Pr Alloys Research Articles

Medium-range order and crystallization in amorphous Al?Ni?Pr alloys

The amorphous structures of Al–Ni–Pr alloys with different compositions have been studied by X-ray diffraction (XRD). A distinct prepeak which characterizes the medium-range order (MRO) occurs at values of scattering vector Q=10–20 nm−1 in the structure factors of the amorphous alloys. The position of the prepeak shifts to smaller Q values as the concentration of Pr increases. The structure unit size increases with increasing Pr concentration. The addition of Pr can improve the interaction between unlike atoms. The crystallization behavior of Al–Ni–Pr alloys has been investigated by XRD, differential scanning calorimetry (DSC) and transmission electron microscopy (TEM) techniques. Depending on composition, Al–Ni–Pr amorphous alloys devitrify by either primary crystallization of pure, nanometer-sized fcc-Al phase or by the simultaneous precipitation of fcc-Al and intermetallic compounds. The prepeak in the structure factor is related to the strong chemical bonds that cause the intermetallic compounds (Al3Ni, AlPr) formation.

Structure and magnetic properties of RFe6−xGa6+x (R=rare earth)

The crystal structures and magnetic properties of RFe6−xGa6+x (R=Ce, Pr, Nd, Sm, and Gd) alloys have been investigated by x-ray powder diffraction and magnetic measurement. A ternary intermetallic compound with an orthorhombic ScFe6Ga6 type structure is found in these alloys. The lattice parameter contraction is observed when the higher atomic number lanthanides are substituted into the intermetallic. In each unit cell, there are six nonequivalent crystal positions, i.e., 2a, 4e, 4f, 4g, 4h, and 8k, which are occupied by 2R, 4GaI, 4(FeI,Ga), 4GaII, 4GaIII, and 8FeII, respectively. The RFe6−xGa6+x alloys have ferromagnetic ordering but the magnetic transitions have been found in Nd based alloy. The RFe6−xGa6+x alloys show a soft magnetic behavior but the magnetization hysteresis loops have been observed in the Nd and Sm alloys at 5 K. The saturated magnetic moments per molecule tend to increase from Ce to Nd. However, a drastic decrease of magnetic moment in GdFe6Ga6 alloy is observed and is likely due to the Gd spin alignment being antiparallel to Fe spin. The saturation magnetic moments of these alloys are calculated and agree with the experimental values.

Influence of Pr on the magnetic structure of Er

Time-of-flight neutron diffraction has been used to determine the temperature dependence of the magnetic structure of three binary hexagonal Er–Pr alloys, Er90Pr10, Er80Pr20, and Er60Pr40. In overall agreement with magneto-thermal measurements performed on these compounds, the addition of Pr initially increases the Curie temperature and decreases the Néel temperature, observed at 20 K and 86 K, respectively, for pure Er. The neutron diffraction data for Er90Pr10, however, also clearly show that a ferromagnetic phase, with moments parallel to the c-axis, coexists with modulated structure components, with increasing temperature up to 35 K, above which a pure sine modulated structure sets in up to the Néel temperature at approximately 65 K. A similar behavior is observed for Er80Pr20, where the sine modulated phase is observed to disappear at 48 K. In sharp contrast, only one magnetic phase, identified as ferromagnetic with moments parallel to the c-axis, is observed for Er60Pr40 from low temperatures up to the Curie point at 35 K. The propagation vectors of the sine modulated phases are found to be temperature dependent.

Evidence for the precipitation of the Fe2Pr phase in the Fe–Pr binary system

Directional solidification experiments were employed on Fe–Pr alloys at several low cooling rates in order to observe the solidification sequence displayed along the length of the samples. Measurements of the transition temperatures around the eutectic temperature of this system were also performed using a Calvet-type calorimeter. The results show the precipitation of the Fe2Pr phase and its peritectic formation, described as Fe17Pr2+L→Fe2Pr. The calorimetric measurements give the temperature of this reaction as being 669 °C. The system presents only one eutectic reaction at 664 °C, described as L→Fe2Pr+Pr, with a feathered morphology under metallographic analysis. Thermomagnetic measurements give the Curie temperature of the Fe2Pr phase as 44 °C. A sequence of reactions during solidification of the alloys around the eutectic point for the Fe–Pr binary system is proposed.

Radiation defects production in pure nickel and dilute nichel alloys irradiated by 30 mev electrons at high temperatures

Kinetics of both residual resistivity and longitudinal magnetoresistivity Δρ‖ variation has been studied in pure nickel and Ni/0.044 at. % Sc, 0.690 at. % Sc, Ni/0.038 at. % Pr alloys during 30 MeV electron irradiation. The irradiation was performed at 523 and 703 K temperatures. It was found that increasing of scandium concentration up to 0.690 at. % caused the radiation-induced resistivity growth. The similar effect is observed in Ni/Sc, Ni/ Pr alloys by increasing of radiation temperature. The results have been discussed in terms of depleted zone formation due to the residual impurity redistributing in solid solution. From comparative analysis of the dependencies Δρ(D) and Δρ‖(D) in Ni/Sc alloys, it is shown that “clusters” of scandium atoms in supersaturated solid solution are additional sinks for radiation point defects.

Thermal Stability and Magnetic Properties of Fe–Co–Pr–B Amorphous Alloys with a Supercooled Liquid Region

The thermal stability, crystallized structure and magnetic properties of melt-spun Fe 70-x Co 10 Pr x B 20 (0 ≤ x? 6) amorphous alloys have been investigated. The glass transition followed by a supercooled liquid region (ΔT x ) was observed in the composition range of 2 to 5 at%Pr and the value of the ΔT x is in the range of 23 to 43 K. The good hard magnetic properties were obtained for the alloys containing 2.5 to 5 at%Pr subjected to an optimum heat treatment. The ΔT x and reduced glass transition temperature (T g /T m ) of the 3.5 at%Pr alloy are 43 K and 0.57, respectively. The crystallized structure consists of (Fe, Co) 3 B, α-(Fe, Co) and Pr 2 (Fe, Co) 4 B phases and their average grain sizes after annealing for 420s at 863K are about 25 nm. The remanence (B r ), coercivity ( i H c ) and maximum energy product (BH) max of the optimally annealed the 3.5 at%Pr alloy are 1.36 T. 211 kA/m and 107 kJ/m 3 , respectively. The good hard magnetic properties in the crystallized state of the Fe-Co-Pr-B amorphous alloys with high glass-forming ability indicates the possibility of future fabrication of a bulk hard magnetic material by the simple process of the formation of a bulk amorphous alloy followed by crystallization.

High anisotropy in Pr–Fe–Co–B–Zr HDDR powders

The magnetic behaviour of HDDR powders prepared from a Pr 13.7 Fe 63.5 Co 16.7 B 6 Zr 0.1 alloy has been investigated. It has been shown that it is possible to produce highly anisotropic HDDR material from this alloy in the homogenised state (1373 K for 20 h). Remanent magnetisation in the easy direction of the aligned powder was 126±2 J/Tkg whereas, in the hard direction, it was 30±0.6 J/Tkg. HDDR powder based on the corresponding Nd-based alloy (subjected to the same heat treatments) and commercially available, HDDR powder, have both been used as a comparison. The degree of alignment for the HDDR powder based on the Pr alloy was higher (76%) than that of the commercial HDDR powder (69%).

Studies on magnetic properties and microstructure of melt-spun nanocomposite R 8(Fe,Co,Nb) 86B 6 (R=Nd, Pr) magnets

Fe-rich R 8(Fe,Co,Nb) 86B 6 (R=Nd, Pr) alloys consisting of a mixture of exchange-coupled magnetically hard 2 : 14 : 1 and soft Fe(Co) phases have been studied for the development of more economical and medium strength permanent magnets. The nanocomposite structure with a grain size around 15–30 nm is obtained by crystallizing the as-made amorphous melt-spun ribbons. The coercivity is found to depend mainly on the grain size of the soft phase which is very sensitive to the sample composition. The average grain size is about 30 nm in R 8Fe 86B 6, but the microstructure is not homogeneous and there are several large α-Fe grains with size up to 50–100 nm. The coercivities are 3.3 kOe in Nd 8Fe 86B 6 and 4.9 kOe in Pr 8Fe 86B 6 samples. Nb substitution significantly reduces the grain size of α-Fe and increases the coercivity. The highest coercivities obtained are 5.5 kOe in Nd 8(Fe 0.97Nb 0.03) 86B 6 and 9.3 kOe in Pr 8(Fe 0.92Nb 0.08) 86B 6 samples. Co substitution for Fe increases the grain size of both the 2 : 14 : 1 phase and α-Fe and dramatically decreases the coercivity. Increasing the B content in Co substituted samples leads to the formation of a more homogeneous and finer microstructure and thus to a partial recovery of the coercivity from 2.3 kOe in Nd 8((Fe 0.5Co 0.5) 0.97Nb 0.03) 86B 6 to 4.3 kOe in Nd 8((Fe 0.5Co 0.5) 0.97Nb 0.03) 82B 10 and from 2.1 kOe in Pr 8((Fe 0.5Co 0.5) 0.94Nb 0.06) 86B 6 to 6.5 kOe in Pr 8((Fe 0.5Co 0.5) 0.94Nb 0.06) 82B 10. It is further found that Co substitution significantly increases the Curie temperature of the 2 : 14 : 1 phase and improves the temperature dependence of the saturation magnetization.

Microstructural and Magnetic Improvements in Tube-Cast Pr-Fe-B-Cu Alloys Via Heat Treatments and Rapid Upset Forging

ABSTRACTAlloys of Pr-Fe-B-Cu were cast into Cu and stainless steel tubes. It could be seen that a preferred crystallographic orientation was obtained after cooling. Fine platelets of Pr2Fe1 4B matrix phase were formed, surrounded by various grain boundary phases, and there was a significant reduction in the amount of free Fe present, in comparison to conventional slab cast alloys. In order to improve the magnetic properties in the as-cast state, two alternative routes were used. The first involved a series of two step heat treatments to develop an improved microstructure. After an optimum heat treatment of 1000 'C for 24 hours + 500°C for 3 hours, significantly improved magnetic properties were obtained for a 17.5 % Pr alloy; Br = 752 mT, Hci = 613 kAm−1 and BHmax = 96 kJm−3. The second route involved a rapid upset forging [RUF] process, with a strain rate of 11.5 s−1, to hot deform the alloys. Following post-forging heat treatments, properties of Br = 966 mT, Hci = 780 kAm−3 and BHmax = 160 kJm−3 were obtained for a 15% Pr alloy. That nature of the improvements in properties as a result of heat treatments and RUF were investigated and are discussed in the present work.

Thermodynamic properties of Cobalt–Praseodymium alloys

The thermodynamic properties of Co–Pr alloys have been determined between 973 and 1073 K by electromotive force measurements on galvanic cells employing CaF 2 as a solid electrolyte. Results yield a complete set of thermodynamic functions for the intermetallic phases (Co), Co 17Pr 2, Co 5Pr, Co 7Pr 2, Co 3Pr, and Co 2Pr which are compared with data for analogous alloys available from the literature and with predicted values from the Miedema model. The influence of the electronic structure of the components on the energetics of alloy formation is discussed.

Large magnetoresistance in rare-earth based alloys

The results of magnetoresistance ( Δϱ/ ϱ) measurements at low temperatures on the alloys, CeIr 2B 2, Pr 0.2R 0.8Cu 2Ge 2, Pr 0.2R 0.8Ni 2Si 2, and Pr 0.2R 0.8Cu 2Si 2 (RLa, Y), are reported. The Δϱ/ ϱ of CeIr 2B 2 at 5 K (in the ferromagnetically ordered state) is large (−60%) at 70 kOe. In the case of Pr alloys, Δϱ/ ϱ is positive thereby proving that the Kondo effect is absent in these alloys. One of the Pr alloys, Pr 0.2La 0.8Cu 2Si 2, also exhibits a large positive Δϱ/ ϱ at 5 and 10 K about (28% at 70 kOe). Relevance of these findings to the current topic of interest on giant magnetoresistance will be pointed out.

MBE growth and characterisation of light rare-earth superlattices

The molecular beam epitaxy growth techniques which have already successfully produced a range of heavy rare-earth superlattices have now been extended to produce superlattices of two light rare-earth elements, Nd Pr , as well as superlattices and alloy films of a heavy/light system, Ho Pr . High-resolution X-ray diffraction analysis shows the Nd Pr superlattices to be of high structural quality, while the Ho Pr superlattices are significantly less so. In the Ho Pr superlattices, Pr is found to retain its bulk dhcp crystal structure even in thin layers (down to 6 atomic planes thick) sandwiched between thick layers of hcp Ho. In addition, neutron diffraction studies of the Ho Pr superlattices have shown that the helical Ho magnetic order is not coherent through the dhcp Pr layers, in contrast to previous hcp hcp superlattices Ho Y , Ho Lu and Ho Er . The series of Ho:Pr alloy films has shown structural trends similar to bulk alloys, with a range of compositions between Ho 0.55Pr 0.45 and Ho 0.35Pr 0.65 where the Sm δ-structure is stable, separating more extensive regions of hep and dhcp solid solutions.

Praseodymium alloy ion source for focused ion beam implantation in superconductors

We have investigated the emission characteristics of a liquid alloy ion source for focused ion beam implantation of praseodymium (Pr) ions in high-Tc superconductors. The element Pr was used in a ternary Au–Si–Pr alloy with a low melting point and a low vapour pressure. The melting properties of the alloy were determined by differential thermal analysis. We have measured the emission current stability, the current–voltage characteristics and the mass spectra using a single magnetic mass spectrometer. The ion source exhibits a good performance even after storage for several months in air. The mass spectra show a high intensity of double charged Pr ions.

Magnetic modulation vectors in Nd rich NdPr alloys

The temperature dependencies of the magnetic modulation vectors for two single crystals of Nd0.75Pr0.25 and Nd0.65Pr0.35 have been determined from neutron diffraction experiments.

Structure and properties of rapidly solidified Mg-based MgPr alloys

Mg-based alloys containing 1 to 15wt% Pr were rapid-quenched by melt-spinning. Lattice parameters of αMg, microstructure and microhardness of as-quenched ribbons were studied using optical microscope, XRD and TEM. Lattice parameters a and c of αMg solid solution were increased with increasing alloy content up to 5 to 10wt% Pr indicating that the solid solubility of Pr in αMg could be extended to 5–10wt% Pr by melt-spinning. Microhardness of the as-spun ribbons was also increased from 53 to 167 kg/mm2 with increasing alloy content from 1 to 15 wt% Pr. TEM study showed that grained αMg equiaxed in cross section with few fine second phase along grain boundaries formed in Mg-1 wt%Pr ribbon while primary αMg with coarser second phase plus degenerated eutectic formed in Mg-15wt%Pr ribbon. The solid solubility extension of Pr in αMg and possible significant of the result for development of microcrystalline light-weight Mg-based alloys are discussed.

Standard enthalpies of formation of some praseodymium alloys by high-temperature direct synthesis calorimetry

The standard enthalpies of formation of eight Pr alloys were determined by direct synthesis calorimetry at 1473 ± 2 K. The following values of ΔHskƒ/°(kJ/g atom) are reported: PrNi5, −(25.6 ± 1.0); PrRu2, −(16.9 ± 1.5); PrRh2, −(60.4 ± 1.7); PrPd, −(78.8 ± 2.5); PrPd2, −(82.7 ± 3.1); PrIr2, −(70.7 ± 2.8); PrPt, −(103.4 ± 2.7); and PrPt2, − (93.5 ± 2.4). The results are compared with data from available literature for some of the Pr alloys and with predicted values from the model of Miedemaet al.

Structural changes in amorphous Fe80-xRxB20 (R = Y, Sm, Pr) alloys

The radio-frequency (rf) collapse of the magnetic hyperfine structure in the Mössbauer spectra is employed to study changes in the short-range order in amorphous metals via the electric quadropole hyperfine interaction. The structural changes in amorphous Fe80-xRxB20 (where R = Y, Sm, Pr) alloys were studied in detail as a function of x. It was found that such substitutions induce considerable changes in the short-range order. A low concentration of substituting atoms (x<4) causes a large distortion of the nearest surroundings of Y, Sm and Pr atoms. Larger contents (x>4) lead to collective changes in the structure.

The magnetic properties of nanocrystalline melt spun iron-didymium-boron alloys

The results of a systematic study of the effect of Nd: Pr ratio on the magnetic properties of melt spun Fe-didymium-B alloys (where didymium is a mixture of Nd and Pr) are presented. Evidence is shown in all the isotropic alloys studied of remanence, J r >0.5 J s due to the nanocrystalline structure resulting from the melt spinning process. Evidence is also shown of interaction between the Nd and Pr in the alloys leading to Curie temperatures higher than expected from measurements on the pure Nd and Pr alloys.

Preparation of oxide superconductors by oxidation of amorphous Ln-Ce-Cu (Ln=Pr, Nd or Sm) alloy tapes

On etudie la formation de phase amorphe dans les alliages ternaires Ln-Ce-Cu (Ln=Pr, Nd ou Sm) par filage a l'etat fondu, et la preparation d'oxydes supraconducteurs par oxydation de rubans d'alliages amorphes

Magnetostriction of rapidly quenched Sm(FeCo) and Pr(FeCo) alloys

Magnetostriction of the crystalline and amorphous Sm 1− y (Fe 1− x Co x ) y (0≤ x≤1.0; y=0.67, 0.75, 0.78, 0.83 and 0.89) and Pr 1− y (Fe 1− x Co x ) y (0≤ x≤1.0; y=0.67, 0.75, 0.78, 0.79, 0.83 and 0.89) alloys prepared by melt spinning has been measured at room temperature. Sm 0.33(Fe 0.8Co 0.2) 0.67 shows the largest magnetostruction (λ≈-1250×10 -6) of the crystalline Sm(FeCo) system. The magnetostruction λ amorphous Sm(FeCo) alloys around x=0.2 and y=0.67−0.75 exceeds -450x 10 -6. In the crystalline Pr(FeCo) system, the λ value exhibits the maximum of about λ≈480×10 -6 at x=0.4 and y=0.78, where the metastable Pr(FeCo) 2 compound (cubic MgCu 2 type) is formed due to a rapid solidification.