Increasing Pr Content Research Articles

Structure, magnetic properties and magnetostriction of laves compounds Nd 1−xPr x(Fe 0.35Co 0.55B 0.1) 2

The C15 Laves phases with composition Nd 1− x Pr x (Fe 0.35Co 0.55B 0.1) 2 (0⩽ x⩽1) have been synthesized by arc melting and subsequent annealing. The Curie temperature T c and the saturation magnetizations M s at 5 and 295 K decrease with increasing Pr content. The linear anisotropic magnetostriction λ a= λ ∥− λ ⊥ at room temperature for Nd 1− x Pr x (Fe 0.35Co 0.55B 0.1) 2 alloys with 0⩽ x⩽0.4 initially reaches a negative minimum, then increases and changes its sign with increasing magnetic field H, and the λ a for the alloys with x⩾0.6 is positive and increases as magnetic field H increases.

Angular dependence of coercivity of grains in nanocrystalline permanent magnets

In this paper magnetization remanence curves were studied for nanocrystalline Pr8Fe87B5, Pr12Fe82B6 and Pr15Fe77B8. Initially the sample was at remanence following saturation along z-axis. After rotating the magnet by 5n degrees (n = 0, 1, …, 18) a field H was applied along z-axis and then decreased to zero, and the remanence Jnr was measured as a function of H. The curves were compared with those calculated based on the nucleation of reverse domain model and domain wall pinning model. The latter model succeeds in simulation much better than the former, and it is concluded that the magnetization reversal is dominated by domain wall pinning for all the samples. The nucleation mechanism contribution, while remains small, increases with the increase of Pr content.

Magnetostriction of Tb0.1Ho0.9−xPrx(Fe0.9B0.1)2 (x=–0.4) compounds

The structural and magnetic properties of Tb0.1Ho0.9−xPrx(Fe0.9B0.1)2 (x=0, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, and 0.4) compounds are investigated. The compounds with 0⩽x⩽0.25 are found to stabilize in single cubic Laves phase structures. Small quantities of the (Tb,Ho,Pr)2Fe14B phase and rare-earth phases for x⩾0.3 and also the (Tb,Ho,Pr)(Fe,B)3 phase for x⩾0.35 are observed along with the Laves phase. The saturation magnetization and Curie temperature are found to decrease with Pr content. However, the magnetostriction (at 10kOe) is found to increase with Pr content. The x=0.15 compound is found to exhibit a possible anisotropy compensation between the (Tb∕Ho) and Pr sublattices. The easy magnetization direction (EMD) is found to rotate toward ⟨113⟩ as the Pr content increases, up to x=0.25, and for x⩾0.35 there is a tendency for the EMD to shift toward ⟨111⟩.

Magnetic and magnetostrictive properties and anisotropy compensation in Tb0.1Ho0.9−xPrx(Fe0.9B0.1)2 (⩽x⩽0.4) compounds

Tb 0.1 Ho 0.9 − x Pr x Fe 2 and Tb0.1Ho0.9−xPrx(Fe0.9B0.1)2 (0⩽x⩽0.4) alloys were prepared by arc melting and subsequent annealing. It was found that the addition of boron is helpful for the formation of MgCu2-type Laves phase. The spin reorientation temperature of Tb0.1Ho0.9−xPrx(Fe0.9B0.1)2 compounds decreases and the easy magnetization direction rotates from ⟨100⟩ to ⟨111⟩ when x is increased from 0 to 0.4, demonstrating the anisotropy compensation between Ho3+ and Pr3+ ions. The anisotropic magnetostriction λa=λ∥-λ⊥ at room temperature increases with increasing Pr content when x⩽0.2, which is ascribed to the much larger magnetostriction of PrFe2 than of HoFe2 and the decrease of the anisotropy due to compensation. The Tb0.1Ho0.7Pr0.2(B0.1)2 compound close to the anisotropy compensation point has the largest magnetostriction at room temperature.

Magnetic properties, phase evolution, and microstructure of melt-spun (Sm1−xPrx)Co7−yHfyCz (x=0–1; y=0.1–0.3; z=0–0.14) ribbons

Magnetic properties, phase evolution, and microstructure of melt-spun (Sm1−xPrx)Co7−yHfyCz ribbons have been investigated. For (Sm1−xPrx)Co7−yHfy (x=0–1; y=0.1–0.3) ribbons, the magnetization increases, but coercivity decreases, with increasing Pr content. However, the phase constitution and microstructure have not been influenced by modifying Pr content x. The attractive magnetic properties of Br=6.5kG, Hci=6.1kOe, and (BH)max=7.2MGOe could be obtained for (Sm0.8Pr0.2)Co6.9Hf0.1 ribbons. A slight addition of C in (Sm0.8Pr0.2)Co6.9Hf0.1Cz (z=0.06–0.14) ribbon not only refines the microstructure, but also induces nanoscale fcc-Co precipitation in the matrix, leading to the stronger exchange-coupling effect between magnetic grains and the enhancement of remanence and magnetic energy product. As a result, the improved magnetic properties of Br=7.1kOe, Hci=8.5kOe, and (BH)max=11.2MGOe can be achieved for (Sm0.8Pr0.2)Co6.9Hf0.1C0.12 ribbons.

The structures and magnetic properties of Ti-substituted Pr2(Fe,Co)14(C,B)-type nanocomposites

The phase evolution, microstructure, and magnetic properties of PrxFe80−xTi2Co10B4C4 (x=9,10.5) melt-spun ribbons were studied. All these ribbons consist mainly of three phases, namely, 2:14:1, α-(Fe,Co), and 2:17 phases. The Hci significantly increases and Br slightly decreases with increasing Pr content. It was found that increasing Pr content from 9to10.5at.% leads to marked grain refinement in the ribbons. Increasing Pr content also helps suppress the formation of metastable 2:17 phase and the grain growth of the α-(Fe,Co) phase during the annealing treatment, thus avoiding the formation of extensive soft magnetic regions. The refined and uniform structure tends to enhance the exchange-coupling interaction between magnetic grains, which results in a significant improvement of the demagnetization-curve shape and magnetic properties accordingly. High coercivity Hci of 10.2kOe, remanence Br of 9.6kG, and maximum energy product (BH)max of 17.4MGOe have been achieved in Pr10.5Fe69.5Ti2Co10B4C4 ribbons after optimal annealing.

Particle Size Distribution of ZrO<sub>2</sub>:Pr3<sup>+</sup> – Influences of pH, High Power Ultrasound, Surfactant and Dopant Quantity

The aim of the work was to examine the influence of pH, high power ultrasound, surfactant and dopant quantity on the particle size distribution of ZrO2:Pr3+, with praseodymium content varying between 0.05 and 10 %. The nanopowders were obtained via a hydrothermal microwave driven process. To establish if the dopant was located on the surface of the zirconia nanoparticles, the particle size distribution, as a function of pH, was measured to obtain an estimate of the isoelectric point of the samples. All results indicated that the dopant was concentrated on the surface: the measurements of the particle size distribution show that the pH corresponding to maximum average particle size changes towards higher values when the Pr content increases. Measurements of the particle size distribution dependency on the application of high power ultrasound and the addition of the sodium dodecyl sulphate surfactant show that, under certain conditions, there is a better stabilisation of the nanopowders in a dispersion and undesirable agglomeration is hindered.

LOCAL STRUCTURAL CHANGE AND SUPERCONDUCTIVITY IN Y1-XPRXBA2CU3OY

To further understand the argument about the superconductivity in PrBa 2 Cu 3 O y , We try to change YBa 2 Cu 3 O y to PrBa 2 Cu 3 O y gradually, studying the detailed change during the change, and hope to find some clue to the argument. The single-phase samples of Y 1- x Pr x Ba 2 Cu 3 O y ( x = 0, 0.1, 0.2, 0.3, 0.5, 0.6, 0.8, 1.0, respectively) were synthesized and characterized by DC magnetization measurement and X-ray diffraction. The structure of the samples was refined by Rietveld method. After careful analysis, it is found that as the x increasing, Ba moves toward the Cu - O (1) plane, the bond length between Y - Ba , Y - Cu (2), and Ba - O (1), and Cu (1)-0(4) increase simultaneously. It demonstrates that as the Pr content increases, the distance between the active block and the carrier reservoir block becomes farer and farer, and the area of the carrier reservoir block increases. It is suggested that the doping of Pr to Y in YBa 2 Cu 3 O y changes some local structure and result in the suppression and vanishing of the superconductivity.

Synchrotron radiation x-ray photoelectron spectroscopy study on the interface chemistry of high-k PrxAl2−xO3 (x=0–2) dielectrics on TiN for dynamic random access memory applications

Engineered dielectrics combined with compatible metal electrodes are important materials science approaches to scale three-dimensional trench dynamic random access memory (DRAM) cells. Highly insulating dielectrics with high dielectric constants were engineered in this study on TiN metal electrodes by partly substituting Al in the wide band gap insulator Al2O3 by Pr cations. High quality PrAlO3 metal-insulator-metal capacitors were processed with a dielectric constant of 19, three times higher than in the case of Al2O3 reference cells. As a parasitic low dielectric constant interface layer between PrAlO3 and TiN limits the total performance gain, a systematic nondestructive synchrotron x-ray photoelectron spectroscopy study on the interface chemistry of PrxAl2−xO3 (x=0–2) dielectrics on TiN layers was applied to unveil its chemical origin. The interface layer results from the decreasing chemical reactivity of PrxAl2−xO3 dielectrics with increasing Pr content x to reduce native Ti oxide compounds present on unprotected TiN films. Accordingly, PrAlO3 based DRAM capacitors require strict control of the surface chemistry of the TiN electrode, a parameter furthermore of importance to engineer the band offsets of PrxAl2−xO3∕TiN heterojunctions.

Crystal structure and its correlation to intrinsic and extrinsic magnetic properties of epitaxial hard magnetic Pr-Co films

Pulsed laser deposited epitaxial ${\mathrm{Pr}}_{x}{\mathrm{Co}}_{100\ensuremath{-}x}$ $(x=8.7\char21{}27.6\phantom{\rule{0.3em}{0ex}}\mathrm{at.}\phantom{\rule{0.2em}{0ex}}%)$ thin films were systematically studied as a function of Pr content. Structural and magnetic measurements reveal different phases for specific composition ranges. In some cases, the phases observed are in contrast to their bulk counterparts. Uniaxial anisotropy at room temperature is observed in all the films enabling excellent hard magnetic properties. Polarization decreases monotonically with the increase of Pr content, whereas coercivity exhibits a broad maximum near the highly anisotropic $\mathrm{Pr}{\mathrm{Co}}_{5}$ composition. For the optimum combination of coercivity and polarization, the measured ${(BH)}_{\mathrm{max}}$ reaches values of $310\phantom{\rule{0.3em}{0ex}}\mathrm{kJ}∕{\mathrm{m}}^{3}$, which exceeds the highest-energy product value reported for RE-Co $(\mathrm{RE}=\text{rare}\text{\ensuremath{-}}\text{earth})$ systems. Temperature-dependent ac susceptibility measurements reveal that films with $x=8.7\char21{}20.4$ undergo a spin reorientation from easy axis to easy cone, but films with $x=22.9\char21{}27.6$ maintain their uniaxial anisotropy throughout the temperature range of investigation. From the comparison of the structural investigations and the spin reorientation temperature measurements, it is concluded that the spin reorientation temperature is insensitive to the change in the lattice parameter of the $\mathrm{Pr}{\mathrm{Co}}_{5\ifmmode\pm\else\textpm\fi{}\ensuremath{\delta}}$ phase.

Effect of the substitution of PR for LA on the microstructure and electrochemical properties of [formula omitted] hydrogen storage electrode alloys

In this paper, the effects of substitution of Pr for La on the microstructure and electrochemical properties of La 0.7 - x Pr x Mg 0.3 Ni 2.45 Co 0.75 Mn 0.1 Al 0.2 ( x = 0.00 – 0.30 ) hydrogen storage alloys have been studied systematically. XRD Rietveld analyses showed that all alloys consisted of ( La , Mg ) Ni 3 phase and LaNi 5 phase. With the increase in Pr content, the lattice parameters and cell volumes of the component phases all decreased. The electrochemical studies showed that the maximum discharge capacity decreased from 366 to 346 mAh/g when x increased from 0.00 to 0.30. However, the cycling stability of the alloy electrodes was improved with the increase in Pr content. Moreover, the high rate dischargeability, the exchange current density I 0 , the limiting current density I L and the hydrogen diffusion coefficient D of the alloy electrodes all increased first then decreased with increasing x, reaching an extreme when x is 0.15, which indicated that the alloys’ kinetics of hydriding/dehydriding increased first up to x = 0.15 and then decreased with further increasing x to x = 0.30 .

Synthesis, sinterability and ionic conductivity of nanocrystalline Pr-doped La 2Mo 2O 9 fast oxide-ion conductors

A new series of nanocrystalline La 2− x Pr x Mo 2O 9 (0.2 ≤ x ≤ 0.8) powders are synthesized through the pyrolysis of polyacrylate salt precursors prepared via in situ polymerization of the metal salts and acrylic acid. The polymeric precursors are characterized by thermogravimetric and differential thermal analysis (TG/DTA) to determine the thermal decomposition and crystallization temperature, which is found to be at 510 °C. X-ray diffraction analysis indicates that the substitution of La by Pr preserves the single-phase La 2Mo 2O 9 structure up to a Pr dopant concentration of x ≤ 0.7. The particle size and the α → β phase transition of the Pr-doped La 2Mo 2O 9 samples are studied by using a transmission electron microscope (TEM) and differential scanning calorimetry (DSC), respectively. The sintering behaviour of the Pr-doped samples are examined via isothermal and non-isothermal experiments. It demonstrates that the synthesized nanocrystalline powders have good sinterabilty and a relatively low sintering temperature of 800 °C for 4 h is sufficient to reach ∼99% of the theoretical density with good microstructures. Furthermore, the oxide-ion conductivity increases with increasing Pr content and the maximum conductivity is attained at x = 0.5 in La 2− x Pr x Mo 2O 9.

Effect of Pr and Dy substitution on the impact resistance of sintered Nd–Fe–B magnets

The impact resistance of sintered Nd–Fe–B magnets with nominal compositions (Nd 1− x Dy x ) 16Fe 78B 6 ( x = 0, 0.05, 0.10, 0.15) and (Nd 1− y Pr y ) 16Fe 78B 6 ( y = 0, 0.33, 0.67, 1) has been investigated by the falling-weight impact test. The bending strength and the Vickers hardness were measured. It shows that the Dy substituted magnets have better impact resistance than the Pr substituted magnets. The impact resistance of the investigated magnets improves monotonously with increasing Dy content, and reduces with increasing Pr content, which seems to relate closely to the change of the density or of the hardness.

Spin-State Transition in La1-xPrxCoO3

We have investigated the crystalline structure and the magnetic properties of La 1- x Pr x CoO 3 single crystals. The crystalline symmetry is rhombohedral R \bar3 c for 0 ≤ x ≤0.3, and orthorhombic P n m a for 0.7 ≤ x ≤1. The lattice volume decreases monotonically with increasing Pr content due to the smaller ionic radius of Pr 3+ than La 3+ . The temperature dependence of the magnetic susceptibility [χ( T )] arising from Co 3+ ions in La 1- x Pr x CoO 3 was evaluated using La 1- x Pr x AlO 3 as a reference. The temperature dependence of the effective magnetic moment arising from Co ions is interpreted by the three spin-states low-spin (LS), intermediate-spin (IS) and high-spin (HS). The energy of the IS-state (Δ 1 ) increases with increasing Pr content through the chemical pressure. The chemical pressure dependence of Δ 1 agrees with the hydrostatic pressure dependence. In contrast to the first spin-state transition, the second spin-state transition is almost independent of the Pr content.

Multiband Superconductivity in Filled-Skutterudite Compounds (Pr1-xLax)Os4Sb12: An Sb Nuclear-Quadrupole-Resonance Study

We report on Sb nuclear-quadrupole-resonance (NQR) study in filled-skutterudite compounds (Pr_1-xLa_x)Os_4Sb_12. The Sb-NQR spectra have split into two sets, arising from different Sb_12 cages containing either Pr or La, which enables us to measure two kinds of nuclear spin-lattice relaxation time T_1^Pr and T_1^La. In the normal state, the temperature (T) dependence of 1/T^Pr_1T showed almost the same behavior as that for PrOs_4Sb_12 regardless of. In contrast, 1/T^La_1T markedly decreases with increasing La concentration. In the superconducting state for x=0.05 and 0.2, 1/T_1^Pr exponentially decreases down to T=0.7 K with no coherence peak below T_c as well as in PrOs_4Sb_12. A remarkable finding is that the residual density of states at the Fermi level below T_c is induced by La substitution for Pr. These results are proposed to be understood in terms of a multiband-superconductivity model that assumes a full gap for part of the FS and the presence of point nodes for a small 4f^2-derived FS inherent in PrOs_4Sb_12. For x=0.8 and 1,1/T^La_1 exhibits a coherence peak and the nodeless energy gap characteristic for weak-coupling s-wave superconductors. With increasing Pr content, T_c and the energy gap increases. The novel strong-coupling superconductivity in PrOs_4Sb_12 is inferred to be mediated by the local interaction between 4f^2-derived crystal-electric-field states with the electric quadrupole degree of freedom and conduction electrons. This coupling causes a mass enhancement of quasi-particles for a part of FS and induces a small FS, which is responsible for point nodes in the superconducting gap function. Note that the small FS does not play any primary role for the strong-coupling superconductivity in PrOs_4Sb_12.

Structural properties and Raman spectroscopy of orthorhombic (Eu 1− xPr x) 0.6Sr 0.4MnO 3 (0≤ x≤1.0)

The effect of Pr doping on structural properties and room temperature Raman spectroscopy measurements is investigated in manganites (Eu 1− x Pr x ) 0.6Sr 0.4MnO 3 (0≤ x≤1.0) with fixed carrier concentration. The result of the Rietveld refinement of x-ray powder diffraction shows that these compounds crystallize in an orthorhombic distorted structure with a space group Pnma. It is evident that, with increasing Pr substitution, three types of orthorhombic structures can be distinguished. The phonon frequencies of the three main peaks, in room temperature Raman-scattering measurements, have been discussed together with their structural characteristics, such as bond-length, bond-angles, and the change of orthorhombic structure type. With the increase of Pr content, the mode at 491 cm −1 also shows a corresponding change. A step effect becomes evident, which seems to indicate the close dependence between the frequency shift of this mode and the change in crystal symmetry. This further supports the notion that the mode at 491 cm −1 is closely correlated with the Jahn–Teller distortion. Moreover, we have found that the lowest frequency peak (assigned as an A 1g phonon mode) depends linearly on the tolerance factor t .

The glass-forming ability of Pr–Ni–Al bulk metallic glasses

A series of Pr–Ni–Al bulk metallic glasses (BMGs) was prepared by a copper mold casting method. The effect of the alloy composition on the glass transition temperatures ( T g) and supercooled liquid regions (Δ T x ) was studied. It showed that the increase in Pr content to a certain degree, though at which the alloy remained fully amorphous, caused the disappearance of T g and Δ T x . Continuous and isothermal annealing methods were used to investigate the disappearance mechanism of T g and Δ T x on the representative Pr 55Ni 25Al 20 and Pr 65Ni 25Al 10 BMGs. X-ray diffraction (XRD) analysis on crystallization products showed that the disappearance of T g and Δ T x for Pr 65Ni 25Al 10 was not due to the precipitation of different kinds of crystalline products but due to the decrease in glass stability (GS) resulted from the larger quantities of the first precipitating Pr 7Ni 3 phase at relative lower temperatures. As a whole, the alloy composition dependence of T g and Δ T x was also discussed in the framework of the three empirical rules for achievement of high glass-forming ability glasses.

Transport, magnetic and thermal properties of Pr dopedLaSr2Mn2O7: a Kondo-type behaviour of resistivity

The interplay of spin, charge and lattice degrees of freedom inLaSr2Mn2O7 (tetragonal,space group I4/mmm) yields a variety of properties such as a CE-type charge ordering and an A-typespin ordering. We have studied the effect of partial replacement of La by Pr onthe magnetic and thermal properties of this system. Compounds of the typeLa1−xPrxSr2Mn2O7 (0≤x≤1) have been prepared and are found to crystallize in the same tetragonal structure.Magnetization, electrical resistivity and specific heat measurements have beencarried out on these compounds. Replacing La by Pr in this system affectsboth the electronic and the magnetic state of the system. It is observed thatthe charge ordering temperature and the net magnetic moment reduce with theincorporation of Pr in the lattice. In the antiferromagnetic state, the charge carriers inLa1−xPrxSr2Mn2O7 behave like a weakly scattered two-dimensional gas whose resistivity(ρ) is a logarithmicfunction of temperature, T (), over a certain temperature interval. This behaviour is enhanced with increasingconcentration of Pr in the samples and is proposed to originate from quantum interference.The electronic part of the specific heat shows the presence of the two transitions atTCO and TN and a contribution from antiferromagnetic magnons at low temperatures.

Fluctuation conductivity and pseudogap in Y1−xPrxBa2Cu3O7−y films

The fluctuation conductivity (FC) and pseudogap (PG) in Y1−xPrxBa2Cu3O7−y with x≈0.1 are investigated. It is shown that the temperature dependence of the FC is the same as in YBa2Cu3O7−y containing defects. At the same time, the temperature dependence of the PG differs from the analogous dependence obtained for YBa2Cu3O7−y films. An increase of the coherence length and decrease of the characteristic temperature T* in Y1−xPrxBa2Cu3O7−y is observed with increasing Pr concentration.

Structural and magnetic properties of Laves compounds Dy1−xPrx(Fe0.35Co0.55B0.1)2 (⩽x⩽1)

Dy 1 − x Pr x ( Fe 0.35 Co 0.55 B 0.1 ) 2 (0⩽x⩽1) Laves compounds with a cubic MgCu2-type structure were synthesized by arc melting and subsequent annealing. The lattice parameter of the Laves compounds linearly increases, while the Curie temperature TC decreases with increasing Pr content. The saturation magnetization Ms at 5K or 295K for the Dy1−xPrx(Fe0.35Co0.55B0.1)2 alloys decreases to reach a minimum, then increases with increasing Pr content. The composition for magnetic moment compensation is about x=0.55 at 295K and x=0.65 at 5K, respectively. The magnetostriction λ‖ or λ⊥ at room temperature was investigated either parallel or perpendicular to the applied field using a standard strain gauge technique.