arXiv subjects

Stanisław M. Dubiel

Publications and source records attributed to Stanisław M. Dubiel.

15 recordsLinked to original sources

arXiv2022

Kinetics of transformation, border of metastable miscibility gap in Fe-Cr alloy and limit of Cr solubility in iron at 858 K

The study was aimed at determination of the position of the Fe-rich border of the metastable miscibility gap (MMG) and of the solubility limit of Cr in iron at 858 K. Towards this end a Fe73.7Cr26.3 alloy was isothermally annealed at 858 K in vacuum up to 8144 hours and Mössbauer spectra were recorded at room temperature after every step of the annealing. Three spectral parameters viz. the average hyperfine field, , the average isomer shift, , and the probability of the atomic configuration with no Cr atoms in the two-shell vicinity of the probe Fe atoms, P(0,0), gave evidence that the transformation process takes place in two stages. All three parameters could have been well described in terms of the Johnson-Mehl-Avrami-Kolmogorov equation, yielding kinetics parameters. The first stage, associated with the phase decomposition, proceeded much faster than the second stage, associated with the alpha-to-sigma phase transformation. The most reliable estimation of the position of the MMG and that of the value of the Cr solubility limit was obtained from the annealing time dependence of , namely 24.5 at.% Cr for the former and 20.3 at.% Cr for the latter. A comparison of these figures with the recent phase diagrams pertinent to Fe-Cr system was done.

cond-mat.mtrl-sci↗

arXiv2022

A Simple Method for Determining Center Shift and Spectral Area of a Mössbauer Spectrum

A very simple method for determining the center (isomer) shift, CS, and the spectral area, A, of a Mössbauer spectrum is outlined. Its applicability is demonstrated in two examples viz. pyrite and a ternary sigma-phase Fe-Cr-Ni compound. Sets of the spectra recorded in the temperature interval of 78-295 K for the former, and 78-295 K for the latter were analyzed with the simple and a standard method. CS(T)- and A(T)-data obtained with both ways of the spectra analysis were analyzed in terms of the Debye model. The determined values of the Debye temperatures agree well within the error limit with each other proving that this very simple method is suitable for a quick determining of CS and A spectral parameters.

cond-mat.other↗

arXiv2022

Effect of Magnetism on Lattice Vibrations: Mössbauer Spectroscopic Evidence

Based on the available literature reviewed are results pertinent to the effect of magnetism on lattice dynamics obtained by Mössbauer spectroscopy at 57Fe and 119Sn probe atoms. Presented and discussed are sigma-phase Fe-Cr, Fe-V, Fe-Cr-Ni and lambda-phase (C14 Laves) NbFe2 compounds that belong to the Frank-Kasper family of phases, metallic chromium and iron mono-arsenide, FeAs. The common feature of all these metallic systems is itinerant character of their magnetism. Two spectral parameters relevant to the lattice dynamics viz. the center shift, CS, and/or the recoil-free fraction, f, are considered as figures of merit. Their temperature dependences show anomalies at magnetic ordering temperatures giving evidence that that vibrations in the magnetic phase are different than those in the paramagnetic phase. The lower the magnetic ordering temperature, the stronger the difference.

cond-mat.str-el↗

arXiv2022

Simplistic approach for Determining Center Shift of Mössbauer Spectrum: exemplified on two cases

A very simple method for determining the center (isomer) shift, CS, of a Mössbauer spectrum is outlined. Its applicability is demonstrated on two examples viz. pyrite and a ternary sigma-phase Fe-Cr-Ni compound. Sets of the spectra recorded in the temperature interval of 78-295 K for the former, and 5-293 K for the latter were analyzed with the simple and a commonly used methods. CS(T)-values obtained with both ways of the fitting procedures were analyzed in terms of the Debye model. The determined therefrom values of the Debye temperatures agree within the error limit with each other proving thereby that this very simple method gives correct values of CS.

cond-mat.str-el↗

arXiv2022

Further evidence on the effect of magnetism on lattice vibrations:the case study of sigma-phase Fe0.525Cr0.455Ni0.020 alloy

Sigma-phase Fe0.525Cr0.455Ni0.020 alloy was studied by means of Mössbauer spectrometry in the temperature range of 5-293 K. The average center shift, , determined from the recorded Mössbauer spectra was shown to significantly deviate from the Debye model in the temperature range below ca. 50 K i.e. in the magnetic state of the sample. The deviation is obviously due to the effect of magnetism on the lattice dynamics of the studied sample. Analysis of the -data in the paramagnetic phase in terms of the Debye model yielded the value of 437(7) K for the Debye temperature.

cond-mat.str-el↗

arXiv2021

Mössbauer Spectroscopic and XRD Studies of two eta-Fe2Al5 Intermetallics

Two intermetallic FeAl compounds with Al content of 70.68 and 72.17 at.pct were studied using Mössbauer spectroscopy (5 to 296 K) and X-ray diffraction (15 to 300 K). The compounds were found to crystallize in the orthorhombic Cmcm space group (eta-phase). The collected data revealed that dynamics of the Fe atoms (harmonic in entire temperature range) is significantly different that Al atoms. For the latter strong anharmonicity was evidenced. Moreover, it was found that partial filling of the different Al sites leads to occurrence of low and high symmetry coordination of Fe atoms, which was reflected in occurrence of two distinct doublets in Mössbauer spectra. All spectral parameters of the doublets as well as the Debye temperature, force constant, kinetic and potential energies of vibrations were determined. Those results revealed significant differences between both alloys, likely originating from approaching the stability boundary of the eta-phase for Fe-Al 72.17 at.pct alloy.

cond-mat.mtrl-sci↗

arXiv2020

Magnetism of Sigma-Phase Fe68V32 Compound

The magnetic phase diagram in the H-T coordinates has been determined for σ-Fe68V32 from the ZFC/FC magnetization measurements. The re-entrant character of magnetism, going from paramagnetic through ferromagnetic to spin-glass (SG) states, has been evidenced. The SG phase is magnetically heterogeneous, because two sub phases can be identified i.e. with the strong (SG-SI) and the weak (SG-WI) irreversibility. The ireversibility, T_irr and the crossover, T_cros, temperatures were quantitatively analysed using the mean-field theory and ϕ_irr=1.6(2) and ϕ_cros=0.91(9) values were obtained. A qualitative agreement with the Gabay-Toulouse model was reached. The isothermal magnetization measurements point to a soft magnetic behaviour of the studied sample. The γ critical exponent was determined with the Kouvel-Fisher approach yielding the value of γ=1.0(1) in line with the mean-field theory.

cond-mat.str-el↗

arXiv2020

Effect of magnetism on lattice dynamics in metallic chromium

Single-crystal sample of chromium doped with ca.0.2 at.%119Sn was studied by means of a transmission Mössbauer spectroscopy in the temperature range of 310-315 K. An anomaly in the temperature behavior of the center shift was found at ca. 313 K, a temperature that coincides well with the Néel temperature of chromium. The anomaly gives evidence that the vibrations of atoms in the studied system are affected by the magnetism.

cond-mat.str-el↗

arXiv2020

Crystal structures of Fe-gluconate

Fe-gluconate, Fe(C_6H_11O_7_2xH_2O is a well-known material widely used for iron supplementation. On the other hand, it is used in food industry as a coloring agent, in cosmetic industry for skin and nail conditioning and metallurgy. Despite of wide range of applications its physical properties were not studied extensively. In this study, Fe-gluconate with three different amount of water viz. x=2 (fully hydrated, 0 < x < 2 (intermediate) and x=0 (dry) was investigated by means of X-ray diffraction (XRD) and Mössbauer spectroscopic (MS) methods. The former in the temperature range of 20-300 K, and the latter at 295 K. Based on the XRD measurements crystallographic structures were determined: monoclinic (space group I2) for the hydrated sample and triclinic (space group P1) for the dry sample. The partially hydrated sample was two-phased. Unit cells parameters for both structures show strong, very complex and non-monotonic temperature dependences. Mössbauer spectroscopic measurements gave evidence that iron in all samples exist in form of Fe(II) and Fe(III) ions. The amount of the latter equals to ca.30% in the hydrated sample and to ca.20% in the dry one.

physics.chem-ph↗

arXiv2020

Mössbauer Spectroscopic Study of Amorphous Fe-Gluconate

Amorphous Fe-gluconate was studied by means of the X-ray diffraction and Mössbauer spectroscopy. Spectra measured in the temperature range between 78 and 295 K were analysed in terms of three doublets using a thin absorber approximation method. Two of the doublets were associated with the major Fe(II) phase (72%) and one with the minor Fe(III) phase (28%). Based on the obtained results the following quantities characteristic of lattice dynamical properties were determined: Debye temperature from the temperature dependence of the center shift and that of the spectral area (recoil-free factor), force constant, change of the kinetic and potential energies of vibrations. The lattice vibrations of Fe ions present in both ferrous and ferric phases are not perfectly harmonic, yet on average they are. Similarities and differences to the crystalline Fe-gluconate are also reported.

cond-mat.mtrl-sci↗

arXiv2020

Revealing magnetic component in crystalline Fe-gluconate

Low temperature Mössbauer spectroscopic and magnetization measurements were performed on a crystalline sample of Fe-gluconate. Fe atoms were revealed to exist in two phases i.e. a major (90-94 pct.) and a minor (6-10 pct.). Based on values of spectral parameters the former can be regarded as ferrous and the latter as ferric. A sub spectrum associated with the ferric phase shows a significant broadening below ca. 30 K corresponding to 7.5 kGs. A magnetic origin of the effect was confirmed by the magnetization measurements. Evidence on the effect of the magnetism on the lattice vibrations of Fe atoms in both components was found. The Debye temperature, T_D, associated with the vibrations of Fe2+ ions is by a factor of about 2 smaller in the temperature range below ca. 30 K than the one determined from the data measured above ca. 30 K. Interestingly, the T_D-value found for the Fe3+ ions from the data recorded below ca.30 K is about two times smaller than the corresponding value determined for the Fe2+ ions.

physics.chem-ph↗

arXiv2019

On the Magnetism of C14 Nb(Fe89.4Al10.6)2 Laves Phase Intermetallic Compound

C14 Nb(Fe89.4Al10.6)2 Laves phase intermetallic compound was investigated by DC magnetization (M) measurements performed in the temperature (T) interval of 20 to 175 K,under an applied magnetic field (H) ranging between 50 and 1250 Oe. Magnetization curves were recorded in the field-cooled (FC) and in the zero-field-cooled (ZFC) modes. They clearly showed an irreversible character that vanished at H=1250 Oe. Both magnetization curves exhibited well-defined peaks around T_N =72.3 K whose positions were H-independent, so they were identified as the compound's Néel temperature. The existence of irreversibility which decreases with H testify to a re-entrant character of magnetism in the studied compound. An increase of both MFC and MZFC observed below TN likely indicates a mixed i.e. ferromagnetic and antiferromagnetic ground magnetic state of the studied system.

cond-mat.mtrl-sci↗

arXiv2019

Kinetics of phase separation, border of miscibility gap in Fe-Cr and limit of Cr solubility in iron at 832 K

Kinetics of phase decomposition accompanied by precipitation of sigma-phase in a Fe73.7Cr26.3 alloy isothermally annealed at 832 K was studied by means of Mössbauer spectroscopy. Two stage decomposition process has been revealed by three different quantities viz. the average hyperfine field, , the short-range parameter, alpha1, and the probability of atomic configuration with no Cr atoms within the first two coordination shells around the probe Fe atoms, P(0,0). The first stage, that has terminated after ca.300 h of annealing, has been associated with the decomposition into Fe-rich phase in which the concentration of Cr, determined as 20.9 at.%, can be interpreted as the border of the metastable miscibility gap at 832 K. The second stage can be regarded as a continuation of the phase decomposition process combined with a precipitation of sigma. The three relevant parameters for this stage have also saturation-like behavior vs. annealing time and the saturation can be interpreted as termination of the two processes. The concentration of Cr in the Fe-rich phase has been determined as 19.8 at.% and this value can be regarded as the limit of Cr solubility in iron at 832 K. Both stages of the kinetics were found to be in line with the Johnson-Mehl-Avrami-Kolgomorov equation yielding values of the rate constant and the Avrami exponent. The activation energy of the second-stage process was determined to be by ca.12 kJ/mol higher.

cond-mat.mtrl-sci↗

arXiv2019

Debye temperature of single-crystal Cr with incommensurate and commensurate magnetic structure

Single-crystals of Cr and Cr3%Mn doped with ca. 0.2 at.% 119Sn were studied by means of 119Sn-site Mössbauer spectroscopy. Mössbauer spectra recorded in the temperature range of 78-300 K were analyzed using a hyperfine field distribution method. Derived therefrom values of a center shift, CS, analyzed in terms of the Debye model yielded values of the Debye temperature, T_D = 477(56)K for Cr and T_D=282(16)K for Cr3%Mn. The difference in the T_D-value can be regarded as evidence that a spin-phonon interaction is different for the incommensurate and commensurate antiferromagnetic structure of chromium.

cond-mat.str-el↗

arXiv2019

Determination of the magnetic phase diagram in the H-T plane for a sigma-phase Fe47Mo53 alloy

Magnetization measurements were carried out in the in field-cooled (FC) and in zero-field-cooled (ZFC) conditions versus temperature, T, and external magnetic field, H, on a sigma-phase Fe47Mo53 compound. Analysis of the measured M_FC and M_ZFC curves yielded values of characteristic temperatures: magnetic ordering (Curie) temperature, T_C, irreversibility temperature, T_ir, temperature of the maximum in M_ZFC, T_m, identified as the Nėel (T_N) temperature, and cross-over temperature, T_co. Based on these temperatures a magnetic phase diagram in the H-T plane was outlined. The field dependences of the characteristic temperatures viz. of the irreversibility and of the cross-over temperatures were described in terms of a power law with the exponent 0.5(1). In the whole range of H i.e. up to 800 Oe, except the one H>50 Oe, a rare double re-entrant transition viz. PM-FM-AF-SG takes place. For small fields i.e. H<50 Oe a single re-entrant transition viz. PM-FM-SG is revealed.

cond-mat.str-el↗