Effect Of Rare Earth Doping Research Articles

Effects of rare earth doping on the superconducting properties of MgB2

Doping effects of rare earth oxides (REOy: RE=La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu) on the superconducting properties of MgB2 were investigated. Large fraction of the added RE turned into impurity phases: REB6 for RE=La–Gd and Yb, and REB4 for RE=Tb–Tm and Lu. We observed an increase in c-axis length from 3.523 to 3.533Å when doped with Lu. Clear decreases in transition temperatures were observed in samples doped with Sm, Eu, Gd, Tm, Yb and Lu, indicating that these elements were successfully substituted for Mg. The decreases in Tc were most drastic in Yb-doped samples (Tc∼32K).

The effect of rare earth doping on the glow peak positions of [formula omitted

Thermoluminescence of the rare earths (Ho, Tb, Gd, Sm, Ce or La) doped LiNaSO 4 and irradiated at room temperature was studied in the temperature range 300–673 K. The glow curves of this material consistently illustrate the presence of two groups of glow peaks that behave differently. The first group occurs in the temperature range 350–450 K, and the individual peaks occur at the same temperature for all dopants. The second group (500–650 K), which contains the dosimetric peak, is noted to move in temperature with the size of the RE dopants. The switch in behavior of the glow peaks is attributed to a possible phase transition of the host material near 500 K. Additionally, the relatively simple glow curve, low fading and the presence of the dosimetric peak at high temperatures with 80–100% of the total glow-curve area contained within the complex above 500 K make the material suitable for radiation dosimetry at high temperature.

The effect of rare earth dopants on grain boundary cohesion in alumina

The effect of rare earth (RE) grain boundary segregation on mode of fracture in alumina has been investigated. In order to isolate the effects of microstructure (i.e. grain size and residual porosity) from those due to grain boundary chemistry, the fracture behaviour of virtually pore-free (i.e. nearly transparent) undoped alumina has also been studied. This showed that mode of fracture becomes increasingly transgranular as grain size is reduced, a trend which has been explained by thermal expansion anisotropy effects. The addition of RE (i.e. Yb, Gd or La) dopants to alumina resulted in a substantial increase in the proportion of intergranular fracture relative to the undoped material of similar grain size. This can be explained by the significant reduction in the free surface energy that results from RE segregation at grain boundaries, which reduces the work of fracture for intergranular failure. This is expected to lead to a reduction in strength compared to undoped aluminas with equivalent microstructures, although this is often more than offset by the improved microstructures that using a RE dopant can provide.

Effect of rare-earth doping on the electrical properties of InSe single crystals

The effect of rare-earth doping (R = Gd, Dy, Ho) to different levels (0, 10−5, 10−4, 10−3, 10−2, and 10−1 at %) on threshold switching and low-frequency current oscillations in single crystals of indium selenide, a layered III–VI semiconductor, has been studied in broad ranges of temperatures (77–400 K), wavelengths (0.30–3.50 μm), and illuminances (up to ∼102 lx). The results are interpreted in terms of the anisotropic chemical bonding in n-InSe and its response to rare-earth doping.

Effect of Rare Earth Doping on the Catalytic Activity of Copper‐Containing Hydrotalcites in Phenol Hydroxylation

AbstractThe copper‐containing hydrotalcites (Cu‐HTLcs) are synthesized under microwave irradiation, the effect of rare earth elements (RE) on the synthesis of Cu‐HTLcs, wherein RE stands for rare earth elements, e.g., La, Y, Sm and Ce, is also investigated in the present work. The hydrotalcite structure of the synthesized samples is verified by XRD and FT‐IR. The results of their catalytic performances in phenol hydroxylation show that the doped rare earth elements can promote the catalytic activity of Cu‐HTLcs, exhibiting a good trend as follows: La>Y>Sm>Ce. XPS results show that the Cu+ species are produced after the interaction of La‐Cu‐HTLcs with H2O2. Combining with the catalytic test results, we propose a new mechanism about the generation of HO. radicals in phenol hydroxylation, it is assumed that HO‐Cu+‐OH species are first formed by the reduction of HO‐Cu2+‐OH located in hydrotalcites in the presence of H2O2, and then react with H2O2 to give rise to HO. radicals.

Heat transport ofLa2−yEuyCuO4andLa1.88−yEuySr0.12CuO4single crystals

To study the rare-earth doping effect on the phonon heat transport of La-based cuprates and shed light on the mechanism of phonon scattering, both $ab$-plane and c-axis thermal conductivities ($\kappa_{ab}$ and $\kappa_c$) are measured for La$_{2-y}$Eu$_y$CuO$_4$ ($y$ = 0, 0.02 and 0.2) and La$_{1.88-y}$Eu$_y$Sr$_{0.12}$CuO$_4$ ($y$ = 0 and 0.2) single crystals. It is found that the phonon peak (at 20 -- 25 K) in $\kappa_{ab}(T)$ of La$_{2-y}$Eu$_y$CuO$_4$ shows an anomalous Eu-doping dependence: it completely disappears for $y$ = 0.02, which is discussed to be due to the local lattice distortions around Eu dopants, and reappears for $y$ = 0.2 with much smaller peak magnitude compared to $y$ = 0 sample. In contrast to the strong suppression of the phonon peak in Eu-doped La$_2$CuO$_4$, Eu-doping to La$_{1.88}$Sr$_{0.12}$CuO$_4$ enhances the low-$T$ phonon heat transport that results in the reappearance of the phonon peak in this charge-carrier-doped system. The data clearly show that the establishment of static stripe phase rather than the structural change is responsible for the reappearance of phonon peak.

Rare earth doping effect on the structural and electrical properties of Mg–Ti ferrite

The electrical properties, shrinkage, porosity and X-ray diffraction analysis for Mg–Ti ferrite of the general formula Mg 1+ x Ti x R y Fe 2−2 x− y O 4; x=0.5, y=0, 0.025 and R=(Nd, Gd and La) were studied. The investigated samples were crystallized in the spinel phase. The measurements of the electrical properties were carried out at different temperatures (295–750 K) as a function of the applied frequency (50–1000 kHz). The experimental results show that the rare earth ions initiate new sites called dodecahedral (C-sites) and at the same time increase the valence exchange between the different metal ions existing in the different sites. This behavior takes place at certain concentrations of the rare earth ions. The low rare earth concentration as well as the high sintering times (100 h) leads to an inflection in the electrical properties. Verwey conduction mechanism and hopping are used to interpret the conductivity of the samples.

Effect of Rare-Earth Doping on the Microhardness of Silicon and Germanium

The effect of rare-earth (Gd, Dy, Er, and Nd) doping on the mechanical properties of Si and Ge single crystals was studied. The results demonstrate that rare-earth dopants may both increase and decrease the microhardness of Si and Ge, depending on their concentration. This behavior results from the competition between two processes. On the one hand, rare-earth atoms and their accumulations hinder dislocation movement, thereby raising the microhardness of covalent semiconductors. On the other hand, the gettering of unintentional impurities by rare-earth dopants in the melt leads to a reduction in microhardness in the seed-end portion of the ingot.

Effect of rare-earth dopants on the growth and properties of triglycine sulphate single crystals

The effect of rare-earth ion dopants La, Ce and Nd on the growth aspects and ferroelectric properties of triglycine sulphate single crystals is reported. The incorporation of dopants into the grown crystals is far below the concentration in the mother solution. The dopants significantly modify the morphology of the crystals. Dielectric measurements revealed that the dielectric constant of Ce doped triglycine sulphate (TGS) increases rapidly at the transition temperature. Well-saturated rectangular hysteresis loops have been observed for all the doped crystals. Lenticular ferroelectric domain patterns were observed on the [0 1 0] plane of the grown crystals. Among the three dopants, La doped TGS possess a high Curie temperature and coercive field values.

Effect of rare earth doping on sol-gel derived PZT thin films

We have studied the effect of rare earth dopants (Nd, Gd and Ce) on the phase formation behavior and electrical properties of sol-gel derived Pb1.05(Zr0.53Ti0.47)O3 thin films. In all these films the perovskite phase is obtained up to 5 at% doping and beyond that pyrochlore phase was found to coexist with the perovskite phase. Ce and Gd doping(1-2 at%) exhibited improved ferroelectric and dielectric properties as compared to the undoped PZT films. Nd doping (2 at%) was found to be effective to increase the retained switchable polarization of undoped PZT from 63% to 84%. The transition temperature of undoped PZT film was found to be reduced with Nd doping. The Nd doped films also exhibited typical relaxor behavior and a diffuse phase transition, characteristic of the relaxor material. Introduction of Nd into the PZT lattice probably introduces disorder in the B site of ABO3 lattice which causes the observed relaxor behavior

Investigation of the effect of rare earth doping on the electrical and photovoltaic properties of chromotrope 2R thin film devices

Praseodymium (Pr) doped and Samarium (Sm) doped chromotrope 2R (CHR) were used for the fabrication of Schottky devices, by the spin coating technique. The diode in which doped CHR behaves as an n-type organic semiconductor exhibits rectification behaviour in the dark. Doping with rare earths imparts an accelerated improvement in the n-type conductivity as well as in the rectification effect. The observed rectification effects are explained by n-type semiconductivity of the doped CHR thin films. The formation of a blocking contact (Schottky barrier) indium tin oxide with (ITO) electrode and an ohmic contact with Al or ln, also confirms its n-type behaviour. The position of the Fermi level shifts toward the conduction band edge on rare earth doping. Additionally, the concentration of free carriers and mobility of electrons also increase upon doping, with the simultaneous decrease in trap concentration. Various electrical parameters such as barrier height (φb), density of ionized donor (Ns) and depletion layer width (W) were calculated from the detail capacitance–voltage analysis of (C–V) characteristics. The photo-action spectra of the devices and absorption spectra of doped CHR layer reveal the formation of a Schottky barrier at the ITO-doped CHR interface and an Ohmic contact at the Al-doped CHR interface. Photovoltaic measurements of these devices provide parameters such as short circuit photocurrent (Jsc), open circuit voltage (Voc), fill factor (FF) and power conversion efficiency (η). The effect of rare earth doping on the electrical and photovoltaic parameters are discussed in detail. © 1998 Chapman & Hall

Structural phase transformations of rare-earth modified transition alumina to corundum

The effect of rare-earth dopant on transformations of the γ→θ→α phases in fine alumina powders under vacuum was investigated by in situ neutron diffraction from 500 to 1300°C. La-doped (1 mol%) Al2O3 powders (surface area ∼170 m2/g) were prepared by an impregnation technique. Below 800°C both samples contain a dominant γ-phase. Above 1000°C, transformation of the γ-phase to the intermediate θ-phase, and then completely to the α-phase (corundum) was observed. Addition of 1 mol% of La in Al2O3 effectively shifts the α-phase formation temperature from ∼1125°C for pure alumina to ∼1250°C, probably due to the larger size of La compared to Al ions, which hinders ionic diffusion in the processes of sintering and transformation. Consequently, doping La in alumina improves the surface-area and thermal stability at high temperatures, which is important for catalytic applications.

Effect of rare-earth doping on the electrical and photoelectrical properties of furazano [ 3,4- b] piperazine (FP) thin-film devices

Schottky diodes of rare-earth, praseodymium (Pr)-doped and samarium (Sm)-doped furazano [3,4- b] piperazine (FP), sandwiched between Al and indium-tin oxide (ITO) were made by a spin-coating technique. The diodes, in which doped FP behaves as a p-type organic semiconductor, exhibit rectification behaviour. The p-type semiconductivity and rectification properties of the devices improve with rare-earth doping. The electrical effects observed in these devices are explained in terms of the p-type semiconducting behaviour of the doped FP thin films and the formation of a blocking contact (Schottky barrier) with the Al electrode and ohmic contact with the ITO electrode. Various electrical parameters such as carrier mobility, position of Fermi level, free carrier concentration, trap density, trap level and conductivity of doped FP are calculated and discussed. It is found that the position of the Fermi level shifts toward the valence band on rare-earth doping; concentration of free carriers and carrier mobility increase on doping. From the capacitance-voltage ( C-V) measurements, various electrical parameters such as barrier height, density of ionized acceptor atoms and depletion layer width are calculated and discussed. From the action spectra and absorption spectra it is confirmed that the Al-doped FP interface forms a Schottky barrier and the ITO-doped FP interface shows ohmic contact. The photovoltaic measurement on the two devices reveals that the short circuit current, open circuit voltage, fill factor and power conversion efficiency increase on rare-earth doping.

Photoassisted Carbon Dioxide Reduction to Organic Compounds Using Rare Earth Doped Barium Titanate and Lithium Niobate as Photoactive Agents

AbstractThe effect of rare earth dopants on the large bandgap semiconductors, barium titanate and lithium niobate, in the photoassisted reduction of carbon dioxide was studied in aqueous suspensions, by illumination with high pressure mercury lamps. The yields of the reduction products formic acid and formaldehyde was enhanced by the presence of low concentrations of the oxides of europium, neodymium, samarium and cerium in the above semiconductors. The optical properties of the materials were studied by diffuse reflectance spectroscopy.

Effects of rare-earth dopants on transition to the superionic state of fluorites

An explanation is suggested for the observation that in fluorites the temperature of transition to the superionic state is depressed by rare-earth dopants.