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![Crystal structure of barium aluminate. The stuffed-trydimite structure of barium aluminate at RT (space group P6 3 22, lattice constants a = b = 5.2211(1) Å, c = 8.7898(1) Å and V = 207.501(5) Å 3 ). The unit cell is depicted by solid lines. Green and blue polyhedra highlight BaO 9 and AlO 4 units, respectively, and red spheres represent O. A three-dimensional network of the corner-sharing AlO 4 tetrahedra, has tunnels along [001] direction where the relatively large, compensating Ba 2+ ions are located. The existence of such passageways might provide potential transportation of oxygen within a crystal lattice.](publication/336741439/figure/fig4/AS:817158565154817@1571837192489/Crystal-structure-of-barium-aluminate-The-stuffed-trydimite-structure-of-barium.jpg)
Crystal structure of barium aluminate. The stuffed-trydimite structure of barium aluminate at RT (space group P6 3 22, lattice constants a = b = 5.2211(1) Å, c = 8.7898(1) Å and V = 207.501(5) Å 3 ). The unit cell is depicted by solid lines. Green and blue polyhedra highlight BaO 9 and AlO 4 units, respectively, and red spheres represent O. A three-dimensional network of the corner-sharing AlO 4 tetrahedra, has tunnels along [001] direction where the relatively large, compensating Ba 2+ ions are located. The existence of such passageways might provide potential transportation of oxygen within a crystal lattice.
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Inorganic materials that enable a link between the storage and release of molecular oxygen offer a fertile ground in continuous quest for the applications that can potentially reduce energy consumption and thus minimize adverse effects on the environment. Herein, we address reversible intake/release of an oxygen within the BaAl2O4 material as evide...
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... that the mechanism of reversible process of the oxygen storage and release as demonstrated by unexpected and unusual magnetic behaviour, might be related to some specific structural features of stuffed trydimite-like structure. Structural determination from the XRPD data showed that the BaAl 2 O 4 lattice contains tunnels along the c-direction (Fig. 7) which allow uptake and storage of ...
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... Figure 3 depicts the XPS spectra of O 1 s, Sr 3d, Al 2p and Dy 3d core levels of the SAO from the photoelectron signals. The photoelectron signal from O 1 s observed at 531.5 eV is attributed to the formation of metal oxides [37]. Binding energy at 74.1 eV represented as Al 2p state present in the phosphor and two peaks present at ∼133.6 eV and ∼135.3 eV confirm the presence of Sr 3d, which is well-matched with the reported data [38]. ...
... Al 2p spectrum consists of peak at ∼ 74 eV (2P 1/2 ), which affirms the presence of Al-O. Photoelectron signal from O 1 s, observed at 530 eV and 531 eV can be attributed to the formation of metal oxides and metal carbonates [37]. Ce 3d composed of two multiplets to spin-orbit split 3d 5/2 and 3d 5/2 , respectively. ...
Rare earth (Dy³⁺, Ce³⁺) ions doped aluminates, specifically SrAl2O4 (SAO) and BaAl2O4 (BAO), were successfully synthesized by using the solid-state reaction route. Structural and morphological analysis of the synthesized phosphors was carried out using X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). Surface composition analysis was performed using X-ray photoelectron spectroscopy (XPS). Electrochemical behavior for energy applications was primarily assessed through cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) studies. Emission colors of the phosphors were confirmed through photoluminescence studies, and their corresponding CIE coordinates were plotted. The most prominent photoluminescence (PL) emission band observed at 472 nm for Dy³⁺ doped SAO was attributed to the ⁴F9/2–⁶H15/2 transition in the blue region under excitation at a wavelength of 347 nm. The PL emission band at 589 nm for Ce³⁺ doped BAO was assigned to the 5D excited level corresponding to the ²F5/2 transition in the yellow region under an excitation wavelength of 318 nm. Thermoluminescence studies on the samples confirmed that 0.3 M% Dy³⁺ doped SAO could function as a dosimeter (offline radiation detector) for measuring high dose rates in industrial settings. The electrochemical results affirmed the suitability of the as synthesized phosphors for electrochemical energy applications.
... In addition, a sharp rise in M-T is also observed below 20 K, which can be attributed to the large paramagnetic (PM) contribution from rare-earth Gd. The small change in magnetization (S-15 and S-40) around 55 K has extrinsic origin (oxygen peak) [39]. The FC-ZFC splitting in M-T curves of S-60 below T c indicates the presence of magnetocrystalline anisotropy. ...
The magnetism and magnetocaloric effect in double perovskites is an alluring area of research due to its tunable nature. In particular, the exchange interactions and local ordering of magnetic sublattices are sensitive to the chemical substitution, synthesis/growth conditions, and strain. Here we study the effect of strain on magnetism in Gd2NiMnO6 double perovskite thin films grown using pulsed laser deposition on SrTiO3 (001) substrate. Magnetostructural study finds tensile strain to be the origin of perpendicular magnetic anisotropy in Gd2NiMnO6. Further, the anisotropic nature prevails in magnetocaloric effect as well. Magnetic entropy change along the in-plane direction is observed to be 21.82 J Kg−1K−1, which reduces to 9.84 J Kg−1K−1 along the out-of-plane direction. Our theoretical calculation reveals a ferrimagnetic ground state of Gd2NiMnO6. The relative spin orientation of Ni and Mn changes from parallel configuration for strained Gd2NiMnO6 to antiparallel configuration for strain-relaxed Gd2NiMnO6.
... However, the most interesting is rare-earth-doped BaGa 2 O 4 ceramics. Most investigations of such material are limited to X-ray diffraction (XRD), optical studies, etc. [15][16][17][18][19][20][21][22][23][24] Nevertheless, doping of such ceramics not only leads to modification of their luminescent properties and changes in phase composition, but also causes structural transformation. [25][26][27] Such significant transformation of the inner structure in ceramics facilitates the formation of additional defect-related free volumes. ...
The BaGa2O4 ceramics doped with Eu3+ ions (1,3 and 4 mol%) were obtained by solid‐phase sintering. The evolution of defect‐related extended free volumes in the BaGa2O4 ceramics due to the increase of the content of Eu3+ ions has been studied using positron annihilation lifetime spectroscopy technique. It is established that the increase in the number of Eu3+ ions in the basic BaGa2O4 matrix leads to the agglomeration of free‐volume defects with their subsequent fragmentation. The presence of Eu3+ ions result in the expansion of nanosized pores and increase in their number with their future fragmentation. This article is protected by copyright. All rights reserved.
... However, the most interesting are rare-earth-doped BaGa 2 O 4 ceramics. Most investigations of such material are limited to X-ray diffraction (XRD), optical studies, etc. [15][16][17][18][19]. Nevertheless, the doping of such ceramics not only leads to the modification of their luminescent properties and changes in phase composition, but also causes structural transformation [20,21]. ...
BaGa2O4 ceramics doped with Eu3+ ions (1, 3 and 4 mol.%) were obtained by solid-phase sintering. The phase composition and microstructural features of ceramics were investigated using X-ray diffraction and scanning electron microscopy in comparison with energy-dispersive methods. Here, it is shown that undoped and Eu3+-doped BaGa2O4 ceramics are characterized by a developed structure of grains, grain boundaries and pores. Additional phases are mainly localized near grain boundaries creating additional defects. The evolution of defect-related extended free volumes in BaGa2O4 ceramics due to the increase in the content of Eu3+ ions was studied using the positron annihilation lifetime spectroscopy technique. It is established that the increase in the number of Eu3+ ions in the basic BaGa2O4 matrix leads to the agglomeration of free-volume defects with their subsequent fragmentation. The presence of Eu3+ ions results in the expansion of nanosized pores and an increase in their number with their future fragmentation.
... 7,8 Our earlier study extended the field of BaAl 2 O 4 applications to the oxygen-driven storage capacity of this material, initiated by the unique antiferromagnetic transition in crystalline oxygen. 9 The BaAl 2 O 4 crystallizes in a hexagonal assembly at room temperature (RT), within P6 3 (space group (s.g.) no. 173 with lattice constants a = 10.449(1) ...
... no. 182 with lattice constants a = 5.2211(1) Å and c = 8.7898(1) Å) 9 symmetries, depending on the subtle preparation conditions. The hexagonal packing described by the space group P6 3 construes two different barium sites, Ba1 and Ba2, positioned on two inequivalent crystallographic sites 2a and 6c, respectively, and coordinated by nine oxygen ions with average Ba−O distances of 2.85 Å for the Ba1 site and 2.95 Å for the Ba2 site. ...
... A selection of refined metal−oxygen distances along with the values of Al1−O5−Al2 and Al3−O6−Al4 angles in the structure of samples S1 and S2 is listed in Table 3. The substitution of Al 3+ cations by Co 3+ at Al3 sites led to an increase of the average tetrahedral bond lengths from 1.72 (8) in sample S0 to 1.74 (9) in sample S2. Cobalt substitution simultaneously induced a slight decrease in average tetrahedral symmetries around Al1 sites from 1.77 (8) in sample S0 to 1.76 (7) in sample S2. ...
Undoped and Fe-doped NiO nanoparticles were successfully synthesized using a lyophilization method and systematically characterized through magnetization techniques over a wide temperature range, with varying intensity and frequency of the applied magnetic fields. The Ni 1-x Fe x O nanoparticles can be described by a core-shell model, which reveals that Fe doping enhances exchange interactions in correlation with nanoparticle size reduction. The nanoparticles exhibit a superparamagnetic blocking transition, primarily attributed to their cores, at temperatures ranging from above room temperature to low temperatures, depending on the Fe-doping level and sample synthesis temperature. The nanoparticle shells also exhibit a transition at low temperatures, in this case to a cluster-glass-like state, caused by the dipolar magnetic interactions between the net magnetic moments of the clusters. Their freezing temperature shifts to higher temperatures as the Fe-doping level increases. The existence of an exchange bias interaction was observed, thus validating the core-shell model proposed.
Ce³⁺/Li⁺-activated barium aluminate phosphor (BAO) was synthesized by conventional solid-state reaction method. The crystal structure of the synthesized phosphor was analyzed by X-ray diffraction (XRD) and Raman spectroscopy analysis. Fourier transformed infrared spectrum results revealed the characteristic vibration bands present in the synthesized phosphor. Surface composition analysis of the prepared samples was examined using X-ray photoelectron spectroscopy (XPS). Photoluminescence emission band observed at 589 nm was assigned to 5D excited level corresponding to ²F5/2 transition in yellow region under the excitation wavelength of 320 nm. Yellow light emission was confirmed by the Commission Internationale de L’Eclairage (CIE) chromatic coordinate graph. The synthesized phosphors BAO: 0.5Ce³⁺, BAO: 0.5Ce³⁺, 0.1Li⁺ displayed a color purity and lifetime decay of 78.4%, 81.3% and 4.333 ns, 4.738 ns, respectively.
The thin films of Ga doped hematite (α-Fe2O3) were grown on p-Si <111> substrate using Pulsed Laser Deposition technique. The as-grown films indicated crystalline peaks of rhombohedral structure. The films exhibited enhancement of ferromagnetic properties. The reduction of dimensionality of the materials in thin films (2D) has shown unusual magnetic spin order and exchange bias effect at temperatures < 70 K. The ferromagnetic parameters (magnetization, coercivity) showed dependence on composition, deposition conditions and heat treatment of the films. The as-grown films showed a good signature of ferroelectric polarization. The as-grown films of Fe1.8Ga0.2O3, having relatively large surface roughness, exhibited smaller magnetic moment in comparison to as-grown films of Fe1.6Ga0.4O3 with small surface roughness. The X-ray photoelectron spectroscopy measurements confirmed a chemically homogeneous state of high spin Fe³⁺ ions in as-grown films of Fe1.6Ga0.4O3 composition, whereas chemical state of Fe ions is consisting of the mixture of high spin Fe³⁺ and Fe²⁺ states in as-grown films of Fe1.6Ga0.4O3.
Magnetodielectric (MD) properties of as-prepared (AP) and air-annealed Bi1−xCaxFe1−yTiyO3−δ nanoparticle ceramics made by spark plasma sintering process are investigated as a function of temperature. Aliovalent Ca2+ substitution at Bi3+ site creates oxygen vacancies (VO) in the lattice disrupting the intrinsic spin cycloid of BiFeO3, which are suppressed when the charge compensating Ti4+ is co-substituted. In addition, cation substitution reduces the grain size and increases surface oxygen vacancies. These lattice and surface VO defects play a significant role in enhancing the magnetic properties. Zero-field-cooled magnetization curves of all AP samples show a sharp Verwey-like transition at ∼120 K, which weakens on air-annealing. A coexistence of positive and negative MD [MD = Δɛ(H)ɛ(H=0); Δɛ(H)=ɛ(H)−ɛ(H=0)] response is observed, with the former dominating at 300 K and the latter at 10 K. As-prepared 5 at.% (10 at.%) Ca and Ca-Ti substituted BiFeO3 ceramics exhibit a maximum MD response of –10% (∼+3%) at 10 K (300 K). Negative MD response diminishes for air-annealed Bi1−xCaxFe1−yTiyO3−δ ceramics due to the reduction in VO concentration. Samples exhibiting dominant positive MD response show a similar trend for MD vs H and M2 vs H plots. This agreement between M2 and Δɛ(H) demonstrates a strong inherent MD coupling. On the contrary, negative MD does not follow this trend yet shows a linear relationship of MD vs M2, suggesting a strong coupling between the magnetic and dielectric properties. Temperature-dependent MD studies carried out at 5 T show a gradual change from negative to positive values. Negative MD at low temperatures could be activated by the spin-lattice coupling, which dominates even at high frequency (1 MHz) under the applied field. Other contributions, including Verwey-like transition, magnetoresistance, and Maxwell-Wagner effects, do not influence the observed MD response. A prominent role of oxygen vacancies in altering the MD behavior of BiFeO3 is discussed in detail.
