RE-doped Samples Research Articles

Doping rare earth cations with an additional chemical reduction synergistically weakened the photocatalytic performance of ceria.

Chemical reducing or rare earth cations (RE) doping was normally employed to promote the photocatalytic performance of ceria, aimed to evaluate their cooperation influences, ceria was obtained by decomposing homogenously RE (RE = La, Sm, and Y)-doped CeCO3OH in H2. XPS and EPR results evidenced that the excess oxygen vacancies (OVs) were formed in RE-doped CeO2 compared to the un-doped ceria. However, all the RE-doped ceria unexpectedly showed an impeded photocatalytic activity towards to methylene blue (MB) photodegradation. The 5% Sm-doped ceria had the best MB photodegradation ratio of 81.47% after 2-h reaction in all RE-doped samples, which was lower than that of 87.24% for the un-doped ceria. After doping RE cations and chemical reducing, the band gap of ceria were almost narrowed, while the PL spectra and photo-electro characterizations indicated that the separation efficiency of photo-excited e-/h+ (electrons/holes) was reduced. The RE dopants and formed excess OVs including inner and surface OVs was proposed to promote the recombination of e-/h+ which further hindered the generation of active species of ·O2- and ·OH, and finally weakened the photocatalytic activity of ceria.

Sensitivity of As K-edge absorption to rare earth (RE) doping in [formula omitted]: A first principles study

Systematic density functional theory-based first principles studies on As K-edge electron energy loss near edge structures are presented for rare earth (RE)-doped iron-based superconducting materials Ca1−xRExFeAs2 (known as 112 compounds). The As K-edge electron energy losses near edge differ for two different types of As atoms (belonging to Fe–As plane and As2 chains between the planes). The As K-edge spectra (of both As atoms in chain and plane) are very sensitive to the nature of RE doping (RE = La, Ce, Pr, Nd, Sm, Gd). For example, the As K-edge shifts to higher energies successively with decreasing RE size (La → Gd), indicating larger binding energies and hence stability of the corresponding compound. In contrast, the white-line peak successively shifts to lower energies for La → Gd doping, resulting in complete suppression of another low energy absorption peak for Gd. These are in essence an artifact of heavy electron doping caused by RE atoms. Interrelationship between the electron doping and corresponding shift in the white-line feature for various RE-doped samples is established through Bader charge analysis. Each absorption spectra consists of several peaked features of particular significance; they are thoroughly analyzed in terms of the unoccupied partial density of states. To emphasize the influence of the “core-hole” effect, absorption spectra in the presence and absence of core-holes are presented separately. Relevance of our results with respect to experimental scenarios are also discussed.

Thermoelectric properties of rare-earth doped Fe2VAl Heusler alloys

The low-temperature electrical transport properties of the rare-earth (RE) Ce, Dy, Sm element doped Fe2VAl Heusler alloys have been investigated. A significant enhancement in the Seebeck coefficient S (peak values of about −125 to −160 μV K−1) is observed as compared to the pure Fe2VAl (peak value of about 40 μV K−1). It is observed that the thermal conductivity reduced by 50% in RE-doped samples. The single parabolic band model has been used to analyze the experimental data and to understand the role of fundamental parameters like the Lorenz number. The lattice contribution to the total thermal conductivity was analyzed through the Callaway model, which in turn provided the insight into the phonon scattering in these alloys. Finally, we demonstrate a significant improvement in power factor and figure of merit at all temperatures for the RE-doped Fe2VAl alloys.

Structural, optical and magnetic properties of pure and rare earth-doped NiO nanoparticles

Pure and a series of rare earth element (RE) (Er, Sm, Gd, Pr and Y)-doped NiO nanoparticles (NPs) were fabricated by co-precipitation method in the presence of polyvinyl alcohol as a capping agent. X-ray diffraction (XRD) and transmission electron microscope (TEM) techniques were used to investigate the crystal structure and morphology of the prepared samples, respectively. The XRD patterns indicated that all the samples exhibited a single phase of face-centered cubic crystalline structure. TEM images displayed a spherical morphology of weakly agglomerated NPs. Furthermore, the chemical compositions were identified by proton-induced X-ray emission and Rutherford backscattering analysis. The metal oxide (Ni–O) functional group was confirmed by Fourier transform infrared spectroscopy with its observed band varying from 419.3 to 433.3 cm−1, depending on the RE doping element. The optical properties of the RE-doped NiO NPs were studied using UV–Vis absorption and photoluminescence (PL) spectroscopy. A small blueshift was obtained in the optical spectra of the RE-doped samples as compared to the undoped samples, implying an increase in the optical band gap. The study of the room temperature magnetic properties was done using the vibrating sample magnetometer, which revealed the coexistence of antiferromagnetic and weak ferromagnetic ordering in pure and RE3+-doped NiO NPs. The magnetization increased depending on the magnetic moments of RE dopant ions. Also, the origin of the anomalous ferromagnetism in the prepared samples may be mainly related to Ni vacancy defects, which were evinced from the results of PL.

Structure of Centers of Matrix Emission of the Undoped and RE-Doped Scheelite-Type Lead Tungstate Crystals

The paper reports the investigation of a structure of luminescence spectra of PbWO4 (PWO) crystals. The doping of the samples with rare earth (RE) impurities is used in order to obtain more information about the composition of spectra of the PWO matrix emission and the structure of its luminescence centers. The decomposition of the emission spectra onto individual bands has shown that 5 bands contribute to the total spectra of all the undoped and RE-doped samples at 10 K. The maxima of the obtained bands are 1.95, 2.2, 2.45, 2.7, and 3.0 eV. Effects of the RE-doping and the annealing on relative intensities of these bands are considered. The nature of luminescence and the structure of the centers involved in the excitation and emission processes responsible for each of the separated bands are discussed.

Structural and optical characteristics of Ce, Nd, Gd, and Dy-doped $$\hbox {Al}_{2}\hbox {O}_{3}$$ Al 2 O 3 thin films

We present the optical properties of rare earth (RE)-doped \(\hbox {Al}_2\hbox {O}_3\) thin films and discuss their possible use in applications like gate dielectric material and in coating industry. Aluminum oxide films doped with RE elements such as Ce, Nd, Gd, and Dy are synthesized on glass substrate using ultrasonic spray pyrolysis technique at \(400{^\circ }\hbox {C}\). The concentration of rare earth element is varied from 0.5 to 5 mol\(\%\) in 0.1 M solution of \(\hbox {Al}_{2}\hbox {O}_{3}\). The X-ray diffraction analysis indicates that the thin films deposited with and without rare earth doping have an amorphous structure. Further, the optical properties of RE-doped \(\hbox {Al}_{2}\hbox {O}_{3}\) thin films are studied by using UV–visible spectroscopy and photoluminescence measurement. The band gap is found to be 4.06 eV for \(\hbox {Al}_{2}\hbox {O}_{3}\) thin film. A small blue shift is seen in the optical spectra of RE-doped samples as compared to undoped \(\hbox {Al}_{2}\hbox {O}_{3}\) film. Dielectric constant of alumina thin film increases with doping of Gd and Dy while it decreases with Ce and Nd doping. Concentration quenching effects are observed in the photoluminescence spectra of Ce, Nd, Gd, and Dy-doped \(\mathrm{Al}_2\mathrm{O}_3\) films. Among all these RE-doped \(\hbox {Al}_{2}\hbox {O}_{3}\) thin films, Gd and Dy-doped \(\hbox {Al}_{2}\hbox {O}_{3}\) films exhibit a potential for the construction of dielectric gate in transistors or as a coating material in the semiconductor industry.

Structural and Morphological Characteristics of Polyaniline Synthesized in Pilot Scale

Polyanilines have many applications in Aerospace, especially in their doped form. Studies on their synthesis in a pilot scale can contribute to obtain products with desirable characteristics for such applications. The present study reports the chemical oxidative synthesis of polyaniline in pilot scale and different reaction times in order to determine if there are variations in the polyaniline structure, morphology and conductivity due to these synthesis conditions. It is very common to analyze these data for polymers obtained through bench scale. However, several parameters change the properties of final material in major scales, such as thermal, mechanic and diffusive variables. Therefore, the reaction time is the only variable into the 9 syntheses carried out, and polyaniline is obtained in a doped form, being dedoped with ammonium hydroxide and redoped with dodecylbenzenesulphonic acid. The doped and redoped samples were characterized by their molecular structure, thermal behavior, crystallinity and morphology. The electrical conductivity of redoped samples was determined. Some differences in the structure and morphology of doped and dedoped forms, identifying the doping structures, were reported. This paper aims to present the relationship between changes on structure and morphology of doped and undoped polyaniline obtained by the mentioned experiments. Furthermore, some addicts on conductivity are carried out. It was possible to contribute in order to obtain a more conductive polyaniline in pilot scale.

Scintillation properties of rare-earth doped NaPO3-Al(PO3)3 glasses

We systematically investigated photoluminescence (PL), scintillation and dosimeter properties of rare-earth (RE) doped NaPO3-Al(PO3)3 (NAP) glasses. The NAP glasses doped with a series of RE ions (La-Yb, except Pm) with a consistent concentration (0.3 wt%) were prepared by the conventional melt-quenching method. The PL and scintillation decay time profiles showed fast (ns) and slow (μs or ms) components: the fast components from 15 to 100 ns were due to the host or 5d-4f transition emission, and the slow components from 15 μs to 5 ms were due to the 4f-4f transitions of RE. The thermally stimulated luminescence (TSL) was evaluated as a dosimeter property, and glow peaks appeared around 400 °C in all the samples. The TSL dose response function was examined in the dose range from 10 mGy to 10 Gy. Among the samples tested, Nd and Tb doped glasses showed higher signal by at least one order of magnitude than those of non-doped and other RE-doped samples. Over the dose range tested, the TSL signals are linearly related with the incident X-ray dose, showing a potential for practical applications.

The Change in Physical Properties of Bi2Ca2Co2O8 Thermoelectric Materials Induced by Pb and Rare-Earth Dopings

We report in this paper the change in the physical properties due to dopant effect in Bi2Sr2Co2O8 parent compound system. The doped samples consists of Pb-doped samples (Bi2Sr2Co2O8, x = 0, 0.5, 1.0, 1.5, and 2.0) and RE-doped samples (Bi2-xPbxCa1.9RE0.1Co2O8, RE = Y, La, Pr, Sm, Eu, Gd, and Ho). The structure of this layered oxide system consist of an alternate stack of CoO2 layer and Bi2Sr2O4 block along the c-axis with misfit structure along b-direction. From the analysis of XRD data it is found that the c-axis parameter reduced significantly in the RE-doped samples compared with those of Pb-doped samples, while the value of misfit degree almost the same. The changes in these lattice structures are accompanied by variation in the spin-state of Co-ions and electrical conductivity. We argue that these structural changes and its effect on the electrical transport properties as well as control of the magnetism plays a pivotal role in determining the thermopower in this class of magnetic thermoelectric materials through the entropy of the charge carriers. This, in turn, will determine the thermoelectric performance for application.

Monitoring the Structural and Vibrational Properties in RE-Doped SrTiO3 Ceramic Powders

X-ray diffraction and Raman spectroscopy were employed to analyze the effect of the rare earth (RE) doping (ionic radii and concentration) on the crystalline structure of Sr0.97RE0.03TiO3 (RE = Sm3+, Eu3+, Gd3+, Dy3+, Tm3+, Yb3+, Lu3+) and Sr1–xEuxTiO3 (x varying from 0.01 to 0.19) ceramic powders. We notice drastic changes in both structural and vibrational properties of the investigated samples for increasing dopant concentration into the SrTiO3 (ST) lattice. The results showed evidence of RE incorporation into both A- and B-sites of the ST structure. Also, tetragonal local symmetry (I4/mcm space group) was observed in RE-doped samples at room temperature from the cubic (Pm3m) phase exhibited by phase-pure ST ceramics. The results obtained for the Sr1–xEuxTiO3 ceramic powders showed that these samples undergo a clear cubic-to-tetragonal phase transition for x ≥ 0.13 at room temperature.

Superconducting Transition Temperatures of up to 47 K from Simultaneous Rare-Earth Element and Antimony Doping of 112-Type CaFeAs2

The effects of simultaneous Sb doping on the superconductivity of 112-type Ca1-xRExFeAs2 (RE = La, Ce, Pr, and Nd) were studied through measurements of the magnetization and electrical resistivity. In Sb-free materials, the superconducting transition temperature Tc of the La-doped sample was 35 K, while those of the Pr- and Nd-doped samples were ~10 K; no superconductivity was observed in the Ce-doped sample. Sb doping increased the Tc of all RE-doped samples: Tc increased to 47, 43, 43, and 43 K for RE = La, Ce, Pr, and Nd, respectively. We also found that the enhanced superconductivity results from the increase in the lattice parameter b, which increases the As-Fe-As bond angle to be closer to the ideal tetrahedron value. These observations provide insight for further increasing the Tc of the 112 phase.

Structure and transport properties in Ca3Co4−xMxO9 (M=Re and Pt) ceramics

The effect of Re and Pt doping on the structural, electrical and thermal transport properties of Ca3Co4−xMxO9 (0≤x≤0.2, M=Re and Pt) samples have been investigated systematically. As Re7+ or Pt4+ ions are doped into Ca3Co4O9 lattice, the resistivity and the metal–insulator-transition temperature increase monotonously with increasing x, indicating that both Re- and Pt-substitution can result in more stable spin-density-wave state. For Re-doped samples, the thermopower increases with increasing x, while the thermopower of Pt-doped samples decreases monotonously. Although the decreased thermal conductivity of both Re- and Pt-doped samples is beneficial to the thermoelectric performance, their ZT value decreases with increasing x. The result shows that both Re and Pt doping may indeed exert a significant influence in the structural and transport properties of Ca3Co4O9 system, which are suggested to originate from the variations of carrier concentration and electronic correlation induced by Re or Pt doping.

Photocatalytic hydrogen production in the water/methanol system using Pt/RE:NaTaO3 (RE = Y, La, Ce, Yb) catalysts

Perovskite type RE-doped NaTaO3 (where RE represents Rare Earths elements like Y, La, Ce, Yb) catalysts, derived from solid state synthesis method, have been used for the photocatalytic hydrogen production from water using methanol as sacrificial agent. The photocatalytic activity of NaTaO3 in H2 production is improved on its doping with Y, La or Yb elements. In contrast, Ce-doped sample shows a worsening of the photoactivity, which is even lower than the un-doped catalyst. The characterization of the materials reveals that the monoclinic structure and the presence of Ce4+ do not favour to increase the performance of NaTaO3. Previous reports proved that La-doping boosted the water splitting photoactivity of NaTaO3. However the results of this work reveal an increase in the H2 production by the use of Y as dopant. This enhancement in the photoactivity could be related with the modification of the opto-electronic properties of NaTaO3 with the inclusion of RE elements (Y, La, Yb) in the orthorhombic structure of this perovskite. Moreover, the catalytic activity of all the RE-doped samples is further increased on their modification with Pt nanoparticles (NPs) loading that act as photo-generated electron scavenger facilitating the reduction reactions.

Visible light responsive sulfated rare earth doped TiO2@fumed SiO2 composites with mesoporosity: Enhanced photocatalytic activity for methyl orange degradation

Visible light (VL) responsive mesoporous sulfated rare earth ions (Nd3+, La3+, Y3+) incorporated TiO2@fumed SiO2 photocatalysts were prepared by sol–gel method with P123 (EO20PO70EO20) as a template. The resultant samples were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), N2 adsorption–desorption measurements (BET), UV–vis diffuse reflectance spectroscopy, photoluminescence (PL) spectra, Fourier transform infrared spectroscopy (FTIR) and thermal analyses (TG-DTA). In comparison with nondoped sample, RE-doped samples showed not only an increase in the surface areas and pore volumes, but also an inhibition of titania phase transition from anatase to rutile. Photo-degradation results revealed that RE-doped samples could greatly improve the photocatalytic activity, and the experimental degradation rates of methyl orange (MO) were higher than that catalyzed by undoped samples and Degussa P-25, obeyed the order of Nd3+>La3+>Y3+. Nd-doped sample expressed the highest photoactivity and the optimal dosage was 0.25mol%, which resulted in MO degradation rates of 99.8% and 90.05% irradiation under UV for 60min and VL (λ>400nm) for 40h, respectively. The enhanced photocatalytic activity could be attributed to the higher specific area, good crystallinity, strong VL absorption and effective separation of photogenerated electron–hole pairs in the catalyst.

Bismuth silicate glass as host media for some selected rare-earth ions and effects of gamma irradiation

Ultraviolet, visible and infrared spectral measurements were used to investigate prepared undoped and rare-earth doped (2.5%) bismuth silicate glasses (80% Bi2O3–20%SiO2) before and after being subjected to gamma irradiation (8 Mrad). The base bismuth silicate glass reveals strong extended UV–near visible absorption bands which are attributed to the presence of trace iron impurities in the raw materials together with absorption due to sharing of Bi3+ ions. The RE-doped samples show the same strong UV–near visible bands as the undoped glasses beside extra narrow characteristic bands mostly in the visible and near-infrared regions due to the respective studied rare-earth ions. The base undoped and all RE-doped samples except CeO2 sample reveal quite resistance to the effect of gamma irradiation due to heavy atomic mass Bi3+ ions present in high content (80%) and the rare-earth ions are known to be weakly affected due to the known 5s, 5p shielding. The exceptional effect of CeO2-doped sample is related to the ability of Ce3+ ions to change its oxidation state through photochemical reaction by irradiation or exchange with Fe3+ present as trace iron impurities. The FT infrared spectra of the prepared glasses reveal characteristic absorption bands which are related to the silicate groups together with the sharing of vibrational modes due to Bi–O groups. The IR spectra are slightly affected by gamma irradiation indicating the stability of the structural network groups consisting of SiO4 and BiO6 units.

The Preparation, Characterization, and their Photocatalytic Activities of Rare-Earth-Doped TiO2 Nanoparticles

RE/TiO2 photocatalysts were prepared by the sol–gel method using rare earth (RE=La3+, Ce3+, Er3+, Pr3+, Gd3+, Nd3+, Sm3+) metal salts and tetra-n-butyl titanate as precursors, and were characterized by XRD, IR, UV–vis diffuse reflection, and transient absorption spectra. Their photocatalytic activities were evaluated using nitrite as a decomposition objective. As a result, suitable content of doping rare earth in TiO2 can efficiently extend the light absorption properties to the visible region. At the same time, it is beneficial to NO2− adsorption over the catalysts due to rare earth doping. RE/TiO2 samples can enhance the photocatalytic activity to some extent as compared with naked TiO2. The increase in photoactivity is probably due to the higher adsorption, red shifts to a longer wavelength, and the increase in the interfacial electron transfer rate. Nitrite is almost completely degraded over RE/TiO2 catalysts after longer irradiation, which is different from Degussa P-25 with a plateau of activity after ca. 20 min irradiation. Gd3+-doped TiO2 showed the highest reaction activity among all concerned RE-doped samples because of its specific characteristics. The amount of RE doping was an important factor affecting photocatalytic activity; the optimum amount of RE doping is ca. 0.5 wt%, at which each RE/TiO2 sample shows the most reactivity. The photocatalytic degradation reaction of nitrite over Gd3+-doped samples and P-25 follows apparent first order kinetics, which is different from that of Sm3+, Ce3+, Er3+, Pr3+, La3+, and Nd3+-doped TiO2 catalysts, which obey zero-order kinetics, indicating that these processes were dominated by electron–hole recombination.

Re-induced Raman active modes inHgBa2Can−1CunO2n+2+δcompounds

A comparative Raman study of Re-free and Re-doped ${\mathrm{HgBa}}_{2}{\mathrm{Ca}}_{n\ensuremath{-}1}{\mathrm{Cu}}_{n}{\mathrm{O}}_{2n+2+\ensuremath{\delta}}$ with $n=1,3,4,5$ is presented in an attempt to further clarify the structural and phononic modifications brought about by Re substitution. A number of extra high-frequency phonon peaks show up in the spectra of the Re-doped samples and are attributed to the oxygen modes of a strongly bound, almost decoupled ${\mathrm{ReO}}_{6}$ octahedron. As regards the apex oxygen in the Hg site, a clear transfer of spectral weight from the 590 to the 570 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ apex phonon band is observed upon Re substitution. Such a change may well be accounted for assuming increased excess oxygen content for the Re-doped samples. Another interesting result is the enhancement upon Re doping of a narrow peak probably attributed to c-axis vibrations of Ba whose frequency shows a distinctive change with the number n of the ${\mathrm{CuO}}_{2}$ layers, providing an easy way to identify the various phases in a sample.

Magnetization and relaxation in Hg-1223: bulk vs. surface irreversibility, anisotropy and the influence of Re-doping

Particle-size fractionization is used to separate bulk and surface hysteresis in pure and Re-doped Hg(15%)-1223. Re-doped samples have smaller surface barriers and higher bulk current densities than undoped Hg-1223. Neutron-irradiated samples exhibit practically no surface barrier effect. A `pinning roughness' model is suggested to unify the observations. The fractionization technique is extended to relaxation of magnetically aligned Hg-1223. In wide temperature regions, both surface and bulk currents do relax. However, near the irreversibility temperature, bulk currents decay to zero, whereas surface relaxation continues. Relaxation is a complex interplay of bulk/surface effects, which subsequent investigations in this field must regard. From magnetization measurements on magnetically oriented samples, anisotropy parameters are estimated to γ≈9±3 (Hg-1223) resp. γ≈4.5±2 (Hg(15% Re)-1223). This is a very drastic effect of Re-doping on the superconducting properties of Hg-1223.

Effects of Re-doping on microstructure and superconductivity of HgBa 2Ca 2Cu 3O 8+δ

In order to study the solubility of Re in HgBa 2Ca 2Cu 3O 8+δ and the influence of Re-doping on microstructure and superconductivity, samples of Hg 1− x Re x Ba 2Ca 2Cu 3O 8+δ with x=0.05, 0.10, 0.15, 0.20, 0.25 and 0.30, have been synthesized. Grain size and shape change with nominal Re content while the intra-grain microstructure which is dominated by stacking faults remains the same. Both, EDX and X-ray diffraction (XRD) measurements suggest a change of solubility of Re in HgBa 2Ca 2Cu 3O 8+δ at about x=0.10–0.15 towards lower solubility. For x≥0.15 a Re-rich secondary phase appears. The critical temperature, T c, of the Re-doped samples is above 130 K and the magnetic hysteresis, Δ M, shows a maximum for x=0.15.