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In the present research, polycrystalline samples of La0.5Sm0.2Sr0.3Mn1−xCrxO3 are prepared using the self-combustion method.

Lithium ferrite (LiFe5O8) in the cubic crystal system is a very important and versatile material for several technological applications as it possesses very attractive electric and magnetic behaviors. Herein, we report an ecofriendly first approach sol-gel route, mediated by pectin, for the preparation of LiFe5O8. Pectin, a natural polysaccharide, was explored because it is a very attractive gelling agent to produce ceramic materials by the sol-gel method. The influence of the sintering temperature (800–1200 °C) applied on the pressed pellets, was evaluated by correlating the electric and magnetic properties with its structural and morphological characteristics. LiFe5O8 pellets sintered at 1000 and 1100 °C had the lowest dielectric losses and the most interesting dielectric behaviors in this regard, due to quasi-independence of the loss tangent through the temperature and frequency range studied. The magnetization, at 300 K, of LiFe5O8 monophasic pellets, sintered at 1100 and 1200 °C, are among the best values reported in the literature, 65 and 71 emu/g, respectively. Thus, the LiFe5O8 prepared by this sol-gel route shows particularly notable magnetic properties that can be explored for several applications.

Apatites (AP) ceramics are important due to their application in the orthopaedics field as bioceramic material. Several processes to produce apatites such as oxyapatite (OAP) and hydroxyapatite (HA) materials are used to apply as a temporary substitute for human bone. In the present work, AP powders were prepared by high-energy ball milling and then by laser floating zone (LFZ) technique to transform into a dense cylinder (fibre). The effect of LFZ processing conditions was assessed by structural and electric characterization. Fibres present strong densification and a uniform polycrystalline microstructure, which could favour the use for natural bone treatments and as bio-sensors. However, further work must be assessed to optimize laser processing conditions.

Synthetic hydroxyapatite {HAp, Ca10(PO4)6(OH)2} is a bioactive and biocompatible material widely used in healthcare for bone implants and grafts, due to its chemical and structural similarity with biological hydroxyapatite present in bone tissues. In this work, HAp was processed by calcination of tilapia fish bones from fish reared in net tanks and slaughtered at the age of 360 days. The bones were cleaned and dried, calcined at 900°C for 8 h and submitted to high energy milling for 8 h, to produce HAp powder. The thermogravimetric analysis and differential thermal analysis (TGA-DTA), dynamic light scattering (DLS), x-ray diffraction (XRD), Rietveld refinement, Fourier-transform infrared spectroscopy (FTIR) with attenuated total reflection (ATR), Raman spectroscopy and scanning electron microscopy (SEM), were techniques used to characterize the material produced. The results indicate that the methodology employed is effective for the production of nanostructured HAp powder, with particle size ranging from 600 nm to 1200 nm and grain size between 0.25 and 1.1 µm (evaluated by SEM in one piece of calcined bone). TGA-DTA analysis indicates complete removal of organic components at temperatures above 600°C. XRD analysis and refinement by the Rietveld method indicated the presence of a single crystalline phase, HAp, with a Ca/P ratio of 1.66. The results obtained by Raman spectroscopy and FTIR-ATR show the presence of characteristic vibrational bands of HAp. In conclusion, the results of this work showed that the methodology used allowed the production of a natural and crystalline hydroxyapatite, with a Ca/P molar ratio of 1.66, with potential for use in bone reconstruction.

This work reports an analysis of the dielectric properties of reduced graphene oxide mixed into epoxy resin, diglycidyl ether of bisphenol A, in the frequency range 10 $$^{\mathrm {2}}$$ –10 $$^{\mathrm {6}}$$ Hz and over the temperature range of 300–400 K, using impedance spectroscopy. For this study, a series of samples were prepared with various filler contents. Using the electric modulus formalism, it has been found that these composites exhibit below and above the percolation threshold $$\phi _{c} $$ a critical behavior of the dielectric relaxation phenomenon due to the single $$\alpha $$ -relaxation, which is associated with the glass–rubbery transition of the epoxy matrix above the glass transition temperature. The Cole–Cole model of dielectric relaxation was used for modeling the relaxation processes from which we extract the relaxation parameters. The obtained relaxation parameters suggest a behavior close to single relaxation time.

Background Peri-implantitis is considered the most challenging biological complication in implantology, as untreated disease can progress and result in implant loss. Therefore, disease prevention is crucial in daily clinical practice. It has been reported that the use of bioactive glass, as an implant coating, can stimulate tissue integration and accelerate tissue regeneration. Besides these properties, it is possible to promote bacterial activity by inserting silver into the bioglass Methods Bioglass with composition 45S5 was synthesised by the fusion method, replacing the amount of Na2CO3 by AgNO3 (BG 2% wt). The implants were resealed by the CoBlast® technique. Clinical cases with pathology of the mandible/maxilla were selected and implants dimensioned for the canine bone structure were applied. Results Three months after implantation, imaging exams, namely CT scans, showed no signs of early rejection by septic or cytotoxic loss. No decrease or loss of peri-implant bone was observed. In all cases the implants remained without signs of instability, and with sufficient support for the application of the exo-prosthesis or dental crown. The results of histological analysis showed no signs of infection or osteolysis. The zone of peri-implant fibrosis was not observable in the samples, showing a good evolution in implant osteointegration. Conclusions The results show promising evidences for the use of this biomaterial as a coating, since aseptic rejection, later on, and that related to the shape and biomaterials used in the implant's design, usually begins during the first 3 months.

Niobium oxides are presently very important materials for electronic device applications. In this work, a new approach, using the proteic sol–gel route, was used to prepare niobium pentoxide powders. This approach uses powdered coconut water (PCW) for the powders production. The obtained powders, with an amorphous structure, were heat-treated at different temperatures and their structural and morphological properties were studied and related to their dielectric properties. Dielectric measurements as a function of frequency (100 Hz–1 MHz) and temperature (200–400 K) were performed. The heat-treatment promotes the formation of crystalline structures, mainly Nb2O5 with orthorhombic structure, which transforms to monoclinic with treatments at 1000 °C. The formation of CaNb2O6 and NaNbO3 crystallites, in the samples treated at 800 and 1000 °C is related to the PCW base composition. The samples revealed a quasi-independence of the dielectric constant with temperature and frequency, presenting a $$\varepsilon^{\prime}$$ ≈ 70 and tan ≈ 0.006, at room temperature and 100 kHz.

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.

The development and understanding of the corona triode charging technique, in the seventies and in the eighties is intimately related to Brazilian researchers and academic institutes. Contrarily to older two-electrode systems, the corona triode system comprises three electrodes: the discharge point electrode, the metallic grid and the plane electrode, where the charging current can be measured and controlled. It has been widely applied in the electrical charging of polymer foils for electret production, in the research of the charge stability and charging/injection processes in dielectric materials, principally in film/foil form and in electrostatic separation processes. Corona-based electrostatic precipitators have found widespread application in the treatment of contaminated gases and also in the separation of metals and non-metal components. It has, among others, the advantages not to require the deposition of an electrode on the sample surface exposed to the discharge, allowing the reversal of the discharge polarity (positive or negative), to pole/charge samples with complex non-planar geometries and it is well suited for large scale film poling/charging. A new a corona triode system developed in our facilities is presented, including some theoretical background behind this technique. This system can operate on a more traditional method and also on a more sophisticated principle based on a feedback circuit that continuously adjusts the voltage applied to the metallic grid in order to maintain the charging current flowing through the sample constant. Thus, the sample surface potential buildup can be monitored in real-time by the metallic grid voltage. Charging results on bioactive hydroxyapatite [Ca10(PO4)6(OH2) – Hap] pellets, prepared from commercial Hap powders, are presented and discussed.

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.

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.

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.

The intrinsic objective of this work is to investigate the structural (RX, MEB, TGA and IR) and magnetic properties of La1 La1-x⎕xMnO3 (x = 0.1; 0.2 and 0.3) series prepared through the sol–gel method. All these systems crystallize in the rhombohedral structure, $$ {{\rm R}\bar{3}{\rm c}} $$ space group, with the presence of a secondary phase for x = 0.3. We recorded the increase of a unit cell volume when the La deficiency amount increases, which refers to the fact that the vacancy is characterized by a radius other than zero. Another point that can be quoted is the increase of Mn–O–Mn bond angle and the decrease of Mn–O length with lanthanum deficiency (x), confirming the increase of the unit cell volume. The evaporation of water rose by the weight loss as a function of temperature in all samples. The FT-IR measurement revealed one peak corresponding to the Mn–O bond; this can be explained by the Jahn–Teller effect where the Mn ion makes an internal movement against the MnO6 octahedron. The thermal variation of the magnetization indicates the existence of a paramagnetic–ferromagnetic transition at Curie temperature with the increase of lanthanum deficiency. Saturation magnetization and Curie temperature increased with x (0.1; 0.2 and 0.3) deficiency. Hysteresis cycles confirm the ferromagnetic character at low temperatures and paramagnetic state with temperature increase. The increase of saturation magnetization can be accounted for in terms of the change of high spin Mn3+ to low spin Mn4+. Departing from the study of magnetic properties in terms of Arrott plots, the nature of magnetic transitions proves to be of second order.

The authors are grateful by the FEDER funds through the COMPETE 2020 Program and National Funds through FCT?Portuguese Foundation for Science and Technology under the project UID/CTM/50025/2013, UCIBIO, REQUIMTE UID/Multi/04378/2013, and DENTALBLAST project (ref. n? 17956). Bacterial infections affect about 1 in 5 patients who receive a dental implant within 5 years of surgery. To avoid the implant rejection it is necessary for the development of innovative biomaterials, with addition or substitution of the ions, for implant coatings that promote a strong bond with the new host bone and antibacterial action. The objective of this work was to synthesize a bioactive glass with different silver concentrations to evaluate their antibacterial performance. The glasses were synthesized with up to 2% silver content by melt-quenching. Structural, morphological, biological, and electrical properties of all samples were studied. The biological behavior was evaluated through cytotoxicity tests and antibacterial activity. The structural analysis shows that the introduction of silver do not promote significant changes, not altering the advantageous properties of the bioglass of the bioglass. It was verified that the glasses with a silver content from 0.5% to 2%, completely prevented the growth of both Staphylococcus aureus and Escherichia coli while being nontoxic toward mammalian cells. Therefore, these bioglasses are promising materials to be used in the production of dental implants with antimicrobial activity. authorsversion published

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.

Among the applications of phosphate glasses, one of the most promising is their potential as catalysts for water dissociation into hydrogen and oxygen and to absorb hydrogen in its structure, making them good candidates to be used as electrolytes in intermediate temperature fuel cells (200–500 °C). Phosphate based glasses with molar composition 30PO 5/2 –25NbO 5/2 –10WO 3 –25Na 2 O–10[(1-x)BaO–xSrO], with x = 0, 20, 50, 60, 80 and 100 mol% were prepared by the melt quenching technique. The as-prepared samples revealed to be transparent, mechanical and thermally stable at room temperature. Differential thermal analysis (DTA) measurements showed Tg values around 500 °C, and high thermal stability. The structure of the samples was studied by X-Ray powder Diffraction (XRD) Raman spectroscopy, and the morphology by Scanning Electron Microscopy (SEM). Dc (σ dc ) and ac (σ ac ) conductivities and dielectric spectroscopy measurements were performed as function of temperature (100–370 K) presenting a conductivity predominantly ionic (σ electronic /σ ionic of about 10 − 4 ). The dielectric spectroscopy was measured in the frequency range 100 Hz–1 MHz.

The measurement of thermally stimulated depolarization currents, a technique usually known by its initials (TSDC), has contributed substantially to the knowledge and understanding of charge storage and charge decay processes in several types of electret materials, i.e., materials that can have electrical polarization arising from kinetically trapped charges. The polarization of these materials may increase the magnitude of the applied electric field, until the point of dielectric breakdown. A similar, and sometimes complementary, technique consists in the measurement of thermally stimulated polarization currents (TSPC). This contribution discusses experimental and theoretical considerations regarding both techniques. Additionally, it also includes a case study regarding LiNbO3 glass-ceramics, synthesized by the melt-quenching process.

In this work, new phosphate glasses with the molar composition 20.7P2O5–17.2Nb2O5–13.8WO3–34.5A2O–13.8B2O3 where A = Li, Na and K were prepared using the melt quenching technique. These types of glasses have potential to absorb hydrogen in its structure, which makes them promising materials to be used as electrolytes in intermediate temperature fuel cells. Additionally, niobium phosphate glasses can also have applications such as glass fibers, optical lenses, hermetic sealing and electrodes. The structure of the obtained samples was analyzed using Differential Thermal Analysis (DTA), X-ray powder diffraction (XRD), and Raman spectroscopy and the morphology by Scanning Electron Microscopy (SEM). The DTA measurements revealed values of glass transition temperature around 415 °C, and the Raman analysis showed that the amount of alkali and niobium oxides included on the studied compositions, successfully disrupted the P–O–P chains characteristic of the phosphate glasses. Dc (σdc) and ac (σac) conductivities and dielectric spectroscopy measurements were performed as function of the temperature (200–370 K) which presented conductivity predominantly ionic (σelectronic/σionic of about 10−4). The dielectric spectroscopy was measured in the frequency range 100–1 MHz. Keywords: Phosphate glasses, Hydrogen absorption, Differential thermal analysis, Electrical measurements, Raman spectroscopy, X-ray powder diffraction

TeO 2 based glasses with molar composition (70- x - y )TeO 2 –20WO 3 –10Y 2 O 3 – x Er 2 O 3 – y Yb 2 O 3 , where x = 0 and 0.5 mol% and y = 0, 0.5, 1, 2 and 4 mol%, were prepared by the melt quenching technique. At room temperature all the samples are transparent, mechanical and thermally stable. The XRD results showed the amorphous nature of all the samples and the Raman spectra showed a band distribution related with Te O and W O bond vibrations. The introduction of WO 3 results in a bandwidth substantially larger when compared to SiO 2 based glasses and even other TeO 2 based glasses, making this vitreous system promising for Raman optical amplification. In this work, the measurement and analysis of the electrical properties of this glass system was made. It was found that the hopping of small radius polarons, for small concentrations of networks modifiers, is the dominant process in the charge transport mechanism for the dc conductivity. For higher concentrations of ions structurally inserted in the glass network, the ionic conductivity starts to have an important role in the transport mechanism. The ac conduction mechanism was attributed to a dipolar process between the interstitial modifier cations and the nonbridging oxygen ions. For all samples, the dielectric constant is practically independent of the temperature and the frequency. This quantity tends to decrease with the increase of the concentration of Yb 3+ cations. No dielectric relaxation phenomenon was observed in the temperature and frequency measurement range.

TeO 2 based glasses with molar composition (70− x − y )TeO 2 -20WO 3 -10Y 2 O 3 - x Er 2 O 3 - y Yb 2 O 3 , where x = 0 and 0.5 mol% and y = 0, 0.5, 1, 2 and 4 mol%, were prepared by the melt quenching technique. At room temperature, all the samples are transparent, mechanical and thermally stable. This vitreous system was found to be promising for potential applications in optical amplification, in particular in erbium doped fiber amplifiers (EDFA), Raman optical amplifiers and also in spectral conversion for applications in photovoltaic technology. The Raman spectrum of the base glass (Er0Yb0), using laser excitation of 532 nm, showed vibrational bands related to Te O and W O bonds. The introduction of WO 3 results in a higher bandwidth relatively to SiO 2 based glasses and even other TeO 2 based glasses, making this vitreous system promising for Raman optical amplification. With regard to the optical analysis, an increase of the intensity of the upconversion emission with the increase of the content of the sensitizer ions Yb 3+ was observed. The Er 3+ emission around 1540 nm has a full width at half maximum of about 100 nm in the temperature range of 70–300 K, which is a very interesting value relatively to those reported for other glassy systems, considering optical amplification as a potential application.

Lithium niobate is an artificially synthesized material with wide technological applications, due to its numerous physical properties, such as: ferroelectricity, birefringence and large pyroelectric, piezoelectric, non-linear, acousto-optic, electro-optic and photo-elastic coefficients. It also exhibits very strong bulk photovoltaic and photo refractive effects. In the present work, LiNbO3 powders were prepared by the Pechini (sol–gel) method. The heat-treatment of the base amorphous powders, at 450 °C promotes the formation of LiNbO3 crystalline phase. The electrical characterization, in function of the heat-treatment time, shows that the dc conductivity depends on the quantity of crystalline phase, which increases with the increase of heat-treatment time. The sample treated for 96 h shows a dielectric constant value of ~35, at low frequencies. A dielectric relaxation phenomenon independent of the temperature of measurement was detected in the samples treated at 48 and 96 h, shifting to higher frequencies with the increase of the heat-treatment time.

The combination of electric impedance and Raman spectroscopies at the analysis of the supercooled water phase transition enables the detection of adsorbed water clusters in garnet minerals of leucogranite samples. This transition is revealed by a change in the parameters measured by both techniques at low temperatures, [Formula: see text], and it is attributed to adsorbed water clusters in the walls of garnet cracks. The study of this transition gives important insights into the water-rock interaction, one of the most important points in the study of rock alteration. The dielectric spectra were fitted to the Havriliak-Negami model of dielectric relaxation and enabled the estimation of the activation energy of the dielectric relaxation process as [Formula: see text], which is higher than the energy attributed to water molecule reorientation in bulk ice. We determined that this energy should be related with the interaction forces between the adsorbed water clusters and the crack walls that hinder the reorientation of those molecules. The logarithmic frequency dependence of the critical transition temperature was also verified. Raman spectra allowed the identification of the water cluster vibration band, [Formula: see text], in the garnet minerals. The band disappears for temperatures around 423 K where the joint action of the laser beam and the temperature evaporates the adsorbed water clusters. This excludes the possibility that the observed supercooled phase transition could be related with structural water in chlorite minerals. The samples had low apparent porosity [Formula: see text], specific surface area, and adsorption average crack width (using the Brunauer-Emmett-Teller method) of [Formula: see text] and [Formula: see text], respectively.

TeO2 based glasses with the molar composition (70-x-y)TeO2-20WO3-10Y2O3-xEr2O3-yYb2O3, where x = 0 and 0.5 mol% and y = 0, 0.5, 1, 2 and 4 mol%, were prepared by the melt quenching technique. The Raman spectra of the vitreous samples, using laser excitation line of 532 nm showed a band distribution related with Te-O and W-O bond vibrations. The introduction of WO3 results in a higher bandwidth relatively to SiO2 based glasses and even other TeO2 based glasses, making this vitreous system promising for Raman optical amplification. The use of UV laser excitation line of 325 nm induced surface modifications on the samples.

In this work, phosphate-borate based glasses with molar composition 20.7P2O5–17.2Nb2O5–13.8WO3–34.5A2O–13.8B2O3, where A = Li, Na, and K, were prepared by the melt quenching technique. The as-prepared glasses were heat-treated in air at 800 °C for 4 h, which led to the formation of glass-ceramics. These high chemical and thermal stability glasses are good candidates for several applications such as fast ionic conductors, semiconductors, photonic materials, electrolytes, hermetic seals, rare-earth ion host solid lasers, and biomedical materials. The present work endorses the analysis of the electrical conductivity of the as-grown samples, and also the electrical, dielectric, and structural changes established by the heat-treatment process. The structure of the samples was analyzed using X-Ray powder Diffraction (XRD), Raman spectroscopy, and density measurements. Both XRD and Raman analysis confirmed crystals formation through the heat-treatment process. The electrical ac and dc conductivities, σac and σdc...