Increasing Pr Doping Research Articles

Pr/ Co co-doping endows perovskite manganite with enhanced magnetic refrigeration capacity

It is recognized that new environmentally friendly and economical cooling methods are needed. In this paper, we focus on the effect of different doping amounts of Pr on the performance of magnetic refrigeration materials in the presence of trace doping of Co ions at the B-site. The samples La0.67Sr0.33−xPrxMn0.975Co0.025O3 (LSPMCO x = 0.10,0.125 and 0.15) in this paper were prepared by sol-gel method. The X-ray diffraction (XRD) and selected area electron diffraction (SAED) diffraction data determined that the samples were pure phases without impurities belonging to the R-3c space group (No. 167). Scanning electron microscope (SEM) and transmission electron microscope (TEM) showed that the samples were not regular particles of submicron size, and the size of the grains decreased gradually with increasing Pr doping. The experimental data have shown that the samples underwent second order phase transitions near the Curie temperature (Tc). Tc is closest to room temperature at 300 K at a doping level of 0.10. The maximum magnetic entropy change (−∆SMmax) at 5 T is 3.79 (J/kg∙K) (x = 0.15) and the relative cooling power (RCP) is 352.78 (J/kg) (x = 0.15). The results demonstrated that the doping of Pr has an enhanced effect on the performance of the magnetic refrigeration La0.67Sr0.33Mn0.975Co0.025O3 material. This may provide a reference for improving the performance of magnetic refrigeration materials in future research.

Analysis of Pr co-doped Al:ZnO thin films using feasible nebulizer spray technique for optoelectronic technology

The rare earth element, i.e., praseodymium (Pr) co-doped aluminium zinc oxide (AZO) thin films is coated on a well-cleaned glass substrate by facile and cost-effective nebulizer spray technique. The Pr co-doping concentrations varied from 0 to 1.5% with the AZO structure in the steps of 0.5%. The structural analysis was characterized by X-ray diffraction (XRD), showing that all the diffracted peaks exhibit polycrystalline hexagonal wurtzite structure and the size of the crystallites is abridged with increasing Pr doping level due to lattice defects. In Raman analysis, the existence of high mode peak E2 at 437 cm−1; confirmed ZnO wurtzite structure. From the morphological study, it is clearly visualized that the film possesses spherical shaped grains which were uniformly distributed without any pinholes and voids. The surface roughness of the films was increased considerably from 22 to 39 nm on growing Pr doping from 0 to 1.5% as seen using atomic force microscope. Energy dispersive X-ray analysis and elemental mapping images clearly showed the subsistence of Al, Zn, O and Pr elements in Pr:AZO film. The prepared films exposed good transmittance range between 84 and 90% and the optical band gap was found to be 3.28 eV for initial Pr (0.5%) doping concentration. The PL spectra clearly showed that a high intense emission peak observed at 390 nm are associated with NBE which indicates that the film has good optical quality. Hall measurement revealed that the prepared film, i.e., 1.5% Pr-doped AZO film has low resistivity and high carrier concentration which is perfectly suit for optoelectronic device applications.

Effect of Pr3+doping on key properties of CdO thin films deposited by spray pyrolysis using perfume atomizer

High quality Cadmium oxide thin films doped with Praseodymium (Pr) were prepared using perfume atomizer based spray pyrolysis technique at substrate temperature near 350 °C. Structural analysis of films was examined by XRD and confirmed that the films are cubic in structure. All un-doped and doped films were good crystalline in nature with smooth and flat surface without significant modifications owed to doping. Optical transmittances of doped films was decrease in the visible and IR range with increasing Pr doping concentration. Band gap widened from 2.42 to 2.20 eV when doped with Pr from 0 to 5 at. %. In addition, the photoluminescence property of the films was also observed. Further, the electrical studies were performed on pure and doped samples Viz., the electrical resistivity, carrier concentration (ρ) and Hall mobility (μ). It confirmed that the deposited films has good structural environments in terms of grain size, absolute stress correspond and low resistivity. Current-voltage measurements on the nanostructured Al/Pr-nCdO/p-Si/Al device showed a non-linear electric characteristics indicating diode like behavior.

Effects of electron injection on the magnetic and magnetocaloric behavior of Sr2FeMoO6 double perovskite

With the aim of determining and distinguishing the influence of rare-earth doping on the strength of magnetic interactions, magnetic and magnetocaloric properties of Sr2-xPrxFeMoO6 (x = 0.0, 0.1, 0.2, 0.3) double perovskite were investigated. The X-ray diffraction analysis revealed that all the samples crystallized in a tetragonal structure with I4/mmm space group. The temperature dependent magnetization and Arrott analysis suggested a second order of ferromagnetic phase transition in all the synthesized samples. The competing interaction between the electron injection and steric effect resulted in a non-monotonic evolution of the Curie temperature (TC). In the low Pr doped samples the raising of the Curie temperature is mainly due to the electronic effects while the decrease in TC observed for higher Pr doping (x = 0.3) is attributed to the steric effects. The magnetization was observed to increase with the increasing Pr doping (up to x = 0.2) indicating a progressive increase in cationic ordering. The magnetic entropy change was evaluated from the measurement of isothermal magnetization with respect to the magnetic field at different temperatures. The maximum magnetic entropy change and the relative cooling power were found to increase with the increasing Pr doping (x ≤ 0.2). The tunability of magnetization as well as Curie temperature simply by adjusting the dopant concentration and synthesis conditions makes Sr2FeMoO6 a potential candidate for exploring the new kind of magnetic refrigerants.

ANALYSIS OF FLUCTUATION CONDUCTIVITY OF GRANULAR Gd1-xPrxBa2Cu3O7-δ SUPERCONDUCTOR

Single phase polycrystalline Gd 1-x Pr x Ba 2 Cu 3 O 7-δ (0 ≤ x ≤ 0.10) samples have been prepared by standard solid state reaction technique and characterized by SEM, X-ray diffraction and electrical transport experiments. The samples were granular and homogeneous. It was observed that the critical temperature decreases and that the transition width increases with increasing Pr doping. Systematic measurements of fluctuation conductivity are reported. Special attention is taken above the critical temperature, where Gaussian and critical regimes are observed. Below the critical temperature, on approaching the zero resistance state, our results show a power-law behavior consistent with a phase transition from a paracoherent to a coherent state of the granular array.

Electrical-Transport Studies on (La1-xPrx)2/3Ba1/3MnO3 Compounds

The magnetic and transport properties of (La1-xPrx)2/3Ba1/3MnO3 (x = 0, 0.1677, 0.333, 0.500, 0.677, 0.833, 1.000) compounds, prepared by the solid state reaction have been investigated. The metal-insulator transition (Tp) was determined by using the standard four-point probe resistivity measurement between of 30 and 300 K. With increasing Pr doping, Tp shifted to lower temperatures, which are greater than 300, 270, 250, 226, 202, 186 and 158 K for x = 0, 0.1677, 0.333, 0.500, 0.677, 0.833 and 1.000, respectively. By analyzing the data using several theoretical models, it was concluded that the metallic (ferromagnetic) part of the resistivity (ρ), (below TP), fits well with the equation ρ = ρ0 + ρ2T2. This indicates that ρ0 is due to the grain/domain boundary effects. The second term ~ρ2T2 appears to be attributed to electron-electron scattering. In the high temperature range (T>TP) (the paramagnetic insulating regime) adiabatic small polaron models fit well in different temperature regions, thereby indicating that polaron hopping might be responsible for the conduction mechanism. The activation energy (Ea) also increases as the doping concentration increases.

EFFECT OF Pr DOPING ON FERROELECTRIC BEHAVIORS OF Pb(Zr0.65Ti0.35)O3

Pr -doped Pb ( Zr 0.65 Ti 0.35) O 3 ( Pb 1-x Pr x( Zr 0.65 Ti 0.35)1-x/4 O 3, PPZT) ceramic samples are prepared using conventional solid-state sintering method, and their structural, dielectric, ferroelectric, and piezoelectric properties are investigated, focusing on the effects of Pr -doping. Upon increasing Pr doping level x, a transition of the crystallographic structure from rhombohedral symmetry to tetrahedral and finally to pseudocubic symmetry is observed at x ~ 0.08. The detailed dielectric measurements present a clear indication of relaxor-like behaviors at x = 0.08, while the samples at x < 0.08 offer slightly improved ferroelectric properties compared with pure Pb ( Zr 0.65 Ti 0.35) O 3. In spite of the dielectric relaxor behaviors induced by Pr -doping, both the ferroelectric and piezoelectric properties of PPZT are degraded at x = 0.08. The physics underlying the Pr -doping induced relaxor behaviors is then discussed.

High-temperature relaxor ferroelectric behavior in Pr-dopedSrTiO3

Temperature-dependent Raman scattering, dielectric, and powder x-ray diffraction studies have been carried out on Pr-doped $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_{3}$ ceramic samples. Activation of $\mathrm{T}{\mathrm{O}}_{2}$ and $\mathrm{T}{\mathrm{O}}_{4}$ polar modes indicated increasing degree of polar distortion by Pr doping. Dielectric measurements revealed that the system exhibits dielectric relaxation peaks at $\ensuremath{\sim}500\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The softening tendency of the polar $\mathrm{T}{\mathrm{O}}_{1}$ soft mode decreases with increasing Pr doping. X-ray diffraction results show no evidence of symmetry breaking across the dielectric peak temperatures. The system exhibits features of high-temperature relaxor ferroelectrics.

Electrical and thermal transport properties of the Pr-doped La 0.9− xPr xTe 0.1MnO 3 [formula omitted] manganites

The effect of Pr doping at the La site on electrical and thermal transport properties of the electron-doped manganites La 0.9− x Pr x Te 0.1MnO 3 ( 0 ≤ x ≤ 0.9 ) has been investigated. For the samples with x ≤ 0.36 , there is a insulator–metal (I–M) transition while the samples with x ≥ 0.54 display semiconducting behavior over the whole measured temperature range. For x ≤ 0.36 , the thermopower S changes sign from negative to positive with decreasing temperature and the crossover temperature increases with increasing Pr doping content x . For the samples with x ≥ 0.54 , S shows a positive sign over the whole temperature range studied. Both ρ ( T ) and S ( T ) data in the high temperature range can be well described by the variable-range-hopping (VRH) model for all samples studied. In the low temperature region, the ρ ( T ) and S ( T ) data for the sample with x ≤ 0.36 are analyzed on the basis of the electron–magnon scattering mechanism. As regards the thermal conductivity k ( T ) , the low temperature k peak is suppressed by Pr doping and k decreases with increasing Pr doping level. The result is analyzed as regards the combined effect of the disorder and antiferromagnetic (AFM) interaction induced by Pr doping.

Magnetic field effects on electrical resistivity of (Gd 1−x Pr x )Ba 2 Cu 3 O 7−δ and Gd(Ba 2−x Pr x )Cu 3 O 7+δ

The magnetoresistance measurements of single phase polycrystalline Gd(Ba2−xPrx)Cu3O7+δ and (Gd1−xPrx)Ba2Cu3O7−δ samples have been compared and analyzed by the Ambegaokar and Halperin phase slip model. The derived power law dependences of pinning energy to applied magnetic field and temperature have been studied for different amounts of Pr doping. The power factors depend on the Pr doping. Moreover, in both systems, the magnetic field dependence of the pinning energy power factor increases for small amounts of Pr doping, while for larger amount of Pr doping, it decreases. The critical current power law dependence to magnetic field decreases with increasing Pr doping. Pr substitution at Ba or rare earth site, decreases the pinning energy and the critical current density, playing the role of weak links. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Neutron diffraction studies ofNd1−xPrxBa2Cu3O7−δ: Evidence for hole localization

Sintered samples of Nd1-xPrxBa2Cu3O7-delta with x=0, 0.05, 0.10, 0.15, 0.20, and 0.30 have been studied by neutron diffraction, x-ray diffraction, and resistivity measurements. Sample stoichiometry was carefully checked. Atomic distances within the unit cell and the oxygen content were shown to be almost independent of Pr doping. Bond valence sums (BVSs) were calculated from the neutron diffraction data assuming either a constant valence or a mixed valence for Cu and Pr ions. The planar Cu2 valence is independent of Pr doping and the chain Cu1 valence is roughly constant, while the hole concentration in the planes and chains decrease with increasing Pr doping for both BVS calculation methods. All together, this indicates that hole localization on the Nd(Pr) site is a main reason for the decrease of the hole concentration in the planes. A consistent relation between the hole concentration in the planes calculated from the constant valence method and the depression of the critical temperature is also obtained, both for Pr-doped Nd-123 and for Y(Pr)-123 studied previously.

Pr at Gd or Ba site inGdBa2Cu3O7: Appearance of superconductivity

$\mathrm{Gd}({\mathrm{Ba}}_{2\ensuremath{-}x}{\mathrm{Pr}}_{x}){\mathrm{Cu}}_{3}{\mathrm{O}}_{7+\ensuremath{\delta}}$ single phase polycrystalline samples with $0.0<~x<~1.0$ were investigated for their structural and electronic properties. Due to the solubility limit, the 123 structure forms in the $0.0<~x<~0.50$ range; for $x>~0.6,$ a decomposition of the perovskite-type phases occurs. For $x=0.2,$ there is an orthorhombic-tetragonal phase transition, concurrent with a metal-insulator transition, which is evident in the normal state resistivity. For ${x}_{c}=0.35,$ the superconductor-insulator transition occurs. An unusual hump has been observed on the resistivity vs temperature curve of the samples for particular values of Pr doping. Based on the Rietveld refinement of the x-ray diffraction patterns, and bond valence sum calculations, we have found that the Ba atom substitution at the rare earth site could lead to superconductivity in some parts of the grains at ${T}_{m}\ensuremath{\sim}80--90\mathrm{K},$ which appears as a hump on the $\ensuremath{\rho}(T)$ curve. Our result is in line with the previously proposed possibility of the existence of superconductivity in Pr-123 due to the Ba atom substituted at the Pr site. We have also concluded that with increasing Pr doping, O(4) atoms migrate from their sites, and the O(5) occupation increases. So, perovskite substructures with Pr at the rare earth or Ba site, become identical. Hence, Pr at the Ba or rare earth site suppresses the superconductivity by the same mechanism(s).

Pr-induced superconductivity suppression in Y xPr 1− xBa 2Cu 4O 8 probed by soft-X-ray absorption spectroscopy: a comparative studies of Y xPr 1− xBa 2Cu 4O 8 and Y xPr 1− xBa 2Cu 3O 7

The variation of hole states with Pr doping for Y x Pr 1− x Ba 2Cu 3O 7 and Y x Pr 1− x Ba 2Cu 4O 8 has been investigated by O K-edge X-ray absorption spectroscopy. Upon Pr substitution, T c suppression rate in Y x Pr 1− x Ba 2Cu 4O 8 is slower than that in Y xPr 1− x Ba 2Cu 3O 7. For both systems, hole carriers in the CuO 2 planes and CuO chains decrease monotonically with increasing Pr doping level. The depletion rate of hole carriers in the CuO 2 planes with Pr doping in Y x Pr 1− x Ba 2Cu 4O 8 is considerably slower than that in Y x Pr 1− x Ba 2Cu 3O 7. The oxygen content affects the depletion rate of hole carriers in cuprates with Pr doping.

Magnetoresistance in Gd(Ba 2− xPr x)Cu 3O 7+ δ system

The magnetoresistance measurements of single phase polycrystalline Gd(Ba 2− x Pr x )Cu 3O 7+ δ and (Gd 1− x Pr x )Ba 2Cu 3O 7− δ samples have been compared and analyzed by the Ambegaokar and Halperin phase slip model. The derived power law dependences of pinning energy to applied magnetic field and temperature have been studied for different amounts of Pr doping. The power factors depend on the Pr doping. Moreover, in both systems, the magnetic field dependence of the pinning energy power factor increases for small amounts of Pr doping, while for larger amount of Pr doping, it decreases. The derived critical magnetic field at zero temperature limit is in good agreement with other model-based and experimentally measured values. The critical current power law dependence to magnetic field decreases with increasing Pr doping. Pr substitution at Ba or rare earth site, decreases the pinning energy and the critical current density, playing the role of weak links.

Soft x-ray absorption spectroscopy studies of doped Pr-containing cuprates

Using high-resolution O K-edge x-ray absorption near-edge-structure (XANES) spectroscopy, unoccupied states of the ${\mathrm{Y}}_{x}{\mathrm{Pr}}_{1\ensuremath{-}x}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7}$ $(x=0--1)$ thin films and polycrystalline ${\mathrm{Pr}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7}$ $(x=0--0.3)$ as well as ${R}_{0.8}{\mathrm{Pr}}_{0.2}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7}$ samples $(R=\mathrm{Tm},$ Dy, Gd, and Sm) are investigated. In ${\mathrm{Y}}_{x}{\mathrm{Pr}}_{1\ensuremath{-}x}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7},$ hole numbers in the ${\mathrm{CuO}}_{2}$ planes decrease significantly with increasing Pr doping level. Hole carriers generated via Ca doping in ${\mathrm{Pr}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7}$ are directed predominantly into both the Zhang-Rice and Fehrenbacher-Rice (FR) states, while those in the ${\mathrm{CuO}}_{3}$ ribbons remain almost unchanged with Ca substitution. In ${R}_{0.8}{\mathrm{Pr}}_{0.2}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7},$ the hole content in the ${\mathrm{CuO}}_{2}$ planes decreases monotonically with increasing ionic size of the ${R}^{3+}$ ions, confirming the hole depletion effect based on the $\mathrm{Pr}4f--\mathrm{O}2p$ hybridization. We demonstrate the spectroscopic evidence of the existence of the FR states. The present XANES results provide a deeper understanding of the nature of hybridization and the origin of the ionic size effect.

Thermoelectric power and resistivity of Nd 1−xPr xBa 2Cu 3O 7− δ

The structural and transport properties of Nd 1− x Pr x Ba 2Cu 3O 7− δ ( x=0.0, 0.05, 0.10, and 0.15), have been studied by X-ray powder diffraction, electrical resistivity measurements, and thermoelectric power measurements. The decrease of the superconducting critical temperature with doping is described by a parabolic term and a linear term. The c-axis lattice parameter and the cell volume decrease with doping up to x=0.10. Analyses of the thermoelectric power, critical temperature, c-axis lattice parameter, and the cell volume suggest that the Pr ions have a valence close to +4 at low doping concentration. The room temperature resistivity indicates that hole concentration decreases with increasing Pr doping. The room temperature thermoelectric power is positive for all samples and increases with increasing Pr doping due to a decrease in the carrier concentration. We analyzed the thermoelectric power as a function of temperature with a two-band model with an additional linear T term. An excellent agreement between model and data was obtained. The band width of the narrow band increases and its peak position moves away from the Fermi energy with increasing doping concentration.

Planar tunneling spectroscopy ofY1−xPrxBa2Cu3O7thin films as a function of crystallographic orientation

We present a systematic study of the charge transport and quasiparticle tunneling properties of ${\mathrm{Y}}_{1\ensuremath{-}x}{\mathrm{Pr}}_{x}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7}$ thin films. Pr doping increases the resistivity along the copper oxide planes and suppresses the superconducting critical temperature ${T}_{c},$ ultimately inducing a superconductor-insulator transition. The tunneling conductance is reproducible and correlated with the crystallographic film orientation. The crystallographic dependence can be divided into two distinct categories: tunneling into (001)-oriented $(c$-axis) films and tunneling into (100)-, (110)-, and (103)-oriented $(ab$-oriented) films. c-axis tunneling data exhibit a conductance dip at zero bias and a broad temperature-dependent peak over $\ensuremath{\sim}15--40$ mV that decreases in magnitude but stays fixed in energy for increasing Pr doping levels. $\mathrm{ab}$-plane tunneling data exhibit a zero-bias conductance peak and a gaplike feature at an energy that scales roughly linearly with ${T}_{c}$ for $x=0.0,$ 0.2, and 0.4. When $x=0.5,$ the resistivity is not linear in temperature and a zero-bias conductance dip is observed. The background conductance that ensures conservation of states in the low-temperature $\mathrm{ab}$-plane data exhibits temperature- and doping-dependent structure over $\ensuremath{\sim}15--40$ mV that is very similar to the peak observed in c-axis tunneling. Finally, analysis of the temperature and magnetic field dependence of the zero bias conductance peak indicates that states are conserved to within $\ensuremath{\sim}20%,$ supporting its interpretation as a feature of a superconducting density of states.

Origin of superconductivity suppression in (Dy1−xPrx)Ba2Cu3O7studied by soft-x-ray absorption spectroscopy

O K-edge and Cu ${\mathrm{L}}_{23}$-edge x-ray-absorption near-edge structure (XANES) spectra for the series of (${\mathrm{Dy}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Pr}}_{\mathrm{x}}$)${\mathrm{Ba}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ compounds (x=0--0.7) were measured to investigate how the variation of hole states related to the superconductivity. Near the O 1s edge, prepeaks at \ensuremath{\sim}527.6 and \ensuremath{\sim}528.4 eV are assigned to transitions into O 2p holes located in the ${\mathrm{CuO}}_{3}$ ribbons and ${\mathrm{CuO}}_{2}$ planes, respectively. Both the O 2p hole concentration in the ${\mathrm{CuO}}_{2}$ planes and ${\mathrm{CuO}}_{3}$ ribbons decrease monotonically with increasing Pr doping, giving evidence in support of the hole depletion model proposed by Liechtenstein and Mazin. It clearly demonstrates that the suppression of superconductivity with Pr-doping results predominantly from the hole depletion effect. In the Cu 2p absorption edge, the high-energy shoulders originating from Cu ${3\mathrm{d}}^{9}$L defected states show a linear decrease in spectral weight as the Pr doping increases, where L denotes the ligand O 2p hole on the ${\mathrm{CuO}}_{3}$ ribbons and the ${\mathrm{CuO}}_{2}$ planes.

Growth and characterization of (Y 1 − xPr x)Ba 2Cu 3O 7 − δ single crystals

We report on the growth and characterization of single crystals in the solid solution system (Y 1 − x Pr x )Ba 2Cu 3O 7 − δ with 0 ≤ x ≤ 0.6 using a BaCuO 2-CuO flux together with a slow cooling method. By means of in situ decanting of the remaining flux, nearly flux-free single crystals can be grown for all concentrations. Although the c-axis parameter is not significantly influenced by increasing Pr doping, we find that the anisotropy is increased, which renders the system more two-dimensional.