Search

Abstract: Calcium zirconate (CaZrO3), because of its high melting point, low thermal expansion coefficient, high strength and excellent corrosion resistance against alkali oxides, is a good candidate for a novel refractory material. CaZrO3 is mostly synthesized by the reaction in the solid state but the material obtained in such a way often suffers low bulk density, high porosity and other defects which lower its potential application value. To overcome these obstacles a novel synthesis method by an electric arc melting technique was proposed. The crystal structure of melted CaZrO3 was compared with a conventionally synthesized material. According to X-ray measurements the obtained material has an orthorhombic perovskite-like structure. Its stoichiometry was confirmed by the scanning electron microscope and EDS analysis. The material is almost poreless with its density close to theoretical. The estimated crystal structure parameters were used to calculate the electronic structure of CaZrO3 using the full potential linear augmented plane wave (FLAPW) method. It has been found that CaZrO3 is an insulator with the energy band gap of 4.1eV. The Ca–O bond is typically ionic while Zr–O bond is of a significant covalent character. [Copyright &y& Elsevier]

Abstract: The consequences of Fe/Ni substitution in Tb 0.27 Dy 0.73(Fe 1−x Nix )2 intermetallics, with a starting compound Tb 0.27 Dy 0.73 Fe 2 known as Terfenol – D, were studied. Ni substitution introduces a local area, at sub-nanoscale, with different Fe/Ni neighbourhoods of the 57Fe atoms. 57Fe Mössbauer effect measurements for the intermetallic system Tb 0.27 Dy 0.73(Fe 1−x Nix )2 carried out at 4.2 K evidence an [100] easy axis of magnetization. Hyperfine interaction parameters – an isomer shift, a magnetic hyperfine field and a quadrupole interaction parameter – were determined from the fitting procedure of the spectra, both for the local neighbourhood area and, as averaged values, for the sample as bulk. As a result of Fe/Ni substitution, a Slater–Pauling type dependence for the average magnetic hyperfine field vs. Ni content is observed. Electronic band structure calculations using the Full-Potential Linearized Augmented Plane Waves (FLAPW) method were performed. The relation between the experimentally determined magnetic hyperfine field and the weighted magnetic moment calculated per transition metal atom is discussed. [ABSTRACT FROM AUTHOR]

Abstract: This paper concerns synthesis, X-ray analysis (300K), electrical resistivity and 57Fe Mössbauer effect studies (4.2K) of complete Tb0.27Dy0.73(Mn1−x Fe x )2 intermetallic series, with a borderline compound Tb0.27Dy0.73Fe2 known as Terfenol-D. A cubic Laves phase Fd3m of the MgCu2-type is observed across the series. The lattice parameter decreases parabolically with x. Electrical resistivity was measured in a wide temperature region across the Tb0.27Dy0.73(Mn1−x Fe x )2 series and the parameters which characterize resistivity dependence on temperature, including Debye temperature, were determined. Residual, phonon and magnetic contributions were separated from electrical resistivity. The magnetic contribution to electrical resistivity was applied to estimate Curie temperatures. The Curie temperature increases significantly with x. 57Fe Mössbauer effect measurements for the Tb0.27Dy0.73(Mn1−x Fe x )2 intermetallic system evidence an [100] easy axis of magnetization. Mn/Fe substitution introduces a local area, at sub-nanoscale, with different Mn/Fe neighbourhoods of the tested 57Fe atoms. Hyperfine interaction parameters, an isomer shift, a magnetic hyperfine field and a quadrupole interaction parameter were determined from the spectra both for the local neighbourhood area and, as averaged values, for the sample as bulk. The average magnetic hyperfine field increases parabolically with x. The correlation between Curie temperatures and magnetic hyperfine fields is discussed. [ABSTRACT FROM AUTHOR]

Abstract: A consequence of Co/Ni substitution in the intermetallics Dy(Fe0.4Co0.6−x Ni x )2 was tested in this paper. Mössbauer effect measurements for the intermetallic system were carried out at 4.2K and the determined hyperfine interaction parameters as functions of composition are reported. The magnetic hyperfine field as well as the Curie temperature is strongly reduced with a composition parameter x. Band structure calculations using the full-potential linearized augmented plane waves (FLAPW) method were performed. Some properties of the 3d bands of the Fe, Co and Ni constituents are discussed. The 3d band splitting energies and the magnetic moments of transition metals reduce with x. The experimentally determined magnetic hyperfine field correlates linearly with the calculated stoichiometrically weighted magnetic moment of 3d atoms and correlates linearly with the weighted splitting energy between 3d subbands. The Curie temperature changes nonlinearly with the squared magnetic hyperfine field or with the calculated squared weighted splitting energy between 3d subbands. [Copyright &y& Elsevier]

Abstract: Synthesis and X-ray analysis (300 K) of a new series were performed. The lattice parameter is considerably reduced with x. Electrical resistivity for the intermetallic series was measured in a wide temperature range and the parameters characterising the dependence of resistivity on temperature and composition were determined. The magnetic part of the resistivity was used to estimate Curie temperatures. The Curie temperature is strongly increased as a result of Mn/Co substitution. The obtained -results are related to the data known for the and series. [Copyright &y& Elsevier]

Abstract: The valence band electronic states of Dy(Co1−x Fe x )2 Laves phases with x =0, 0.05, 0.1, 0.7 and 1.0 were measured by the ultraviolet photoemission spectroscopy (UPS) in room temperature. The Curie temperatures were determined from the electrical resistivity measurements and from the temperature dependence of the hyperfine fields by 57Fe Mössbauer spectroscopy. The UPS spectra showed the very pronounced composition dependent emission at the Fermi energy E F, the broad band within 0 and −4eV binding energy interval below E F and two strong features at about −6.5 and −9.0eV. The spectra were compared with the band structure calculations using the full-potential linearized augmented plane waves (FLAPW) method. From the comparison we concluded that the intensities at E F are correlated with the values of the Curie temperatures, the broad band comes entirely from different 3d Co and/or Fe states and the strong two features come entirely from 4f electrons of dysprosium. [Copyright &y& Elsevier]

Abstract: Electrical resistivities of the Dy(Fe1−x Co x )2 intermetallic series were measured in a wide temperature region and the residual, phonon and magnetic contributions to the resistivities across the series were determined. The magnetic ordering temperatures were estimated for the Dy(Fe1−x Co x )2 compounds using the magnetic contribution to the electrical resistivity. The splitting energies between the 3d subbands of iron for the Dy(Fe1−x Co x )2 series were estimated using the magnetic hyperfine fields at 57Fe nuclei. The Curie temperatures obtained for the Dy(Fe1−x Co x )2 intermetallics and the Curie temperatures reported in the literature for the Dy(Mn1−x Fe x )2 and Dy(Mn0.4−x Al x Fe0.6)2 series correlate linearly with the squared energy splitting between the 3d subbands. [Copyright &y& Elsevier]

Abstract: Electrical resistivity measurements for the Dy(Mn0.4−x Al x Fe0.6)2 intermetallics were performed in a wide temperature region and the parameters characterising the resistivity dependence on temperature were determined. Mössbauer effect studies were performed in the temperature range around the Curie temperatures. From both the methods the magnetic ordering temperatures were estimated. For the Dy(Mn0.4−x Al x Fe0.6)2 and Dy(Mn1−x Fe x )2 series the splitting energies between the 3d subbands were estimated. It was found that the Curie temperatures obtained for the Dy(Mn0.4−x Al x Fe0.6)2 intermetallics and the Curie temperatures reported in the literature for the Dy(Mn1−x Fe x )2 series correlate linearly with the squared energy splitting between the 3d subbands. [Copyright &y& Elsevier]

It was previously found that the magnetic hyperfine fields observed at 57Fe nuclei (4.2 K) in the Dy(Mn1-xFex)2 and Dy(Fe1-xCox)2 intermetallics form a Slater–Pauling curve. Both 3d subbands in the Dy(Mn0.4Fe0.6)2 compound are filled up only partially with 3d electrons. The consequence of Mn/Al substitution, in the Dy(Mn0.4Fe0.6)2 compound was studied in the present paper. For this purpose the synthesis and X-ray analysis (300 K) of the series Dy(Mn0.4-xAlxFe0.6)2 were performed. The cubic, MgCu2-type Fd3m crystal structure was observed across the series. Nevertheless for x=0.35 and 0.40 a stoichiometric admixture of the hexagonal, MgZn2-type, P63/mmc was evidenced. 57Fe Mössbauer effect measurements for the series were performed at 4.2 K. The magnetic hyperfine fields form a separate branch of the Slater–Pauling curve. This branch is compared to the magnetic hyperfine field previously obtained for the Dy(Mn0.4Fe0.6-xAlx)2 series (the Fe/Al substitution). The possible 3d electron band structure is discussed qualitatively within the Stoner model. [Copyright &y& Elsevier]

It was previously found, that the magnetic hyperfine fields observed at 57Fe nuclei (4.2 K) in the Dy(Mn1-xFex)2 and Dy(Fe1-xCox)2 intermetallics form a Slater–Pauling curve. Both 3d sub-bands in the Dy(Mn0.4Fe0.6)2 compound are filled up only partially with 3d electrons. The consequence of Fe/Al substitution, in the Dy(Mn0.4Fe0.6)2 compound, was studied in the present paper. For this purpose the synthesis and X-ray analysis (300 K) of the series Dy(Mn0.4Fe0.6-xAlx)2 were performed. The cubic, MgCu2-type, Fd3m crystal structure was observed across the series. 57Fe Mössbauer effect measurements for the series were realized at 4.2 K. The obtained crystallographic data and the hyperfine interaction parameters are presented. The magnetic hyperfine fields form a separate branch of the Slater–Pauling curve. The data are qualitatively related to the Stoner model. [Copyright &y& Elsevier]

161Dy Mössbauer effect studies were performed for the Dy[(Fe0.7Co0.3)1-xAlx]2 and Dy[(Fe0.4Co0.6)1-xAlx]2 series (4.2 K) and the hyperfine interaction parameters were determined from the experimental Mössbauer spectra. It was found that, as a result of the (Fe0.7 Co0.3 )/Al (first series) or (Fe0.4Co0.6)/Al (second series) substitution, the 161Dy magnetic hyperfine fields decrease nonlinearly with the Al-content and form new branches of the 161Dy Slater–Pauling dependence previously determined for the Dy(M–M)2 series (M–M=Mn–Fe, Fe–Co, Co–Ni). Additionally, using the 57Fe Mössbauer effect the magnetic ordering temperatures were obtained. The influence of Al-substitution, i.e., the reduction of the number of 3d-electrons, on the 3d-band and the 5d-band structure is qualitatively discussed. [Copyright &y& Elsevier]

It was previously found that the magnetic hyperfine fields observed at 57Fe nuclei (4.2 K) in the Dy(Mn1−xFex)2 and Dy(Fe1−xCox)2 intermetallics form a Slater–Pauling curve with a maximum hyperfine field for the Dy(Fe0.7Co0.3)2 compound. The Fe/Al substitution in the Dy(Fe0.7Co0.3)2 compound was studied in the present paper. The intermetallic series Dy(Fe0.7−xAlxCo0.3)2 was prepared and data of an X-ray analysis are presented (300 K). The cubic, MgCu2-type, Fd3m crystal structure was observed. 57Fe Mo¨ssbauer effect measurements for the series were performed (4.2, 77, 293 K) and the obtained hyperfine parameters are presented. The magnetic hyperfine fields form a separate branch of the Slater–Pauling curve. The data related to a possible band structure are qualitatively discussed within the frame of the Stoner model. [Copyright &y& Elsevier]

MgO–ZrO 2 ceramics were obtained by three different methods: conventional sintering, arc melting and field assisted sintering. The present study was undertaken in order to determine the influence of the different sintering techniques on the structural properties of MgO–ZrO 2 ceramics. The phase compositions of the obtained samples consisted of MgO and ZrO 2 cub. ss (doped by MgO). The amount of all phases in the final product and their average crystallite sizes are strongly influenced by the sintering method. The smallest crystallites were realized for ceramics consolidated by the field assisted sintering method (20.1 ± 2.5 nm for MgO and 27.0 ± 2.7 nm for ZrO 2 cub. ss ). About ten times larger crystallites resulted by conventional sintering. The average crystallite size in the material obtained by arc melting technique was around 116 ± 20.4 nm. It was observed that the microstructures of the samples prepared by arc melting and field assisted sintering are similar. [ABSTRACT FROM AUTHOR]

Abstract: Electrical resistivity studies performed in a wide temperature range across the complete Fe/Co substituted Tb0.27Dy0.73(Fe1−x Co x )2 intermetallic series, with a borderline compound Tb0.27Dy0.73Fe2 known as Terfenol-D are presented. Parameters characterizing the dependence of resistivity on temperature, including the Debye temperature, are determined. Residual, phonon and magnetic contributions are separated from electrical resistivity. The magnetic contribution to electrical resistivity is applied to estimate Curie temperatures. Regions of weak and strong ferromagnetism of the transition metal sublattice are evidenced. The Curie temperature increases with x, approaches a maximum for x = 0.3 and reduces across the rest of the series. Some results of electronic band structure calculations using the Full-Potential Linearized Augmented Plane Waves (FLAPW) method are also presented. A distribution function for the densities of 3d states is introduced and a formula to estimate the band splitting energy is proposed. The obtained 3d and 4s band splitting energies for iron, cobalt and average for transition metal are presented. The Curie temperature across the Tb0.27Dy0.73(Fe1−x Co x )2 system is described using a formula relating to both the FLAPW calculated magnetic moments and the statistical properties of the substituted transition metal sublattice. [Copyright &y& Elsevier]

Abstract: Glasses of the SiO2–P2O5–K2O–MgO–CaO–Fe2O3 system acting as slow release fertilizers were synthesized by the melt-quenching technique. The influence of iron addition on the structure of glasses was evaluated by FTIR spectroscopy (with spectra decomposition) and 57Fe Mössbauer spectroscopy. The chemical activity of glasses in the 2 mass% citric acid solutions was measured by the ICP-AES method. It has been found that the formation of domains with structure similar to phosphates with chemically stable P–O–Fe3+ and P–O–Fe2+ bonds decreases the glass solubility under conditions simulating the soil environment. [Copyright &y& Elsevier]

Abstract: The after-effects of Fe/Co substitution in the intermetallic series , with a starting compound known as Terfenol-D, were studied. Co substitution introduces a local area, at sub-nanoscale, with random Fe/Co neighbourhoods of the atoms. Mössbauer effect measurements for the intermetallic system carried out at 4.2K evidence an easy axis of magnetization. Hyperfine interaction parameters: isomer shift, a magnetic hyperfine field and a quadrupole interaction parameter were obtained from the fitting procedure of the spectra, both for the local area and for the sample as bulk. As a result of Fe/Co substitution, a Slater–Pauling type curve for the average magnetic hyperfine field vs. Co content is observed. It is found that the magnetic hyperfine fields corresponding to the local area sorted out against Co contribution in the Fe/Co neighbourhoods also create a dependence similar to a Slater–Pauling type curve. Band structure calculations using the Full-Potential Linearized Augmented Plane Waves (FLAPW) method were performed. The experimentally determined magnetic hyperfine field correlates linearly with the weighted magnetic moment calculated per transition metal atom. [Copyright &y& Elsevier]

Abstract: X-ray powder diffraction measurements (295K) show that the cubic, MgCu2-type, crystal structure appears in compounds. The lattice parameter is considerably and weakly nonlinearly reduced with x. The electrical resistivities of the intermetallic series were measured over a wide temperature range and the parameters characterising the dependence of resistivity on temperature and composition were determined. In order to separate the residual, phonon and magnetic contributions to total resistivity the Matthiesen formula was used. The magnetic part of the resistivity was used to estimate Curie temperatures. The Curie temperature is strongly and nonlinearly reduced as a result of Co/Ni substitution. The obtained results are related to data known for the and series. [Copyright &y& Elsevier]

Abstract: A consequence of Fe/Ni substitution in the intermetallics Dy(Fe0.7−x Ni x Co0.3)2 was tested in this paper. Mössbauer effect measurements for the intermetallic system were carried out at 4.2K. The obtained hyperfine interaction data are presented. The magnetic hyperfine field as well as the Curie temperature is strongly reduced with a composition parameter x. Band structure calculations using the Full-Potential Linearized Augmented Plane Waves (FLAPW) method were performed. The experimentally determined magnetic hyperfine field correlates linearly with the weighted magnetic moment calculated per transition metal atom and correlates linearly with the average splitting energy between 3d subbands. The Curie temperature changes in an approximate linear fashion with the squared magnetic hyperfine field or with the calculated squared splitting energy between 3d subbands. [Copyright &y& Elsevier]

Abstract: From X-ray analysis (295 K) it was found that the cubic, -type, crystal structure appears across the Gd(Fe1−x Co x )2 series. Electrical resistivity measurements for the Gd(Fe1−x Co x )2 intermetallics were performed in a wide temperature region and the parameters characterizing the resistivity dependence on temperature and composition were determined. The differential of the electrical resistivity against temperature was used to estimate Curie temperatures. The Curie temperature versus x, high and moderately increasing in the iron-rich area, rapidly drops in the cobalt-rich region. The obtained results are compared with the data known for the Dy(Fe1−x Co x )2 series. The Curie temperature is related to both the number of 3d electrons and the de Gennes factor. [Copyright &y& Elsevier]

The structural and physical properties of nickel-diluted Tb 0.27 Dy 0.73 ( Fe 0.7 − x Ni x Co 0.3 ) 2 intermetallics were studied by X-ray diffraction, four-probe dc electrical measurements and standard strain gauge method. X-ray analysis shows that all samples crystallize in a cubic Laves structure. The lattice parameter decreases linearly with the nickel content. Electrical resistivity was measured in a temperature range of 15–1100 K. The parameters involved in the dependence of resistivity on temperature and composition were determined. Residual, phonon and magnetic resistivity were separated from the electrical resistivity using both the Matthiessen and Bloch-Grüneisen formulas. The compounds’ Curie temperatures, which decrease nonlinearly with x , were obtained from the magnetic resistivity curves. The maximum values of magnetostriction attained for the Tb 0.27 Dy 0.73 ( Fe 0.6 Ni 0.1 Co 0.3 ) 2 compound exceed about 851 ppm. Electronic 3d-band structure and magnetic moment calculations were performed using the Full-Potential Linearized Augmented Plane Waves method. The distribution function for the densities of 3d-states was used to characterise the transition metal subbands. [ABSTRACT FROM AUTHOR]

Abstract: This paper looks at synthesis, electrical resistivity and Mössbauer effect studies on intermetallic compounds . Cubic Laves phase of MgCu2-type were observed across the series. The lattice parameters linearly increase with Gd concentration and the lattice parameters of the intermetallics series are compared to data previously observed for the series (R=Y, Dy, Gd) and series (M=Fe, Co). Electrical resistivity for the intermetallic series was measured in the temperature range 15–1100K. Parameters characterizing the resistivity dependence on temperature were determined. Residual, phonon and magnetic resistivity were separated from the measured electrical resistivity using both the Matthiesen formula and the Bloch–Gruneisen formula. Curie temperatures of the studied series were determined using both electrical resistivity and Mössbauer effect measurements, with the Mössbauer effect measured in the temperature range around the magnetic ordering temperature. The Curie temperature increases with x. The obtained Curie temperatures for the are similar to data known for the series (R=Y, Dy, Gd) and series (M=Fe, Co). [Copyright &y& Elsevier]

Abstract: Synthesis, X-ray analysis (300K), electrical resistivity and Mössbauer effect studies in the intermetallic compounds Y(Fe1−x Co x )2 are reported. Cubic Laves phases MgCu2-type, were observed across the series. Crystal lattice parameter is considerably reduced with Co concentration. The lattice parameters of the Y(Fe1−x Co x )2 series are compared to analogous data previously observed for the Gd(Fe1−x Co x )2 and Dy(Fe1−x Co x )2 series. Electrical resistivity for the Y(Fe1−x Co x )2 intermetallic series was measured in the temperature range 15–1000K. Parameters characterizing the resistivity dependence on temperature including Debye temperature were determined. Residual, phonon and magnetic resistivity were separated from the measured electrical resistivity. Curie temperatures of the Y(Fe1−x Co x )2 series were determined using both electrical resistivity and Mössbauer effect measurements. The Curie temperature increases with x, reaches maximum approximately at x =0.3 and than strongly decreases as a result of Fe/Co substitution. The obtained Curie temperatures for the Y(Fe1−x Co x )2 series are related to the data known for the Dy(Fe1−x Co x )2, Gd(Fe1−x Co x )2 and other series. Numerical formula, which approximates Curie temperatures of intermetallics is proposed. [Copyright &y& Elsevier]

Abstract: It is well documented that adding some active elements (such as Y, Ce, La, Er, others) to austenitic stainless steels helps to improve their high temperature oxidation resistance. In the present work we report preliminary results of incorporation of Ce and La into austenitic stainless steel AISI 316L using a new approach based on high intensity pulsed plasma beams. The characteristic feature of this approach relies upon the fact that incorporation of Ce–La occurs in the transiently melted near-surface layer of the substrate. Improving the near surface layer properties was connected with two facts: (i) material melting and cooling with very high rate and (ii) incorporation Ce–La to the molten phase. Modified samples were oxidized at 1000°C for 80h in air at atmospheric pressure. The obtained effects were similar to those observed in chromia-forming alloys doped by other conventional surface treatment techniques: oxide scales formed on the treated samples were more fine-grained, compact and adhered better than those formed on the un-treated samples, whereas the protective layer was produced closer to the surface. [Copyright &y& Elsevier]

Abstract: Synthesis by arc melting, the structural and the electric properties of Y(Co1−x Ni x )2 alloys were studied by X-ray diffraction (XRD) and four probe dc electrical measurements. XRD analysis (300K) shows that all samples crystallize in a cubic MgCu2-type structure. The lattice parameters linearly decrease with Ni content. Electrical resistivity for the Y(Co1−x Ni x )2 intermetallic series was measured in a temperature range of 15–1100K. The parameters involved in the dependence of resistivity on temperature were determined. Residual, phonon and spin fluctuations resistivity were separated from electrical resistivity using both the Matthiesen formula and the Bloch–Gruneisen formula. The spin fluctuations resistivity of the Y(Co1−x Ni x )2 series are compared to the mean square amplitudes of spin fluctuations previously calculated by the Linear Muffin Tin Orbital-Tight Binding Approach method for these series in the literature. The contribution of spin fluctuations to total resistivity is proportional to T 2 at low temperatures. The proportionality parameter strongly reduces across the Y(Co1−x Ni x )2 series. [ABSTRACT FROM AUTHOR]

Abstract: Findings from X-ray powder diffraction measurements (295 K) show that the cubic, -type, crystal structure appears in compounds.The lattice parameter is considerably reduced with x. Electrical resistivity for the intermetallic series was measured in a wide temperature range and the parameters characterising the dependence of resistivity on temperature and composition were determined. The magnetic part of the resistivity was used to estimate Curie temperatures. The Curie temperature is strongly reduced as a result of Fe/Ni substitution. The obtained -results are related to the data known for the and series. [Copyright &y& Elsevier]

The transformation from the amorphous into the crystalline structure at temperatures close to temperature of glass transition of 750 °C was investigated in a 47SiO2–22Al2O3–17MgO–2ZnO–12TiO2 glasses with X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high-resolution electron microscopy (HREM). The investigations indicated that heat treatment of this glass results in the formation of rod-like crystals of high-temperature quartz structure. At the early stages of crystallisation, the formation of (Mg, Al) titanates was observed. TEM of glasses heat-treated at 725 °C showed nucleation and growth of small dendrite-like precipitates enriched in Ti and depleted in Si. High-resolution transmission electron microscopy (HRTEM) has indicated that the crystallisation is occurring through a local ordering of the atoms in the amorphous glass structure, within areas up to 5 nm. Above 900 °C an enstatite (Mg, Zn)SiO3 phase is formed. [Copyright &y& Elsevier]