The structure, hyperfine interactions and magnetic properties of the series of multiferroic Bim+1Ti3Fem−3O3m+3 Aurivillius compounds with m=4–8 were studied using X-ray diffraction, 57Fe Mössbauer ...spectroscopy and vibrating sample magnetometry. Samples were prepared by the conventional solid-state sintering method. Bulk magnetic measurements showed that for m=4 the compound is paramagnetic down to 2K while in the compound with m=5 the antiferromagnetic type transition was observed at 11K. In the case of compounds with m=6–8 much more complex magnetic behavior was found. For these compounds a gradual spin freezing and antiferromagnetic spin glass-like ordering were observed on decreasing temperature. The temperature of spin glass freezing was determined as 260, 280 and 350K for m=6, 7 and 8, respectively. Room-temperature Mössbauer spectra of all the compounds studied confirm their paramagnetic state. However, liquid nitrogen and liquid helium temperature measurements reveal magnetic ordering with a residual paramagnetic phase contribution for the compounds with m=5–8.
•Aurivillius compounds prepared by solid-state sintering.•Coexistence of antiferromagnetic and paramagnetic phases seen by Mössbauer spectra.•Hyperfine interactions parameters of compounds determined.•Antiferromagnetic spin glass-like ordering observed down to 10K.
The microstructure and corrosion properties of Fe-Cr-Si alloys prepared by mechanical alloying method were studied using the 57Fe transmission Mössbauer spectroscopy (TMS), x-ray diffraction (XRD), ...and scanning electron microscope (SEM). The initial ternary mixture in Fe:Cr:Si atomic ratio of 85:10:5 was prepared on the basis of high-purity Fe, Cr, and Si powders. The studied samples were obtained after 10 h (MA-10h), 20 h (MA-20h), and 50 h (MA-50h) of alloying process in planetary ball mill. The SEM results indicate that the mean particle size of prepared material is strongly dependent on milling time and the estimated mean particle sizes were 15.4 (±3.0) μm, 9.0 (±1.5) μm, and 1.73 (±23) μm for MA-10h, MA-20h, and MA-50h, respectively. The XRD and TMS measurements reveal that all the prepared powders are alloys with body-centered cubic (bcc) structure. Moreover, TMS was used to investigate corrosion of Fe-Cr-Si powders during exposure to air at high temperature. The obtained results suggest that reduction of mean particle size of mechanically synthesized alloy drastically decreases its corrosion resistance properties. Finally, the hyperfine field distributions p(B) obtained for MA-10h, MA-20h, and MA-50h samples before and after annealing were compared with the simulated p(B) for a random bcc Fe0.85Cr0.10Si0.05 alloy. This comparison shows that the amount of Cr and Si atoms dissolved in Fe-Cr-Si bcc alloy changes significantly with time of mechanical alloying as well as with annealing.
In this work, BiFeO
3
powders were synthesized by a sol–gel method. The influence of annealing temperature on the structure and magnetic properties of the samples has been discussed. X-ray ...diffraction studies showed that the purest phase was formed in the temperature range of 400 °C to 550 °C and the samples annealed at a temperature below 550 °C were of nanocrystalline character. Mössbauer spectroscopy and magnetization measurements were used as complementary methods to investigate the magnetic state of the samples. In particular, the appearance of weak ferromagnetic properties, significant growth of magnetization, and spin-glass-like behavior were observed along with the drop of average grain size. Mössbauer spectra were fitted by the model assuming cycloidal modulation of spins arrangement and properties of the spin cycloid were determined and analyzed. Most importantly, it was proved that the spin cycloid does not disappear even in the case of the samples with a particle size well below the cycloid modulation period
λ
= 62 nm. Furthermore, the cycloid becomes more anharmonic as the grain size decreases. The possible origination of weak ferromagnetism of the nanocrystalline samples has also been discussed.
Ceramic solid solution described by formula Bi0.5Nd0.5FeO3 was prepared by standard solid-state sintering method. X-ray diffraction proved the formation of a single-phase sample with orthorhombic ...structure typical of NdFeO3. Vibrating sample magnetometry revealed weak ferromagnetic behavior of the ceramics up to the Curie temperature Tc = 642 K. Local atomic configurations and local magnetic fields were investigated by 57Fe Mössbauer spectroscopy. It was shown that substitution of a single Nd3+ ion by Bi3+ ion in the orthorhombic NdFeO3 lattice causes a decrease of hyperfine magnetic field experienced by 57Fe ion by the value of 0.186 T. Measurements of the magnetoelectric effect showed that the maximal registered value of the magnetoelectric voltage coefficient was equal to 0.46 mV/(cm·Oe).
Aurivillius Bi5Ti3FeO15 (BTF) and Bi5-xNdxTi3FeO15 (BNTF) ceramics were successfully synthesized by a simple solid state reaction method. Ceramics were prepared from simple oxide powders Bi2O3, ...TiO2, Nd2O3 and Fe2O3. The microstructure, structure, chemical composition and dielectric properties of the obtained materials were examined. Dielectric properties were investigated in a wide range of temperatures (T = 25ºC-550ºC) and frequencies (20Hz-1MHz).
Aurivillius Bi5-xHoxTi3FeO15 (BHTFO) multiferroic ceramics with different holmium doping contents were synthesized by conventional solid state reaction. The effect of holmium doping on the ...microstructure, structural and dielectric behaviors of BHTFO ceramics were investigated in details. Microstructure and crystalline structure studies of ceramics were carried out at room temperature while dielectric properties were investigated in a wide range of temperature (T = 25ºC-550ºC) and frequency (20Hz-1MHz).
•Bi1−xNdxFeO3 ceramic solid solutions were prepared by solid-state sintering.•Structural phase transition from rhombohedral to orthorhombic was observed.•The lattice parameters decrease with an ...increase of Nd concentration.•The value of hyperfine magnetic field monotonically increases with Nd content.•The isomer shift typical for high-spin Fe3+ ions decrease with Nd content.
The series of polycrystalline ceramic powders, Bi1−xNdxFeO3 (x=0.1−1) was successfully synthesized by mixed oxide method followed by pressureless sintering. X-ray diffraction and Mössbauer spectroscopy were used as complementary methods to study structure and hyperfine interactions of the samples. It was found that with an increase of Nd content, within the range of x=0.2−0.3 a structural phase transition from rhombohedral to orthorhombic system occurs. The lattice parameters and unit-cell volume decrease with an increase of Nd concentration. The Mössbauer spectra registered for Bi1−xNdxFeO3 are characterized by sextets with slightly broadened lines and reveal distributions of hyperfine magnetic fields. It was found that the value of the hyperfine magnetic field induction monotonically increases with Nd content. The mean values of isomer shift are typical for Fe3+ ions in a high spin state and slightly decrease from 0.40mms−1 for x=0.3 to 0.37mms−1 for x=0.9. The small value of quadrupole shift confirms octahedral coordination of the iron ions. The structural transition is accompanied by an increase of isomer shift and a change of sign of quadrupole shift.
•For the first time the harmonized forest availability for wood supply is quantified for Europe.•Economic viability is the main restriction to availability of forests for wood supply.•The harmonized ...forests available for wood supply (FAWS) represent 75–95 % of forest area and biomass.•The reference definition of FAWS is suitable for international reporting.
The quantification of forests available for wood supply (FAWS) is essential for decision-making with regard to the maintenance and enhancement of forest resources and their contribution to the global carbon cycle. The provision of harmonized forest statistics is necessary for the development of forest associated policies and to support decision-making. Based on the National Forest Inventory (NFI) data from 13 European countries, we quantify and compare the areas and aboveground dry biomass (AGB) of FAWS and forest not available for wood supply (FNAWS) according to national and reference definitions by determining the restrictions and associated thresholds considered at country level to classify forests as FAWS or FNAWS.
FAWS represent between 75 and 95 % of forest area and AGB for most of the countries in this study. Economic restrictions are the main factor limiting the availability of forests for wood supply, accounting for 67 % of the total FNAWS area and 56 % of the total FNAWS AGB, followed by environmental restrictions. Profitability, slope and accessibility as economic restrictions, and protected areas as environmental restrictions are the factors most frequently considered to distinguish between FAWS and FNAWS. With respect to the area of FNAWS associated with each type of restriction, an overlap among the restrictions of 13.7 % was identified. For most countries, the differences in the FNAWS areas and AGB estimates between national and reference definitions ranged from 0 to 5 %. These results highlight the applicability and reliability of a FAWS reference definition for most of the European countries studied, thereby facilitating a consistent approach to assess forests available for supply for the purpose of international reporting.
The aim of these studies was to obtain single phase cubic modification of Li7La3Zr2O12 by mechanical milling and annealing of La(OH)3, Li2CO3 and ZrO2 powder mixture. Fritsch P5 planetary ball mill, ...Rigaku MiniFlex II X-ray diffractometer, Setaram TG-DSC 1500 analyser and FEI Titan 80-300 transmission electron microscope were used for sample preparation and investigations. The applied milling and annealing parameters allowed to obtain the significant contribution of c-Li7La3Zr2O12 in the sample structure, reaching 90%. Thermal measurements revealed more complex reactions requiring further studies.
The aim of this research was to fabricate and study the properties of Bi1-x DyxFeO3 (for x = 0, 0.05, 0.07, 0.1) ceramics materials. Simple oxide powders Bi2O3, Dy2O3 and Fe2O3 were used to fabricate ...Bi1-xDyxFeO3 ceramics by mixed oxide method followed by free sintering. The study presents changes in microstructure and crystal structure as well as in dielectric properties and magnetic properties caused by modification of BiFeO3 with dysprosium dopant.
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