Strontium bismuth tantalate (SrBi
2
Ta
2
O
9
) was synthesized by a co-precipitation method. The sample was characterized by x-ray powder diffraction patterns (XRD), Fourier-transform infrared ...spectroscopy (FTIR) and scanning electron microscopy (SEM). The results of the dielectric properties are reported at room temperature. No secondary phases were found while heating the powder at 850°C and the pure SrBi
2
Ta
2
O
9
phase was formed, as revealed by XRD. The characteristic bands for SrBi
2
Ta
2
O
9
were observed by FTIR at approximately 619 cm
−1
and 810 cm
−1
. SEM micrographs for the sample displayed thin plate-like grains. The grain size was less than 1
μ
m and the crystallite size of about 24 nm. Dielectric response at room temperature shows that the SrBi
2
Ta
2
O
9
ceramic has low loss values, and the flattening of the dielectric constant at higher frequencies. The observed Curie temperature is comparable with those reported in the literature.
We report a systematic investigation of the structure, micro-structure, dielectric, ferroelectric and piezoelectric properties of CuO added SrBi4Ti4O15 ceramics. All the samples were prepared by ...solid state reaction technique, where the wt% of CuO in SrBi4Ti4O15 was varied as x = 0, 0.05, 0.2, 0.5. The addition of CuO increased the density of SrBi4Ti4O15 ceramics which in turn resulted in the improvement of dielectric, ferroelectric as well as piezoelectric properties. However, no change either in the crystal structure or lattice parameter was observed with CuO addition. Further a dense micro-structure with improved electrical properties is expected to be due to liquid phase sintering. Raman spectra and specific heat measurements were also performed for getting further insight into the properties.
The structural parameters, density of states, electronic band structure, charge density, and optical properties of orthorhombic SrBi2Ta2O9 have been investigated using the plane-wave ultrasoft ...pseudopotential technique based on the first-principle density functional theory (DFT). The calculated structural parameters were in agreement with the previous theoretical and experimental data. The band structure showed an indirect (S to Γ) band gap with 2.071 eV. The chemical bonding along with population analysis has been studied. The complex dielectric function, refractive index, and extinction coefficient were calculated to understand the optical properties of this compound, which showed an optical anisotropy in the components of polarization directions (100), (010), and (001).
Složena vjerska i etnička slika Boke Kotorske stvorena je prije nekih sedam stotina godina i do danas se nastavila mijenjati. No relativno pouzdane informacije o etničko-brojčanim suodnosima dobivamo ...tek od vremena Druge austrijske uprave (1814. – 1918.), tijekom koje se Boka Kotorska nalazi u okvirima Kraljevine Dalmacije. Pritom su od posebne važnosti suvremeni popisi stanovništva provedeni 1857., 1869., 1880., 1890., 1900. i 1910. Ti popisi nisu registrirali etničku pripadnost, već vjersku, a od 1880. i jezičnu. Stoga se do pokazatelja o etničkom sastavu Boke može doći samo kombinacijom tih podataka. Unatoč tome što popisi iz 1880. i 1890. dopuštaju taj tip kalkulacija, ipak su neprikladni za stjecanje cjelovite slike, prvenstveno stoga što su kod njih ukupnoj populaciji pridodavani brojni vojnici stacionirani na bokeljskom prostoru, i to bez mogućnosti da ih se u cilju uvida u narodnosni karakter Boke izdvoji iz stvarne mase stanovništva. Od popisa iz 1900. takvo je izuzimanje moguće. Dakle tek su njime stvorene pretpostavke da se posrednim proračunima, što će biti predmetom ovoga rada, utvrde brojčani suodnosi različitih etničkih zajednica na tlu Boke Kotorske, i to do razine svih njenih naselja.
Layered perovskite compounds of SrBi2Nb2−xVxO9 (x = 0.0, 0.02, 0.04, 0.06, and 0.08) were synthesized via a solid-state reaction method. Their optical properties, electronic band structures, and ...photocatalytic activities under visible light irradiation were investigated for the first time. The incorporation of vanadium into the SrBi2Nb2O9 lattice reduced the bandgap energies, allowing the compounds to effectively absorb visible light. Electronic band structure calculations revealed that the V 3d orbitals caused bandgap narrowing by forming an additional band below the conduction band, while the O 2p and Bi 6p orbitals dominantly contributed to the formation of the valence band. The photocatalytic activity tested under visible light irradiation (>420 nm) revealed that it increased linearly with the V content in the SrBi2Nb2−xVxO9 compounds until saturation at x = 0.06, which was attributed to improved visible light absorption originating from the reduced bandgap energies.
SrBi1.8Ce0.2Nb2O9 (SBCN) and SrBi1.8Ce0.2Ta2O9 (SBCT) powders were prepared
via solid-state reaction method. X-ray diffraction analysis reveals that the
SBCN and SBCT powders have the single phase ...orthorhom-bic Aurivillius
structure at room temperature. The contribution of Raman scattering and FTIR
spectroscopy of these samples were relatively smooth and resemble each other.
The calcined powders were uniaxially pressed and sintered at 1250?C for 8 h
to obtaine dense ceramics. Dielectric constant, loss tangent and AC
conductivity of the sintered Ce-doped SrBi2Nb2O9 and SrBi2Ta2O9 ceramics were
measured by LCR meter. The Ce-doped SBN (SBCN) ceramics have a higher Curie
temperature (TC) and dielectric constant at TC (380?C and ?? ~3510) compared
to the Ce-doped SBT (SBCT) ceramics (330?C and ?? ~115) when measured at
100Hz. However, the Ce-doped SBT (SBCT) ceramics have lower conductivity and
dielectric loss.
nema
The contamination of aquatic environments by colored and toxic dyes such as rhodamine-B causes many problems for the human health. Their high stability is a major problem for the removal of dyes. The ...adsorption technique can be used for the treatment of dyes efficiently. In this study, SrCo
x
Bi
4
Ti
4-x
O
15
nanostructures with different cobalt ions ratios (x = 0.0, 0.01, 0.03 and 0.05) are synthesized and characterized by XRD, XRF, FT-IR, Uv-vis, Uv-DRS, PL and TEM measurements. Ethanolamine is used as a precipitating agent. All samples crystallized in an orthorhombic crystalline system according to the XRD patterns and have layered morphology as determined by the TEM analysis. Compared with SrBi
4
Ti
4
O
15
, samples doped with cobalt (II) ions show a shift toward lower angles in their XRD patterns, a shift toward lower wavelength side, and higher bond gap energy. In addition, the luminescence intensity is decreased with the increase in the Co
2+
concentration. The adsorption capacity of SrCo
x
Bi
4
Ti
4-x
O
15
nanostructures on the removal of rhodamine B (RB) from the aqueous medium was investigated under ambient temperature. The effective parameters on the adsorption such as catalyst dosage, dye concentration, pH and time are optimized. In comparison with the pure SrBi
4
Ti
4
O
15
, compounds doped with Co
2+
have better adsorption capacity for RB.
Gestational diabetes mellitus (GDM) is a common complication of pregnancy that is characterized by glucose intolerance, leads to dyslipidemia, and is aggravated by obesity. Cholesterol is taken up by ...the placenta as part of lipoproteins through the scavenger receptor class B type I receptor (SRBI), low-density lipoprotein receptor (LDLR), and very low density lipoprotein receptor (VLDLR), and its efflux is then mediated by ABCA1 and ABCG1. PCSK9 is involved in the degradation of LDLR and VLDLR. The goal of this study was to evaluate the impact of GDM and prepregnancy body mass index (BMI) on cholesterol transport through the modulation of the expression of several key players. Human full-term placenta, maternal, and venous cord blood samples were obtained at delivery from normal-weight women without GDM (n = 10), normal-weight women with GDM (n = 6), and overweight/obese women with GDM (n = 6). Lipids (total cholesterol, high-density lipoprotein, low-density lipoprotein, triglycerides, free fatty acids, apolipoprotein A1, apolipoprotein B100) levels were evaluated in blood samples. Messenger RNA and protein expression levels (LDLR, VLDLR, SRBI, ABCA1, ABCG1, proprotein convertase subtilisin/kexin type 9, liver x receptors, peroxisome proliferator-activated receptors) were assessed in human full-term placenta, respectively, by real-time RT-PCR and Western blots. Lipoprotein lipase activity was evaluated using a commercial kit on tissue homogenates. Overall, our study demonstrates that GDM affects the maternal and neonatal lipid profiles as well as different key players of placental cholesterol transfer from the maternal to the fetal circulation, depending on the maternal BMI. These changes could affect the fetal metabolism and predispose the fetus to future metabolic diseases.
The heat capacities and enthalpy increments of strontium bismuth niobate SrBi
2Nb
2O
9 (SBN) and strontium bismuth tantalate SrBi
2Ta
2O
9 (SBT) were measured by the relaxation method (2–150
K), ...Calvet-type heat-conduction calorimetry (305–570
K) and drop calorimetry (773–1373
K). The temperature dependences of non-transition heat capacities in the form
C
pm
=
324.47
+
0.06371
T
−
5.0755
×
10
6/
T
2
J
K
−1
mol
−1 (298–1400
K) and
C
pm
=
320.22
+
0.06451
T
−
4.7001
×
10
6/
T
2
J
K
−1
mol
−1 (298–1400
K) were derived for SBN and SBT, respectively, by the least-squares method from the experimental data. Furthermore, the standard molar entropies at 298.15
K
S
m
°
(
SBN
)
=
327.15
±
0.80
and
S
m
°
(
SBT
)
=
339.23
±
0.72
J
K
−
1
mo
l
−
1
were evaluated from the low-temperature heat capacity measurements.
The crystal structure, surface morphology, dielectric and electrical properties of tungsten doped SrBi2(WxTa1-x)2O9 (x = 0.0-0.20) ferroelectric ceramics were investigated. Dielectric measurements ...performed as a function of temperature at 1, 10 and 100 kHz showed an increase in Curie temperature over the composition range of x = 0.05-0.20. W6+ substitution in perovskite-like units resulted in a sharp dielectric transition at the ferroelectric Curie temperature with the dielectric constant at their respective Curie temperature, increasing with tungsten doping. The dielectric loss reduced significantly with tungsten addition. The temperature dependence of ac and dc conductivity, vis-a-vis tungsten content, showed a decrease in conductivity, attributed to the suppression of oxygen vacancies. The activation energy calculated from the Arrhenius plots increased with tungsten content. 32 refs.
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