The structural and magnetic features of perovskite oxides La1–xSrxMnO3+δ (x = 0.05, 0.10, 0.20) depending on the strontium doping content and heat treatment

Sr-doped (0<x < 0.2) ceramic samples of the lanthanum manganite oxides were obtained via sol-gel method to investigate the influence of doping on structural, magnetic end electronic responses, and their correlations. Synthesized samples of non-stoichiometric compositions are rhombohedral single-phase. After annealing the formation of a phase-separated system as a mixture of orthorhombic phases was found. The R-3c and PnmaI, PnmaII* and PnmaII phases have been studied using Mössbauer spectroscopy, XRD, SEM analysis and magnetic measurements. The magnetic temperature-concentration phase diagram of La_1–xSr_xMnO_3+δ (x = 0.05, 0.10, 0.20) was obtained.The Jahn-Teller effect or the orbital order breaking, as well as the competition between Mn³⁺–O^2—Mn⁴⁺ double- and Mn³⁺–O^2-–Mn³⁺ superexchange interaction was demonstrated under the effect of cation doping compound and interstitial oxygen value (δ). The relaxation character of the Mössbauer spectra and the type of magnetization dependences revealed nanosized magnetic clusters with fluctuation of their magnetic moment in all perovskite phases. Results are interpreted in terms of matrix – clusters: regions of sample with ferromagnetic type of ordering (cluster) exist in antiferromagnetically or ferromagnetically (with different exchange parameter) ordered matrix. Exchange interaction frustrations of the cluster with the matrix can lead to relaxation behavior of the magnetic moment of the cluster. The clusters size vary from about 3.9 to 5.7 nm. All samples are characterized by the presence of particles agglometates with a typical size about 0.4–0.8 μm; for annealed samples additional non-conducting regions with 80–220 nm in size were found. It is shown that the annealing time significantly affects the production of materials with determined properties and be useful in the applied field in technological processes.     

Influence of samarium doping on magnetic and structural properties of M type Ba–Co hexaferrite

Sm doped Ba–Co hexaferrite with composition BaCo_0.8Sm_xFe_(11.2−x) O₁₉ (x=0.2, 0.4 and 0.6) were prepared via a citrate precursor method. After appropriate heat treatments, the ferrite samples were characterised by using different measurement techniques. X-ray diffraction (XRD) confirmed the formation of M phase with an average crystallite size of 35–45 nm. Observed tensile strain leads to the elongation of Ba–Co grains and was calculated using Williamson Hall plot. Surface morphology of these samples was studied by using field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). σ–H loops of these samples were measured at room temperature up to an applied field of 22,000 Oe using vibrating sample magnetometry (VSM). With an increase in concentration of Sm ions in Ba–Co lattice, specific saturation magnetisation (σ_s), coercivity (H_c) and retentivity (σ_r) values were found to decrease. At x=0.2, excellent values of H_c (2690.20 Oe) and squareness ratio (SQR=0.5619) were simultaneously found. These parameters make this material a promising candidate for the applications such as high density magnetic recording and enhanced memory storage.     

Influence of component manipulation on the structural,mechanical, thermophysical and electrical properties of La0·2Ce0.2Nd0.2(ZrxY1−x)0.4O2−δ high-entropy ceramics

A series of high-entropy ceramics (HECs) with compositions of La_0·2Ce_0.2Nd_0.2(Zr_xY_1−x)_0.4O_2−δ (x = 0.5, 0.6, 0.7, 0.8, 0.9 and 1.0, the corresponding names being HEC(Zr_0·5/Y_0.5, Zr_0·6/Y_0.4, Zr_0·7/Y_0.3, Zr_0·8/Y_0.2, Zr_0·9/Y_0.1, Zr_1·0/Y₀)) were sintered in air at 1600 ^°C for 10 h. When x is in the range of 0.5–0.7, a fluorite phase is formed. Then, as x exceeds 0.7, a second pyrochlore-structured phase appears, and its content gradually increases with the increasing x. The grain growth of the samples is inhibited by increasing in the relative Zr content. The grain refinement and the formation of second phase reduce the thermal conductivity and reinforce the mechanical properties of the samples. HEC(Zr_0.9/Y_0.1) has the lowest thermal conductivity (50–500 °C) and brittleness index, as well as the highest fracture toughness among all samples. In addition, La_0·2Ce_0.2Nd_0.2(Zr_xY_1−x)_0.4O_2−δ ceramics have excellent thermal stability under Ar atmosphere in 50–1400 °C. The thermal expansion coefficients of the samples marginally change regardless of the variation in x. All samples show higher oxygen barrier property than Y₂O₃-stabilized ZrO₂.     

Influence of transition metal doping on the structural,optical, and magnetic properties of TiO2 films deposited on Si substrates by a sol–gel process

Transition metal (TM)-doped TiO₂ films (TM = Co, Ni, and Fe) were deposited on Si(100) substrates by a sol–gel method. With the same dopant content, Co dopants catalyze the anatase-to-rutile transformation (ART) more obviously than Ni and Fe doping. This is attributed to the different strain energy induced by the different dopants. The optical properties of TM-doped TiO₂ films were studied with spectroscopic ellipsometry data. With increasing dopant content, the optical band gap (E_OBG) shifts to lower energy. With the same dopant content, the E_OBG of Co-doped TiO₂ film is the smallest and that of Fe-doped TiO₂ film is the largest. The results are related to electric disorder due to the ART. Ferromagnetic behaviors were clearly observed for TM-doped TiO₂ films except the undoped TiO₂ film which is weakly magnetic. Additionally, it is found that the magnetizations of the TM-doped TiO₂ films decrease with increasing dopant content.     

Influence of mono- and triple (Cr–La–Ba) doping on the mechanical,optical and gas diffusion properties of corundum

The effect of triple doping with chromium, lanthanum and barium on the mechanical, degassing and gas diffusion properties of fine-crystalline corundum synthesized in a supercritical water fluid was studied. The influence of chromium monodoping on the mechanical and optical properties of fine-crystalline corundum was also investigated. It was found that even small amounts of dopants of lanthanum and chromium during triple and monodoping of corundum significantly improve its mechanical properties (increase the abrasive ability) and reduce it several times the content of volatile gas-liquid impurities, which contributes to increase transparency of the resulting ceramics. The role of the interaction of a chromium impurity with oxygen vacancies in corundum on the increase in the static strength of crystals was suggested. The diffusion coefficients of water in doped corundum were determined. Comparison of the degassing and diffusion properties of corundum doped with La, Cr, Ba with undoped corundum and corundum doped with lanthanum was carried out. The results obtained contribute to the creation of new materials based on doped corundum with high abrasive, luminescent, and gas diffusion characteristics.     

Synthesis and structural,morphological, compositional,optical and electrical properties of DBSA-doped PPy–WO3 nanocomposites

Synthesis of DBSA-doped PPy–WO₃ (organic–inorganic) nanocomposites, using a novel approach, has been proposed, and further envisaged for their structural, compositional, morphological, optical and electrical properties. DBSA-doped PPy–WO₃ nanocomposites demonstrate superior above mentioned properties than their counterparts i.e. either PPy or WO₃. The XRD spectra of nanocomposites supported to conclude that both i.e. PPy and DBSA have no impact on the crystallinity of WO₃ nanoparticles. The chemical structure of DBSA-doped PPy–WO₃ nanocomposites have been elucidated using FTIR spectra. The morphologies and surface roughnesses of the DBSA-doped PPy–WO₃ nanocomposites were confirmed using scanning electron microscope and atomic force microscope images, respectively. Interconnected type morphology and 13 nm average surface roughness were confirmed for DBSA doped PPy–WO₃ hybrid nanocomposites. The EDX and XPS analyses evidence that, the formation of DBSA doped PPy–WO₃ hybrid nanocomposites without any elemental impurities. The absorption peak of DBSA-doped PPy–WO₃ nanocomposites shift towards the lower wavelength side as compared to the PPy–WO₃ (50%) hybrid nanocomposites. Anionically charged sulfonate group which is supposed to stabilize doped state of the DBSA-PPy–WO₃ nanocomposites, may be responsible for this shift. The dc electrical conductivity of DBSA-doped PPy–WO₃ nanocomposites increases as the content of DBSA is increased from 10 to 50% this could be accounted for by the generation of conduction path through the PPy–WO₃ nanocomposites as DBSA has anionic surfactant nature by preventing an agglomeration of functional material.     

Effect of MnO2 addition on microstructure and electrical properties of ZnO–V2O5-based varistor ceramics

The microstructure and electrical properties of ternary system ZnO–0.5 mol% V₂O₅–MnO₂ ceramics sintered were investigated in accordance with MnO₂ content by sintering at 900 °C. For all samples, the microstructure of the ternary system ZnO–V₂O₅–MnO₂ ceramics consisted of mainly ZnO grain and secondary phase Zn₃(VO₄)₂. The incorporation of MnO₂ to the binary system ZnO–V₂O₅ ceramics was found to restrict the abnormal grain growth of ZnO. The breakdown field in the E–J characteristics increased from 175 to 992 V/cm with the increase of MnO₂ content. The incorporation of MnO₂ improved non-ohmic properties by increasing non-ohmic coefficient. The highest non-ohmic coefficient (27.2) in the ternary system ZnO–0.5 mol% V₂O₅–MnO₂ was obtained for MnO₂ content of 2.0 mol%.     

Effects of copper doping on the structure,electrical and low-field magnetoresistance properties of (1–x)La0.67Sr0.33MnO3/xCu (x=0–0.15) composite coatings

The doping effect of metallic Cu on the performances of manganite coatings has been investigated. The (1–x)La_0.67Sr_0.33MnO₃/xCu (x=0–0.15) composites were prepared by the sol-gel based screen printing method. XRD and SEM measurements revealed CuO phase to form by oxidation and to distribute mainly at grain boundaries (GBs) of the manganite matrix. Excess Cu entered the manganite lattice without changing its rhombohedral structure, resulting in a slight lattice expansion. The surface morphology of composite samples changed dramatically with different Cu contents, and average particle size refined with a low concentration of Cu. As the Cu content increased, the resistivity of the samples increased while the metal–insulator transition temperature decreased. The enhanced magnetoresistance (MR) effect close to the percolation threshold has been ascribed to the introduction of local disorder at GBs.     

Synthesis,structural and electrical properties of Bi1−xDyxFeO3 multiferroic ceramics

Polycrystalline ceramic samples of dysprosium (Dy³⁺) doped bismuth ferrite of general formula Bi_1?xDy_xFeO₃ (x=0.00, 0.01, 0.05 and 0.1) have been prepared by standard solid state reaction method. Powder X-ray diffraction (XRD) analysis reveals that all the samples crystallize in the rhombohedral structure with noncentrosymmetric R3c space group. The refined lattice parameters decrease with the increase of Dy concentration within the same structure symmetry. The bond lengths among atoms for all the compounds were calculated by the Rietveld analysis. The frequency and temperature dependent dielectric constants (real and imaginary parts) have been measured. The real part of dielectric constant reveals that the Neel temperature decreases with the increase of Dy-substitution down to ～200 °C for 10% substitution to the Bi site.     

Influence of hafnium oxide on the structure and properties of powders and ceramics of the YSZ–HfO2 composition

Using the X-ray diffraction, internal friction, 4-point bending, and electron microscopy methods we have studied the structural compatibility and influence of Y₂O₃ and HfO₂ dopants addition on the structure and phase composition of ZrO₂ powders and ceramics based on them. The mechanical properties of ZrO₂–Y₂O₃-HfO₂ (YSZ) system have been investigated.It was determined that the similarity of the structure and properties of yttrium and hafnium oxides is not complete. The individual structural features of ZrO₂, Y₂O₃, and HfO₂ oxides reviled themselves during the formation of ternary systems of the YSZ-Hf type. Studies of the nY₂O₃–ZrO₂ - mHf₂O₃ system in the range of hafnium amount from 1 to 15 wt% and yttrium oxide concentration from 0 to 12 mol% showed the possibility of increase in the values of physical and mechanical properties of common two-component zirconium ceramics by the forming ternary systems of the YSZ-Hf type.     

Influence of structural parameters on the properties of electrolytic Ni–Mn–S deposits

Microstructural parameters such as coherent domain size, microstrain, dislocation density and texture of electrolytically plated Ni–Mn–S layers were investigated by X-ray analysis. Structural parameters, layer composition and the macroproperties are discussed and explained. With the help of a statistical regression analysis the correlation coefficient r2 and its relationship with the investigated parameters is determined. It is shown that the microstructural parameters play an important role in determining the macroscopic properties. The manganese concentration is shown to influence the structural parameters, but no influence of sulphur is found. It seems that a relationship of the structural parameters with the macroscopic properties is valid in general and is not a special case. There structural correlations can be used in general for processing electrolytic deposits for required applications.     

Effect of annealing atmosphere on the structural and electrical properties of BiFeO3 multiferroic ceramics prepared by sol–gel and spark plasma sintering techniques

Phase-pure BiFeO₃ powders were synthesized by sol–gel technique. Based on these powders, high-density BiFeO₃ ceramics were prepared by spark plasma sintering (SPS) at 700 °C along with annealing for 2 and 4 h, respectively, at 650 °C under atmospheres of air and oxygen. X-ray diffraction analysis revealed that the 4 h-oxygen-annealed sample contained a single rhombohedral perovskite phase while the samples annealed in the other conditions contained small quantities of impurity phases besides the rhombohedral perovskite phase. The relative density of the 4 h-oxygen-annealed sample was about 96%, being apparently higher than that of the other samples. In comparison with the 4 h-air-annealed sample, the dielectric constant of the 4 h-oxygen-annealed sample was relatively higher. The activation energy for electrical conduction was about 1.17 eV for the 4 h-oxygen-annealed sample while it was about 0.98 eV for the 4 h-air-annealed sample, showing that the former would have a lower room-temperature conductivity (~2.6×10⁻¹⁴ S cm⁻¹) than the latter (~2.1×10⁻¹³ S cm⁻¹). It is therefore anticipated that the oxygen-annealed sample could possess better ferroelectric properties as compared to the air-annealed sample.     

Influence of stabilizing ions and sintering process on the thermal conductivity of α-SiAlON ceramics

α-SiAlON ceramics with different stabilizing ions of Yb, Dy, Nd, Y, Ca, and binary stabilizing ions of (Yb + Ca) and (Yb + Nd) were prepared by spark plasma sintering at 1600°C and gas pressure sintering at 1800 and 1900°C, and their thermal conductivity was investigated. It was found that α-SiAlON ceramics with larger and heavier stabilizing ions had lower thermal conductivity and the thermal conductivity could be further reduced by using binary stabilizing ions, which can be explained by phonon scattering from point defects. At the same time, the samples prepared at lower sintering temperatures showed smaller grain sizes and lower thermal conductivity. The relationship between the thermal diffusivity of samples and temperature was studied, where the dependence of inverse thermal diffusivity on temperature was better fitted by a quadratic fitting function than the usual linear one over a wide temperature range from 25 to 800°C.     

Effect of ZnO on the structural,physio-mechanical properties and thermal shock resistance of Li2O–Al2O3–SiO2 glass-ceramics

The composition of lithium aluminosilicate (LAS) with different zinc oxide-magnesium oxide (ZnO–MgO) contents that ranged from 0 to 1.45 wt percent (wt%) was investigated to determine the thermal shock resistance properties of the glass-ceramics. The LAS glasses were melted in an alumina crucible at 1550 °C for 5 h, and the green compact samples were then heat-treated at 1100 °C for 3.5 h. The presence of zinc oxide (ZnO) in the compositions did not change the major crystal phase of β-spodumene. However, the addition of ZnO shifted the pronounced peak to a lower angle and increased the percentage of crystallinity from 55% to 59%. Additionally, the function of ZnO in LAS glass-ceramics as the network modifier was confirmed through Fourier Transform Infrared Spectroscopy (FTIR) analysis. The physio-mechanical properties were improved when 1.45 wt% ZnO was added to the LAS glass-ceramics. The results showed increased density (2.42 g/cm³), low porosity (0.85%), high flexural strength (125.23 MPa), and low coefficient of thermal expansion (25–800 °C) (CTE_{(25–800 °C)}) value of 1.73 × 10^?6 °C^?1. Meanwhile, the thermal shock resistance properties evaluation of the LAS glass-ceramics at different ZnO contents were conducted at different thermal shock temperatures of 200 °C, 500 °C, and 800 °C. The critical temperature of the LAS specimens with 1.45 wt% ZnO demonstrated the ability to withstand a thermal shock at 800 °C while preserving 87% of their initial strength of 108.40 MPa, exemplifying the best LAS glass-ceramics properties for rapid high-temperature change applications.     

Influence of post-deposition annealing on electrical and optical properties of (Ta2O5)1-x - (TiO2)x thin films,x ≤ 0.08

Tantalum (Ta) and titanium (Ti) metal targets were direct current (DC) magnetron sputtered in the oxygen environment by varying its relative areas to deposit (Ta₂O₅)_1-x- (TiO₂)_x (TTO_x) thin films, with x = 0, 0.03, 0.06, and 0.08, onto the boron-doped p-silicon (1 0 0) and optically polished quartz substrates, at room temperature; and were annealed at 500, 600, 700, and 800 °C, for 1.5 h. The thin films annealed at and above 600 °C show the Ta₂O₅ structure. The leakage current density and capacitance-voltage (C–V) characteristics were measured for TTO_x, x ≤ 0.08, assisted Ag/TTO_x/p-Si metal– oxide– semiconductor (MOS) structures. The leakage current density was found minimum, for the films annealed at 800 °C, for all the prepared TTO_x films, x ≤ 0.08. The minimum leakage current density 1.6 × 10^?8 A/cm², at 3.5 × 10⁵ V/cm electric field, was observed for x = 0.03, annealed at 800 °C, among the prepared compositions. The prepared TTO_0.03 films, annealed at 700 °C show maximum dielectric constant 39, at 1 MHz. The optical parameters, viz., refractive index (n), extinction coefficient (k), and optical band gap (E_g) of the films, with x = 0.03, prepared on quartz substrates, were determined from their optical transmittance plots. The values of n and k of the crystalline films were observed increasing from 2.123 to 2.143, and 0.099 to 0.130, respectively, at 550 nm wavelength; and E_g decreasing from 3.95 to 3.89 eV with the increasing annealing temperature, from 600 to 800 °C. Ohmic emission, in the lower electric field; Schottky and space-charge- limited current conduction mechanisms, in the intermediate to higher electric fields, were generally envisaged from the current-voltage characteristics in the prepared Ag/TTO_0.03/p-Si structures.     

Phase structure and electrical properties of lead free Na0·5Bi0·5TiO3–CaTiO3 ceramics

Abstract

Abstract

(1?x)Na_0·5Bi_0·5TiO_3?xCaTiO₃ ceramics with x?=?0–0·2 were prepared by solid state sintering method. Structural and morphology studies carried out by X-ray diffraction and scanning electron microscopy indicate the change in crystal structure from rhombohedral to orthorhombic symmetry (R3C to Pnma). The morphotropic phase boundary of this system was found to lie around x?=?0·08–0·14, where the orthorhombic and rhombohedral symmetries coexist. The orthorhombic phase is stabilised for x>0·14, indicating that the rhombohedral phase of Na_0·5Bi_0·5TiO₃ is susceptible to orthorhombic distortion brought about by Ca substitution. Calcium substitution in Na_0·5Bi_0·5TiO₃ caused an obvious decrease in peak temperature and a decrease in relative permittivity. The compositional variation of the fundamental dielectric behaviour is discussed in relation to the crystal chemistry of the system. The highest piezoelectric constant d₃₃ of 85 pC N^?1 is achieved for x?=?0·1, with the coercive field of 18 kV cm^?1 and the dielectric maximum temperature of 148°C.     

Morphological,structural, dielectric and electrical properties of PEO–ZnO nanodielectric films

The morphological, structural, dielectric and electrical properties of aqueous solution-cast prepared poly(ethylene oxide)–zinc oxide (PEO–ZnO) nanocomposite films have been investigated as a function of ZnO nanoparticle concentrations up to 5 wt%. Scanning electron microscopy (SEM) images of these films show that the morphology of pristine PEO aggregated spherulites changes into fluffy, voluminous and highly porous with dispersion of ZnO nanoparticles into the PEO matrix. X-ray diffraction (XRD) study confirms that the crystalline phase of PEO greatly reduces at 1 wt% ZnO, and it again increases gradually with further increase of ZnO concentration. The dielectric relaxation spectroscopy (DRS) over the frequency range 20 Hz–1 MHz reveals that the real part of complex dielectric permittivity at audio frequencies decreases non-linearly whereas it remains almost constant at radio frequencies for these polymeric nanocomposites. Dispersion of nanosize ZnO particles into the PEO matrix reduces the values of dielectric permittivity which also exhibits a correlation with the dispersivity of ZnO nanoparticles. The relaxation peaks observed in the dielectric loss tangent and electric modulus spectra reveal that the electrostatic interactions of nanoscale ZnO particles with the ethylene oxide functional dipolar group of PEO monomer units decrease the local chain segmental dynamics of the polymer. Real part of ac conductivity spectra of these films have been analyzed by power law fit over the audio and radio frequency regions, respectively, and the obtained dc conductivity values for these regions differ by more than two orders of magnitude. The temperature dependent relaxation time and dc conductivity values of the nanodielectric material obey the Arrhenius relation of activation energies and confirm a correlation between dc conductivity and PEO chain segmental motion which is exactly identical to the characteristics of solid polymer electrolytes. Results imply that these nanocomposite materials can serve as low permittivity flexible nanodielectric for radio frequency microelectronic devices and also as electrical insulator for audio frequency operating conventional devices in addition to their suitability in preparation of solid polymer electrolytes.     

Influence of the substrate on the phase composition and electrical properties of 0.65PMN–0.35PT thick films

Thick films with the nominal composition 0.65Pb(Mg_1/3Nb_2/3)O₃–0.35PbTiO₃ (0.65PMN–0.35PT) were produced by screen-printing and firing paste prepared from an organic vehicle and pre-reacted powder. The films were fired for 2 h at 950 °C on alumina (Al₂O₃), platinum (Pt), aluminium nitride (AlN) and 0.65PMN–0.35PT substrates. The films were then characterized using scanning electron microscopy, X-ray diffraction and dielectric constant measurements. The X-ray analysis did not detect the presence of any undesirable pyrochlore phase, and the differences in the phase compositions were determined with a Rietveld refinement. The variations of the cell parameters vs. the temperature for the monoclinic and tetragonal phases were calculated. It was demonstrated that under similar processing conditions the microstructures, phase compositions and dielectric properties strongly depended on the stress in the thick films due to the different temperature expansion coefficients of the thick films and the substrates. The 0.65PMN–0.35PT thick films under compressive stresses (for the case of the Al₂O₃ and Pt substrates) exhibited a tetragonal phase in addition to the monoclinic one. The films were sintered to a high density and with a coarse microstructure. These microstructures favour a high dielectric constant. In contrast, for the films under a tensile stress, like the films on AlN substrates, the films were sintered to a lower density and the microstructure consisted of smaller grains. The X-ray analysis showed mainly a monoclinic phase, while the tetragonal phase was not detected. These results indicate the importance of the stresses in 0.65PMN–0.35PT thick films and their influence on the structural and electrical characteristics of the films.     

Effect of the maleic anhydride content on the structural,thermal, rheological and film properties of the n-butyl methacrylate–maleic anhydride copolymers

Various copolymers of n-butyl methacrylate (nBMA)-maleic anhydride (MA) were synthesized by free radical solution polymerization using xylene as a solvent, with monomer ratio of (nBMA/MA) 80/20, 65/35 and 50/50 wt%. The nBMA/MA copolymers were analyzed by Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance (¹H NMR), gel permeation chromatography (GPC) differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), rheology, acid value, microhardness and friction resistance. The formation of the nBMA/MA copolymers was proven by FTIR and ¹H NMR. The conversion percentage, glass transition temperature (T_g), thermal stability, hardness and the friction resistance of the nBMA/MA copolymers increased with the MA contents in the copolymers. All copolymers presented a thinning-shear rheological behavior due to the presence of entanglements. All films of the copolymers showed a good chemical resistance to HCl and NaCl solutions, but in the presence of NaOH solutions the films exhibited a blister.