Mechanochemical synthesis of bismuth ferrite

A powder mixture of Bi2O3 and Fe2O3 was mechanically treated in a planetary ball mill in an air from 30 to 720 minutes. It was shown that the mechanochemical formation of BiFeO3 (BFO) phase was initiated after 60 min and its amount increased gradually with increasing milling time. A detailed XRPD structural analysis is realized by Rietveld’s structure refinement method. The resulting lattice parameters, relative phase abundances, crystallite sizes and crystal lattice microstrains were determined as a function of milling time. Microstructural analysis showed a little difference in morphology of obtained powders. The primary particles, irregular in shape and smaller than 400 nm are observed clearly, although they have assembled together to form agglomerates with varying size and morphology. Dense BFO ceramics were prepared by conventional solid-state reaction at the temperature of 810ºC for 1h followed immediately by quenching process. [Projekat Ministarstva nauke Republike Srbije, br. III45007: Zero- to Three-Dimensional Nanostructures for Application in Electronics and Renewable Energy Sources: Synthesis, Characterization and Processin

Mechanochemical Synthesis of Nanocrystalline Multiferroics Based on Bismuth Manganite

Multiferroic materials simultaneously possess two or more ferroic orders, and enable a coupling interaction between them. Multiferroic bismuth manganite is known as a material that exhibits both ferromagnetic and ferroelectric properties making it interesting for various technological applications. Unfortunately, preparation of BiMnO3 is not possible by conventional solid state reaction and BiMnO3 has been synthesized from the mixture of oxides only at high pressures (>40 kbar). The aim of this work was to synthesize BiMnO3 (BMO) without additional heating or application of high pressures. Nanocrystalline single-phased BMnO3 was prepared for the first time by mechanochemical synthesis directly from the highly activated constituent oxides, Bi2O3 and Mn2O3, in a planetary ball mill. The obtained materials were characterized by X-ray diffraction, SEM with EDS analysis, HRTEM and magnetization measurements. All the samples were found to be tetragonal perovskite with P4mm crystallographic group. The broad maxima reflections of BMO samples can be ascribed to an amorphous/disordered phase. HRTEM micrographs give clear evidence of core-shell structure with amorphous shell around the nanocrystalline BMO particles. The magnetic hysteresis behavior is similar to that of a soft ferromagnet. The magnetic properties of the obtained BMO powders were found to change as a function of milling time in a manner consistent with the variation in the nanocomposite microstructure

Mechanochemical synthesis of multiferroic yttrium manganite

Multiferroic yttrium manganite (YMnO3) is known as a material that exhibits both ferromagnetic and ferroelectric properties making it interesting for various technological applications. In this work single-phased YMnO3 was prepared for the first time by mechanochemical synthesis in a planetary ball mill. The YMnO3 can be formed directly from the highly activated constituent oxides, Y2O3 and Mn2O3, after 60 min of milling time and subsequently grows during prolonged milling. The cumulative energy introduced into the system during milling for 60 min was 86 kJ/g. X-ray analysis indicates that the as-prepared samples crystallize majority with hexagonal (P63cm) and minorly with orthorhombic (Pnma) YMnO3 structure. The morphology, structure and chemical composition of the powder were investigated by SEM with EDS and TEM. The magnetic properties of the obtained YMnO3 powders were found to change as a function of milling time in a manner consistent with the variation in the nanocomposite microstructure

Nanostructured Fe2O3/TiO2 thick films prepared by screen printing

Nanostructured single layered (pure TiO2 , pure α-Fe2O3 and mixed Fe2O3 /TiO2 with two different oxide ratios, 2 : 3 and 3 : 2) and double layered (TiO2 layer over a Fe2O3 layer) thick films have been fabricated by screen printing technology on a glass substrate. The pastes used for film preparation were obtained by adding an organic vehicle to the oxide powders together with a small percentage of binding glass frit. Samples were dried up to 100 °C and sintered at 650 °C/60 minutes. Structural, morphological and optical studies have been carried out using XRD, SEM analyses and UV/Vis spectroscopy. The prepared pure and mixed Fe2O3 /TiO2 thick films had a homogenous nanostructure without secondary phases. Indirect band gaps were determined from the measured transmission spectra and the obtained values are in the range of literature data. [Projekat Ministarstva nauke Republike Srbije, br. III45007

Mesoporous TiO2 spheres as a photoanodic material in dye-sensitized solar cells

Mesoporous TiO2 films with spherical architectures and promising performance in dye-sensitized solar cells (DSSCs) were prepared. The morphology of the films was investigated by scanning electron microscopy. Transmission electron microscopy analysis of the spheres disclosed the elongated shape of sub-20 nm primary particles, while BET analysis revealed their high surface area of 135 m2/g. Anatase presence was observed in the films based on X-ray diffractometry, selected-area electron diffraction analysis and Raman spectroscopy analyses. Increased light scattering of the spheres in visible region was observed by UV-VIS-NIR spectroscopy. Photovoltaic performance of the operating N719-sensitized cells was tested using electrochemical impedance spectroscopy and current density-voltage (J-V) curves under simulated AM1.5 spectrum. The 0.25 cm2 cells exhibited photo-to-electric power efficiency of 4.9%, which is among noteworthy values for DSSCs with similar photoanodic structures

The effect of gadolinium substitution on the structural, ferroelectric and magnetic properties of bismuth ferrite ceramics

Bi1-xGdxFeO3 (x = 0.01; 0.05; 0.075; 0.09; 0.10; 0.20; 0.30) powders were synthesized by hydro-evaporation method. The optimization of sintering conditions indicated that temperature of 870 °C and time of 6 hours (after pressing at 9 t/cm2) provided the densest ceramics samples (up to 88 % of theoretical density) and the lowest amount of secondary phases ( 5.5 wt%). The increase of gadolinium content resulted in polar-to-nonpolar (R3c Pnma) structural phase transition at about x = 0.10, which was reflected on deterioration of ferroelectric property. Structural analysis indicated decrease of unit cell volume with the increase of x, but the (Bi,Gd)–Fe distance did not exhibit regularity in change. The bismuth ferrite ceramics samples doped with x = 0.075 and x = 0.09 of gadolinium showed the greatest lattice distortion along the [111] axis. These samples also exhibited larger values of remnant electric polarization and less leakage processes than the pure bismuth ferrite ceramics samples. Magnetic behavior of Bi1-xGdxFeO3 samples revealed that the weak ferromagnetic moment strengthened with increase of the gadolinium content

Quantum sensors for gas mixture detection

Numerous methods have been utilized for molecular detection, including optical, calorimetric, acoustic, and techniques based on changes in electrical properties, such as metal oxide semiconductor sensors [1,2]. Recent research endeavors have led to a significant rise in sensitivity, detecting parts per billion (ppb) [3], but the challenges of selectivity and cross-sensing remain crucial areas of investigation. Developing a gas sensor with high selectivity to efficiently analyze multi-gas mixtures would be of great significance, with potential applications in various fields such as technology, environmental control, biology, and medicine. Quantum sensors are a promising new technology for the detection of gas mixtures. They offer a number of advantages over traditional methods, including high sensitivity, selectivity, and response time. In the presentation, we propose a new method based on the resonant interaction of dipole molecules with ac fields, in the presence of a dc electric and magnetic field that creates Zeeman and Stark splitting of molecular levels specific to certain molecules, ensuring selectivity [4]. In this talk, we present some preliminary experimental results obtained for the molecule NO on the use of quantum sensors for the detection of gas mixtures. Our results demonstrate the potential of quantum sensors for a variety of applications in gas sensing. We believe that quantum sensors have the potential to revolutionize the field of gas sensing. 1. X. Liu, et al. Sensors (Basel), 12 (2012) 9635–9665. 2. S. Lakkis, R. Younes, Y. Alayli, M. Sawan, Sensor Review, 34 (2014) 24–35. 3. J.-H. Lee, J.-Y. Kim, J.-H. Kim, S. S. Kim, Sensors (Basel), 19 (2019) 726. 4. Z. Branković, Y. Rostovtsev, Sci. Rep., 10 (2020) 1537

Nanostructured Fe2O3/TiO2 thick films

Thick films of nanostructured pure TiO2, -Fe2O3, Fe2O3/TiO2 (ratio 2:3 and 3:2) and a hetero-junction in the form of a TiO2 layer over a Fe2O3 layer have been fabricated by screen printing technology on a glass substrate. The pastes used for film preparation were obtained by adding an organic vehicle to the oxide powders together with a small percentage of binding glass frit. Samples were dried up to 100oC and sintered at 650oC/60 minutes. Structural, morphological and optical studies have been carried out using XRD, SEM, EDS analysis and UV/Vis spectroscopy. Fe2O3/TiO2 thick films had a homogenous nanostructure and no new compounds were formed. Indirect band gaps were determined from the measured transmission spectra

Spectroscopic study of spinel ZnCr2O4 obtained from mechanically activated ZnO-Cr2O3 mixtures

A mixture of starting ZnO and Cr2O3 powders in equimolar quantities was mechanically activated by grinding using a high energy vibro-mil I for 0, 40 and 80 min. The spinet ZnCr2O4 was prepared from activated mixtures by a conventional solid-state reaction at the temperature of 900 degrees C during 240 min. Raman scattering (RS) and Far-infrared (IR) spectroscopy were applied to study the local structure of zinc chromium oxide spinels. We report on an analysis of the vibrational spectra of the spinet ZnCr2O4 structure using both the classical factor-group theory (O-h(7) spectroscopic symmetry) and a local environmental model. The structural modifications were studied on the basis of vibrations of ZnO4 tetrahedral and CrO6 octahedral units building the crystal lattice. The RS and IR line intensities and positions remained in good agreement with the Fd3m space group. The broadness of IR and Raman bands and the fact that more vibration modes than expected were observed, may be attributed to certain disorder in the crystal symmetry of cubic spinet ZnCr2O4. Formation of the defect spinel structure can be assigned to mechanical activation of the starting oxide mixture

Ultra-high breakdown field varistors prepared from individually synthesized nanoprecursors

Previously synthesized nanocrystalline ZnO doped with cobalt and manganese, Bi2O3 and Sb2O3 were the precursors for high voltage varistors preparation. Varistor ceramics were sintered at 750 degrees C, 770 degrees C or 900 degrees C for 1 h. An amount of 30 mass% of secondary phases and sintering temperature of 770 degrees C were found to be optimal for obtaining varistor with prominent properties. Achieved density was 97% of the theoretical value. Post-sintering phase composition included ZnO, gamma-Bi2O3 and pyrochlore-type with Zn2Bi3Sb3O14 nominal formula. Fine grained microstructure was accompanied with good phase distribution and excellent electrical characteristics: extraordinary high breakdown field of 3200 V mm(-1), high nonlinearity coefficients of 71 and 51 in 0.1-1 and 1-10 mA cm(-2) current density ranges, respectively, and low leakage current of 7.7 mu A cm(-2)