Search

Double perovskite oxide with general formula LaBa0.5Ag0.5FeMnO6 (LBAFMO) has been prepared by the sol–gel-based Pechini method. To study and compare its electrical properties, impedance spectroscopy was carried out in the temperature ranging from 200 K to 340 K and frequency range from 100 Hz to 1 MHz. At room temperature, x-ray diffraction analysis revealed the compound to be single phase and to crystallize in the cubic system in space group Pm-3m. The imaginary part of the impedance (Z″) as a function of frequency indicated non-Debye model relaxation. Impedance data in a Nyquist plot (Z″ versus Z′) was used to determine an equivalent circuit. The complex impedance of LBAFMO revealed the presence of grain and grain-boundary contributions. The alternating-current (AC) conductivity as a function of frequency was interpreted by applying Jonscher’s law to determine the activation energy. Modulus analysis revealed the occurrence of a relaxation process supplemented by a conduction phenomenon.

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.

Bi1 − xFexNbO4 (x = 0.25, 0.50, and 0.75) samples were synthesized by the sol–gel method and its morphologic, structural, dielectric, and magnetic properties were studied. The structure was analyzed by X-ray diffraction and the morphology by scanning electron microscopy. The dielectric characterization that was performed using impedance spectroscopy, in the frequency range of 102–106 Hz, as a function of temperature, revealed that the dielectric constant and the dielectric losses increased with the iron content. The prepared materials presented relaxation processes, with the corresponding activation energies being calculated by fitting the experimental data to the Arrhenius model. The dependence of AC conductivity on frequency was found to satisfy Jonscher’s universal power law at different temperatures. The conduction mechanisms are governed by two processes: correlated barrier hopping (CBH) and non-overlapping small polaron tunneling (NSPT). Magnetic susceptibility, for an applied magnetic field of 0.5 T, doubles when the iron concentration goes from 0.25 to 0.5 and doubles again when the iron concentration rises to 0.75. The increase in magnetization with the concentration of iron is also observed in the curves M vs. H at 7 K. The remaining magnetization and the coercive field do not exist for x = 0.25 (paramagnetic behavior); it is small for x = 0.5 and is already observed when x = 0.75.

This paper reports the effect of chromium’s substitution in magnetic oxides with perovskite structure La0.5Sm0.2Sr0.3Mn1-xCrxO3 (x = 0, 0.1, 0.15 and 0.2) compounds which have been produced with the glycine-nitrate process (GNP). The four compounds have an orthorhombic crystal structure with ‘Pnma’ space group. We note that they undergo a second-order paramagnetic-ferromagnetic (PM-FM) phase transition. Substitution manganese by chromium leads to a drop of the Curie temperature TC from 278 K (x = 0) to 205 K (x = 0.2). Their magnetocaloric effect has been evaluated by their magnetic entropy change $$\left(-\Delta {S}_{M}^{max}\right)$$ under a magnetic field change up to 5 T. All relative cooling power (RCP) suggests that these compounds are suitable candidates for magnetic refrigeration.

The bismuth-based pyrochlore, Bi1.34Fe0.66Nb1.34O6.35, was prepared by the sol–gel method and synthesized at low temperature. The phase structure and the morphology were studied by x-ray diffraction and scanning electron microscopy. Even with treatments performed at low temperature, the obtained powders showed high crystallinity and nanosized grains. To investigate the dielectric performance, the impedance spectroscopy technique was used in the frequency range of 102-106 Hz, in function of the temperature (200-330 K). The prepared samples presented two temperature-dependent relaxation processes, with the corresponding activation energies being calculated by fitting the experimental data to the Arrhenius model.

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.

In this paper, we investigated the impact of the substitution of barium (Ba) by strontium (Sr) in site A of the BaTiO3 perovskite lattice on physical properties. The studied materials were synthesized via the conventional solid-state method. Then, the purity and the crystallographic structure of the prepared materials were carried out at room temperature by X-ray powder diffraction (XRD) proving an orthorhombic system with a P4mm space group. Their morphology and the particle size were evaluated by scanning electron microscope (SEM) which shows a nanoparticle agglomeration of about 2.4 µm and 2.7 µm respectively for BT and BST samples. The investigation of the optical properties by Fourier transform infrared spectroscopy confirms the successful preparation of the perovskite materials. The study of the dielectric properties of ceramic materials performed by impedance spectroscopy in a frequency range [100-106 Hz] and temperature range [150−400 K] proves the appearance of the relaxation process in the modulus spectra after Sr substitution. The dc conductivity shows a VRH conduction process for both samples at lower temperatures and an SPH one at higher temperature with an increase in the activation energy for BT material and a decrease in the BST one. The ac conductivity data were described by Jonscher’s power law indicating a correlated barrier hopping (CBH) conduction process in the BT sample and an overlapping large polaron tunneling (OLPT) one for the BST compound.

This work involves the synthesis and study of physical properties of the La0.8Ca0.1Pb0.1Fe0.975Mg0.025O3 compound, which has been characterized by various experimental techniques, such as X-ray diffraction, SEM and complex impedance spectroscopy. The structural study showed that the La0.8Ca0.1Pb0.1Fe0.975Mg0.025O3 compound crystallized in the orthorhombic structure with the Pnma space group. The particle size and the surface morphology of this compound have been analysed using SEM. The particle size was found to be around 120 nm and we confirmed that one particle contains more than one crystallite. Importantly, the studied compound presented a giant dielectric permittivity (e′ of around 9 × 104 at high temperature and low frequencies). An equivalent electric circuit has been deduced from the Nyquist plots of the complex impedance parts (Z′′ vs. Z′) to correctly describe the electrical behavior of the La0.8Ca0.1Pb0.1Fe0.975Mg0.025O3 compound. The chosen circuit consists of two cells mounted in series corresponding to the grain and grain boundary contributions. The electrode contribution has been detected from the frequency dependence of the imaginary part of modulus where the activation energy of each constitution has been calculated. The relaxation process and the electrical conductivity are attributed to the same type of charge carriers characterized by similar values of the activation energy determined from loss factor tangent (tg(δ)), the imaginary part of the permittivity and the modulus spectrum.

The hexaferrite Ba1−xSrxFe12O19 compounds with x = 0, 0.5 and 1 were synthesized by the autocombustion method. X-ray diffraction (XRD), Raman spectroscopy and transmission electron microscopy (TEM) were used for structural and morphological studies.

La1−2xBaxBixFeO3 (0.00 ≤ x ≤ 0.20) nanoparticles were prepared by the auto-combustion method using glycine as a combustion fuel. X-ray diffractometry (XRD) measurements confirmed the orthorhombic structure of the synthesized compounds with the Pnma space group as a principal majority phase and showed the presence of a very minor secondary phase when x > 0.1. The nanosize criterion of the prepared compounds was confirmed from the crystallite size values calculated using the Williamson–Hall formalism. The relaxation process has been studied by the frequency dependence of the imaginary parts of impedance and modulus (Z′′ and M′′) which satisfied the Arrhenius law. Nyquist plots allowed us to obtain an adequate equivalent circuit involving the grains and grain boundary contributions. The activation energies calculated from Z′′, M′′ and the resistance of both contributions deduced from the Nyquist plots are found to be very similar. The conduction mechanism has been analyzed using the temperature dependence of the exponent Jonscher's power law parameter which confirms the NSPT conduction mechanism type for all compounds with an enhancement of the binding energy of the charge carrier (WH) with the substitution.

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.

The electric conductivity and dielectric properties of polycrystalline La0.53Ca0.47Mn0.5Cr0.5O3 are studied with impedance spectroscopy techniques over a wide range of frequencies and temperatures from 100 to 1 MHz and 100 and to 400 K, respectively. The material exhibits a semiconductor behavior in the whole temperature range, characterized by a change in the slope at a specific temperature with a saturation at ~ 360 K. At low temperature, the conduction mechanism is governed by distributed trap localized charge carrier states described by a variable-range hopping model. At high temperature, the conduction mechanism is thermally activated by a small polaron hopping process. At low frequencies, the high dielectric constants of the material decrease rapidly with frequency and increase with temperature due to the free charges accumulated at the electrode-sample interface (interfacial Maxwell–Wagner polarization). These high dielectric constants can be interpreted by the existence of grain boundaries. Additionally, the Nyquist plots are presented by two depressed not centered semicircles on the real axis, indicating non-Debye behavior for the material. The resistance of the grain boundaries is larger than the resistance of the grains, confirming that the grain boundaries govern the conductivity in La0.53Ca0.47Mn0.5Cr0.5O3. Finally, the modulus analysis indicates a transition of carrier mobility from the long range in the low-frequency region to the short range in the high-frequency region.

In this work, we report the structural, electrical, and optical properties of nontoxic and earth-abundant Na2ZnSnS4 (NZTS) material. NZTS powder has been successfully synthesized using an easy and nontoxic pathway: the solid-state reaction technique. X-ray diffraction, transmission electron microscopy, and Raman spectroscopy were used to study the structural properties of the NZTS. The synthesized powder crystallized in the stannite tetragonal structure with lattice parameters a = 6.48 A and c = 9.12 A. XRD and Raman characterizations showed the occurrence of the secondary phase Na4SnS4. Optical bandgap measurements were obtained from UV–Visible analysis and showed a high optical bandgap value of 3.32 eV and confirmed the presence of Na4SnS4. TEM micrographs provide a description of the morphology of NZTS. The HRTEM images reflect a preferred orientation along the {112} plane, which is consistent with the X-ray diffraction pattern. EDS analysis confirmed the presence of the four constituent elements of the NZTS within their corresponding composition. NZTS powder indicates a conductivity type n. A study of electrical conductivity was carried out by using the impedance spectroscopy. The frequency and temperature dependence of the complex electrical impedance and AC and DC conductivity were explored. These interesting results make the NZTS particularly attractive for solar cell applications and especially suitable as a window layer.

The La0.8Ba0.1Ce0.1FeO3 compounds were prepared by the auto-combustion route and annealed at two different temperatures to study their effect on the structural, morphological and dielectric properties of the Barium- and Cerium-substituted LaFeO3 compound. The X-ray diffraction analysis revealed that both compounds crystallized in the orthorhombic structure belonging to the Pnma space group. The rise of the annealing temperature from 700 to 900 °C was found to lead to the increase of the average grain size value as characterized by SEM. Furthermore, two clear relaxations phenomena have been detected using the Nyquist and Argand’s plots of dielectric impedance and Modulus curves at different temperatures, which are attributed to both grain and grain boundary contributions. Their activation energies have been calculated not only from the frequency dependence of both imaginary parts of impedance (Z″) and modulus (M″) but also from the contribution of the resistances deduced from the Nyquist plots. These plots have been adjusted using two circuits in series, each of which containing a resistance in parallel to a CEP capacitance. The conduction mechanism was analyzed by ac conduction using the Jonscher’s power law. The NSPT conduction model has been confirmed for both compounds in which the rise in heat treatment decreases the binding energy of carriers.

In this work, we report the dielectric study of erbium niobate ceramic synthesised by the sol–gel method. X-ray diffraction patterns confirmed the presence of monoclinic ErNbO4, even at the lowest heat-treatment temperature. The frequency dependence dielectric study shows that the value of the dielectric constant, particularly at lower frequencies, is highly influenced by the secondary phase. Impedance spectroscopy analyses revealed a non-Debye relaxation phenomenon in the sample heat-treated at 800 °C. The Nyquist plot from the complex impedance spectrum showed only one semicircular arc, representing the grain effect in the electrical conduction. The modulus mechanism also indicates the non-Debye type of relaxation in the material, which is supported by impedance data, and confirms that the relaxation process is due to short-range motion of charge carriers. Relaxation times, extracted using the imaginary parts of complex impedance and modulus, were found to follow the Arrhenius law. The thermal evolution of the conductivity of the grains also presents an Arrhenius-type behaviour, revealing that charge carriers have to overcome different energy barriers while conducting and relaxing.

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.

Two compounds with the formula La0.8Ba0.1Bi0.1FeO3 have been prepared by the sol–gel (LBBFO-SG) and the auto-combustion (LBBFO-AC) preparation methods. The effect of the preparation method on structural, morphology, vibrational, electrical, and dielectric properties have been carried out using the X-ray diffraction (XRD), Scanning electron microscopy (SEM), and Raman and impedance spectroscopy. The Rietveld refinement of the XRD diffractograms confirms the crystallization of both compounds through the Pnma space group. Furthermore, the nano-size scale of the prepared compounds was verified by the XRD and the SEM microscopy. From the Raman study, we conclude that the vibration modes are similar to those of the pure LaFeO3 with a slight shape change in some modes. The relaxation processes were analyzed with the Bergmann formalism to validate the presence of two relaxation processes corresponding to grains and boundary grains contributions. These relaxations have been confirmed by studying the dielectric constant also the dielectric loss tangent is used to study the ferroelectric–paraelectric phase transition at around room temperature. The activation energy for both contributions has been calculated from the impedance, the modulus, and the dielectric loss tangent and they have almost the same values. The Nyquist plots (Z″ vs. Z′) have been adjusted using two circuits in series containing each one a resistance in parallel to a CEP capacitance.

(La0.8Ca0.2)1−xBixFeO3 (x = 0.00, 0.05, 0.10, 0.15 and 0.20) (LCBFO) multiferroic compounds have been prepared by the sol–gel method and calcined at 800 °C. X-ray diffraction results have shown that all samples crystallise in the orthorhombic structure with the Pnma space group. Electrical and dielectric characterizations of the synthesized materials have been performed using complex impedance spectroscopy techniques in the frequency range from 100 Hz to 1 MHz and in a temperature range from 170 to 300 K. The ac-conductivity spectra have been analysed using Jonscher's power law σ(ω) = σdc + Aωs, where the power law exponent (s) increases with the temperature. The imaginary part of the complex impedance (Z′′) was found to be frequency dependent and shows relaxation peaks that move towards higher frequencies with the increase of the temperature. The relaxation activation energy deduced from the Z′′ vs. frequency plots was similar to the conduction activation energy obtained from the conductivity. Hence, the relaxation process and the conduction mechanism may be attributed to the same type of charge carriers. The Nyquist plots (Z′′ vs. Z′) at different temperatures revealed the appearance of two semi-circular arcs corresponding to grain and grain boundary contributions.

The double perovskite structure is interesting for many researches in various fields of physics and their technological applications. The LaPbFeTiO6 compound is a very important for many technologies because it has dielectric and electrical properties. It has made an attractive semiconductor material for the electronic field, such as the realization of filters or capacitors. In this work, LaPbFeTiO6 was prepared by the sol–gel method. The structural, morphological, chemical and electrical properties of this sample were studied using different techniques. X-ray diffraction analysis revealed that the sample crystallized in the rhombohedral system with space group R $$\overline{3}$$ C. The chemical composition of the synthesized compound and the morphology of grain size were confirmed by energy dispersion spectroscopy analysis and scanning electron microscopy. The electrical conductivity and dielectric characterizations were studied as a function of frequency and temperature (200–380 K) by impedance spectroscopy. Indeed, the dielectric constant increases with increasing temperature. The AC conductivity obeys the Jonscher power law. The activation energy obtained from the complex impedance and the conductivity are close. The frequency dependence of the electrical impedance shows the existence of a relaxation phenomenon.

Studies indicate that the degree of polymorphism of niobium pentoxide (Nb2O5) is related to the origin of its extraction and that adequate heat treatments can improve its quality concerning the number of structural phases. In this study, the niobium pentoxide extracted from the region of the Triângulo Mineiro in the state of Minas Gerais in Brazil was heat treated and its structural characterization reveals to obtaining the single monoclinic phase (H-Nb2O5). The thermal treatments were carried out from 900 to 1150 °C and the desired single-crystal phase sample was obtained with the treatment at 1100 °C. The treated material was characterized by Dynamic Light Scattering (DLS), and its morphology by scanning electron microscopy (SEM). X-ray diffraction (XRD) and Rietveld refinement show the presence of the crystalline phase and a good agreement between the experimental and the calculated results were obtained. Functional groups, characteristic bands, and peaks were analyzed by infrared spectroscopy using Fourier Transform with Photoacoustic Detection (FTIR-PAS) and Raman spectroscopy. Thermal analysis was also made using thermogravimetric analysis (TGA), differential thermal analysis (DTA), and dilatometry techniques.

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.

ZnO nanoparticles have been prepared by auto-combustion method. Morphological and structural properties of the prepared samples were investigated by SEM, XRD, Raman and XPS characterizations. The XRD diffractogram of the sample indicates that ZnO has a hexagonal wurtzite structure. The crystallites average size, calculated from the Williamson–Hall plot, was 69.3 nm and the estimated by the SEM image (76.86 nm). Raman investigation indicates different modes of atomic displacement which correspond to longitudinal/transversal optical components with different frequencies. These modes are due to the macroscopic electric fields associated with the basic phonon of hexagonal ZnO. The XPS spectra indicate the presence of Zn and O in the structure with a small number of interstitial Zn2+, oxygen vacancies (Vo), and a negligible amount of chemical bonds with carbon (=CO …), confirmed by FTIR spectroscopy. The UV absorbance and reflectance spectra show a high absorbance with gap energy of 3.17 eV, estimated by Tauc's model. The a.c. electrical spectroscopy can be described by the Jonscher universal power-law. The charge carriers move according to the correlated barrier hopping pattern over the dispersive region. At room temperature, the conductivity of ZnO is high (~ 8 × 10–6 S.m−1) making it promises for gas detection applications. The sensor was prepared by spraying the suspension of ZnO nanopowders on alumina substrates with pre-deposited gold interdigitated electrodes. The sensor responses of NO2, for concentrations of 0.5, 0.75 and 1 ppm, were investigated at room temperature under illumination with different wavelengths. The best response of the sensor was obtained for a concentration of 1 ppm NO2 excited by 400 nm (purple) and 380 nm (UV) wavelengths, which were 91 and 88 with response/recovery times equal to 4/6.7 min and 4.4/3.3 min. Higher responses at the lower wavelength are due to the higher excitation energy which tends to excite more electrons, at the material surface, subsequently participating in the detection mechanism with gas molecules

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.

Background Cancer remains as one of the major causes of mortality worldwide. Recent advances in nanoparticles based therapy mark a new era on cancer treatment. Many groups have investigated biological/physical effects of nanoparticles on tumour cells and how these vary with physical parameters such as particle size, shape, concentration and distribution. Magnetic hyperthermia (MHT) can be an alternative or an add-value therapy with demonstrated effectiveness. MHT uses magnetic nanoparticles, which can be directly applied to the tumour, where, by applying an external ac magnetic field, will promote a localized temperature increment that can be controlled. Methods LiFe5O8 nanocrystallites were synthesized by a novel and eco-friendly sol-gel process, using powder coconut water (PCW) has a mediated reaction medium. The dried powders were heat-treated between 400 and 1000 °C, being analysed their structure, morphology and magnetic properties; cytotoxicity and magnetic hyperthermia assays were performed. Results The heat-treated LiFe5O8 powder led to crystallite sizes from 50 nm to 200 nm. Increasing the temperature of the heat treatment, secondary phases tend to disappear. The cytotoxicity results revealed a non-cytotoxicity property, for concentrations below 5 mg/mL. The sample HT at 1000 °C, revealed hysteresis and magnetic saturation of 73 emu.g−1 at 300 K and a specific absorption rate(SAR) of about 80 W/g. Conclusions It was possible to synthesize LiFe5O8 by a novel, eco-friendly and sustainable route. The nanoparticles have a high heat efficiency, especially the sample heat-treated at 1000 °C, with SAR values similar to Fe3O4, showing potential to be used in the treatment of cancer, by MHT.

In this study, La0.67Ca0.2Ba0.13Fe1−xCrxO3 (x = 0 and 0.03) powders were prepared by auto-combustion method. The examination of the purity and crystalline structure of the samples by X-ray diffraction showed a cubic structure formed with the $$Pm\overline{3}m$$ space group. Scanning electron microscopy was used to study the morphology and grains size, indicating an agglomeration of nanometric particles. Impedance spectroscopy in the temperature range from 200 to 360 K was used in order to understand the evolution of the electrical behavior of the substituted perovskites. The real and imaginary parts of the impedance were adjusted with two different equivalent circuits. The activation energies extracted from the imaginary part of the impedance, and the electrical conductivity was very closed indicating a transformation of the electrical behavior. This was confirmed by a decrease in the resistance after substitution of Fe cations by Cr ones. AC conductivity studies showed a Jonscher’s behavior and a change of conduction process from a succession of NSPT and CBH model to the existence of only CBH one after the substitution.

The effect of 5% magnesium doping on the structural, magnetic and gas sensing properties of La0.8Ca0.1Pb0.1Fe0.95Mg0.05O3 (LCPFMO) has been investigated. The nanosize compound was prepared by the Sol–Gel method, using the citric acid route. The Structural study confirms that this compound crystallizes in the orthorhombic structure with the Pbnm space group. From the magnetic measurements, we were able to show that the effect of the Mg doping is to increase the saturated magnetization and to decrease the Ferromagnetic–Paramagnetic magnetic phase transition temperature (TC). A theoretical modulation was derived in order to confirm the domination of the ferromagnetic contribution over the Antiferromagnetic one. The AC-conductivity dependence on both temperature and frequency was studied; the study confirmed the presence of two behaviors; at high-temperature region, it was found to be only temperature dependent, while at low temperatures, it depends on both frequency and temperature parameters. At low temperature, the conduction mechanism is studied according to the NSPT model, where all parameters were discussed. The electrical Sensitivity (S) of the prepared sample to different ethanol gas concentration was investigated, using a broadband dielectric spectroscopy. It was found that 5% of magnesium insertion leads to an improvement in the sensitivity of the LCPFMO sample. This sensitivity was found to be ethanol amount dependent.

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.

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.

La0.75Ba0.25−xSrxFeO3 perovskite compounds with different strontium concentrations were synthesized via the sol–gel method. X-ray diffraction (XRD) data indicated that all obtained samples crystallize in the orthorhombic structure with the Pnma space group. The dielectric properties of these samples, using complex impedance spectroscopy technique have been carried out as function of frequency and temperature as well. An adequate electrical equivalent circuit has been used to evaluate the grain and grain boundary contributions in complex impedance results. Furthermore, the AC conductivity spectra obey to Jonscher’s universal power law. The behavior of the exponent “S” suggests that the conduction mechanism follows the overlapping large polaron tunneling (OLPT) process for x = 0.05, while for both compounds x = 0.10 and x = 0.15 the non-overlapping small polaron tunneling (NSPT) is the applicable model. The behavior of e″ as a function of both frequency and temperature has been described by Giuntini model.

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

The magnetic properties, Mossbauer and the critical behavior of the compound Bi0.8Ba0.1Er0.1Fe0.96Cr0.02Co0.02O3 prepared by sol-gel are the subject of this study. The compound has an R3c structure and exhibits a ferromagnetic to paramagnetic phase transition c.a. 574 K. A theoretical adjustment of the hysteresis cycles at room temperature show two magnetic contributions: Ferromagnetic (FM) and Antiferromagnetic (AFM) with a predominance of the first contribution. Mossbauer spectroscopy revealed two Fe3+ cations differently coordinated. Magnetic measurements versus magnetic field reveal that the sample exhibits a second order magnetic phase transition. The Curie temperature ​​and the critical exponents (β, γ and δ) were determined by different techniques. These values are in agreement with the ones predicted by the mean field model.

Tetragonal Er0.5Nb0.5O2 and monoclinic ErNbO4 micro- and nanoparticles were prepared by the citrate sol–gel method and heat-treated at temperatures between 700 and 1600 °C. ErNbO4 revealed a spherical-shaped crystallite, whose size increased with heat treatment temperatures. To assess their optical properties at room temperature (RT), a thorough spectroscopic study was conducted. RT photoluminescence (PL) spectroscopy revealed that Er3+ optical activation was achieved in all samples. The photoluminescence spectra show the green/yellow 2H11/2, 4S3/2→4I15/2 and red 4F9/2→4I15/2 intraionic transitions as the main visible recombination, with the number of the crystal field splitting Er3+ multiplets reflecting the ion site symmetry in the crystalline phases. PL excitation allows the identification of Er3+ high-energy excited multiplets as the preferential population paths of the emitting levels. Independently of the crystalline structure, the intensity ratio between the green/yellow and red intraionic transitions was found to be strongly sensitive to the excitation energy. After pumping the samples with a resonant excitation into the 4G11/2 excited multiplet, a green/yellow transition stronger than the red one was observed, whereas the reverse occurred for higher excitation photon energies. Thus, a controllable selective excited tunable green to red color was achieved, which endows new opportunities for photonic and optoelectronic applications.

The La0.67Ca0.2Ba0.13Fe1−xMnxO3 perovskite compounds with different manganese concentrations (x = 0.0, 0.03, 0.06) were synthesized by the autocombustion method and annealed at 700 °C. The X-ray diffraction (XRD) data indicated that all obtained compounds crystallize in the cubic structure with the Pm $$\overline{3}$$ m space group. The increase in the substitution rate has been found to lead to the decrease in the crystallite size value characterized by X-ray diffraction. The dielectric properties of these samples, using a complex impedance spectroscopy technique, were also performed as a function of frequency and temperature. A suitable equivalent electrical circuit was used to assess the contributions of electrode, grains, and grain boundaries in the complex impedance results. Activation energies were determined from different methods. Nyquist plots were consistent with three circuits in series, each one with a capacitance in parallel with a resistance. The conduction mechanism follows the NSPT model for the three samples at T

The physical properties of the cubic and ferrimagnetic spinel ferrite LiFe5O8 has made it an attractive material for electronic and medical applications. In this work, LiFe5O8 nanosized crystallites were synthesized by a novel and eco-friendly sol-gel process, by using powder coconut water as a mediated reaction medium. The dried powders were heat-treated (HT) at temperatures between 400 and 1000 &deg, C, and their structure, morphology, electrical and magnetic characteristics, cytotoxicity, and magnetic hyperthermia assays were performed. The heat treatment of the LiFe5O8 powder tunes the crystallite sizes between 50 nm and 200 nm. When increasing the temperature of the HT, secondary phases start to form. The dielectric analysis revealed, at 300 K and 10 kHz, an increase of &epsilon, &prime, (&asymp, 10 up to &asymp, 14) with a tan&delta, almost constant (&asymp, 0.3) with the increase of the HT temperature. The cytotoxicity results reveal, for concentrations below 2.5 mg/mL, that all samples have a non-cytotoxicity property. The sample heat-treated at 1000 &deg, C, which revealed hysteresis and magnetic saturation of 73 emu g&minus, 1 at 300 K, showed a heating profile adequate for magnetic hyperthermia applications, showing the potential for biomedical applications.

Materials for energy storage have been a subject of high interest in recent times. The development of new materials with high dielectric constant and low losses is one of the main goals in scientific research for electronic applications. These properties allow reduction of the size and weight of the electronic devices. In this work, powders of sodium ferrite were prepared by sol-gel, using iron nitrate and sodium acetate as raw materials, according to the Pechini route. In order to optimize the synthesis parameters, the materials were heat-treated, and structural, morphological and dielectric characterization was performed to find the most suitable ones for storing energy. The sample structure was characterized by X-ray diffraction (XRD), Raman spectroscopy and the morphology surface by scanning electron microscopy (SEM). The dielectric properties were studied in a frequency range between 100 Hz and 1 MHz at temperatures from 200 up to 370 K by impedance spectroscopy measurements. The complex permittivity at 2.7 GHz and 5 GHz (T = 300 K) was determined using the small perturbation method through resonant cavities. The sample of sodium ferrite heat-treated at 1100 °C is the most promising for energy storage with a dielectric constant of ≈818 (f = 1 kHz; T = 300 K) and ≈6 (f = 5 GHz; T = 300 K), with low losses. The dielectric constant increases with the presence of Na3Fe5O9 phase and with the grain size and consequently porosity decreases. At low frequencies, this sample presents two relaxation processes described by Cole-Cole model and the relaxation time versus temperature has an Arrhenius behaviour.

Peri-implantitis is an infectious disease that affects about one of five patients who receive a dental implant within 5 years after the surgery. To minimize this reaction the development of new biomaterials with antibacterial action is needed that can be used as a coating material in orthodontic implants. In addition, these biomaterials can be doped with several ions, which add specific properties that may act at the cellular level, such as increasing the angiogenesis efficiency. In this work, 45S5 Bioglass® has been used as the base material because it presents higher bioactivity compared to other biomaterials. To add antibacterial function and increase positive effects on bone metabolism, zinc and magnesium ions were introduced in the glass network. The main objective was the synthesis of the 45S5 glass by melt-quenching and study the biological performance as function of the zinc and magnesium concentrations. The structural and biological properties of the prepared samples are discussed.