microalga Chlorella sorokiniana accumulates environmental Mn excess in the form of a multivalent Mn-O-Ca cluster with structure that is very similar of oxygen-evolving complex (OEC) in photosystem II1. The application of microalgae in the ‘green’ synthesis of catalytic metal clusters is very important, since the use of toxic chemicals for traditional synthesis could be avoided. The aim of this study was to investigate the magnetic, redox and structural properties of this cluster. The magnetic properties of the cluster, were tested using Low-T-EPR spectroscopy and SQUID magnetometry. Based on the analysis of the EPR spectra, it was concluded that the spin of Mn in the cluster is >1/2. In addition, the spin of Mn is not an integer since parallel mode EPR did not deliver any detectable spectrum. The paramagnetic nature of the Mn-O-Ca cluster was confirmed by the SQUID instrument. Effective magnetic moment calculated per ion Mn was ~5 BM (Mn ratio in biomass was 12,1%). For the investigation of redox and structural properties, an extract of cluster from microalga was used. Cluster extraction involved the application of a series of solvents - phenol in Tris-Cl buffer, chloroform, methanol, 0,17% sodium hypochlorite2. Cyclic and differential voltagrams were recorded in the range from -1,5 to 2 mV3. The analysis revealed the presence of different oxidation states of Mn (+2, +3, +4). The peak potentials resembled the potentials in OEC model compounds2.The redox similarities between the Mn-O-Ca cluster in microalgae and OEC imply that cluster may be have a similar catalytic activity. More detailed analysis of activity and structure of Mn-O-Ca cluster is warranted
Deduction in Education: the Case of Serbia
Get PDFThe main goal of the paper is to provide insight into the current state of education in Serbia regarding the use of educational aspects of software re-lated to deduction, geometry and mathematical reasoning. Authors investigate to what extent and for what purposes teachers and students use such software. The consideration of the current state is substantiated by the examples of teaching practices at different school levels, and supplemented by the proposals which tend to contribute to deeper understanding of the topic. The most commonly used automatic deduction and calculation programs in Serbian education are GeoGebra, Photomath, Microsoft Math Solver, Desmos, and Wolfram Alpha. These mathematical software represent an advantageous topic for cross-curricular connection in schools which could be realized in many different ways. It is suggested in the context of connecting mathematics and physics to art, history of science, national history of science, philosophy, logic and psychology
Assessment of the gen-ecological potential of European white elm from the Natural protected area "Veliko ratno ostrvo"
Get PDFEuropean White Elm (Ulmus laevis Pall.) is considered a rare and endangered
species in the forest fund of the Republic of Serbia. One of its native populations in Serbia
is conserved in the natural protected area „Veliko ratno ostrvo” (Belgrade). This research
aimed to assess the genetic and ecological potential of European White Elm from the
protected area „Veliko ratno ostrvo“ based on research conducted in a nursery progeny test.
The selection of test trees was done in the area of “Veliko ratno ostrvo”based on the yield
in spring 2019. The progeny test was established in the nursery of the Faculty of Forestry,
University of Belgrade. The assessment of gen-ecological potential was based on the survival
of the one- and two-year-old seedlings of 6 half-sib lines during two vegetations and their
morphological characteristics (height and root collar diameter). Statistical analyses were
performed with Statgraphics Centurion XVI software. The results of descriptive statistics,
one-way analysis of variance, and the least significant difference test were presented. The
percentage of seedlings' survival at the end of the second vegetation period was above 50%
in all halfsib lines. The differences in the measured characteristics were significant among
all half-sib lines (p<0.05), which indicates a strong effect of genetic control. The highest
mean value of the height and root collar diameter of one- and two-year-old seedlings was
recorded in half-sib line 4. The analysis of the gene-ecological potential of different European
White Elm half-sib lines will be continued in the pilot stand, established on the „Veliko ratno
ostrvo“, which will be used to monitor the survival and development of seedlings over a
longer period. Collected information on the gene-ecological potential of certain half-sib lines
will serve as a basis for further breeding of the species, through the selection of superior
genotypes
Preliminary cytotoxicity testing of newly synthesised SBA-15 material
No full textMaterial SBA-15 with all of its particles in the form of regular spheres was synthesised by template method using Pluronic P123 (non-ionic triblock copolymer) as a surfactant and tetraethoxysilane (TEOS, 98%) as a source of silica. The synthesis of spherical SBA-15 was carried out in acidic conditions according to method proposed by Zhao et al. Instead of expensive commercial cetyltrimethylammonium bromide as a co-surfactant, a spent HCl solution obtained after the chemical treatment of clay in an aqueous solution of HCl was used. The mixture was aged at a higher temperature. After that, the spherical SBA-15 was made by drying at room temperature after washing with distilled water and then calcining in flowing air to decompose the triblock copolymer. The continual presence of spheres of diameters around 2 μm in the entire SBA-15 was confirmed by scanning electron microscopy. The Energy-dispersive X-ray spectroscopy confirmed that the spheres consisted only of SiO2 in composition. In addition, X-ray diffraction and Fourier-transform infrared spectroscopy methods were used to characterise SBA-15 material. To assess the cytotoxic effects of newly synthesised SBA-15 material, HEK 293 cells were treated with particles and extracts obtained from particles incubated 24 hours at 37 °C in serum-free DMEM medium and DMEM with 10% serum. Cells were treated with concentrations of 100, 250, and 500 µg/mL for 72 hours. All treatments reduced cell viability in a concentration dependent manner (p<0.001). Cytotoxicity was more pronounced in particle treatment, indicating that mechanical damage was induced in cells, whereas the extraction process influences the level of toxicity since the sera-free medium had the mildest effect. To acquire safe particles for human use, additional synthesis optimisation is required
What’s the rumpus? Resident temperate forest birds approach an unfamiliar neotropical alarm call across three continents
Get PDFAlarm signals have evolved to communicate pertinent threats to conspecifics,
but heterospecifics may also use alarm calls to obtain social information. In
birds, mixed-species flocks are often structured around focal sentinel species,
which produce reliable alarm calls that inform eavesdropping heterospecifics
about predation risk. Prior research has shown that Neotropical species
innately recognize the alarm calls of a Nearctic sentinel species, but it remains
unclear how generalizable or consistent such innate signal recognition of
alarm-calling species is. We tested for the responses to the alarm calls
of a Neotropical sentinel forest bird species, the dusky-throated antshrike
(Thamnomanes ardesiacus), by naive resident temperate forest birds across
three continents during the winter season. At all three sites, we found that
approaches to the Neotropical antshrike alarm calls were similarly frequent
to the alarm calls of a local parid sentinel species (positive control), while
approaches to the antshrike’s songs and to non-threatening columbid calls
(negative controls) occurred significantly less often. Although we only
tested one sentinel species, our findings indicate that temperate forest birds
can recognize and adaptively respond globally to a foreign and unfamiliar tropical
alarm call, and suggest that some avian alarm calls transcend
phylogenetic histories and individual ecological experiences