Semiconductor-to-metal-like behavior was observed in the BaFe11.9(Ru,Re)0.1O19 ceramic hexaferrite at temperatures above 450 K. X-ray diffraction analysis confirmed its hexagonal structure with minor α-Fe2O3 impurities, while Rietveld refinement revealed significant changes in the lattice parameters, particularly an expansion along the c axis. Atomic positions at the 2b, 4f2, and 12k sites were altered due to the partial substitution of Fe3+ by Ru4+ and Re4+ cations, which have smaller ionic radii than Fe3+. These substitutions modified the bond lengths within the crystal structure, as evidenced by increased Fe–O distances, and led to a partial reduction of Fe3+ to Fe2+, increasing electron density. The AC conductivity, σac(T), showed a transition from semiconducting to metallic-like behavior above ∼450 K. The resistivity, ρac(T), exhibited a plateau near 500 K, indicating a change in the conduction mechanism. The transport mechanism below 450 K was dominated by the non-overlapping small polaron tunneling model, characterized by thermally activated hopping with minimal Coulomb interactions, while above 450 K, the correlated barrier hopping model became dominant. The activation energy for high temperatures, Ea=0.31±0.06 eV, was consistent with the sum of the hopping energy WH=0.20±0.01 eV and half the disorder energy, Ed/2, which increased significantly with temperature. The partial substitution of Ru4+ and Re4+ significantly weakened the magnetic interactions, resulting in reduced saturation magnetization and modifications in coercivity.

The present work conducted a comprehensive study on the structural, microstructural, and electrical properties of Ba 0.9 La 0.1 Fe 12 O 19 hexaferrite doped with Al3+ ions. The Ba 0.9 La 0.1 Fe 12-x Al x O 19 system, with x = 0.0; 0.1; 0.3; 0.5; 0.7; 1.0, and 1.3 were prepared by ball milling assisted solid-state reaction method. The Rietveld method was utilized to refine the crystal structure, revealing an isostructural phase similar to a hexagonal magnetoplumbite mineral within the P63mc centrosymmetric space group (No-186). The lattice parameters (a, c , and V ) reach a minimum at x = 0.7 for Al3+ content, exhibiting similar behavior when considering the other space group P63/mmc. In addition, the crystalline size and microstrain, determined for the size-strain plot method (SSP), are 47.2-142 nm and 1.2 x 10-3 to 3.9 x 10-3, respectively. The micrographic images revealed clusters of particles with an average grain size ranging from 0.57 to 1.48 mu m. The AC conductivity remains constant at low frequencies, indicating the movement of long-range carriers. Dispersion at high frequencies results from electron hopping. The dielectric loss presented a low-frequency dispersion of the Maxwell-Wagner-type and dielectric relaxation at high frequencies. The study is important because it demonstrates the variation in the physical properties of doped barium hexaferrite.

Ceramic samples based on the Ba1-xGdxTiO3 system, where x = 0.001, 0.002, 0.003, 0.004 and 0.005, were prepared via the Pechini's chemical synthesis route. Structural properties, analyzed from X-ray diffraction and Rietveld refinement, revealed the formation of the pure ABO(3) perovskite structure with tetragonal symmetry (P4mm) for all the studied compositions. Doping with Gd3+ promoted a reduction in the unit-cell volume, confirming the preferential substitution of the rare-earth cation at the A-site. The dielectric properties have been analyzed over a wide temperature and frequency range, revealing a significant contribution of the conduction mechanisms in the dielectric response of the studied ceramics. In fact, by using the Davidson-Cole formalism, the observed electrical behavior was found to be associated with relaxation processes related to intrinsic defects mobility promoted by a thermally-activated polaronic mechanism. The obtained values of the activation energy for the relaxation processes, estimated from the Arrhenius' law for the mean relaxation time, revealed a decrease from 0.29 up to 0.21 eV as the Gd-doping concentration increases, which suggests the conduction process to be associated with the polaronic effects due to the coexistence of Ti4+ and Ti3+ ions in the structure. Analysis from the conductivity formalism, by using the Jonscher's universal power-law, confirmed the polaron-type conduction mechanism for the dielectric dispersion, as suggested by the dielectric analysis, being the nature of the hopping mechanism governed by small polaron hopping (SPH) charge transport in the studied Ba1-xGdxTiO3 ceramics.

In the present work, we have investigated the crystal structure and magnetic properties of the Y2.97Gd0.03Fe5−xLaxO12 (Gd-La co-doped YIG) compound (0.00 ≤ x ≤ 0.05) obtained by the citrate sol–gel method. Rietveld refinement of the X-ray diffraction patterns provided the lattice parameter (a) values, which increased from 12.387(2) to 12.468(2) Å as the La3+ content increased. Raman measurements confirmed the single-phase formation, whereas transmission electron microscopy (TEM) revealed elongated and irregular particles. The Mössbauer spectroscopy confirmed the presence of Fe3+ and Fe2+ cations and the coexistence of Fe2+ and La3+ cations in the octahedral and tetrahedral sites. Nonetheless, using a phenomenological model, it was suggested that the Fe2+ and La3+ ions tend to occupy preferentially the octahedral sites in the YIG structure. Further, the correspondence between the experimental and theoretically predicted saturation magnetization values indicated that the compound stoichiometry can be described by the chemical formula Y3+2.97Gd3+0.03Fe3+5−x−yLa3+xFe2+yO2−12−y/2. Magnetic parameters such as saturation magnetization, anisotropy constant, remanent magnetization, and coercive field values were computed and discussed as a function of cations distribution in the YIG crystal structure.

An experimental and theoretical investigation of the magnetic properties of Ti-doped barium hexaferrite (BaM) is conducted. Polycrystalline samples of BaFe12−xTixO19 with x≤ 0.2 were synthesized using the solid-state reaction method. X-ray diffraction (XRD) analyses, along with Rietveld refinement, confirmed the presence of BaFe12O19 as the predominant BaM phase and a minor amount of hematite in all samples. Structural analysis revealed a slight increase in lattice parameters a and c for x=0.2. A result mostly related to the preferential occupation of Ti4+ ions at the 4f2 and 12k sites, coupled with the reduction of Fe3+ ions to Fe2+. It was also found that the magnetic response of samples is affected by Ti4+ substitution. Saturation magnetization slightly decreased from ∼ 45 (x = 0) to ∼ 44 emu/g (x = 0.2), the anisotropy constant from ∼4.08× 105 to ∼4.06× 105 erg/g2, while coercivity slightly increased from ∼ 2456 to ∼ 2468 Oe, and the anisotropy field from ∼ 18.2 to ∼ 18.6 kOe. The magnetic features of the samples were analyzed in terms of a proposed model based on the mean-field theory. Results indicated that the substitution of Ti4+ ions resulted in a decrease in the magnetic moment of the 2b sublattice. Such behavior is influenced by its closest neighboring sites 12k and 4f2 sublattices, which are the preferred occupancy sites for the Ti4+ cations.

Coral-like structures of the Y3-xPrxFe5-yYbyO12,(0.00≤x≤0.04,0.00≤y≤0.02)compound were synthesized using the sol-gel method.Structural investigation certified the YIG cubic crystal structure formation,without any secondary phase.It is shown that,the relatively large ionic radius of the dopant cations results in an expansion of the lattice parameter,variations in the Iona-O-Iond angle,Iona-O,Iond-O and Ionc-O bond distances and decrease in the average crystallite size.Fourier transform infrared(FTIR)and Raman measurements are essential to testify the single-phase formation of YIG crystal structure and are observed changes in the stretching and vibrational modes,respectively.The morphological study,energy dispersive spectroscopy(EDS)spectra and textural properties show coral-like structures,peaks associated with Pr3+and Yb3+atoms and the effect of dopants on surface area,diameter,and pore volume,respectively.The optical analysis from diffuse reflectance spectra witnessed an increase in the optical gap band,a decrease in Urbach energy and blue shift in the charge transfer,correlated with the expansion of the unit cell due to the dopant's insertion in the YIG structure.A typical ferrimagnetic behavior is exhibited by the Y3-xPrxFe5-yYbyO12 compound.The saturation magnetization(Ms),cubic anisotropy constant(K1)and coercive field(Hc)increase with the Pr3+cations content,as consequence of their magnetic nature and distribution around of Fe3+ions due to the coexistence with the Yb3+.Finally,for the first time,antibacterial tests by mean of the direct contact method were per-formed for YIG co-doped with Pr3+and Yb3+and it is shown that,relatively high dosages of Pr3+cations favored the activity against S.aureus,therefore,a new biological property for YIG doped with rare earths is presented.

The correlation between dielectric relaxation and conduction mechanisms in the Ba0.9La0.1Fe12O19 ceramic hexaferrite, at temperatures below 100 K was investigated. The sample was prepared using the conventional solid-state reaction method. X-ray diffraction analysis indicated that the sample is composed of a hexagonal BaFe12O19 phase (lattice parameters a = 5.8778(6) angstrom and c = 23.170(3) angstrom) and a small proportion of hematite (alpha-Fe2O3). The average grain size is 1.48 +/- 0.4 mu m, with irregular hexagonal and agglomerated grains. The magnetic hysteresis curve shows characteristics typical of ferro and ferrimagnetic materials, with an effective magnetic anisotropy coefficient of 0.960 x 10(6) emu/cm(3) and an anisotropy field of 1.587x10(4) Oe. A dielectric relaxation process is observed between 50 and 100 K, with an activation energy of 60.4 +/- 0.4 meV and a characteristic relaxation time of 2.09 x10(-10) s, mainly attributed to the electrical behavior of the grains. Two conduction mechanisms were identified: small polaron tunneling (high temperatures and low frequencies) and correlated barrier hopping of electrons (low temperatures and high frequencies). The activation energy for free polaron formation, according to the Komine-Iguchi hopping polarization model, was 7.12 +/- 0.02 meV. In the dielectric modulus relaxation process between 30 and 54 K, the activation energy was 40.8 +/- 0.9 meV, with a characteristic relaxation time of 2.41x10(-10) s. The small polaron conductivity in the grain region was 67.52 meV and 54.0 meV in the grain boundary region. The results highlight that the polarization and conduction mechanisms in this ceramic at low temperatures are dominated by small polaron hopping and tunneling, and emphasize the influence of La3+ doping on the structural, magnetic, and electrical properties of barium hexaferrite.

An experimental and theoretical investigation of the magnetic properties of Ti-doped barium hexaferrite (BaM) is conducted. Polycrystalline samples of BaFe 12- x Ti x O 19 with x <= 0.2 were synthesized using the solid -state reaction method. X-ray diffraction (XRD) analyses, along with Rietveld refinement, confirmed the presence of BaFe 12 O 19 as the predominant BaM phase and a minor amount of hematite in all samples. Structural analysis revealed a slight increase in lattice parameters a and c for x = 0 . 2. A result mostly related to the preferential occupation of Ti 4+ ions at the 4f 2 and 12k sites, coupled with the reduction of Fe 3+ ions to Fe 2+ . It was also found that the magnetic response of samples is affected by Ti 4+ substitution. Saturation magnetization slightly decreased from similar to 45 (x = 0) to similar to 44 emu/g (x = 0.2), the anisotropy constant from similar to 4 . 08x 10 5 to similar to 4 . 06x 10 5 erg/g 2 , while coercivity slightly increased from similar to 2456 to similar to 2468 Oe, and the anisotropy field from similar to 18.2 to similar to 18.6 kOe. The magnetic features of the samples were analyzed in terms of a proposed model based on the mean-field theory. Results indicated that the substitution of Ti 4+ ions resulted in a decrease in the magnetic moment of the 2b sublattice. Such behavior is influenced by its closest neighboring sites 12k and 4f 2 sublattices, which are the preferred occupancy sites for the Ti 4+ cations.

An experimental and theoretical investigation of the magnetic properties of Ti-doped barium hexaferrite (BaM) is conducted. Polycrystalline samples of BaFe12−xTixO19 with x≤ 0.2 were synthesized using the solid-state reaction method. X-ray diffraction (XRD) analyses, along with Rietveld refinement, confirmed the presence of BaFe12O19 as the predominant BaM phase and a minor amount of hematite in all samples. Structural analysis revealed a slight increase in lattice parameters a and c for x=0.2. A result mostly related to the preferential occupation of Ti4+ ions at the 4f2 and 12k sites, coupled with the reduction of Fe3＋ ions to Fe2＋. It was also found that the magnetic response of samples is affected by Ti4+ substitution. Saturation magnetization slightly decreased from ∼ 45 (x = 0) to ∼ 44 emu/g (x = 0.2), the anisotropy constant from ∼4.08× 105 to ∼4.06× 105 erg/g2, while coercivity slightly increased from ∼ 2456 to ∼ 2468 Oe, and the anisotropy field from ∼ 18.2 to ∼ 18.6 kOe. The magnetic features of the samples were analyzed in terms of a proposed model based on the mean-field theory. Results indicated that the substitution of Ti4+ ions resulted in a decrease in the magnetic moment of the 2b sublattice. Such behavior is influenced by its closest neighboring sites 12k and 4f2 sublattices, which are the preferred occupancy sites for the Ti4+ cations.

Herein, we present a comprehensive crystallographic and magnetic study of the Gd0.03Y2.97Fe5O12 ferrite, synthesized via the sol-gel method. Rietveld refinement and Raman spectrum confirmed the single-phase cubic structure formation. Furthermore, the atomic positions, the local structure distortion, lattice parameters (12.398(1) & Aring;), volume (1905.6(4) & Aring;3), and the average crystallite size (68.3(9) nm) were also determined. Using a phenomenological model was confirmed that the Gd3+ ions prefer to occupy the dodecahedral sites. The micrographic images obtained by scanning electron and transmission microscopies corroborated the agglomerated coral style of the particles. From the magnetic study, it was verified that the Gd3+ ions induce a negative contribution to the net magnetic moment in the Gd0.03Y2.97Fe5O12 ferrite. In addition, was demonstrated that the a-d super-exchange interaction weakening is not the main mechanism that determines the saturation magnetization for the studied compound. Instead, the negative contribution of the Gd3+ ion's magnetic moment in dodecahedral sites is the determining physical mechanism of saturation magnetization.

Herein, we present a study about the effect of Sn-substitution on the electrical conductivity of SrFe12O19 hexaferrite synthesized by the solid-state reaction method. For samples containing Sn(4+)cations, the complex impedance curves showed the existence of conductive processes. The electrical response studied from the equivalent circuit model, provided grain boundary resistance values higher, in one order, in relation to the grain values, which agrees with the Koop model. For the Sn-doped SrM ceramics samples, the conductivity values increase with the dopant cations content. In addition, the Sn4+ cations insertion in the SrM crystal structure contributes to the emergence of two conductive processes: a DC-conductivity process at low frequency and a second frequency-dependent conductive process at high frequency. From the activation energy, the existence of a small polarons tunneling mechanism with long-range mobility and low frequency, that spontaneously occurring with negative activation energy and an electron hopping mechanism that follows a correlated barrier model and activation energy from 0.135 to 0,355 eV were found.

In the present study, we have investigated the influence of La3+ cations insertion on the crystallography, morphology, and magnetic properties of Y3Fe5-xLaxO12 compound, (x = 0.00 and 0.03) obtained by the sol-gel method. To confirm the Fe3+ by La3+ cations replacement and quantify the structural parameters, the Rietveld refinement method was used. The quantitative analysis confirmed that, the La3+ cations insertion in the YIG crystal structure affect significative the lattice constant, crystallite size, microstrain, sites occupancy, bond angles and distances. Room temperature Raman spectra also confirmed the YIG single phase structure. The spectra deconvolution pointed shifts for smaller wavenumber in the sample containing La3+ cations, specifically in the region between 400 and 800 cm-1, correlated with the octahedral and tetrahedral sites. The coral format morphology was confirmed by Scanning and Transmission Electron Microscopies. Lastly, room temperature magnetic measurements demonstrated that the La3+ cations insertion in the YIG crystal structure, provokes an increase in the saturation magnetization (Ms), remanent magnetization (Mr) and magnetocrystalline anisotropy (K1) of 24.8, 17.5, and 9.3%, respectively, respect to the values obtained for undoped YIG sample.

Polymer matrix nanocomposites are extensively explored due to their usefulness and relevant physicochemical properties. Once these properties are present instantaneously, reacting at relative stimuli, multifunctional ap-plications are succeeded. In the current work, we have investigated the structural, magnetic, and electrical properties of a system formed from the SrFe12O19 hexaferrite (SrM) and polylactic acid (PLA). The SrM particles were obtained by solid reaction method and embedded in a PLA thermoplastic polymeric matrix to form the SrM/PLA composite. The structural, magnetic, and electrical properties were investigated from the experimental measurements obtained by X-ray diffraction (XRD), vibrating-sample magnetometer (VSM), and impedance spectroscopy (IS), respectively. The Match-3 Software was used to determine the present phases in each sample. The results suggest the coexistence of both phases independently (SrM and PLA). In addition, the lattice pa-rameters experience minimal variation for the individual phases of the compound. It was noticed that the magnetic properties are modulated as a function of the SrM hexaferrite phase concentrations and the magnetic interactions' nature. Finally, the electrical properties (impedance complex, real and imaginary permittivity) showed wide variability with changes in the phase content. For all samples, the characteristic values of s(300) between 0.9926 +/- 0.0002 and 0.9737 +/- 0.0003 indicated the electron hopping mechanism.

In this work, the variation in the structural and electrical properties of lithium-doped sodium titanate, obtained from an ultrafast (15 min) microwave-assisted synthesis has been reported. X-ray diffraction and Rietveld analysis have been done to identify the present phases, their composition, and lattice parameters. Na2Ti3O7 was identified as the major phase, while Na2Ti6O13 was obtained as a secondary phase in all samples. The phase composition usually varies depending on the content of the doping element. In the sample with 0.5% lithium ions, an additional phase corresponding to NaLiTi3O7 appeared. The microstructure of the ceramic samples showed an increase in the grains size and the appearance of small particles on the surface of the grains. This effect becomes more evident for the samples with 0.5% Li. Finally, the electrical properties of the ceramic samples studied were favored with an increase in doping and σdc values of 1.94 × 10− 5 S cm− 1, 2.51 × 10− 5 S cm− 1, and 4.00 × 10− 5 S cm− 1 were determined for Na2 − xLixTi3O7 with x = 0.0%, 0.1%, 0.5% of Li+.

A new method, the complex impedance formalism, is presented to disclose the relaxation process of conducting materials. This method is an extrapolation of the dielectric modulus formalism in the Bode representation of the impedance. As in the dielectric modulus formalism, the relaxation process can be approached in both the frequency and time domains for non-Debye relaxation type. The complex impedance formalism is tested by analysis of the relaxation process of the solid BaTiO3 material at high temperatures. A combination of complex impedance and dielectric modulus formalism provides us with a better understanding concerning individual relaxation regions. The complex impedance formalism allows the hidden relaxation process at low frequency regime to be accessible, whereas the dielectric modulus formalism discloses the relaxation process at high frequency in mixed electronic-ionic conductors.

The structural and magnetic properties in the Ba0.9La0.1Fe12-xAlxO19 hexaferrite compound were studied as a function of Al3+ concentration (x = 0.0 to 1.3). The samples were obtained by solid-state reaction synthesis and sintered by the conventional ceramic method. The Rietveld refinement method analysis showed the predominance of barium hexaferrite phase with hexagonal structure characterized by P63/mmc space group. The secondary phase of hematite (alpha-Fe2O3), with rhombohedral system and R-3c space group, was found. For the principal phase, the lattice parameters a, c, and the cell volume (V) reached a minimum value in the concentration x = 0.7 of Al3+ ion. Variations in the average bond length and distortion index of the oxygen polyhedra were observed at the Ba(2d) site and at the Fe (2b, 4f(IV), 4f(VI), and 12 k) sites. The Raman spectra showed all bands related to Fe-O bonds at different crystallographic sites. The saturation magnetization reached the minimum value for the composition x = 0.7. The coercive field increased until reaching the maximum value at x = 1.0 of Al3+ concentration. The magneto-crystalline anisotropy field decreased from x = 0.1 to 0.7 and increased at higher concentrations. At room temperatures the total magnetic moment decreases from mu = 10.74 to 4.33 mu B for Al3+ concentration range of 0.1 <= x <= 0.7 and oscillates with mu = 8.18 and 9.44 mu B at compositions of x = 1.0 and 1.3, respectively. The present study is important to understand the impact of Al and La addition on the structural and magnetic properties of barium hexaferrite.

Polycrystalline samples of Sr1_xLaxFe12O19 (x = 0.1, 0.3, and 0.6) hexaferrite were prepared by spark-plasma sintering (SPS) and its structural and magnetic properties have been investigated. The SPS process were performed under vacuum, at 900 C, and in only 5 min. X-ray powder diffraction patterns showed that before SPS sintering samples are composed by several phases where the SrFe12O19 (SrM) is not higher than 12%. From Rietveld refinement method, we have found that after SPS process the content of SrM phase increased, in mean, up to 68%. However, it was found the presence of secondary phase such as alpha-Fe2O3 and LaFeO3 (%) whose phase content also vary with increasing the La-content. A finite element simulation model were used to study the temperature evolution within the sample during the SPS treatment. Magnetization measurements at room temperature yielded values of saturation magnetization between - 43 to - 27 emu/g and coercivities, HcB, in the range 3.11 to 2.88 kOe with increasing x. The influence and possible interaction between detected magnetic phases was studied by means of first-order reversal curves (FORCs) measurements. Results indicated that magnetic behavior of the La-doped strontium hexaferrites obtained by SPS technique are analogous a system composed of a broad distribution particles that are exchange-coupled with a certain number of other of neighboring particles. From FORC maps the coercivity profiles of the studied samples were extracted. The asymmetric behavior of these profiles were related to a broad distribution of the particle size and/or the influence of the secondary magnetic phases.

Abstract This study processed and characterized the biphasic ceramics Na2Ti3O7/Na2Ti6O13 that were obtained from semi-crystalline nanoparticles synthesized using sonochemical methods. Structural characterization techniques, such as X-ray diffraction and Raman spectroscopy, were used to identify the crystalline phases present. The Rietveld refinement revealed, among other structural parameters, the presence of two crystalline phases in compositions of 55.90% and 44.10% for sodium hexatitanate and trititanate, respectively. Via Raman spectroscopy, the presence of the main vibrational modes that correspond to the phases present in biphasic ceramics was confirmed. Finally, by using complex impedance spectroscopy, a decrease in the electrical resistance of both the grain (106 Ω-104 Ω) and its boundary (108 Ω -105 Ω) under increasing temperature was identified.

Mixed phases of sodium titanate ceramics are obtained using both conventional and laser sintering methods. It was observed a clear dependence on the structural, microstructural and electrical resistivity with the employed sintering method. The temperature dependence of the resistivity in the ceramics shows an increase of three orders of magnitude in a narrow range of temperatures, thereby indicating a noticeable positive temperature coefficient of resistivity (PTCR) effect. To explain this observed abnormal behavior, a model based on the structure of the Na2Ti6O13/Na2Ti3O7 composite is proposed. A new class of PTCR materials is reported.

In the present work, was studied the effect of the La3+ cation solubility on the structural, magnetic and electrical properties of M-type barium hexaferrite (BaM). The Rietveld refinement revealed changes in the lattice parameters with increasing the La3+ concentration. Variations in the bond length and the distortion index of 2b, 4f2 and 12k oxygen polyhedral were observed with the La3+ insertion in the BaM structure. In addition to the BaM phase, secondary phases Fe2O3 and LaFeO3 arise, whose concentrations depend on the La3+ solubility. The magnetic properties are strongly affected by the La3+ incorporation in the structure, as well as by the secondary phases. Changes in the oxidation state of Fe3+ to Fe2+ decreases the exchange interaction, resulting in the magnetic moments disturbance. The electrical properties are dependent on the La3+ content and the secondary phase concentration. Undoped sample present the highest impedance values, decreasing linearly in all frequency range. For doped samples, the resistivity decreases in several orders due to the La3+ incorporation, while the ac-conductivity remains constant at low frequencies and presents dispersion at high frequencies. The dielectric permittivity present space charge polarization mechanism generated by electron hopping from Fe3+ to Fe2+ ions. The Non-Debye-type relaxation and the conductivity transition of long and short range are suggested from the results of imaginary impedance and electric module. The bond valence model revealed that the most affected crystallographic sites are 2b, 4f2 and 12k, where the exchange of valence of Fe3+ by Fe2+ ions should take place.