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The As2S3-Cu interface was studied by dielectric spectroscopy measurements on Cu-As2S3-Cu thin film heterostructure samples to assess the charge carriers' contribution to the electrical properties of such an interface. Three-dimensional printed masks ensured good reproducibility during the PLD deposition of heterostructure samples. The samples were tested for electrical conductivity and AC photoconductivity by dielectric spectroscopy measurements. DC bias voltages and light were applied to the samples. The electrical capacity of the thin film heterostructure can be modified electrically and optically. We observed long-term photoconductivity with a time dependency that was not exponential, and a quick change of the electrical capacity, indicating the potential of the heterostructure cells as photodetector candidates. [ABSTRACT FROM AUTHOR]

• Chemical stability of the melt quenched glasses improved by P2O5. • Melting temperature changes the structure of the obtained glasses. • Magneto-optical measurements reveal an S-shape peak of the metallic colloids. • Mobile charges required lower thermally activation energy in Teo nanostructures. Phosphate tellurite glasses, with a nominal composition of 40%ZnO+40%P 2 O 5 +20%TeO 2 , have been synthesized by melt quenching procedure. P 2 O 5 can lead to chemically stable phosphate tellurite glasses, compared with those classical synthesized with H 3 PO 4. Magneto-optical measurements have shown a derivative A 1 term centered at 532 nm originating from a transition to a degenerated excited state associated with tellurium colloids. The glass densities, measured by the Archimedes method at room temperature, display an increasing value with the melting temperature of the samples. The electrical conductivity shifts toward lower frequencies with the increased melting temperature, being influenced by the mobile charges, which require lower thermal activation energy due to the Teo metallic particles. Together with dielectric constant, the electrical conductivity underlines structural changes, by increasing the melting temperature, associated with the presence of Teo nanoclusters. [Display omitted] [ABSTRACT FROM AUTHOR]

New thermotropic lanthanidomesogens based on Eu(III), Sm(III) and Tb(III) with N -alkylated 4-pyridones mesogenic ligands, having two cyanobiphenyl groups attached via long alkoxy spacers, with 6, 9 and 10 carbons atoms in 3,5 - positions of a benzyl unit, have been designed and investigated. The liquid crystal behavior was assessed by differential scanning calorimetry, the mesophases being assigned by polarized light microscopy based on their characteristic textures and confirmed by variable temperature X-ray powder diffraction analysis. The three N -alkylated 4-pyridones nematic ligands reacted with lanthanide nitrates to yield new lanthanidomesogens with a stable and reproducible smectic A phase up to 125 °C. The emission spectra of the complexes have shown the characteristic emission of the lanthanide trivalent ions, over the entire temperature range of SmA phase up to isotropic state. The dielectric spectroscopy measurements performed in the temperature range of existence of the liquid crystal phase, both in the low frequency (LF) domain 0.01–10 MHz and in the high frequency (HF) range, 1 MHz–3 GHz, revealed three dipolar relaxation processes. The characteristic times have been obtained by fitting the spectra of the dielectric loss with a two component Havriliak-Negami function. The activation constant/energy was determined from the Vogel-Fülcher-Tammann law. Unlabelled Image • N -Alkylated 4-pyridones having two cyanobiphenyl mesogenic groups were used to produce glassy liquid crystals based on lanthanides • The new lanthanide nitrates complexes exhibit a stable and reproducible smectic A phase up to 125 °C • Dielectric spectroscopy measurements revealed three dipolar relaxation processes • Activation constant/energy of the new lanthanidomesogens was determined from the Vogel-Fülcher-Tammann law [ABSTRACT FROM AUTHOR]

• Polymer Dispersed Liquid Crystal (PDLC) systems using chitosan biopolymer matrix and the nematic liquid crystal (LC) mixture E7 were obtained. • The N-Iso phase transitions have shifted in the heating DSC scan to lower temperature values for PDLC samples with approximately 2.7 °C. • Dielectric loss and electrical conductivity spectra along with their temperature variation have been analyzed. • Havriliak-Negami function was used for obtaining the characteristic time and the activation energy. Polymer Dispersed Liquid Crystals (PDLC) systems were obtained using chitosan as a biopolymer matrix and the nematic liquid crystal (LC) mixture E7 in various concentrations (30, 40 and 50% E7 in chitosan). Several techniques were used to analyze the obtained films: polarizing optical microscopy (POM), IR spectroscopy (FTIR), differential scanning calorimetry (DSC) and dielectric spectroscopy (DS). FTIR spectroscopy revealed minor changes for all PDLC films, suggesting weak interactions between LC and chitosan matrix. For each sample a clear segregation of the nematic droplets could be observed by POM. DSC measurements show that the phase transitions have shifted to lower temperature values for PDLC samples with approximately 2.7 °C compare to pure E7. The values of α (fraction of LC in the droplets) for compositions of 30, 40 and 50 wt% E7 in Chitosan were 0.48, 0.55 and 0.61 respectively, that are lower than for E7/PMMA system. The qualitative and quantitative analysis of the permittivity spectra obtained by DS reveals the fact that there are no significant changes in the molecular dynamics attributed to pure LC E7 compared to the PDLC composites, leading to the conclusion of the existence of a weak interaction between the two components, fact confirmed by the findings from the FTIR results. [ABSTRACT FROM AUTHOR]

In this paper, new results on the degradation of losartan potassium (LP, (1)), in the absence and presence of excipients, which was induced by UV light, the acid character of phosphate buffer solution (PBS) and alkaline medium, respectively, are reported through correlated studies of FTIR spectroscopy, photoluminescence and dielectric spectroscopy. The photoluminescence (PL) spectra of LP and the drug marked under the name Lorista (LO) are characterized by intense emission bands, peaking at 378 nm and 380 nm, respectively, accompanied by low intensity bands with a maximum at ~450–460 nm. Photodegradation of LO in a solid state is evidenced by a decrease in the intensity of the PL band at 380 nm, a variation that originates both in the adsorption of water vapors from the air and in the interaction of LP with excipients such as cornstarch, silicon dioxide and cellulose. The LP-water interaction is described, taking into account the main electrical parameters, i.e., complex dielectric permittivity and electrical conductivity. Photodegradation of LP and LO also induces an increase in the intensity of the emission band, at ~450–460 nm. The influence of acid and alkaline medium on the LO degradation is analyzed using phosphate buffer (PBS) and NaOH solutions, respectively. In both cases, a decrease in the intensity of the PL band, at 380 nm, is reported. The intensity diminution of the PL spectra of NaOH-reacted LP and LO is the result of the formation of the photodegradation product N-methanolamide-{[2′-(1H-tetrazol-5-yl)(1,1′-biphenyl)-4-yl]methyl} (2). This compound was proven by the studies of FTIR spectroscopy achieved on LP and NaOH-reacted LP. The appearance of the IR band at 1740 cm−1 and the increase in the absorbance in the IR band at 1423 cm−1 indicate that the photodegradation product (2) contains the C=O and C-OH functional groups. [ABSTRACT FROM AUTHOR]

Barium titanate (BaTiO) has been doped in situ with 5 mol% thulium by a sol-gel method. The as-prepared gel powder consists of nanosized grains (20-30 nm) and crystallizes on the cubic BaTiO lattice, at 700°C. BaTmTiO ceramics derived from this powder have tetragonal perovskite structure and contain a small amount of TmTiO pyrochlore phase. These ceramics exhibit dielectric constants of 4282-3240 and dielectric loss (tan δ) of 0.1077-0.0161 at Curie temperature T=132°C and at 10 Hz-100 kHz, respectively. For a drive voltage of 400 V, the hysteresis loop recorded at the frequency of 100 Hz shows a remnant polarization ( P) value of 76 μC/cm and a coercive field ( E) of 124 V and for 1 kHz a remnant polarization ( P) value of 58 μC/cm and a coercive field ( E) of 116 V. [ABSTRACT FROM AUTHOR]

A two-step sintering approach composed of spark-plasma-sintering (SPS) technique at 1000 °C for 1 min and under a uniaxial pressure of 63 MPa followed by conventional sintering at 1400 °C for 3 h is proposed for synthesis of dense Ba(Ti0.87Sn0.13)O3 ceramics. Starting powders had grain size of about 90 nm and were obtained by co-precipitation. The SPS pellets consist of submicron (300–500 nm) grains. X-ray diffraction analysis of as-prepared Ba(Ti0.87Sn0.13)O3 ceramic shows the occurrence of cubic and tetragonal phase coexistence for the pellets obtained after SPS processing and the presence of only tetragonal phase in the samples after the second (conventional) sintering. Grain uniformity in the final product is high, with average size of ~2 μm. The apparent densities of the sintered pellets at temperature of 1400 °C were ~92% of the theoretical value of Ba(Ti0.87Sn0.13)O3. The ceramics exhibit a high relative dielectric constant of 6,550 and a dielectric loss (tan δ) = 0.078 at Curie temperature of 63 °C and 10 Hz. [ABSTRACT FROM AUTHOR]

This paper prepared composites under the free membranes form that are based on thermoplastic polymers of the type of polyurethane (TPU) and polyolefin (TPO), which are blended in the weight ratio of 2:1, and ceramic nanoparticles (CNs) such as BaSrTiO3 and SrTiO3. The structural, optical, and conductive properties of these new composite materials are reported. The X-ray diffraction studies highlight a cubic crystalline structure of these CNs. The main variations in the vibrational properties of the TPU:TPO blend induced by CNs consist of the following: (i) the increase in the intensity of the Raman line of 1616 cm−1; (ii) the down-shift of the IR band from 800 to 791 cm−1; (iii) the change of the ratio between the absorbance of IR bands localized in the spectral range 950–1200 cm−1; and (iv) the decrease in the absorbance of the IR band from 1221 cm−1. All these variations were correlated with a preferential adsorption of thermoplastic polymers on the CNs surface. A photoluminescence (PL) quenching process of thermoplastic polymers is demonstrated to occur in the presence of CNs. The anisotropic PL measurements have highlighted a change in the angle of the binding of the TPU:TPO blend, which varies from 23.7° to ≈49.3° and ≈53.4°, when the concentration of BaSrTiO3 and SrTiO3 CNs, respectively, is changed from 0 to 25 wt. %. Using dielectric spectroscopy, two mechanisms are invoked to take place in the case of the composites based on TPU:TPO blends and CNs, i.e., one regarding the type of the electrical conduction and another specifying the dielectric–dipolar relaxation processes. [ABSTRACT FROM AUTHOR]

Nano-sized lanthanum doped barium titanate Ba 1-x La x TiO 3 (0.00 ≤ x ≤ 0.08) powders were prepared by sol-gel method. These powders with perovskite BaTiO 3 cubic single phase structure, obtained after calcinations of gels precursors at 1100 °C, 3 h in air, were pressed and sintered by spark plasma technique in order to obtain dense ceramics. The optimal sintering temperatures used for Ba 1-x La x TiO 3 powders were dependent on lanthanum amount added to barium titanate and decrease from 1300 °C to 1160 °C when the La concentration increases from 0 to 8 at.% La. An additional annealing treatment was made in air at 900 °C for all the sintered pellets for oxidize and remove the contaminant graphite which migrated in ceramics from the graphite die during the sintering process. The effect of lanthanum concentration on the densification behavior, structure, microstructure, photoluminescence and dielectric properties of the Ba 1-x La x TiO 3 ceramics was investigated in this work. The results shown that as the lanthanum content increases, the grain size of the powders and ceramics increases accompanied by decrease of density of the samples. Also, increase of La amount inserted in BaTiO 3 lattice leads to significant decrease of the dielectric losses and Curie temperature and, increase of dielectric permittivity but the luminescence properties seem to be less affected. [ABSTRACT FROM AUTHOR]

[Display omitted] • Lanthanide complexes with N-substituted-4-pyridones ligands with mesogenic 3,4 or 3,5-di(alkyloxy)benzyl units. • The complexes show typical lanthanide solid state emission and lamellar phases (SmA). • Substitution pattern and length of flexible alkoxy chains control the phase-transition characteristics. • Dielectric spectroscopy was used to evaluate the dipolar relaxation processes and phase transitions. In the present work, new luminescent lanthanide complexes with extended mesomorphic range were prepared by coordination to lanthanide ions (Eu3+, Sm3+ and Tb3+) of the new 4-pyridone based organic ligands (L) with 3,4- (7- n ) and 3,5-di(alkyloxy)benzyl (8- n ) mesogenic groups and variable length (n = 12 or 14 carbon atoms) onto the benzyl unit. The cumulative results of the elemental analyses as well as the 1H, 13C NMR and IR spectroscopies support the structure of the organic derivatives and their lanthanide complexes [LnL 3 (NO 3) 3 ] (9- n /Ln and 10- n /Ln) described in this work. These complexes show characteristic lanthanide solid state emission, both at room and elevated temperatures corresponding to crystalline, glassy or liquid crystal states. The long range SmA phases displayed by all complexes were supported by a combination of characterization methods, including: differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and variable-temperature powder X-ray diffraction (XRD). This work shows that the number, substitution pattern and length of flexible alkoxy chains are important parameters to control the phase-transition characteristics of the lanthanide complexes. Complexes with 3,4-disubstituted pattern (9- n /Ln) show higher clearing temperatures (nearly 60 °C for Eu3+, 70 °C for Sm3+ and 85 °C for Tb3+ complexes) compared to their counterparts with 3,5-disubstituted pattern (10- n /Ln). Moreover, complexes 9- n /Ln crystallize when cooling their LC phase while complexes 10- n /Ln are stable in glassy state at room temperature as a consequence of the different close interdigitated molecular packing evidenced by XRD measurements. Dielectric spectroscopy was employed to detect the changes of order degree specific to each phases (crystalline, LC or isotropic). The variation of dielectric constant and the electrical conductivity versus temperature shows three transition intervals for selected complexes 10- 14 /Sm and 10 - 14 /Tb, which delimit the main intervals: 45–60 °C, 90–110 °C; 140–160 °C corresponding to the Cr 1 -Cr 2 , Cr 2 – SmA and SmA-Iso transitions, and agree very well with the DSC results. The change of characteristic time, obtained by Havriliak-Negami fit function, with temperature also provides a very good correlation with the DSC and POM results. [ABSTRACT FROM AUTHOR]

We obtained a new system containing nematic liquid crystal doped with nanostructured copolymer-clay particles. The clay (Cloisite-type) was modified by copolymerization of maleic anhydride and divinyl benzene and the nanocomposite has intercalated structure. Current-voltage characteristics of the liquid crystal/copolymer-clay systems were analyzed and the electro-optical response at heating -cooling cycles for different applied electric fields is discussed. Dielectric spectroscopy measurements in the low frequency domain have shown different regimes of its temperature dependence as function of the sample nature and the applied voltage. Comparison is made with the bulk liquid crystal. Changes of the phase transition temperature are thus revealed. [ABSTRACT FROM AUTHOR]

Abstract: The molecular mobility of 4-butyl- and 4-pentyl-4′-cyanophenyl benzoate (CP4B, CP5B) and their composites prepared from aerosil A380 was investigated by broadband dielectric spectroscopy in a large temperature range. Thermogravimetric and infrared investigations were additionally performed. High silica density (larger than 7g aerosil/1g of liquid crystal) was selected to observe a thin layer adsorbed on the surface of the silica particles. The data were compared with those of the member of the series with six carbon atoms in the alkyl tail. Bulk CP4B and CP5B show the dielectric behaviour expected for liquid crystals. For the composites one relaxation process is observed at frequencies much lower than those for the corresponding bulk, which was assigned to the dynamics of the molecules in a surface layer. The temperature dependence of the relaxation rates (and of the dielectric strength) shows a crossover behaviour with two distinguished regimes. At higher temperatures the data obey the Vogel–Fulcher–Tammann law, whereas an Arrhenius law is observed at lower temperature, in a close similarity to the behaviour of a constrained dynamic glass transition. The estimated Vogel and crossover temperature is independent on the tail length, while the activation energy for the low temperature branch increases weakly with increasing the alkyl tail. [Copyright &y& Elsevier]

Abstract: Composites prepared from aerosil A380 and liquid crystals (LCs) of 4-n-alkyl-4′-cyanophenyl benzoate type, with four to six carbon atoms in the alkyl chain were investigated by infrared spectroscopy. Their high silica content (of 2–7g aerosil/1g of LC) was given by thermogravimetric investigations and allows the observation of a rather thin LC layer on the silica particles. Several surface species onto the external surface of the grains were demonstrated. Arguments are given that monomer and dimer species are present in the bulk cyanophenyl benzoate materials while bulk-like species along with hydrogen-bonded ones coexist in the so-called surface layer of the composites. The main interaction of LC molecules with the aerosil surface is by hydrogen bonding taking place with the involvement of the cyan group. There is a contribution of ester carbonyl group to these surface interactions but this cannot be well quantified. [Copyright &y& Elsevier]

• Ba 1–x Tb x TiO 3 x = 0.00, 0.01 and 0.05 powders were synthesized by hydrothermal route. • Ba 1–-x Tb x TiO 3 ceramics were sintered at 1325 °C, for x = 0.00, 0.01 and 0.05, respectively. • Ba 1–x Tb x TiO 3 ceramics exhibited good permittivity and low dielectric losses. • The band gap energy of BaTiO 3 decreases with the Tb–doping. Multifunctional materials integrating optical and electric properties into a composite or into a doped single–phase material have attracted much attention from scientists for future optoelectronic devices. In this work, polycrystalline Ba 1–x Tb x TiO 3 , x = 0.00, 0.01 and 0.05 materials were synthesized by hydrothermal route and their photoluminescence and dielectric properties were studied. The as–prepared powders showed a microstructure consisting of grains with the shape of cube; and average particle size ranging from 75 nm to 150 nm. The investigated temperature dependence of dielectric permittivity of Ba 1–x Tb x TiO 3 ceramics revealed a decrease of the Curie temperature (Tc) with increasing terbium content, and a more pronounced degree of diffuseness of phase transition. The resistivity at room temperature was discussed in terms of positive temperature coefficient of resistance (PTRC) effect. UV–vis reflectance spectra of Ba 1–x Tb x TiO 3 samples showed a decrease of the band gap energy with the increase of Tb amount, due to the band–gap narrowing effect. The photoluminescence spectra recorded for Tb doped BaTiO 3 materials, at 80 K, evidenced the typical f–f luminescence lines of the Tb3+ accompanied the broad luminescence band at about 425 nm due to self–trapped exciton recombination. These results demonstrated that the terbium enhances the dielectric properties and photoluminescence simultaneously, being suitable for electronic applications. [ABSTRACT FROM AUTHOR]

The influence of nickel substitutions on the local structure, dielectric and magnetic properties of Ba hexaferrites is investigated in this study for use as rare earth free permanent magnets and microwave devices, especially. For this purpose, BaNi x Fe 12–x O 19 (x = 0.0, 0.2, 0.5, 0.8 and 1.0) powders were prepared by auto–combustion of their citrate–nitrate gels precursor whilst spark plasma sintering and conventional sintering techniques were used in order to prepare BaNi x Fe 12–x O 19 sintered ceramics samples. Structure, microstructure, dielectric and magnetic properties of BaNi x Fe 12–x O 19 materials were investigated by X-ray diffraction, scanning electron microscopy (SEM), dielectric measurements, Mössbauer spectroscopy and SQUID magnetometry. X-ray diffraction analyses indicated that BaNi x Fe 12–x O 19 , x = 0.0–1.0crystallized on the hexagonal BaFe 12 O 19 structure and, the lattice parameters a and c , decrease as the Ni content increases. Raman spectroscopy analysis confirmed the formation of the BaFe 12 O 19 phase. The presence of Fe in the +3 oxidation state (Fe3+) and of Ni2+ is confirmed by X-ray photoelectron spectroscopy (XPS). The SEM investigations on BaNi x Fe 12–x O 19 powders showed the change of the morphology from a granular-like structure to a platelet-like structure with increasing the nickel content which influences the dielectric and magnetic properties of these materials. Dielectric measurements performed on BaFe 12−x Ni x O 19 ceramics showed consistent differences between the two sintering methods. Impedance analysis shows a contribution of grains and grain boundaries in all samples. The Mössbauer spectroscopy results evidenced the five Wyckoff crystallographic iron positions and their site occupancy with respect to Ni substitutions content. The permanent magnet characteristics of the hexaferrites were confirmed by the high values of coercive field (up to ∼ 1.7 kOe) and remanence (∼28 emu/g), while the saturation magnetization values are found up to 95 emu/g at low temperatures and 70 emu/g at room temperature (for x = 0.8). The coercive field, remanence and maximum energy product decrease with nickel content, while the saturation magnetization behaves unmonotonically due to the specific variation of the site occupancy. More insight into the link between local structure and magnetic properties of Ni substituted Ba hexaferrite was given. • BaNi x Fe 12–x O 19 (x = 0.0–1.0) hexaferrites were prepared by gel auto–combustion. • Dielectric properties are influenced by different sintering methods. • Magnetic moments are sensitive to the local structure of Fe ions. • Ni2+ ions have an improper crystallographic occupation, affecting M S. • Ni2+ substitution caused decrease of H C , M R and (BH) max. [ABSTRACT FROM AUTHOR]

Herein we report on novel multiferroic core–shell nanostructures of cobalt ferrite (CoFe2O4)–bismuth, sodium titanate doped with barium titanate (BNT–BT0.08), prepared by a two–step wet chemical procedure, using the sol–gel technique. The fraction of CoFe2O4 was varied from 1:0.5 to 1:1.5 = BNT–BT0.08/CoFe2O4 (molar ratio). X–ray diffraction confirmed the presence of both the spinel CoFe2O4 and the perovskite Bi0.5Na0.5TiO3 phases. Scanning electron microscopy analysis indicated that the diameter of the core–shell nanoparticles was between 15 and 40 nm. Transmission electron microscopy data showed two–phase composite nanostructures consisting of a BNT–BT0.08 core surrounded by a CoFe2O4 shell with an average thickness of 4–7 nm. Cole-Cole plots reveal the presence of grains and grain boundary effects in the BNT–BT0.08/CoFe2O4 composite. Moreover, the values of the dc conductivity were found to increase with the amount of CoFe2O4 semiconductive phase. Both X-ray photoelectron spectroscopy (XPS) and Mössbauer measurements have shown no change in the valence of the Fe3+, Co2+, Bi3+ and Ti4+ cations. This study provides a detailed insight into the magnetoelectric coupling of the multiferroic BNT–BT0.08/CoFe2O4 core–shell composite potentially suitable for magnetoelectric applications. [ABSTRACT FROM AUTHOR]

This paper proposes a novel, flexible, low cost administration patch which could be used as a non-invasive, controlled transdermal drug delivery system. The fabricated device consists in a flexible microfiber architecture heater covered with a thermoresponsive hydrogel, namely poly(N-isopropylacrylamide), as a matrix for the incorporation of active molecules. The manufacturing process consists of two main steps. First, the electrospun poly(methyl methacrylate) fiber networks are sputter coated with a thin gold layer and attached to flexible poly(ethylene terephthalate) substrates to obtain the heating platforms. Second, the heaters are encapsulated in poly(ethylene terephthalate) foils and covered with poly(N-isopropylacrylamide) hydrogel sheets. In order to illustrate the functionality of the fabricated patch, the hydrogel layer is loaded with methylene blue aqueous solution and is afterwards heated via Joule effect, by applying a voltage on the metalized fibers. The methylene blue releasing profiles of the heated patch are compared with those of the unheated one and the influence of parameters such as hydrogel composition and morphology, as well as the applied voltage values for microheating are investigated. The results indicate that the fabricated patch can be used as a drug administration instrument, while its performance can be tuned depending on the targeted application. [ABSTRACT FROM AUTHOR]