MnO3 Nanopowder Research Articles

Determination of the crystalline size of hexagonal La1-xSrxMnO3 (x = 0.3) nanoparticles from X-ray diffraction - a comparative study.

The electronic, magnetic, optical and elastic properties of nanomaterials are governed partially by the crystallite size and crystal defects. Here, the crystalline size of hexagonal La1-xSrxMnO3 (x = 0.3) nanoparticles was determined using various methods. Single-phase La0.7Sr0.3MnO3 nanopowders were produced after 10 h of milling in a commercial high-energy SPEX 8000D shaker mill, and then they were heated at 700 °C and 800 °C to study the effect of calcined temperature on the crystallization of nanoparticles. The modified Scherrer, Williamson-Hall, size-strain, and Halder-Wagner methods were used to determine the crystallite sizes and the elastic properties, such as intrinsic strain, stress, and energy density, from the X-ray diffraction peak broadening analysis. The obtained results were then compared with one another. The difference in crystallite sizes calculated from the different methods was due to the different techniques.

A STRING MAGNETOMETER USING THE METHOD OF SMALL PERTURBATIONS

Subject and Purpose. The existing interest in nanosized magnetic materials requires equipment for express post-synthesis measurements of magnetic properties of these nanostructures in such a way as to exclude any mechanical displacement of the sample. Although there exist plenty of methods and devices for studying magnetic properties of materials, the development of novel schemes based on the known techniques for examining properties of magnetic nanomaterials, for example magnetic nanopowders, is a hot problem. Th e measurement equipment of the sort will detect changes in the magnetic properties of materials over time and under the infl uence of various factors, such as temperature, external magnetic fi elds, stabilizing substances. Method and Methodology. The developed setup for registering magnetic hysteresis loops is based on the method of small perturbations performed by an alternating magnetic fi eld. The devised scheme combines conventional physical principles of both hysterometers and vibrating-sample magnetometers. Results. With the aid of the developed setup, magnetic hysteresis loops of La 0.775 Sr 0.225 MnO3 nanopowder have been obtained and compared with the data provided by the well-known technique. A good agreement was observed. Th e measurement error was 10%. Conclusion. The suggested scheme can be used for the express registration of magnetic hysteresis loops of miscellaneous magnetic materials of various compositions, including nanoscale magnets.

Effect of organic additions on crystal growth behavior of La0.8Sr0.2MnO3 nanopowders prepared via sol–gel process

The effects of the addition of AcOH and ethanol on phase composition and crystal growth behavior of La0.8Sr0.2MnO3 nanopowders prepared via sol–gel process were investigated. As a result, the phase composition of final products was not affected by the addition of ethanol or AcOH in the raw solution. The activation energy for crystal growth was firstly decreased and then increased with the continuous addition of ethanol or AcOH, while it was obviously influenced by the content of AcOH. After the addition of AcOH, the activation energy for crystal growth was reduced from 26.60 kJ/mol to 23.59 kJ/mol, and then was gradually augmented to 39.75 kJ/mol with the continuous increase. Correspondingly, the crystallite size of final products was controlled to be 48.5 nm, and the lowest activation energy for crystal growth of La0.8Sr0.2MnO3 nanopowders was obtained with water as the solvent and the AcOH/Mn molar ratio of 1:2, which was beneficial to the crystallization of La0.8Sr0.2MnO3 grains.

XPS on Nd0.6-xBixSr0.4MnO3 nano powders

The structural and electronic properties on Nd0.6-xBixSr0.4MnO3 nano powders with x = 0, 0.05 and 0.1 are reported. The compounds were prepared using sol-gel combustion method. X-ray diffraction studies confirm that all samples crystallize in orthorhombic structure having Pnma space group. The powders consist of spherical particles that tend to agglomerate, with average grain sizes of about 40–50 nm. XPS measurements reveal a shift toward lower binding energies of Mn 3s, Mn 2p, Nd 3d, and O 1s core levels with increasing Bi content, which can be explained by the larger ‘c’ lattice parameter and therefore larger atomic distances. The analysis of the core level XPS spectra proves the existence of both Mn4+ and Mn3+ ions in all samples, as well as the localization of Bi3+ ions in the perovskite lattice. The XPS valence-band is dominated by extensively hybridized Nd 4f-O 2p states, with contributions from Mn 3d-O 2p bonding and Mn 3d states.

Synthesis, characterization and electrical susceptance studies of Polypyrrole/La0.7Ca0.3MnO3 Nano composites

La0.7Ca0.3MnO3 Nano powder was synthesized by Sol gel method. In-situ polymerization of Pyrrole (Py) / La0.7Ca0.3MnO3 composite was carried out in the presence of oxidizing agent ammonium per sulphate to synthesize Polypyrrole (PPy)/La0.7Ca0.3MnO3 composite. The PPy/ La0.7Ca0.3MnO3 (LCM) composites were synthesized with various compositions viz., 10, 20, 30, 40 and 50 wt. % of La0.7Ca0.3MnO3in Pyrrole. The surface morphologies of these composites were analyzed using Scanning Electron Microscopy (SEM).The images show that La0.7Ca0.3MnO3particles is embedded in PPy chain. The AC Electrical susceptance measurement of PPy/La0.7Ca0.3MnO3 was studied using impedance analyzer. The study shows that Electrical susceptance is frequency dependent and found to decrease with increase in frequency.

Structural, magnetic and magnetocaloric properties of La0.7Sr0.3MnO3 manganite oxide prepared by the ball milling method

Structural, magnetic and magnetocaloric properties of La0.7Sr0.3MnO3 sample have been investigated. Powder sample has been elaborated by the ball milling method. The Rietveld analysis of the powder X-ray diffraction shows that the sample crystallizes in the orthorhombic structure with Pnma space group. Magnetic measurements showed that the sample exhibits a ferromagnetic-to-paramagnetic transition at a Curie temperature close to 370 K. The magnetic entropy change (\( \Delta S_{M}\)) has been deduced by the Maxwell relation method. The maximum value of the magnetic entropy change \(| \Delta S_{M}^{\max} |\) is found to be 1.1 J/kgK for an applied magnetic field of 2T. At this value of magnetic field the relative cooling power (RCP) is 49 J/kg. At high temperature, large change in magnetic entropy has been observed in the sample. Our result on magnetocaloric properties suggests that La0.7Sr0.3MnO3 nanopowder is attractive as a possible refrigerant for high temperature magnetic refrigeration.

Synthesis and Characterization of Thermochromic La0.75Ca0.25MnO3 Perovskite Manganites Nano-powders by Microwave-assisted Solution Combustion Synthesis

The microwave-assisted solution combustion synthesis was developed for application with initially synthesized thermochromic perovskite manganese oxide La0.75Ca0.25MnO3 nano-powders. Dry and very fine powders were obtained after one-step combustion reaction for less than 10 min in a modified domestic microwave oven. The thermal behavior, phase formation and purity of the precursor, and as-synthesized and calcined powders, were investigated by TGA/DTA, X-ray diffraction (XRD) and FT-IR techniques. The morphology of the powder obtained was characterized using a scanning electron microscope (SEM). The XRD pattern and FT-IR results showed that as-synthesized La0.75Ca0.25MnO3 powders were crystalline, and the monophasic perovskite phase occurred with an average crystallite size of 30.46 ± 5.54 nm for 6 h at a relatively low calcination temperature of 900°C. The small particle size obtained by SEM suggested a high specific surface area and high sinterability. This method was found to be simple, rapid and cheap, and an effective way to prepare nano-size perovskite powders.

Morphology, Structural, Magnetic, and Magnetocaloric Properties of Pr0.7Ca0.3MnO3 Nanopowder Prepared by Mechanical Ball Milling Method

A sample of Pr0.7Ca0.3MnO3 nanopowder was prepared by the ball milling method. The crystal structure examined by X-ray powder diffraction indicates that the sample is single phase and crystallizes in the orthorhombic perovskite system with Pnma space group at room temperature. The average crystallite size of 29 nm was obtained by X-ray diffraction. Magnetic measurements showed that the sample exhibits a ferromagnetic-to-paramagnetic transition at a Curie temperature close to 120 K. The magnetic entropy change |ΔS M | has been deduced by the Maxwell relation method. The maximum value of the magnetic entropy change $\vert \Delta {S}_{M}^{\max} \vert$ obtained from the M(H) plot data is found to be 0.86 J/kg K for an applied magnetic field of 2 T. At this value of magnetic field the relative cooling power (RCP) is 44.05 J/kg. At low temperature, large change in magnetic entropy has been observed in the sample. Our result on magnetocaloric properties suggests that Pr0.7Ca0.3MnO3 nanopowder is attractive as a possible refrigerant for low-temperature magnetic refrigeration.

La0.7Sr0.3MnO3 nanopowders: Synthesis of different powders structures and real magnetic properties of nanomanganites

The difference in the magnetic properties between two lanthanum manganite nanopowders with identical phase and chemical composition is discussed in terms of the influence of nanopowder synthesis conditions on their properties.The aim of this investigation was to show the influence of precursor type and structure on the structure and properties of final La0.7Sr0.3MnO3 nanopowders obtained by precipitation technique. The forming of a complex structure of precursor materials during drying and inheritance at firing stage led to the formation of bimodal particle size distribution and magnetic properties typical of coarse powders. The correct choice of precursor material and the technological conditions of the drying and firing stage were allowed for the creation of a uniform powder structure with special magnetic properties.We showed that the magnetic properties of nanopowders were not always determined by chemical or phase composition and mean particle size of synthesized powders. The difference in precipitation process can lead to unpredictable and catastrophic results, and masked the effect of nanoparticles on the magnetic properties of the material.

Magnetic anisotropy of La0.7Sr0.3MnO3 nanopowders

The magnetic anisotropy of La0.7Sr0.3MnO3 nanopowders was measured as a function of temperature by the modified singular point detection technique. In this method singularities indicating the anisotropy field were determined analyzing ac susceptibility data. The observed relationship between temperature dependence of anisotropy constant and temperature dependence of magnetization was used to deduce the origin of magnetic anisotropy in the nanopowders. It was shown that magnetic anisotropy of La0.7Sr0.3MnO3 nanopowder is determined by the two-ion (dipolar or pseudodipolar) and single-ion mechanisms.

Large infrared magnetotransmission effect in composite and nano-composite based on Nd0.5Sr0.5MnO3

Large negative magnetotransmission effect Δt/t0 = (tH − t0)/t0 (where tH, t0 are the light transmissions with and without magnetic field, respectively) of up to 9% was revealed in composites contained coarse-grained and nano-powders of Nd0.5Sr0.5MnO3 in the infrared (IR) range near the Curie temperature in magnetic field H = 8 kOe. The optical density spectra and magnetotransmission effect of the composites are discussed in the context of the polar centers phase model. In the nano-powder composite, the significant magnetotransmission of ∼7% takes place in wide temperature region far below TC. This fact is explained by the existence of the localized charge carriers and spin disorder at the nano-particles surface. An applied magnetic field reduces spin disorder and the localization of charge carriers resulting in negative magnetotransmission effect. Two magnetic phase transitions and phase separation in Nd0.5Sr0.5MnO3 promote the large magnetotransmission effect in a wide temperature range. The Nd0.5Sr0.5MnO3 nano-powder composite is a promising material for magnetooptical devices with a wide working temperature range.

Thermoelectric properties of Ca0.8Dy0.2MnO3 synthesized by solution combustion process

High-quality Ca0.8Dy0.2MnO3 nano-powders were synthesized by the solution combustion process. The size of the synthesized Ca0.8Dy0.2MnO3 powders was approximately 23 nm. The green pellets were sintered at 1150-1300°C at a step size of 50°C. Sintered Ca0.8Dy0.2MnO3 bodies crystallized in the perovskite structure with an orthorhombic symmetry. The sintering temperature did not affect the Seebeck coefficient, but significantly affected the electrical conductivity. The electrical conductivity of Ca0.8Dy0.2MnO3 increased with increasing temperature, indicating a semiconducting behavior. The absolute value of the Seebeck coefficient gradually increased with an increase in temperature. The highest power factor (3.7 × 10-5 Wm-1 K-2 at 800°C) was obtained for Ca0.8Dy0.2MnO3 sintered at 1,250°C. In this study, we investigated the microstructure and thermoelectric properties of Ca0.8Dy0.2MnO3, depending on sintering temperature.

Synthesis, structural and magnetic properties of nanostructured Ca0.9Gd0.1MnO3 obtained by modified glycine nitrate procedure (MGNP)

Ca0.9Gd0.1MnO3 nanopowders with perovskite type crystal structure were synthesized by modified glycine nitrate procedure. Nanopowders were prepared by combining glycine with metal nitrates and/or metal acetates in their appropriate stoichiometric ratios. Modification of the procedure was performed by partial replacement of nitrates by acetates, in order to control the burn-up reaction. Obtained Ca0.9Gd0.1MnO3 powders were calcinated in the temperature interval from 850°C to 950°C for 10min. Properties such as phase evolution, lattice parameters, chemical composition and magnetic properties were monitored by DTA, X-ray diffraction, SEM/EDS and magnetic measurements. Magnetic measurements performed at the sample with the smallest crystallite size showed that a 10% of Gd3+ substituted Ca2+ ions changes antiferromagnetic properties of CaMnO3 by the introduction of ferromagnetic interaction due to a double exchange between Mn3+ and Mn4+ ions. Presence of competing interactions and their randomness lead to a formation of a spin glass state below Neel temperature TN=110K. From the high temperature magnetic susceptibility measurements effective magnetic moment of manganese ions is determined which lies between the values for Mn3+ and Mn4+ ions.

Thermoelectric Properties of Polycrystalline Ca0.9Yb0.1MnO3 Prepared from Nanopowder Obtained by Gas-Phase Reaction and Its Application to Thermoelectric Power Devices

Ca0.9Yb0.1MnO3 nanopowder prepared by a gas-phase reaction (GPR) consisted of well-dispersed particles with an average diameter of 47 nm. Sintering of this GPR powder proceeded rapidly and at a lower temperature than that required for a comparable powder prepared by conventional solid-state reaction (SSR). The sintered bulk material from the GPR powder (GPR-bulk) consisted of small grains with an average diameter of 620 nm; this morphology is completely different to that of the SSR-bulk in which larger grains bind together to form a network-like structure. A maximum power factor of 0.19 mW·m-1·K-2 was obtained for GPR-bulk at 973 K; this value is higher than that of SSR-bulk, mainly as a result of the lower electrical resistivity of GPR-bulk. The thermal conductivity of GPR-bulk is also lower than that of SSR-bulk, possibly because of increased phonon scattering at the grain boundary. The maximum value of the dimensionless figure of merit of 0.13 was obtained for GPR-bulk at 1073 K; this value is about 1.5-fold higher than that for SSR-bulk at 773 K. A unicouple device consisting of a p-type Ca2.7Bi0.3Co4O9 leg and an n-type Ca0.9Yb0.1MnO3 (GPR-bulk) leg was fabricated. Both oxide legs used for the measurement are 3.1–3.5 mm in both width and thickness and ∼5 mm in height. The device generated up to 0.14 W of power when the hot- and cold-side temperatures at the ends of the oxide legs were 1095 and 390 K, respectively.

Magnetic properties of La0.7Sr0.3MnO3 nanopowders

The peculiarities of the magnetization of a nanopowder (particle size 12nm) of the manganite La0.7Sr0.3MnO3 are investigated. It is shown that for temperatures below the Curie point the magnetization of the powder is of the ferromagnetic type with a relatively small value of the remanent magnetization. The minimum of the derivative of the spontaneous magnetization with respect to temperature lies 20K below the Curie temperature determined by extrapolation of the temperature dependence of the coercivity. These features of the magnetization are a consequence of a large variance of the anisotropy fields of the particles, the distribution function for which was determined from incremental hysteresis loops. It is also found that the Curie temperature of the powder has a strong variance, with an rms deviation of at least 20K. The mean value of the Curie temperature of the particles is 325K. The spontaneous magnetization of the powder particles does not have (even in the low-temperature region) a saturation region. This temperature dependence of the spontaneous magnetization influences the trend of the temperature dependence of the coercive field, leading to a deviation from the Néel–Brown law. It is also shown that for the given ensemble of particles the blocking temperature corresponds to the temperature of the maximum of the ratio of the magnetization measured after cooling in the zero-field regime to the spontaneous magnetization.