The structural relaxation effect on functional properties of Fe - based amorphous alloys

Ispitivan je uticaj strukturnih promena izazvanih primenom spoljašnjih parametara (toplotno dejstvo, magnetno dejstvo, mehaničko naprezanje) u toku procesa strukturne relaksacije i kristalizacije na funkcionalna svojstva tri legure na bazi gvožđa, različitog hemijskog sastava: Fe89.8Ni1.5Si5.2B3C0.5, Fe81B13Si4C2 i Fe73.5Cu1Nb3Si15.5B7. Legure su dobijene brzim hlađenjem rastopa na rotirajućem disku (melt-spinning). Uzorci su bili u obliku trake dužine 20 cm, širine 2 mm i debljine 3 μm. Strukturna stabilnost i strukturne transformacije legura ispitane su primenom difrakcije Xzraka. Pokazana je egzotermna termička stabilnost ispitivanih legura u temperaturskom intervalu od 200C - 7000C, primenom diferencijalne skanirajuće kalorimetrije (DSC). Ovaj temperaturski interval obuhvata relaksaciju deformisane strukture, gubitak feromagnetičnosti i konačno kristalizaciju, rekristalizaciju i rast kristala formiranih faza. Proces kristalizacije obuhvata formiranje različitih stabilnih i nestabilnih faza u zavisnosti od hemijskog sastava ispitivanih legura. Ispitana je kinetika procesa strukturne relaksacije ovih legura, pri različitim naprezanjima i temperaturama odgrevanja. Zatim je ispitan uticaj strukturne relaksacije na promenu gustine stanja elektrona na Fermi-evom nivou. Pokazano je da strukturne promene imaju velikog uticaja na električna i magnetna svojstva ovih legura. Utvrđeno je da relaksirana amorfna struktura legure poseduje znatno bolja električna i magnetna svojstva kako u odnosu na polaznu leguru, tako i u odnosu na iskristalisalu leguru sa stanovišta mogućnosti praktične primene. Takođe je ispitana i mogućnost primene ovih legura kao senzora sile. Uspostavljena je jasna korelacija strukturne promene – funkcionalna svojstva i dato fundamentalno tumačenje međuzavisnosti strukturna relaksacija – promena gustine stanja elektrona na Fermi-evom nivou – električna svojstva – magnetna svojstva, što je i cilj ove disertacije.The effect of structural changes was investigated, induced by the application of external parameters (thermal influence, magnetic influence, mechanical strain) within the structural relaxation process and crystallization, over the functional properties of three Fe-based alloys of various chemical content: Fe89.8Ni1.5Si5.2B3C0.5, Fe81B13Si4C2 and Fe73.5Cu1Nb3Si15.5B7. The alloys were obtained by rapidly quenching of the melt on a rotating disk (melt-spinning technique). The samples were ribbon-shaped, 20 cm long, 2 mm wide and 3 μm thick. The structural stability and structural transformations of the alloys were investigated by X - ray diffraction. Exothermal stability of the investigated alloys in the temperature range from 200C to 7000C was determined, by the differential scanning calorimetry method (DSC). This temperature range presumes relaxation of deformed structure, the loss of ferromagnetic properties and finally crystallization, recrystallization and growth of the crystallites of formed phases. The crystallization process includes the formation of various stable and unstable phases depending on the chemical content of the investigated alloys. The kinetics of the structural relaxation process of these alloys was investigated at different strain intensities and annealing temperatures. Furthermore, the structural relaxation effect on the electron state density change at Fermi level was investigated. It has been shown that the structural changes have significant effect on electrical and magnetic properties of these alloys. It has been determined that the relaxed amorphous structure of the alloy possesses far better electrical and magnetic properties as compared to both the as-cast alloy and the crystallized alloy, from their technological applicability aspect. In addition, the possibility of application of these alloys as power sensors has also been investigated. A clear correlation of structural changes – functional properties has been determined, as well as the given fundamental interpretation of the interdependence structural relaxation – electron state density change at Fermi level – electrical properties – magnetic properties, which is the aim of this dissertation

The influence of mechanochemical activation and thermal treatment on magnetic properties of the BaTiO3 -FexOy powder mixture

Powder mixture of 50 mass % of barium titanate (BaTiO3) and 50 mass % of iron (Fe) was prepared by solid-state reaction technique, i.e. ball milled in air for 60 min, 80 min, 100 min, 120 min and 150 min. During mechanochemical activation it was observed the iron powder transitsion to iron oxides. Depending on the activation time the content of iron oxides FeO, Fe2 O3 and Fe3O4 varies. Simultaneously, with the content change of the activated system, magnetic properties change as well. The XRD analysis of milled samples shown that as the activation time increase, the iron oxide percentage increases to, whereby the percentage of BaTiO3 in a total sample mass decreases. The percentage of iron oxides and BaTiO3 in annealed samples changes depending on annealing temperature. The thermomagnetic measurements performed by Faraday method shown that the powder mixture milled for 100 minutes exhibit maximum magnetization prior to annealing. The increase of magnetization maximum was observed after annealing at 540 oC with all milled samples, and at room temperature it has enhancement from 10 % to 22 % depending on the activation time. The samples milled for 100 min and 150 min and then sintered at 1200 oC exhibit magnetoelectric properties. © 2015 International Institute for the Science of Sintering (IISS). All rights reserved

The Influence of Synthesis Parameters and Heat Effect on Magnetic Properties of Powder System FexOy - BaTiO3

Powder mixture of 60 mass % of iron (Fe) and 40 mass % of barium titanate (BaTiO3) has been activated in planetary mill for 100, 120, 150, 180, 210 and 240 min in the air. During the activation the iron powder transits into iron oxides FeO, Fe2O3 and Fe3O4. Depending on the activation time the percentage of iron oxides varies. Simultaneously, with the content change of the activated system, magnetic properties change as well. The thermomagnetic measurements in the temperature interval from 200C up to 6200C have shown that the powder activated for 120 minutes exhibits maximum magnetization prior to annealing. After multiple annealings of the same sample it has been shown that the maximum magnetization of the cooled sample is obtained upon annealing at 5600C during 10 min for all activation times of as-cast powder sample. The sample obtained from pressed powder mixture activated for 120 min has the maximum magnetization, upon isothermal sintering of samples at 12000C during 2h, being M = 2,9 Am2/kg. With additional annealing of the same sample up to Curie temperature (TC = 4300C) and subsequent cooling of the sample in the magnetic field of H = 20 kA/m, the sample is permanently magnetized. The magnetization of sample cooled in the magnetic field with intensity of 20 kA/m being M = 10,15 Am2/kg

Structural And Functional Investigation Of Fe/Pb/Zr-co-doped Barium Titanate Ceramics: From Theory To The Experiment

Mixtures of high purity powders of 50 mass% Fe, 4 mass% Pb, 3 mass% Zr and 43 mass% BaTiO3 were activated in a rotary ball mill for durations ranging from 30 min to 300 min; samples were then sintered in the air atmosphere for 2 hours at 1200 °C. Crystal structure prediction has been performed using Bond ValenceCalculation (BVC) method.Moreover, theoretical stability of theperovskite structure for synthesized and calculated Fe/Pb/Zr-codoped barium titanatecompounds has been investigated using the Goldschmidttolerance factor (Gt) and global instability index (GII).It was observed that magnetization of the system decreased after the sintering, with the most dramatic drop of 90.11% belonging to the sample activated for 150 min. In comparison with initial powders, X-ray powder diffractiondata confirmed the presence of newphases of BaFe12O19 and Ba1.696Ti0.228O3 in sintered samples. Utilizing the field emission scanning electron microscopy (FESEM), it was found that with the increase of activation time the morphology of the samples progressed from irregural, spherical grains to mostly rod-like ones. Energy dispersive X-ray (EDX) analysis identified the presence of Pb and Zr occupying the same locations on the surface of sintered samples, whilst Fe was uniformly deployed regardless of the activation time

Uticaj faznog sastava i temperature sinterovanja na fizička svojstva BaTiO3/NixZn1-xFe2O4 (x =0, 0.5, 1) kompozita sintetisanih metodom termalne dekompozicije

In order to examine the influence of phase composition and sintering temperature on the functional properties of perovskite/spinel composites, BaTiO3/NixZn1−xFe2O4 (x = 0, 0.5, 1), NiFe2O4, ZnFe2O4, and Ni0.5Zn0.5Fe2O4 were in situ prepared by thermal decomposition onto BaTiO3 surface. Acetylacetonate complexes were used as the precursors. The obtained powders were compressed to pellets and sintered at 1150 °C and 1300 °C. X-ray powder diffraction (XRPD) and scanning electron microscopy (SEM) coupled with electron dispersive spectroscopy (EDS) were used for the comprehensive investigation of phase composition and morphology. The magnetic, dielectric, and ferroelectric properties were performed in detail. The optimal phase composition was found in the BaTiO3/NiFe2O4 composite sintered at 1150 °C, which resulted in a wide frequency range stability. Furthermore, particular phase composition led to suitable properties such as low conductivity and ideal-like hysteresis loop behavior [1]. These functional properties of BaTiO3/NiFe2O4 make this composite a “material of choice“ for further studies on applications of multiferroic devices.U cilju ispitivanja uticaja faznog sastava i temperature sinterovanja na funkcionalna svojstva perovskit/spinel kompozita BaTiO3/NixZn1−xFe2O4 (x = 0, 0,5, 1), NiFe2O4, ZnFe2O4, i Ni0,5Zn0,5Fe2O4 pripremljeni su in situ metodom termalne dekompozicije. U sintezi su korišćeni acetilacetonatni kompleksi kao prekursori. Dobijeni prahovi su komprimovani u tablete i sinterovani na 1150 °C i 1300 °C. Za detaljno ispitivanje faznog sastava i morfologije sintetisanih kompozita korišćene su metode rendgenske difrakcije praha (XRPD) i skenirajuće elektronske mikroskopije (SEM) spregnute sa energetsko disperzivnom spektroskopijom (EDS). Ispitivana su i magnetna, dielektrična i feroelektrična svojstva sinterovanih kompozita. Ustanovljeno je da optimalni fazni sastav pronađen kod kompozita BaTiO3/NiFe2O4 sinterovanog na 1150 °C dovodi do stabilnosti u širokom opsegu frekvencija. Optimalni fazni sastav pomenutog kompozita povoljno je uticao na funkcionalna svojstva kao što su niska provodnost i feroelektrično ponašenje koje se ogleda u zadovoljavajućem izgledu histerezisa [1]. Ova svojstva nedvosmisleno ukazuju da je kompozit BaTiO3/NiFe2O4 odgovarajući izbor za dalja istraživanja posvećena primeni multiferoičnih materijala

BaTiO3/NixZn1−xFe2O4 (x = 0, 0.5, 1) Composites Synthesized by Thermal Decomposition: Magnetic, Dielectric and Ferroelectric Properties

To investigate the influence of spinel structure and sintering temperature on the functional properties of BaTiO3/NixZn1−xFe2O4 (x = 0, 0.5, 1), NiFe2O4, ZnFe2O4, and Ni0.5Zn0.5Fe2O4 were in situ prepared by thermal decomposition onto BaTiO3 surface from acetylacetonate precursors. As-prepared powders were additionally sintered at 1150 °C and 1300 °C. X-ray powder diffraction (XRPD) and scanning electron microscopy (SEM) coupled with electron dispersive spectroscopy (EDS) were used for the detailed examination of phase composition and morphology. The magnetic, dielectric, and ferroelectric properties were investigated. The optimal phase composition in the BaTiO3/NiFe2O4 composite, sintered at 1150 °C, resulted in a wide frequency range stability. Additionally, particular phase composition indicates favorable properties such as low conductivity and ideal-like hysteresis loop behavior. The favorable properties of BaTiO3/NiFe2O4 make this particular composite an ideal material choice for further studies on applications of multi-ferroic devices

BaTiO3/NixZn1−xFe2O4 (x = 0, 0.5, 1) Composites Synthesized by Thermal Decomposition: Magnetic, Dielectric and Ferroelectric Properties

To investigate the influence of spinel structure and sintering temperature on the functional properties of BaTiO3/NixZn1−xFe2O4 (x = 0, 0.5, 1), NiFe2O4, ZnFe2O4, and Ni0.5Zn0.5Fe2O4 were in situ prepared by thermal decomposition onto BaTiO3 surface from acetylacetonate precursors. As-prepared powders were additionally sintered at 1150 °C and 1300 °C. X-ray powder diffraction (XRPD) and scanning electron microscopy (SEM) coupled with electron dispersive spectroscopy (EDS) were used for the detailed examination of phase composition and morphology. The magnetic, dielectric, and ferroelectric properties were investigated. The optimal phase composition in the BaTiO3/NiFe2O4 composite, sintered at 1150 °C, resulted in a wide frequency range stability. Additionally, particular phase composition indicates favorable properties such as low conductivity and ideal-like hysteresis loop behavior. The favorable properties of BaTiO3/NiFe2O4 make this particular composite an ideal material choice for further studies on applications of multi-ferroic devices

The correlation between structural relaxation process and the change in magnetic permeability of the Fe73.5Cu1Nb3Si15.5B7 amorphous alloy under the thermal influence

Fast cooling of 106 K/s, according to the melt-spinning method, led to the Fe73.5Cu1Nb3Si15.5B7 amorphous alloy formation. X-ray diffraction analysis method (XRD) showed that the obtained alloy is in amorphous state. The differential scanning calorimetry method (DSC) has defined the temperature interval of the crystallization process to be from 510ºC to 540ºC. The same temperature interval has also been confirmed by measuring electrical resistivity dependence over temperature. The heating of alloy sample in the temperature interval from 25ºC to 600ºC, leads to structural changes in the alloy under the thermal influence. Structural relaxation and crystallization processes have been investigated by thermoelectromotive force measurement (TEMF) of thermocouple amorphous alloy - copper. Based on the change in temperature coefficient of TEMF thermocouple annealed at various temperatures, relative changes in electron state density near Fermi level have been determined. It has been shown that the changes in normalized magnetic permeability in correlation with appropriate structural changes, which cause changes in electron state density near Fermi level

Piezoelectric And Pyroelectric Properties Of Fe/Pb/Zr-co-doped Barium Titanate Ceramics

Powdery mixtures of 50 mass% Fe, 4 mass% Pb, 3 mass% Zr and 43 mass% BaTiO3 were mechanochemically activated via planetary ball mill for time periods spanning from 30 min to 300 min and subsequently sintered for 2 hours at 1200 °C in the dynamic atmosphere of air. Of all the samples, the one activated for 270 min exibited the most prominent piezoelectric effect of up to 1.17 mV under the applied pressure of 113 kPa with the relaxation time of 85 s. The pressure dependence of voltage showed three successive, distinct domains in which the voltage rise differed, with the rate of 0.09 mV/kPa in the initial one (ranging from 0.00 kPa to 5.66 kPa of the external pressure), 0.01 mV/kPa in the second one (from 5.66 kPa to 56.60 kPa) and ultimately the plateau occuring from approximately 60 kPa onwards. When heated to 200 °C, the same sample manifested the biggest pyroelectric effect as well, being 0.55 mV with no external field applied, as well as 1.04 mV when subjected to the homogenous magnetic field of 50 kA/m, thus yielding a 89% net increase of the incited voltage observed

The effect of temperature and frequency on magnetic properties of the Fe81B13Si4C2 amorphous alloy

In this study it was investigated influence of temperature and frequency on permeability, coercivity and power loses of Fe81B13Si4C2 amorphous alloy. Magnetic permeability measurements performed in nonisothermal and isothermal conditions was confirmed that efficient structural relaxation was occurred at temperature of 663 K. This process was performed in two steps, the first one is kinetic and the second one is diffuse. Activation energies of these processes are: Ea1 = 52.02 kJ/mol for kinetic and Ea2 = 106.9 kJ/mol for diffuse. It was shown that after annealing at 663 K coercivity decrease about 30% and therefore substantial reduction in power loses was attained. Investigated amorphous alloy satisfied the criteria for signal processing devices that work in mean frequency domain