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Graphene and Multi Walled Carbon Nanotubes (MWCNT) admixtured Bismuth Iron Oxide (hereafter referred to BIO) nanocomposite ceramics have been synthesized using the sol-gel process. A comparative study on their structural, optical, dielectrical and electrochemical sensing properties has also been made for the first time in an “as-prepared” state. The X-ray diffraction (XRD) peaks clearly indicate the existence of mixed crystalline phases of BIO with graphene and MWCNT. SEM images reveal the distinct morphologies of BIO nano structures, even in the admixtured phase with graphene and MWCNT. The characteristic vibrations and possible scattering modes of BIO admixtured carbonaceous materials (graphene & MWCNT) have been identified through FT-IR and Raman spectra. Band gap (Eg) variation was noticed in the synthesized composites upon loading graphene and MWCNT on the BIO matrix. Enhancement of relative permitivity (er) has been witnessed in the graphene admixtured BIO composite. This increase is significant, when compared to the MWCNT-BIO composite and it may be due to the effective dispersion of graphene over BIO. The pseudo capacitive behaviour of the BIO composite powder with graphene and MWCNT was also ascertained from the Cyclic Voltammetry (CV) studies.

This work shows a simple method utilizing electrophoretic deposition (EPD) of commercial SnO2 nanoparticles films on fluoride-doped tin oxide (FTO) substrate. In this process at constant voltage, depositions cycles are well controlled to achieve SnO2 films with different grain and pore sizes. The experimental results indicate that the method utilizing electrophoretic deposition to SnO2 films plays an important role with photoelectrode in DSSCs compared others methods of deposition because do not presence surfactantes and other contaminants waste. In addition, it was found that reduced film porosity can concentrate dye molecules and be responsible for reducing the electron supply. Effects of the bulk traps and surface states within the SnO2 films on the recombination of the photo-injected electrons strongly depend on the SnO2 film compression. The best device (with a average grain size of 156.0 nm and with an average pore size of 468.0 nm) gives a conversion efficiency of 3.89%, having a short circuit current density exclusive of 14.27 mA/cm2 to incident light of 100 mW/cm2.

A spinel ferrite sample Zn0.4Ni0.6Fe2O4 was prepared by a conventional solid-state reaction method at high temperature. This compound was found to exhibit a single phase and crystallize in a cubic structure with Pm3 m Space group. The complex impedance was investigated in the temperature range 400–700 K and in the frequency range 100 Hz - 1 MHz. The Z-impedance analysis revealed that the relaxation phenomenon is strongly dependent on temperature and frequency. The impedance plane plot showed semi-circle arcs at different temperatures, and a proposed electrical equivalent circuit explained its results. The temperature and frequency dependence of the ac conductivity was shown to obey the universal Jonscher's power law. The activation energy, inferred from the impedance spectrum, was confirmed to match very well with those estimated from the conduction mechanism, indicating that the relaxation process and conductivity have the same origin. The magnetization is due to the ferromagnetic interactions between iron ions.

To explore the relationship between optical properties, oxygen vacancies and magnetism in SrTiO3, we prepared a series of SrTiO3-δ (δ = 0.00, 0.125 and 0.250) samples by solid state reaction method followed by the creation of oxygen vacancies-δ. Surface composition and chemical valence state in the synthesized compounds were examined by X-ray photoelectron spectroscopy (XPS). The Fourier Transform Infrared spectroscopy (FT-IR) spectra showed that the transmission properties change with oxygen vacancies introduction. Ultraviolet–visible absorption revealed that optical properties were highly dependent on oxygen vacancies concentrations. When the magnetic field was applied, magnetization showed weak-ferromagnetism at room temperature on SrTiO3-δ non-stoichiometric systems. Yet, it was reversed showing diamagnetism on SrTiO3 perfect crystal. The large concentration of oxygen vacancies (δ = 0.250) reduced ferromagnetism and optical absorption, implying the possible presence of a relationship between the magnetism and the optical properties. Theoretical results showed two types of electronic contributions to magnetism, one of which emanates from localized states below the conduction band minimum, and the other comes from itinerant electrons of Ti atoms lying further away from the oxygen-vacancy. The electronic structures and magnetic properties were calculated by Full-Potential Linear Augmented Plane Wave (FP-LAPW) method within the Generalized Gradient Approximation (GGA) and the atomic relaxations introduced by the oxygen vacancies host in a fully self-consistent way. The results shed some light on the promising magneto-optical properties of the SrTiO3-δ materials.

We have investigated the effect of the substitution of the Mn ions by Fe ions on the structural, magnetic and magnetocaloric behaviors of La0.5Sm0.2Sr0.3Mn1-xFexO3 (0 ≤ x ≤ 0.15) perovskites. The nanocrystalline powders have been synthesized by self-combustion process. Rietveld refinement of fitted and observed X-ray diffractions patterns shows the formation of single-phase compositions with an orthorhombic crystal system (Pnma space group). The variation of magnetization (M) vs. temperature (T) under the field-cooled (FC) and zero-field-cooled (ZFC) modes reveals a ferromagnetic-paramagnetic transition at the Curie temperature (TC). The (TC) decreases linearly with increasing x and changes from 278 K for x = 0 to 94 K for x = 0.15. Arrott plot analyses and a universal curve method were applied for studying the order of the magnetic transition in this system, found to be of second order. Besides, the magnetic entropy change and the related Relative Cooling Power (RCP) values, sensitive to Fe doping, were estimated. In the vicinity of TC, |-ΔSM| reached a maximum value of 3.06 J kg−1 K−1, 2.93 J kg−1 K−1, 2.22 J kg−1 K−1 and 0.77 J kg−1 K−1, whereas the RCP was found to be 268 J Kg−1, 280 J Kg−1, 285 J Kg−1 and 226 J Kg−1 for x = 0.00, 0.05, 0.10 and 0.15, respectively in a magnetic applied field of 5 T. Through these results, La0.5Sm0.2Sr0.3Mn1-xFexO3 materials are strongly suggested for use as active refrigerants for magnetic refrigeration technology near room temperature.

The ethanol sensing properties of SrTiO3-δ (δ = 0.075 and 0.125) ceramics was analyzed by dielectric measurements. The ceramics were prepared by solid state reaction method followed by the creation of oxygen vacancies- δ , through a thermal activated process. The crystal symmetry, space group and unit cell dimensions were derived from the X-ray diffraction (XRD) data using FullProf software whereas grain's size distribution was assessed by scanning electron microscopy (SEM). The prepared samples have been analyzed by impedance spectroscopy over the frequency range from 100 Hz to 1 MHz and temperature range from 240 to 340 K. The dielectric properties of SrTiO 3-δ ceramics showed a quite remarkable stability of giant permittivity (>104 ) as well as a low dielectric loss , which open ways for several applications such as over voltage protections of electronic devices. A low-frequency dielectric relaxation behavior was found, and the carriers for electrical conduction result from the first-ionization of oxygen vacancies . The conductivity and gas sensitivity of SrTiO 3-δ-based sensors were investigated. Results demonstrated that the conductivity decreases after the introduction of the ethanol gas, and p-type semiconductor gas-sensing materials were obtained. Both characteristics present higher responses at lower optimal operating temperatures.

We have investigated the effect of multi-doping in A and B site of the multiferroic prepared by the Sol-gel method Bi0.8Er0.1Ba0.1Fe0.96Co0.02Cr0.02O3 (BEBFCC) on the structural, morphological and electric properties. X-Ray diffraction and Rietveld refinement confirm that the BEBFCC compound presents a rhombohedral structure with the R3C space group. The Ac electrical properties have been measured from 331 to 735 K as a function of frequency (100 kHz - 1 MHz). Debye's theory and Arrhenius relations were used to study the relaxation phenomenon. The frequency dependence of the impedance (Z”: imaginary part) reveals the existence of one relaxation peak, while the Modulus formalism shows two peaks. The presence of two contributions, related to the dielectric relaxations visible in this compound, was confirmed by the Impedance Nyquist plots. The study of the ac conductivity based on Jonsher's power law confirms that the conduction is associated to the Non-Overlapping Small Polaron Tunneling model.

Rare-earth (RE) oxyfluorides compatible for RE doping make a path for efficient near-infrared (NIR) to visible upconversion (UC). This paper describes the efficient use of YOF:Ho3+/Yb3+ phosphor nanoparticles synthesised by the Pechini sol-gel method as thermal sensors using UC in the visible region. Material characterisations such as X-ray diffraction, Raman spectroscopy and scanning electron microscopy (SEM), revealed the structural information of the material and its prominence for RE doping. Average size of 44 nm obtained from SEM with maximum phonon energy of 480 cm− 1 observed from Raman measurements assure the use of RE doped YOF for UC. Excitation of YOF:Ho3+/Yb3+ with NIR (980 nm) revealed intense UC emission in the visible and DS in the NIR region. Although Ho3+ and Yb3+ ions do not have resonance energy levels at 980 nm, three two-photon UC emission bands centred at 538, 655 and 755 nm from 5 F4+5 S2→5 I8, ( 5 F5→5 I8+5 F3→5 I7) and 5 F4+5 S2→5 I7 transitions were obtained through phonon-assisted energy transfer. For the evaluation of thermal sensitivities using 980 nm excitation, fluorescence intensity ratio (FIR) was used based on the thermally non-coupled levels in the visible UC bands between the temperatures 20–300 K. The relative sensitivities (SR) which is the measure of temperature sensing ability of YOF materials with 1 mol % Ho3+ and 10 mol % Yb3+ was found to be 0.32 for UC in visible region was achieved with 980 nm excitation at 300 K. published

Newly synthetized Mercury (II) coordination complex with the following general formula [HgL(Cl)2]2, (L = C12H12N2O2S: 4,4’-diaminodiphenyl sulfone), was obtained by slow evaporation technique at room temperature. Single crystal X-ray diffraction shows that it crystallizes in the monoclinic system with P21/c space group. The studied compound is mainly a chloro bridged binuclear complex with tetrahedral coordination environment around each metal center. The stability of the crystal structure is ensured by mans of hydrogen bonds. In order to examine the interactions between the different present species, Hirshfeld surface analysis (HS) was also carried out. Optical studies, conducted after the thermal examination of the material, reveal that the title compound is apt to be considered as a powerful semiconductor. Lastly, the antibacterial activity was evaluated against Gram positive and Gram negative using the agar diffusion method.

Single crystals of glycine-di-glycinium sulphate (TGS) have been synthesized and grown along direction. The crystals were subjected to gamma irradiation with dosage ranging 10-50 kGy. While observing the low temperature Raman scattering modes, it can be understood that there exists possible bond breaking mechanisms upon gamma irradiation and as its consequence free radical ions appeared to have been formed. Thermo-mechanical parameters such as linear thermal strain, thermal expansion and linear thermal expansion coefficient have been computed by performing thermo-mechanical analysis on the irradiated samples. Gamma irradiation induced crystal imperfections were assessed through the high resolution XRD (HRXRD) measurement and it provides a clue for the development of non-uniform strain in the crystal. Modulation in optical constants, on irradiation was also noticed from the refractive index measurements. Piezoelectric and ac- conductivity measurements confirmed the rupture of bonds and in turn causing deterioration of ferroelectric and piezoelectric properties of the irradiated crystal.

Producción Científica, Lithium ferrites are well known materials due to its numerous technological applications especially in microwave devices. Lithium ferrite nanoparticles were prepared by sol-gel technique by means of Pechini method, and then annealed at different temperatures in 250–1000 °C range. XRD confirms spinel formation with particles sizes in 15–700 nm range, with increased size with annealing temperature, whereas FTIR and Raman measurement confirm that single phase lithium ferrite with ordered cationic structure is obtained. Microwave magnetoabsorption data of the annealed lithium ferrite nanoparticles were obtained with a broadband system based on a network analyzer that operates up to 8.5 GHz. At fields up to 200 mT we can observe a broad absorption peak that shifts to higher frequencies with magnetic field according to ferromagnetic resonance theory. The amplitude of absorption, up to 85%, together with the frequency width of about 5.5 GHz makes this material suitable as wave absorber. FMR parameters like resonance field, linewidth and broadening are analyzed in order to obtain the characteristic parameters and analyze the microwave behaviour., Ministerio de Economía, Industria y Competitividad ( project MAT2016-80784-P)

This work reports on the spectroscopic properties and temperature dependent NIR to visible upconversion of Nd3+ doped barium bismuth tellurite glasses. Raman spectrum analysis was performed to predict the maximum phonon energy. Spectroscopic parameters (Ω2, Ω4, Ω6 and χ) and radiative properties of certain transitions of Nd3+ ions were calculated by applying Judd–Ofelt (J–O) theory. The concentration dependence of NIR emission and visible upconversion intensities of various levels were discussed. Decrease in the experimental lifetime of Nd3+: 4F3/2 level with increase of Nd3+ ion concentration has also been discussed by analysing decay curves of the NIR emission. The variation of upconversion spectral intensities with respect to sample temperature was studied. Thermal quenching was observed in all the upconversion bands and no anomalous variations were observed in the temperature range 14–300 K.

Strontium titanate was prepared by solid-state reaction method. According to the XRD, it was single phase and has a cubic perovskite structure. The Raman spectroscopic investigation was carried out at room-temperature, and the second-order Raman modes were observed. By employing impedance spectroscopy , the dielectric relaxation and electrical properties were investigated over the temperature range of 500–700 K at various frequencies. The activation energies evaluated from dielectric and modulus studies are in good agreement and these values are attributed to the bulk relaxation. The impedance data were well fitted to an (R 1//C1)-(R2//CPE1) equivalent electrical circuit. It could be concluded that the grain boundaries are more resistive and capacitive than the grains. The ac conductivity was found to follow the Jonscher's universal dynamic law ωS and the correlated barrier hopping model (CBH) has been proposed to describe the conduction mechanism.

The effect of annealing temperature on the structure, morphology and dielectric properties of La0.75Ba0.25FeO3 compound prepared by the sol-gel method was investigated. The increase of the annealing temperature from 900 to 1100 °C, promotes an increase of the average grain size value. Two dielectric relaxations are detected using the dielectric modulus formalism, attributed to grain and grain boundary relaxations. This behavior was confirmed by both Nyquist and Argand's plots of dielectric impedance and Modulus results at different measuring temperatures. The ac conductivity could be described by Jonscher's power law revealing the presence of both overlapping large polaron tunneling and non-overlapping small polaron tunneling mechanisms.

Mixed Co2Mn1−xBixO4 (x = 0, x = 0.05 and x = 0.1) samples were prepared by the sol–gel method using the citric acid route and characterized by various techniques. The X-ray diffraction (XRD) and Raman spectroscopic analyses confirmed the formation of inverse spinel cubic structure with Fd 3 ‾ m space group. The introduction of Bismuth (Bi) into Co2MnO4 did not modify the ferrimagnetic character of the parent compound Co2MnO4, whereas the field-cooled magnetizations MFC and the Curie temperature Tc decreased when increasing the Bi content. The electrical properties showed an activation energy (Ea) increase caused by the decrease of the double-exchange interaction following the substitution of Mn3+ by Bi3+. Eventually, the temperature coefficient of resistance (TCR) shows significant values for all samples can be investigated also as good candidates for bolometer applications.

Polycrystalline of La 0 . 5 Pr 0 . 2 Sr 0 . 3 Mn (1−x) Fe x O 3 (x = 0, 0.15 and 0.2) samples have been elaborated by the self-combustion reaction method. Single-phase compound formation was confirmed by preliminary X-ray structural analysis. Detailed studies of the electric and dielectric properties of the compound in the frequency range from 100 Hz to 1 MHz and temperatures between 100 and 400K were investigated using the impedance spectroscopy technique. The results show that all samples exhibit dependence of both ac and dc conductivity on the iron content. Furthermore, the values of dielectric loss, dielectric loss tangent, real and imaginary parts of the impedance, real and imaginary parts of the electrical modulus, ac and dc electrical conductivity were found considerably sensitive to both temperature and applied frequency.

Eu3+ – Tb3+ co-doped Sr3MoO6 (SMO) phosphors have been synthesized by solid-state reaction. Powder X-ray diffraction (PXRD) and Scanning electron microscopy (SEM) were used for the characterization of the synthesized materials, and no significant structural changes have been observed. Photoluminescence (PL) was obtained under the 290 nm excitation where a strong energy transfer from host to active ions and weak energy transfer between the active ions with prominent emission from respective active ions. The fluorescence intensity ratio (FIR) was evaluated as a function of temperature in the range of 14 and 300 K using Eu3+/Tb3+ ratio to obtain absolute (SA) and relative (SR) sensitivities. SMO:Eu/Tb presented maximum SA of 0.0029 K−1 at 300 K and SR of 0.24% K−1 at 300 K, demonstrating that investigated system could be used in temperature sensing applications at low temperature.

Two nanoparticle orthoferrite materials (La0.8Ca0.2)0.9Bi0.1Fe1−yTiyO3 (y = 0.0 and 0.1) have been successfully synthesized via the assisted ball milling solid-state reaction. The effect of Bismuth and Titanium ions insertion in A and B-sites of La0.8Ca0.2FeO3 material on structural, dielectric relaxation and magnetic properties was conducted. Structural study reveals the formation of majoritarian orthorhombic phase in both nanomaterials. Importantly, both compounds present a giant dielectric constant e’ and low dielectric loss tangent tg(δ). Two relaxation processes have been detected at low and high-temperature ranges. The adjustment of the imaginary parts of complex Modulus via the Havriliak-Negami formalism (H-N) confirms a Cole-Cole (grains) and Cole-Davison (grain boundaries) relaxation processes at low and high temperature regions, respectively. The magnetic study reveals the enhancement of magnetization when introducing Titanium ions in B-site which increases the Ferromagnetic interactions. It also confirms an important decrease in the Curie Weis temperature (TC = 450 K).

Three of the possible approaches to optical temperature sensing of a thermographic phosphor were formally compared in upconversion (UC) of Er3+ and Yb3+ doped lanthanum orthoniobate (LNO) phosphor. The three approaches used in the study were namely fluorescence intensity ratio (FIR) of thermally coupled levels (TCL), Valley to Peak ratio (VPR) and the ratio of non-thermally coupled levels (NTCL), respectively. The TCLs in the study were the ratio of intensities of 2H11/2 → 4I15/2 and 4S3/2 → 4I15/2 UC transitions of Er3+ ion. VPR method was verified within 2H9/2 → 4I15/2 transition of Er3+ UC. The other ratios of transitions which are not fit in TCL were investigated through NTCL technique. Ratios of several sets of transitions namely 4S3/2 → 4I15/2/2H9/2 → 4I15/2, 4S3/2 → 4I15/2/2I9/2 → 4I15/2, 4S3/2 → 4I15/2/4F9/2 → 4I15/2, 4F7/2 → 4I15/2/2H11/2 → 4I15/2, 2H11/2 → 4I15/2/4I9/2 → 4I15/2 and 2H11/2 → 4I15/2/2G11/2 were considered for NTCL technique. Moreover, the effect of temperature in the emission color was analyzed and a change from yellow (0.3310; 0.5990) to green (0.2590; 0.6740) was observed when the temperature rise has been increased from 14 to 300 K. Results obtained indicate that the LNO:Er3+/Yb3+ phosphor could be employed in optical thermometry and this phosphor would be a candidate with high potential as sensor operating from low to room temperature using TCL, VPR and/or NTCL methods. The most prominent sensing technique in the case of LNO:Er/Yb material among the three techniques is found to be NTCL with the high relative sensitivity of 1.19% K−1 at 300 K.

Eu3+ doped bismuth gadolinium tungstate (BGW), a simplest member of Aurivillius family of layered perovskites, was synthesized by solid-state reaction method. Structural characterisation has been performed by X-Ray diffraction (XRD), Raman spectroscopy, Fourier Transform Infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Band gap of the host matrix has been calculated using reflectance and absorption spectra. Three different mechanisms were found to explain the excitation of Eu3+ ions and are described in detail. Photoluminescence (PL) spectra of the BGW phosphor doped with Eu3+ ions consist of major emission lines associated with 5D0 → 7FJ (J = 0, 1, 2, 3 and 4) of Eu3+ ion. Site selective PL excitation and emission indicates that Eu3+ ions doped in BiGdWO6 are sensitive to the excitation wavelength without change in the structure. Change in emission spectra were observed when the excitation wavelength was changed. Judd-Ofelt (J-O) parameters were determined from the indirect method to interpret the interactions between the host and dopant ions along with detailed analysis of lifetime measurements.

Bone grafting and surgical interventions related with orthopaedic disorders consist in a big business, generating large revenues worldwide every year. There is a need to replace the biomaterials that currently still dominate this market, i.e., autografts and allografts, due to their disadvantages, such as limited availability, need for additional surgeries and diseases transmission possibilities. The most promising replacement materials are biomaterials with bioactive properties, such as the calcium phosphate-based bioceramics group. The bioactivity of these materials, i.e., the rate at which they promote the growth and directly bond with the new host biological bone, can be enhanced through their electrical polarization. In the present work, the electrical polarization features of pure hydroxyapatite (Hap), pure β-tricalcium phosphate (β-TCP) and biphasic hydroxyapatite/β-tricalcium phosphate composites (HTCP) were analyzed by measuring thermally stimulated depolarization currents (TSDC). The samples were thermoelectrically polarized at 500 °C under a DC electric field with a magnitude of 5 kV/cm. The biphasic samples were also polarized under electric fields with different magnitudes: 2, 3, 4 and 5 kV/cm. Additionally, the depolarization processes detected in the TSDC measurements were correlated with dielectric relaxation processes observed in impedance spectroscopy (IS) measurements. The results indicate that the β-TCP crystalline phase has a considerable higher ability to store electrical charge compared with the Hap phase. This indicates that it has a suitable composition and structure for ionic conduction and establishment of a large electric charge density, providing great potential for orthopaedic applications.

Polycrystalline SrTiO 3- δ powders with cubic perovskite phase were prepared by solid-state reaction method followed by the creation of oxygen vacancies δ- thermal activated. The Raman spectroscopic investigation was carried out in a frequency range of 100–2000 cm −1 , and the second-order Raman modes were observed at room temperature. The Electron Paramagnetic Resonance (EPR) results revealed that SrTiO 3- δ samples had evident EPR signals that increased significantly with oxygen-vacancy concentrations. The incorporation of oxygen vacancies was found to decrease the thermal resistivity. Besides, the electrical sensing measurements showed that sensors based on SrTiO 2.925 (STO1) and SrTiO 2.875 (STO2) exhibited semiconductor behavior, while SrTiO 2.75 -based sensor (STO3) revealed the introduction of a metallic behavior at low temperature. Furthermore, these measurements confirmed that the resistivity increased after the introduction of the ethanol gas, which indicates that our samples can be considered as sensors for ethanol gas detection. The formation of oxygen vacancies under ethanol exposure at the surface of SrTiO 3- δ sensors was evaluated by photoluminescence.

SrTiO3-δ (δ = 0.075, 0.125 and 0.25) were prepared in two steps: the preparation of the parent compound SrTiO3 by the solid state reaction method followed by the creation of oxygen vacancies δ, through a thermally activated process. X-ray diffraction analysis shows that all samples crystallize in the cubic structure with Pm3m space group. The grain's size distribution and the samples' surface characteristics were assessed by scanning electron microscopy. Impedance spectroscopy was used to characterize the ac electrical properties of these materials as a function of frequency at various temperatures (240–340 K). The impedance data was well fitted to an (R1CPE1)//(R2CPE2) equivalent electrical circuit model. It was found that the electrical behavior of the ceramics is dominated by the grain-boundary response and increased conductivity values were found for a large amount of oxygen vacancy. The frequency dependence of the conductivity was investigated through the Jonscher's universal power law and the electrical conduction mechanism was found to be strongly dependent on the oxygen vacancies concentration.

Na2O CuO SiO2 glasses mixed with different concentrations Bi2O3 (ranging from 0 to 20.0 mol%) were prepared. Various dielectric parameters viz., dielectric constant, e′, loss tan δ, electric moduli, M, electrical impedance, Z, and also a.c. conductivity, σ ac(ω), in the frequency region 100 Hz to 1 MHz and in the temperature region 200 K‒400 K were measured as a function of Bi2O3 concentration. The obtained results were analyzed on the basis of space charge and dipolar polarization models. All the dielectric parameters exhibited decreasing trend with increase of Bi2O3 concentration. Our earlier spectroscopic studies of the same glass system indicated that there is a gradual reduction of Cu2+ ions into Cu+ ions with increase of Bi2O3 content in the glass network and these monovalent copper ions were found to participate in the network forming and form linkages with silicate structural units. The gradual increase in the degree of polymerization of the glass network is found to be the reason for the decrease of dielectric parameters. The variation of dielectric loss tanδ and electric moduli with frequency exhibited dipolar relaxation effects. The relaxation intensity is found to decrease, whereas the activation energy for the dipoles and the dielectric relaxation time are found to increase with increase in the concentration of Bi2O3. The observed relaxation effects are attributed to the complexes of divalent copper ions and Bi3+ ions. The variation of a.c. conductivity as a function Bi2O3 content exhibited a decrease (∼three orders of magnitude) with increase of Bi2O3 from 0 mol% to 20.0 mol%. The change of a.c. conductivity is explained in the light of varying oxidation states of copper ions using quantum mechanical tunneling model. The overall, analysis of these results indicated a gradual increase in the insulating character of the studied glass material with increase in the concentration of Bi2O3.

LiNbO3 is a well-known material with high potential for many technological applications. However, conventional preparation techniques require high processing times at high temperatures. In this work, a new and fast approach is proposed, based on laser technology, envisaging obtaining bulk materials of LiNbO3. ´powders. The influence of the laser processing parameters, namely time and incident power beam, on the structure and morphology of the material was investigated and compared with the ones obtained from conventional heat treatment process. The results revealed a net dependence of LiNbO3 crystals’ morphology with both laser power and irradiation time. Increasing the time of irradiation new crystalline phases are promoted (Li3NbO4, Li0,585NbO3 and an “CaNb2O6” isostructural type), which were also detected on samples prepared by the conventional heat treatment process in an air-atmosphere furnace. Moreover, similar morphologies can be also obtained using conventional heat treatment and laser processing. The expected characteristics of LiNbO3 commercial powder (crystalline habit and size) were obtained for the based samples through laser irradiation under 6 W/1000 s and through heat-treatments under 1000 °C/24 h. The laser processing proved to be a suitable technique to form LiNbO3 crystalline powders in a much more reduced time and also provides enough flexibility for tuning locally the grains size and morphology, allowing obtaining a morphological/structural radial gradient in a single step.

Hench et al. developed in 1969 the 45S5 Bioglass® showing high biocompatibility and osteogenic ability, enabling its application in bone tissue engineering. However, the bioactivity level and other physical and chemical properties can be compromised by structural changes. It is also known that the bone growth kinetics is related to the electrical characteristics of the bioglass. This manuscript presents an extensive study on the structural characteristics of the 45S5 Bioglass® endorsing the electrical properties with the structural and morphologic changes established by controlled heat-treatments. The bioglass was synthesized by melt-quenching and the heat-treatments were made at several temperatures from 500 up to 1000 °C. XRD, Raman and FTIR spectra show the occurrence of glass crystallization for treatments above 600 °C, in agreement with the thermal analysis of the base glass. The main phase, in the glass-ceramic samples, is Na2Ca2Si3O9, presenting a secondary phase in the sample treated above 900 °C. SEM micrographs show nanosize particles in the glass-ceramics, except for the sample treated at 1000 °C, which presents submicron-size. The electrical measurements revealed that the crystal phase dominates the conduction process and the dipoles arising from the interfaces lead to relaxations phenomena.

Nickel (Ni7+) Swift Heavy Ion (SHI) irradiation effects on the optical, topological, dielectric, piezo- electric and ferroelectric properties of 〈0 1 1〉 oriented ferroelectric Triglycine sulphate (TGS) single crystals have been investigated. Dielectric constant found to have increased more than 9 fold upon irradiation. A marginal shift in Tc (325–332 K) has been noted upon irradiation. A significant improvement in the piezoelectric coefficient has been observed for irradiated samples when compared to the 〈0 1 1〉 pristine TGS. Ferroelectric studies reveal the decrease in coercive field due to the irradiation with Ni7+ ions. The results obtained from all studies have been discussed in detail.

In this work, we have investigated the electrical and dielectric properties of the Mg doped perovskite (La0.8Ca0.1Pb0.1Fe1-xMgxO3 (x = 0.0, x = 0.1 and x = 0.2)) using the electrical impedance spectroscopy in the temperature range of (200–320 K). The crystal structure evaluated by X-Ray diffraction proved an orthorhombic structure of all the studied compounds with a Pbnm space group. Impedance fitting based on an equivalent circuit and the M″ fitting confirmed the existence of two relaxation phenomena attributed to grains and grain boundaries contributions. The study of the dc electrical conductivity proved that all compounds followed the variable range hopping (VRH) model at low temperature and the Arrhenius model at high temperature range. From conductivity analysis and the temperature dependence of the Jonscher’s power low exponent, we noted an alternation of correlated barrier hopping (CBH) and non-overlap small polaron tunneling model (NSPT) conduction processes at the studied temperature range. The relaxation phenomenon for both contributions and the deduced activation energies were found to be sensitive to the Mg composition; for the grain contribution, a minimum activation energy value was recorded for x = 0.1 compound and increased for suplementary Mg content. While, for grain contribution the activation decreases with the increase in Mg ion concentration. Concerning the evolution of the magnetization versus temperature, it was measured to investigate the effect of the Mg amount on the magnetic behavior of the prepared compounds under the studied temperature range.

Bi1.34Fe0.66Nb1.34O6.35 powders were prepared by the sol-gel method, through the citrate route, and heat treated at 500 °C. The obtained samples were characterized by X-ray diffraction analysis and by high resolution scanning transmission electron microscopy. An X-ray energy dispersive analysis was also performed. The average crystallite size and lattice strain were studied using the Scherrer's formula and the Williamson-Hall (W-H) analysis, assuming Uniform Deformation Model (UDM), Uniform Deformation Stress Model (UDSM) and Uniform Deformation Energy Density Model (UDEDM). The obtained results revealed that the mean crystallite size and lattice strain estimated from the different analysis were highly correlated.

The dielectric properties of BiNbO4 as a function of copper oxide addition level, frequency, and temperature were investigated in this work. The ceramic samples were prepared using the solid-state reaction method and different amounts of CuO were added to BiNbO4. The structural analysis was made by X-ray diffraction, and the Rietveld refinement showed the formation of the Bi1.5Nb1.5CuO7 pyrochlore phase because of the sintering of the BiNbO4 orthorhombic ceramic phase added with CuO. The morphology of the samples was studied by scanning electron microscopy and showed the distribution of grains on the fracture surface. The dielectric properties of BiNbO4, in the low-temperature range (100–370 K), were studied using the impedance spectroscopy technique in the frequency range 100 Hz to 1 MHz. The electrical results obtained, and the low sintering temperature applied, allow the applications in low-temperature co-firing ceramics (LTCC).

Electrochemical Impedance Spectroscopy (EIS) is a leading tool for the characterization of electrochemical processes in a wide class of materials. The combined analysis of EIS with the estimation of Distribution Function of Relaxation Times (DFRT) can help to differentiate overlapped polarizations in the frequency domain and to provide a greater understanding of a suitable electrical circuit to model the impedance data. To ensure that the calculated DFRT agrees with the experimental impedance, a practical procedure is to reconstruct the impedance from the DFRT. In this work, we present a user-friendly, free to use, graphical interface that allows the transformation of DFRT data into a synthetic impedance spectrum that can be compared with the original experimental data. Besides the validation test of the DFRT, our solution allows the adjustment of the DFRT peaks to automatically estimate the resistance, time constants and capacitances of each response.

In this work, FeNbO4 powders were prepared using the sol-gel method. The fine powder particles were pressed into pellets and sintered at temperatures between 500 and 1200 °C. The powder was studied by X-ray diffraction and Raman spectroscopy. The morphology of the grains was investigated by scanning electron microscopy. Heat-treatment of the particles results in higher crystallinity, larger grains, and a decrease in the porosity of the material. The dielectric properties were measured in the frequency range of 102–106 Hz, in function of temperature (200–370 K). In all samples the real (e′) and imaginary (e″) parts of the complex permittivity increase with increasing annealing temperature. The sample heat treated at 1200 °C shows the highest e′, > 104 at 300 K. All samples show a dielectric relaxation phenomenon, analysed using the modulus formalism. The evolution of the ac conduction activation energy and of the activation energy associated with the relaxation mechanism, is directly related with the changes promoted by the heat treatment in the structure and in the morphology of the base powders.

In this work we have synthesized ZnO–Ta 2 O 5 –B 2 O 3 glass ceramics with different concentrations of Ta 2 O 5 . The prepared samples were characterized by XRD, SEM and DSC techniques. The results of these studies indicated that the samples are embedded with well defined randomly distributed crystalline phases with Zn 3 Ta 2 O 8 as the predominant one. The volume fraction of the crystallinity seemed to be increasing with increase of Ta 2 O 5 content. The lattice parameters of this crystal phase and the optical band gap were evaluated theoretically using generalized gradient approximation (GGA) and also the local density approximation (LDA). The obtained results were compared with experimental values. The analysis of the results of IR and Raman spectroscopic studies indicated that the degree of polymerization of glass network increased with increase in the concentration of crystallizing agent (Ta 2 O 5 ) up to 3.0 mol%. To evaluate the insulating strength of the glass ceramics we have studied the dielectric properties over broad ranges of frequency (100 Hz −1 MHz) and temperature (100–370 K) and also dielectric breakdown strength. The quantitative analysis of these results coupled with the results of spectroscopic studies indicated that the glass crystallized with 3.0 mol% of Ta 2 O 5 possesses high insulating strength.

CuO doped sodium silicate glasses mixed with different concentrations of Bi2O3 are synthesized. Photoluminescence, thermoluminescence characteristics have been investigated. Photoluminescence emission spectra exhibited a broad band in the bluish green region under excitation at 325 nm. This band is attributed to 3D1 → 1S0transition of (Cu+)2 pairs. The intensity of this emission band is observed to increase with the concentration of Bi2O3 up to 20 mol%. The increase is attributed to the increase in the concentration of Cu+ ions. Thermoluminescence (TL) emission exhibited a dosimetric peak at about 250 °C. The TL output under this glow peak is observed to decrease with increase of γ–ray dose and also with the increase of Bi2O3 content. The mechanisms responsible for TL emission and the variation in TL output with the concentration of Bi2O3 are quantitatively discussed in terms of electron and hole centers developed due to interaction of γ–rays with the glass network.

In this work, X-ray diffraction analysis and optical properties of pure and Ba-doped ZnO nanoparticles prepared by the precipitation method were investigated. X-ray analysis was employed to evaluate the micro structural parameters of ZnO nanoparticles in terms of crystallite sizes and lattice strain by the Williamson-Hall method. The average crystallite size of Ba-doped ZnO nanoparticles estimated by the Williamson-Hall method varied as the doping concentration increased. The effect of Ba doping on the photoluminescence (PL) emission spectrum of ZnO was also investigated. The temperature dependence of the PL emissions was also studied, and it was found that at low temperature, the samples show stronger emissions than those at room temperature in both UV and visible regions. As a final point, the FT IR reflection spectrum along with Kramers-Kronig (K-K) method and classical dispersion theory was applied to obtain optical properties of the samples at low frequency infrared regime. (C) 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

A new compound of formula (C8H12N)3SnCl6·Cl is obtained at room temperature by slow evaporation of aqueous solution. Structural analysis indicates that this compound crystallizes in the monoclinic system with P21/C space group. The N–ZH⋯Cl hydrogen bonds between (C8H12N)+ cations, Cl− anions and [SnCl6]2− dianions contribute to the cohesion and the stability of the atomic arrangement. One phase transition is detected by differential thermal analysis at 330 K. Dielectric studies of this compound were studied in the frequency from 100 Hz to 1 MHz and a temperature ranging between 290 K and 380 K. The analysis of Nyquist plots are well fitted to an equivalent circuit consisting of series of combination of grains and grain boundary elements. The AC conductivity was studied using the following equation: σ A C ( ω ) = σ s 1 + τ 2 ω 2 + σ ∞ τ 2 ω 2 1 + τ 2 ω 2 + B ω S . The temperature dependence of the power law exponent s and a.c conductivity σac is reasonably interpreted by Correlated Barrier Hopping and Small Polaron Tunneling models.

Ternary glasses with molar composition 50TeO 2 –(50–x)V 2 O 5 –xK 2 O, where 0 ≤ x ≤ 15, were prepared by the press-melt quenching method. Since this type of glasses shows promising application in electrochemical and thermoelectric devices, the structural and electrical properties of the glassy system presented above were investigated in the present work. In order to evaluate the structure of the prepared glasses, X-ray diffraction (XRD), density measurement, and Raman spectroscopy were performed, while the glass transition temperature and thermal stability were determined by Differential Scanning Calorimeter. The vitreous state of the compositions was confirmed by their XRD pattern. The compositional dependence, particularly the K 2 O content, on physical features such as density and molar volume, can be correlated with the non-bridging oxygen formation and the variation in linkages. Raman spectra showed a gradual development, from TeO 3 to TeO 4 structural units, when the mol% of potassium oxide added into the glass network changes from x = 7.5 to x = 15. In addition, for x ≥ 7.5, a decrease of the vanadium coordination from five to four was observed. The effect on the glasses' conductivity, due to the inclusion of K 2 O, was studied by impedance spectroscopy and dc electrical measurements, in a wide range of temperatures. It was found that the dc conductivity mechanism changed from predominantly ionic, for 2.5 7.5.

For the last 75 years several studies have been reporting on the physical properties of niobium oxides, but there is still many contradictory, inconsistent and insufficient information on these metal oxides. This review will begin by describing the niobium oxygen system and the different stoichiometric and non-stoichiometric phases, specifically Nb, NbO, NbO 2 , Nb 2 O 5 and Nb 2 O 5−δ . The crystalline phases and polymorphs of these materials are often inconsistently identified in different works and thus, a clarification of the nomenclature of the several niobium oxides polymorph and their crystalline structure is also presented. Due to their interesting physical properties, many applications of these materials have been suggested such as solid electrolytic capacitors, catalysis, photochromic devices, transparent conductive oxides or memristors, becoming obvious that a good understanding of niobium oxides physical properties and their control is essential and urgent. Additionally, a short review on different types of niobates, namely alkali niobates, columbite niobates and rare earth niobates and the relation of the properties of these materials with niobium oxides will be presented.

BiNbO4 ceramic powders were prepared using the sol-gel method. The fine particles were pressed into cylinders and, then, they were treated at temperatures between 500 and 1150 °C. The structure was studied by X-ray diffraction and Raman spectroscopy and the morphology was observed by scanning electron microscopy. The measurements of the complex permittivity were made in a resonant cavity operating at 2.7 GHz, using the small perturbation method. The reversible phase transformation between β-BiNbO4 and α-BiNbO4 was observed. The density, dielectric constant (e') and the dielectric loss (tg δ) of the prepared powders increase with the sintering temperature, and the sample treated at 1150 °C shows the highest e' and the highest Q × f.

In the present article, optical properties and energy upconversion in Er 3+ /Yb 3+ co-doped BiNbO 4 matrix were investigated. The BiNbO 4 matrix was prepared using the solid-state reaction method. X-ray diffraction of the matrix shows that the crystal structure is consistent with ICSD code 74338. The grain distribution and the behavior of doping with Er 3+ and Yb 3+ on the sample surface were obtained by scanning electron microscope. Raman spectral characterization was carried out to examine the behavior of the vibrational modes of the samples. Upconversion emissions in the visible region at 484.5, 522, 541.5 and 670.5 nm in the matrices BiNbO 4 :Er,Yb and BiNbO 4 :Er were observed and analyzed as a function of 980 nm laser excitation power and rare-earth doping concentration. The results show that BiNbO 4 is a promising host material for efficient upconversion phosphors.

Nanodiamond (ND) attached with magnetite (Fe 3 O 4 ) nanoparticles have been synthesized successfully by in-situ and chemical reduction of Fe 3 + and Fe 2 + cations on the acid treated-ND surface by using sodium hydroxide as a reducing agent. The synthesized magnetic ND-Fe 3 O 4 nanocomposite was characterized by XRD and TEM. The results indicate that Fe 3 O 4 nanoparticles were homogeneously dispersed on the outer surface of the ND particles. The stability of ND-soot, acid treated-ND and ND-Fe 3 O 4 dispersed in distilled water were investigated by zeta potential and optical images. The electrical conductivity was measured by using four probe technique by considering dry ND-Fe 3 O 4 powder make it into 1 cm circular pellet. The stable magnetic nanofluids were prepared by dispersing ND-Fe 3 O 4 nanocomposite in water and ethylene glycol/water mixtures and then measured both thermal conductivity and viscosity with effects of particle loadings and temperatures experimentally. Results indicate that thermal conductivity enhancements are 17.8%, 13.4%, 13.6%, 14.6% and viscosity enhancements are 1.72-times, 2.19-times, 1.50-times, 1.79-times for water, 20:80%, 40:60% and 60:40% EG/W-based nanofluids at 0.2% volume concentration at a temperature of 60 °C, respectively. Correlations for the thermal conductivity and viscosity of nanocomposite nanofluids have been proposed based on the experimental data.