xFexO3 System Research Articles

Sustainable inorganic pigments with high near-infra-red reflectance based on Fe3+ doped YAlO3 for high temperature applications

Non-toxic inorganic pigments based on the Fe(III)-doped YAlO3 with high near-infra-red (NIR) reflectance were synthesized by a modified Pechini method at 1200 °C. A complete solid solution in the YAl1−xFexO3 system (0 ≤x ≤ 1) was prepared, yielding a wide range of colourations from yellow to red, depending on the iron content.Good pigment stability was achieved in a commercial high temperature glaze, used in the ceramic industry to colour glazes on tiles. The pieces coated with the pigmented glazes reached NIR solar reflectance values between 43% and 32%. The temperature protection studies carried out with the glazes pigmented with YAl0.75Fe0.25O3 and YFeO3 compositions, conclude that the pigmented samples reduce the temperature of a building by 5 °C and 4 °C, respectively, in comparison to the unpigmented glaze.Thus, these pigments can be excellent candidates for used in high-temperature applications such as colouring ceramic high temperatures glazes, as well as cool pigments in walls or roofs of buildings.

Effect of trivalent transition metal ion substitution in multifunctional properties of Dy2O3 system

The present work describes the systematic study on inducing multiferroic properties in non-magnetic Dy2O3 system. The ceramic compounds of Dy2−xFexO3 (where x = 0.1–1.5) have been prepared by solid state reaction method. The powder X-ray diffraction patterns of all the prepared compounds reveal the strong influence of transition metal ion (Fe) in the Dy2O3 crystal structure. By Rietveld analysis, it is determined that with respect to increasing concentration of Fe3+ ion at Dy3+ site leads to transformation of crystal structure from Cubic to Orthorhombic with varying concentration of DyFeO3 phase and further increase in Fe3+ concentration leads to the formation of Garnet phase in Dy2−xFexO3 compounds. The scanning electron microscopic images of the samples confirm the change in surface morphology with increasing grain boundaries and porosity due to the substitution of Fe in Dy2O3 system which may effects on the electrical transport properties of the materials and increasing concentration of Fe in Dy2O3 system is also analyzed by energy dispersive analysis spectra. By Raman spectral analysis, it is identified that the strong absorption band of Cubic Dy2O3 compound at 373 cm−1 is gradually shifted to 257 cm−1 which indicates the molecular stretching motion of RE–O bond in REO6 octahedra and the large deviation in position of intense Raman bands below 300 cm−1 confirms the incorporation of Fe3+ ion in the host Dy2O3 lattice and imparting large polarizability in the prepared compounds due to translational motions of ReO6 octahedrons by variation in bond length and reduced mass of the bonding atoms. Diffused reflectance spectroscopy analysis implies the semiconducting nature of all the prepared compounds. It is also identified that the energy gap values goes on decreasing till DyFeO3 and then starts increasing due to change in crystal structure by cubic to orthorhombic and then orthorhombic to garnet phase. From the magnetization studies, it is found that till even substitution of Fe (i.e. x = 0.1–0.9) in Dy2−xFexO3 system, the compounds exhibits paramagnetic nature whereas from x = 1.0 i.e. DyFeO3, the samples exhibits ferromagnetic nature. The variation of magnetization behaviour from paramagnetic to ferromagnetic in higher concentration of Fe explicit the feasibility of attaining ferroic behaviour in Garnet mixed phase ceramic compounds. The electric polarization analysis reveal that while substituting Fe3+ ion in Dy3+ site by more than 50% of molecular ratio, the compounds exhibits non-zero remanance and coercivity values with respect to applied d.c. electric field and evident peculiar ferroelectric characteristic of those compounds. The maximum saturation polarization achieved in Dy0.6Fe1.4O3 compound is 0.2 µC/cm2 and found comparable with the results observed from Bismuth Ferrite related compounds.

Synthesis and characterization of pigments of the LaAl1−xFexO3 system – Application in ceramic and polymer

Pigments from the LaAl1−xFexO3 (x = 0.00 to 1.00) system were synthesized through the citrate method and thermally treated at 910 °C for 4 h. The samples obtained were characterized through X-ray diffraction (XRD), Mössbauer spectroscopy (MS), field effect scanning electronic microscopy (FE-SEM), energy dispersive spectroscopy (EDS) and diffuse reflectance spectroscopy in the UV–Visible (DRS UV–Vis). The XRD analysis revealed the formation of perovskite as a single phase, crystallizing in the rhombohedral crystalline system with values 0.00 ≤ x ≤ 0.80, and in the orthorhombic system with x > 0.80 value. Through the Mössbauer spectroscopy, it was possible to follow the phase transformation and determine at which iron concentrations the coexistence of the perovskite rhombohedral and orthorhombic phases occurred. The electronic microscopy enabled to identify that the pigments presented particles of ideal size to be applied as ceramic pigments. Regarding coloration, the increase in Fe3+ concentration in the LaAl1−xFexO3 system provoked lattice distortions, altering the pigment band gap values and consequently their color. The pigments obtained presented coloration varying from white (LA), greenish-yellow (LAF1 to LAF5) and orange (LAF6 to LF). The pigments were applied to the enameling of ceramic pieces at 850 °C, decorative burning temperature and presented good color and opacity. Thus, the system under study presented suitable properties to be used as pigment to ceramic and polymer, in addition to presenting low toxicity, a fundamental characteristic in the current scenery of environmental and human health concerns.

Magnetocaloric effect in the Fe-doped La0.67Ba0.33Mn1−x Fe x O3 system

The magnetocaloric effect and the magnetization behavior have been studied in the perovskite-type oxides of La0.67Ba0.33Mn1−xFexO3 (x = 0, 0.03, 0.04 and 0.05). Samples were synthesized by using the conventional solid-state reaction method. The Curie temperature (TC) and the magnetic entropy change were determined and compared to those of other perovskite-type ferromagnetic manganese-oxide systems. The Curie temperature decreased from 350 K to 290 K with increasing Fe concentration x. A relatively large magnetocaloric effect compared with other oxides, with a broad peak around the Curie temperature, is observed in the La0.67Ba0.33Mn1−xFexO3 system. In addition, the Curie temperature varies easily with the Fe around room temperature. These Fedoped manganese oxides are possible candidate materials for use in magnetic refrigeration at room temperature.

Multiple temperature-induced magnetization reversals in SmCr1−xFexO3 system

The structural and magnetic properties of the SmCr1−xFexO3 (0≤x≤0.5) system have been investigated. Multiple temperature-induced magnetization reversals were observed in x=0.1. The high-temperature magnetization reversal is due to the special spin structure, in which the net canted moment of the Cr-rich regions and the net moment of the Fe–Cr ordered regions orient in opposite direction; while the low temperature one can be ascribed to the spin reorientation. The sample with x=0.5 exhibits the highest compensation temperature. Coexistence of normal and inverse magnetocaloric effects was observed in all doped samples. Potential applications in magnetic refrigeration based constant temperature bath near room temperature (∼286K) have been demonstrated.

Dielectric relaxation in the DyMn1−xFexO3 system

The dielectric constant and loss of perovskite DyMn1−xFexO3 samples show strong dispersion in various frequencies, which is indicative of relaxation. The activation energies were obtained through Arrhenius law fitting and range from 0.213 eV to 0.385 eV. The Fe content dependence of the characteristic frequency f0 and the activation energy Eα shows two transitions that are well consistent with the change in orbital ordering. Meanwhile, different magnetic orderings could affect the relaxation and induce the change in Eα.

Continuously tunable magnetic phase transitions in the DyMn1−xFexO3 system

The structure and magnetic properties of perovskite DyMn1−xFexO3 samples have been studied. Static orbital orderings are expected to exist in samples with x ≤ 0.2 due to strong Jahn-Teller distortion, which become less stable as x increases and probably disappears in samples with x > 0.5. The antiferromagnetic transition temperature increases as x increases. At the composition x > 0.5, spin reorientation starts to appear. Meanwhile, the spin reorientation temperature and the antiferromagnetic Néel temperature gradually separate and widen the temperature range of the magnetic metastable state between these two transitions. The magnetic competition is discussed based on exchange interaction and Dzyaloshinsky-Moriya interaction.

Electrical and magnetic properties ofLa0.35Sr0.65Ti1−xFexO3 thin films

We report that the La0.35Sr0.65Ti1−xFexO3 system forms a solid solution within the composition range0≤x≤0.5 and a room temperature magnetic semiconductor phase exists atx = 0.20. This system shows an anomalous Hall effect and is ferromagnetic with a large moment perFe ion. The results show that the strong La doping provides sufficient carriers to the systemto maintain carrier-mediated ferromagnetism for low Fe doping. Furthermore, thepresence of ferromagnetism within this phase space raises the possibility thatthe conduction, and hence the magnetism, could be electronically controlled.

Positive magnetoresistance effect in rare earth cobaltites

The structure, magnetic, and magnetotransport properties of the Pr0.5Sr0.5Co1 − x Fe x O3 system have been studied. The ferromagnet-spin glass (x = 0.5)-G-type antiferromagnet (x = 0.7) transitions and the metal—insulator transitions (x = 0.25) have been revealed. It has been established that the magnetoresistance of the metallic ferromagnetic cobaltites changes sign from positive to negative as the external magnetic field increases. The positive component increases and the negative component decreases with decreasing temperature. The negative magnetoresistance increases sharply in the insulating spinglass phase. Possible causes of the low-magnetic-field positive magnetoresistance in the rare earth metallic cobaltites are discussed.

Transport Properties in La0.67Sr0.33Co1−xFexO3 System

Abstract In this paper the influence of Fe doping at Co-site on the electrical transport properties and the colossal magnetoresistance of La 0.67 Sr 0.33 Co 1− x Fe x O 3 is studied. The experimental results indicate that the electrical resistivity exhibits in low-doped ( x ≤0.10) samples while semiconducting behavior exhibits in high-doped ( x =0.20, 0.30) samples. In addition, Fe doping weakens the MR peak near T c but enhances the low-temperature MR . The origin of CMR in La 0.67 Sr 0.33 Co 1− x Fe x O 3 system is interpreted in terms of the spin-state transition induced by applied magnetic field.

Magnetic properties of CaRu1−xFexO3

The occurrence of ferromagnetism was studied in the CaRu1−xFexO3 system by means of magnetic Compton scattering, Mössbauer effect, and magnetization measurements using polycrystalline specimens. Ferromagnetism is induced for extremely small Fe doping (x⩾0.02) to paramagnetic CaRuO3, and the TC increases as the Fe content increases. The temperature dependence of reciprocal magnetic susceptibility shows a characteristic of ferrimagnetism. A sextet with an isomer shift of the Fe3+ ion and the hyperfine field of about 450kOe were observed in the Mössbauer effect measurement below TC, suggesting the existence of magnetic order. The magnetic Compton scattering experiment revealed the occurrence of a large magnetic moment on Ru and an antiferromagnetic coupling between Fe and Ru spin moments. A possible model for the occurrence of ferrimagnetism has been proposed.

Crystal structure and magnetic ordering of theLaCo1−xFexO3 system

The LaCo1−xFexO3 compounds have been investigated by means of neutron powder diffraction(NPD), x-ray powder diffraction (XPD) and magnetization measurements.The NPD and XPD patterns were successfully refined as rhombohedral(x≤0.5) andorthorhombic (x≥0.6). The temperature-induced transition from the rhombohedral phase into theorthorhombic one is characterized by a two-phase crystal structure state.Magnetization and neutron powder measurements have revealed that compounds withx<0.4 exhibit a paramagnetic-like behaviour, whereas forx≥0.4 samplesa weak ferromagnetic component was observed. The NPD patterns were successfully refined by admittinga Gz spatial orientation of the antiferromagnetic vector. The magnetic properties of theLaCo1−xFexO3 samples can be explained assuming a low spin state of theCo3+ ions, whereas antiferromagnetism is caused by magnetic interactions between theFe3+ ions. Based on the obtained data the combined crystal and magnetic phase diagram hasbeen constructed.

Effect of Zn substitution on para- to ferromagnetic transition temperature in La0.67Ca0.33Mn1−xZnxO3 colossal magnetoresistance materials

Structural, magnetic, and thermal measurements are carried out on the La0.67Ca0.33Mn1−xZnxO3 system with x=0.0–0.50. The structural characterization of the samples is done by Rietveld analysis of their neutron diffraction patterns. Zn substitutes at Mn site isostructurally until x=0.30. Oxygen content remains nearly invariant with x. Magnetic and thermal measurements as well as the electrical resistance show a para- to-ferromagnetic transition at Tp, which decreases with an increase of x. For low Zn concentration (until x=0.075) the decrease dTp/dx is smaller than for the larger concentrations of Zn. Relative decrease dTp/dx at higher concentrations (x&amp;gt;0.10) is similar to that observed earlier for the La0.67Ca0.33Mn1−xFexO3 system. For the transition at Tp, the related change of magnetic entropy (ΔStrs) are calculated from the heat capacity data and indicate that for x=0 the expected value ΔStrs=12.8 J/mol K is recovered.