Increase In Pr Concentration Research Articles

Concentration and temperature dependence of Pr3+ f-f emissions in La(PO3)3

La(PO3)3 activated with different concentrations of Pr3+ was synthesized by a solid-state process. The obtained powder was composed of chunks of several microns in size, typical for this type of synthesis. X-ray diffraction confirmed an orthorhombic crystal structure with the C2221 space group. The electronic band structures and density of states of La(PO3)3 and La(PO3)3:Pr3+ are calculated and presented. The visible and near-infrared emissions from Pr3+ [Xe]4f2→ [Xe]4f2 electronic transitions were detected under 442 nm excitation. The red emission from the 1D2 state dominates visible spectra while emissions from the 3P0,1,2 states have smaller intensities. The 1D2 emission centered around 1020 nm is detected in the near-infrared spectral range. Intensities of 3P0 emissions increased with an increase in Pr concentration, while 1D2 emissions decreased in intensity. We found that the main process responsible for the 1D2 state decay is the Pr(1D2) + Pr(3H4) → Pr(1G4) + Pr(3F3,4) cross-relaxation between two Pr ions of electric dipole-dipole character. This finding is supported by 1D2 emission decay measurements, which revealed a reduction of average decay constants from 242 μs for a 0.5 mol% doped sample to 11 μs for a 10 mol% doped sample and an increasingly stronger non-exponential behavior of emission decay patterns with an increase in Pr3+ concentration.

Influence of Pr doping in non-stoichiometric NiFe2O4 on magnetic response and electronic properties: Magnetic Compton scattering and ab-initio studies

Magnetic Compton profiles of 5 % and 15 % Pr-doped non-stoichiometric NiFe2O4 have been measured using synchrotron radiations of energy 182.65 keV at SPring-8, Japan. An analysis of MCPs measured at 6 and 300 K show that the total spin moment decreases with increasing temperature and Pr concentration in Ni0.9-xPrxFe2.1O4 which is consistent with the magnetic moment (spin + orbital) as observed from magnetization measurements data. Spin moments at different sites are deduced using decomposition of MCPs in the elemental profiles of Ni, Pr-4f, Fe and diffused electrons. Spin moments at Ni-site have been found to play crucial role in emergence of absolute spin moments. Spin moments at Pr-site is aligned antiparallel to that of Ni and Fe sites. The orbital magnetic moment is also deduced from the subtraction of MCP based spin moments from the magnetization data. Theoretical FP-LAPW based total and atom specific spin moments are found in consonance with the MCP based data. Total and spin projected density of states are also computed using the FP-LAPW method to validate role of Pr-4f and Fe-3d (Oh) states in amending the total magnetic moment with Pr concentration. The M−H based saturation magnetization derived at 6 and 300 K temperature show that the saturation magnetic moments reduce from 2.21 → 2.05 μB/f.u. at 6 K and 2.10 → 1.98 μB/f.u. at 300 K with increase in Pr concentration from 5 % → 15 %. On the basis of hysteresis curve and coercive force, both the doped compounds show soft magnetism.

Investigation of structural, photoluminescence, and thermoluminescence properties of Praseodymium doped CaWO4 phosphor

The structural, optical, photoluminescence and thermoluminescence behaviors of Praseodymium doped CaWO4 (Ca1−xPr2x/3WO4; x = 0.01, 0.02, 0.03, 0.04, 0.05) phosphors prepared via conventional solid-state reaction route were reported in this paper. X-ray diffraction study revealed the fact that all the synthesized samples crystallize in a tetragonal structure with I41/a (88) space group and the structural parameters were obtained from the Reitveld refinement. The unit cell volume was found to rise with the increase in Pr concentration. The bandgaps of the prepared samples were obtained from the UV-Visible absorbance spectra by using the Wood-Tauc method. Bandgap and unit cell volume of the prepared samples were directly proportional to each other. Photoluminescence behaviors were investigated from the excitation and the emission spectra. The PL spectra highlight that the quenching occurs at x = 0.02 and the critical distance for energy transfer of the phosphor was found to be 20 Å. Dexter theory was applied to determine the mechanism of quenching and confirmed that the concentration quenching was caused by the dipole-dipole interaction. CIE Chromaticity denoted that the phosphors emit red color. Color purity and CCT of the material were calculated. Thermoluminescence behaviors were studied with different durations of UV dose for the composition x = 0.02 and the kinetic parameters were calculated. Variations of TL emission intensity with temperature confirmed the second-order kinetics of the phosphor with a critical quenching concentration at x = 0.02.

Influence of Pr substitution on the physical properties of the Ce1−xPrxCoGe3 system: Combined experimental and first-principles study

We present the results of our investigations of physical properties for the novel Ce$_{1-x}$Pr$_x$CoGe$_3$ system performed with a number of experimental methods: magnetic susceptibility, specific heat, electrical resistivity, magnetoresistance, and thermoelectric power. Moreover, the electronic structure was studied by means of photoelectron spectroscopy measurements and first-principles calculations. All investigated compositions of the Ce$_{1-x}$Pr$_x$CoGe$_3$ series crystallize in the tetragonal BaNiSn$_3$-type structure. The lattice parameters and unit cell volumes decrease with increasing Pr concentration. On the basis of the measurements taken, a preliminary magnetic phase diagram was created. A continuous suppression of the long-range magnetic ordering was observed with increase of Pr concentration. The critical Pr concentration for magnetic moment ordering was determined from linear extrapolation of the ordering temperature $versus$ $x$ to the lowest temperatures ($T = 0$ K) and is equal to about 0.66. Based on the first-principles calculations we show how the substitution of Pr for Ce affects the electronic structure and magnetic properties of the considered alloys. Within a single model we take into account the magnetic ordering, fully-relativistic effects, and Hubbard U repulsion on Ce and Pr. The impact of Hubbard U on the results of calculations is also discussed. We present the valence-band analysis, Mulliken electronic population analysis, and calculated electronic specific heat coefficients. For CeCoGe$_3$ it is found that the $++--$ configuration of magnetic moments on Ce is slightly more stable than the $+-+-$ one, and also that the calculated value of total magnetic moment on Ce (including spin and orbital parts) is in good agreement with the measurements.

Electronic and optical properties of n-pr co-doped anatase TiO<sub>2</sub> from first-principles

ZnO is a wide bandgap semiconductor with the advantages of good stability, strong radiation resistance, and low cost. It has become a hot material in the field of photocatalysis, but it can only absorb purple light. Therefore, it is a valuable problem to study how to expand the response range of ZnO to visible light. Doping modification is a common method to solve this problem. In order to carry out the relevant research, the calculation in this paper are carried out by the CASTEP tool in Materials Studio software based on the first-principles of ultrasoft pseudopotential of density functional theory, the geometric structures of ZnO, Zn<sub>0.875</sub>Pr<sub>0.125</sub>O, ZnO<sub>0.875</sub>N<sub>0.125</sub>, Zn<sub>0.875</sub>Pr<sub>0.125</sub>O<sub>0.875</sub>N<sub>0.125</sub>, Zn<sub>0.75</sub>Pr<sub>0.25</sub>O<sub>0.875</sub>N<sub>0.125</sub>, Zn<sub>0.625</sub>Pr<sub>0.375</sub>O<sub>0.875</sub>N<sub>0.125</sub> are constructed. All the models are based on the optimization of the geometry structure. By using the method of generalized gradient approximation plus U, we calculate the band structure, density of states, population, absorption spectra and dielectric functions of the models. The results show Co-doped system is easier to form than single-doped system, and the stability of the co-doped system increases first and then decreases with the increase of Pr concentration. The population ratio of the shortest Zn-O bond to the longest Zn-O bond in the same system increases first and then decreases with the impurity concentration, which shows that the doping of impurities has a great influence on the lattice distortion of the system, and the distortion is benefit for the separation of photogenerated hole-electron pairs. Therefore, the photocatalytic activity of the materials can be improved. Hybridization of N-2p and Pr-4f states destroys the integrity of crystals and forms crystal fields around impurity atoms, which results in splitting of energy levels and narrowing of bandgap. Compared with intrinsic ZnO, the static dielectric constant of all doped systems increases, especially the constant of Pr-N co-doped systems increases with the increase of doped Pr concentration, which indicates that the polarization ability of the co-doped systems increases with the increase of doped Pr atomic concentration. The main peaks of the dielectric function imaginary part of the doping systems move to the low energy region, and the absorption spectrums are red-shifted. As the concentration of impurity Pr atom increases, in the visible region, the absorption capacity of each co-doped system increases, their response range is enlarged in turn, showing the co-doping of N and Pr is benefit for improving the photocatalytic activity of ZnO.

Structural, optical and photoluminescence properties of Pr-doped β-Ga2O3 thin films

(2¯01) oriented Pr-doped β-Ga2O3 (Ga2O3:Pr) thin films have been grown on (000l) α-Al2O3 substrates using radio frequency magnetron sputtering method. The influences of the dopant contents on the structural and optical properties of the Ga2O3:Pr thin films have been systematically studied. With the increase of Pr concentration, the c-axis lattice parameter of β-Ga2O3 are elongated, with the energy band gap shrinks. The Ga2O3:Pr films show a broad-band blue (∼490 nm) and a pronounced red (∼615 nm) photoluminescence under 255 nm light illumination. The obtained photoluminescence results are related to the energy transfer of cross relaxation process within the 4f2 configuration of the Pr3+. This work may provide a prominent candidate for further developing advanced composite materials incorporated with luminescent ions.

Magnetic and dielectric properties of orthoferrites La1−x PrxFeO3 (x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5)

The Pr doped LaFeO3 are synthesized by the sol–gel citrate method. The crystal structure of the samples can be described by the Pbnm space group. The Raman spectra of the materials show that the vibrational modes are heavily influenced by the magnitude of the orthorhombic distortion. The antiferromagnetic nature of the samples is examined by temperature dependent magnetisation measurements and the corresponding hysteresis loop. A signature of weak ferromagnetic phase is observed in the samples at low temperature due to the canting of the iron sublattices. The frequency dependent dielectric relaxation of the sample has been investigated in the temperature range from 303 K to 513 K in the framework of conductivity and electric modulus formalisms. The complex impedance plots are explained by an electrical equivalent circuit consisting of constant phase element and resistance. A significant change of the conductivity is observed with the increase of Pr concentration.

Structural, vibrational, electrical and magnetic properties of Bi1−xPrxFeO3

Crystalline solid solution of Bi1−xPrxFeO3 (x=0.05, 0.1, and 0.15) ceramics has been successfully synthesized by a low temperature assisted co-precipitation method. Rietveld-refinement of the X-ray diffraction data reveals rhombohedral structure for Bi1−xPrxFeO3 (x=0.05, 0.10) and triclinic for Bi1−xPrxFeO3 (x=0.15). The crystallite sizes of the Bi1−xPrxFeO3 (x=0.05, 0.1 and 0.15) are found to be approximately 33, 27 and 22nm respectively calculated using Debye–Scherrer equation. The SEM images of Bi1−xPrxFeO3 (x=0.05, 0.10 and 0.15) ceramics show grains with almost spherical morphology. 4A1 and 7E Raman modes have been observed in the range 100–650cm−1 and two phonon modes centered around 1150–1450cm−1 have also been observed corresponding to 2A4 (LO), 2E8 (TO) and 2E9 (TO) modes of Bi1−xPrxFeO3 (x=0.05, 0.1 and 0.15). The changes in Raman modes such as prominent frequency shift, line broadening and intensity have been noticed with the increase of Pr concentration in BiFeO3 (BFO) suggesting a structural transformation as revealed by the Rietveld refinement. An anomaly in the temperature dependent dielectric studies has been noticed in all the samples at the vicinity of Neel temperature (TN) indicating a magnetic ordering and an increase in magnetization with increase of Pr concentration is noticed from the room temperature magnetic studies. Further, the leakage current density is found to be reduced with increasing Pr concentration.

Determination of the phase diagrams of the Nd2Fe14B–Pr2Fe14B isopleth

The phase relations in the pseudo-binary Nd2Fe14B–Pr2Fe14B system were investigated and constructed by means of X-ray powder diffraction (XRD), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDS). The results revealed that similar to the end-members of the Nd2Fe14B–Pr2Fe14B system form a continuous solid solutions, all intermediate (Nd1−xPrx)2Fe14B samples belong to tetragonal Nd2Fe14B-type structure (space group P42/mnm). The lattice parameter a almost remains the same, and the lattice parameter c and unit-cell volume V increase linearly with an increase of Pr concentration. Based on the results of DTA measurements and X-ray powder diffraction examinations, the tentative phase diagram of the Nd2Fe14B–Pr2Fe14B isopleth has been constructed.

Effect of Pr-Substitution in Eu<sub>1-<i>x</i></sub>Pr<sub><i>x</i></sub>BaSrCu<sub>3</sub>O<sub>7-<i>δ</i></sub> on the Superconductivity and Transport Properties

The effect of Pr-substitution at the Eu-site on the superconductivity and transport properties in Eu1-xPrxBaSrCu3O7-d (x = 0.0, 0.1, 0.2, 0.4, 0.5) has been investigated. Tc onset for x = 0.0, 0.1, 0.2, 0.4, 0.5 are 86 K, 75 K, 65 K, 38 K, 27 K, respectively. The critical temperature (Tc) decreased linearly with increase in Pr concentration x indicating a magnetic pair-breaking mechanism. The transport critical current density (Jc) decreased with increasing x. Analysis of the structure of the samples via X-ray powder diffraction (XRD) technique showed transformation from orthorhombic to pseudo-tetragonal structure at x = 0.2. Scanning electron microscope (SEM) showed no variation in the microstructure.

Manifestation of vortex depinning transition in nonlinear current–voltage characteristics of polycrystalline superconductor Y 1− xPr xBa 2Cu 3O 7− δ

We present our recent results on the temperature dependence of current–voltage characteristics for polycrystalline Y 1− x Pr x Ba 2Cu 3O 7− δ superconductors with x = 0.0 , 0.1 and 0.3. The experimental results are found to be reasonably well fitted for all samples by a power like law of the form V = R ( I − I c ) a ( T ) . Here, we assume that a ( T ) = 1 + Φ 0 I C ( T ) / 2 π k B T and I C ( T ) = I C ( 0 ) ( 1 − T / T C ) 3 / 2 for the temperature dependences of the power exponent and critical current, respectively. According to the theoretical interpretation of the obtained results, nonlinear deviation of our current–voltage characteristics curves from Ohmic behavior (with a ( T C ) = 1 ) below T C is attributed to the manifestation of dissipation processes. They have a characteristic temperature T p defined via the power exponent as a ( T p ) = 2 and are related to the current induced depinning of Abrikosov vortices. Both T C ( x ) and T p ( x ) are found to decrease with an increase of Pr concentration x reflecting deterioration of the superconducting properties of the doped samples.

Effects of Pr on the structure and magnetic properties of FePt alloys

Abstract The effects of Pr on the structure and magnetic properties of Pr x Fe 60.5- x Pt 39.5 alloys ( x = 0, 0.5, 1.0. and 1.5) were investigated. X-ray diffraction data indicated that the phase transition temperature of FePt based alloys from disordered face-centered-cubic to ordered face-centered-tetragonal cubic decreases with the increase in Pr concentration. Pr plays the role of a grain refiner and it can enhance the exchange coupling between soft magnetic phase and hard magnetic phase. The results indicate that the replacement of Fe by Pr can significantly improve the remanence and coercivity of the Fe 60.5Pt 39.5 alloy. These results can be explained on the basis of phase transformation and microstructure. Both the remanence ratio and coercivity of the FePt based alloy as a function of the Pr content are increased by the optimum addition of 0.5 at.% Pr.

Magetostriction, spin reorientation and M?ssbauer effect studies of Tb0.3Dy0.7－xPrx(Fe0.9Al0.1)1.95 alloys

The effect of Pr substitution for Dy on the structure, magnetostriction, anisotropy and spin reorientation of a series of Tb0.3Dy0.7-xPrx(Fe0.9Al0.1)1.95 alloys (x=0, 0.1, 0.20, 0.25, 0.30, 0.35) at room temperature has been investigated. It was found that the Tb0.3Dy0.7-xPrx(Fe0.9Al0.1)1.95 substantially retained the MgCu2-type C-15 cubic Laves phase structure for compositions with x≤0.1 and the lattice constant increases slowly with increasing x. The magnetostriction of the Tb0.3Dy0.7-xPrx(Fe0.9Al0.1)1.95 alloys decreases drastically with increasing x and the magnetostrictive effect disappears for x>0.2. However, the magnetostriction shows a slightly bigger value at x=0.1 than the free alloys and is saturated more easily with the magnetic field H, showing that a small amount of Pr substitution is beneficial to the decrease in the magnetocrystalline anisotropy. The spontaneous magnetostriction λ111 increases linearly with incresasing x， whereas the spin reorientation temperature increases first and then decreases rapidly. The analysis of the Mssbauer spectra indicated that the easy magnetization direction in the {110} plane deviates slightly from the main axis of symmetry with the increase in Pr concentration x， namely the spin reorientation. Compared with the Al substitution，the effect of Pr substitution for Dy on the spin reorientation is smaller.

Localization of charge carriers by Pr in theTl2Ba2Ca1−xPrxCu2Oysystem

We have measured the resistivity and thermoelectric power of Tl 2 Ba 2 Ca 1 - x Pr x Cu 2 O y samples with x≤0.6 in the temperature range 10-300 K. T c decreases with an increase in the Pr concentration and a crossover from a metallic to insulator state is observed in samples with x≃0.4. In the highly resistive samples (x>0.4) conduction is governed by the in-plane variable range hopping of the carriers while in others, localization of bosons appears to be dominating. A spin gap is observed in the resistivity of these samples. The resistivity and thermoelectric power show the localization of the carriers to increase with an increase in Pr concentration. These data, examined in the light of existing models of conduction by localized carriers, show a preference for the model proposed by Nagaosa and Lee wherein the fermion contribution decreases and that of the bosons increases with the increase in the Pr concentration. The Pr L 3 -edge absorption data show Pr to be present in the mixed (3 + and 4 + ) valent state. Correlating the hole density p determined from T c and thermoelectric power with the valence of Pr estimated from x-ray-absorption edge measurements, we find hole filling along with hybridization to be the dominant mechanism for destablization and eventual suppression of superconductivity in these materials.

Superconducting and normal state properties of Y 1− xPr xNi 2B 2C

Electrical resistivity, magnetoresistance and magnetic susceptibility have been studied for Y 1− x Pr x Ni 2B 2C samples with 0⩽ x⩽1.0. The increase of Pr concentration x results in a rapid suppression of superconductivity, |d T c/d x|=35 K. No indication on superconductivity was observed for PrNi 2B 2C down to T=0.35 K. The absence of superconductivity for PrNi 2B 2C and the large superconductivity suppression rate |d T c/d x| for Y 1− x Pr x Ni 2B 2C correlate with the anomalously high Néel temperature of PrNi 2B 2C ( T N≈4 K). Possible reasons for the absence of superconductivity in PrNi 2B 2C and the large |d T c/d x| value for Y 1− x Pr x Ni 2B 2C are discussed.

Synthesis and magnetic properties of compounds

The synthesis and magnetic properties of have been investigated. The formation of is found to depend strongly on annealing temperature. Pure single-phase compound can be synthesized at ambient pressure when . The main phase of the Laves structure can still be observed up to x = 0.8. The study of crystalline parameters, magnetic moments and Mössbauer spectra for single-phase is performed. Curie temperature and local Fe magnetic moment increase with the increasing Pr concentration. Extrapolating the trends the spontaneous magnetization and anisotropy constant of are 4.98 and at 1.5 K, respectively. Magnetostriction increases with increasing x and the largest saturation magnetostriction, 200 ppm, is observed for x = 0.5. With the increase of Pr concentration, lattice parameter and spontaneous magnetization anomalies exist in a specific range 0.2 < x < 0.5 that can be attributed to the change of Ce ion valence toward tetravalent.

Normal-state Hall-effect measurements on Y1-xPrxBa2Cu3O7- delta single crystals.

The temperature dependence of the Hall effect was studied on single crystals of Y 1-x Pr x Ba 2 Cu 3 O 7-δ with the magnetic field perpendicular to the ab plane and the current flowing in the ab plane. The anomaly in the Hall coefficient at around 120 K found in some of the 1:2:3 compounds is not observed in Pr-doped Y-Ba-Cu-O crystals. We observed that an increase in Pr concentration reduces the mobile carrier density and its strong temperature dependence. The reduction of the total conduction carriers can be attributed to hole filling or hole localization

Electronic properties of Ba2Y1-xPrxCu3O7- delta.

Measurement of the Hall coefficient in the Ba/sub 2/Y/sub 1-//sub x/Pr/sub x/Cu/sub 3/O/sub 7-//sub delta/ system has revealed that an increase in Pr concentration reduces the Hall carrier number (1/eR/sub H/) and its strong temperature dependence. The Cu formal valence calculated from the Pr valence, which has been determined to be /similar to/+3.5, shows a weakly decreasing dependence on Pr concentration. T/sub c/ shows a stronger dependence on the Hall carrier number and the Cu-O formal valence than in the oxygen-depleted Ba/sub 2/YCu/sub 3/O/sub 7-//sub delta/ system. The persistence of the chain band explains this observed difference, suggesting that the actual Cu-O valence dependence of the 90-K superconductor is stronger than that of the 40-K superconductor.