Sc Doping Research Articles

Advances in doping MgB 2 : tuning the Fermi level to the “shape resonance” by Sc substitution

We have synthesized superconducting Mg1−xScxB2 ternary system in order to explore the influence of electron doping on the electronic properties. An accurate characterization of several samples by X-ray diffraction and conductance measurements has been performed. The Tc vanishes at the critical concentration x at which the Fermi level is tuned to the top of the σ band. Sc doping in Mg1−xScxB2 allows to tune the Fermi level to the “shape resonance” of the σ boron superlattice with negligible changes of the lattice and we have found a large Tc amplification by approaching the “shape resonance” as predicted by our previous works. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Nonvolatile photorefractive holographic recording in Sc:Ce:Cu:LiNbO 3

In this paper experimental studies of nonvolatile photorefractive holographic recording in Ce:Cu:LiNbO 3 crystals doped with Sc(0,1,2, 3 mol %) were carried out. The Sc:Ce:Cu:LiNbO 3 crystals were grown by the Czochralski method and oxidized in Nb 2O 5 powders. The nonvolatile holographic recording in Sc:Ce:Cu:LiNbO 3 crystals was realized by the two-photon fixed method. We found that the recording time of Sc:Ce:Cu:LiNbO 3 crystal became shorter with the increase of Sc doping concentration, especially doping with Sc(3 mol%) , which exceeds the so-called threshold, and there was little loss of nonvolatile diffraction efficiencies between Sc( 3 mol %):Ce:Cu:LiNbO 3 and Ce:Cu:LiNbO 3 crystals.

Large lattice effects arising from Sc on magnetic and transport properties inLa0.7Ca0.3Mn1−xScxO3

Structural, magnetic, and transport properties in ${\mathrm{La}}_{0.7}{\mathrm{Ca}}_{0.3}{\mathrm{Mn}}_{1\ensuremath{-}x}{\mathrm{Sc}}_{x}{\mathrm{O}}_{3}$ have been experimentally investigated. A sensitive response on the magnetic and transport properties to Sc substituting for Mn is observed, demonstrated as a rapid decrease in Curie temperature ${(T}_{C})$ and a remarkable enhancement in magnetoresistance. In the range of $x=0--0.03,$ ${T}_{C}$ shifts linearly to a lower temperature with increasing x at a rate of around 37 K for each 1% ${\mathrm{Sc}}^{3+}$ doping. The data of saturation magnetization show no magnetic coupling between Sc and Mn ions. ${\mathrm{Mn}}^{4+}/\mathrm{Mn}$ content increases from 30.5 to 37.7% when x varies from 0 to 0.1, indicative of the small influence on ${T}_{C}.$ Structural refinement reveals a large lattice distortion in the ${\mathrm{MnO}}_{6}$ octahedra with Sc doping because of the dopant-size-induced local strain effect. According to the dependence of the tolerance factor on magnetic phase diagram, it is believed that the enhanced doping effects should be ascribed to the additional local strain effect, as well as the size mismatch between A- and B-site ions, caused by the large ${\mathrm{Sc}}^{3+}$ ions in the lattice.

Improvement of optical properties and radiation hardness of NaBi(WO 4) 2 Cherenkov crystals

On the basis of the data on melt evaporation while growing NaBi(WO 4) 2 Cherenkov crystals, the formation of nonstoichiometry and most probable types of dot defects of the crystals have been considered. The influence of melt nonstoichiometry and doping with Sc on optical transmission and radiation hardness of the crystals has been experimentally investigated. The surplus of WO 3 has been established to increase optical transmission and radiation hardness and lack of Bi 2O 3 in the melt to reduce radiation hardness. Sc doping is shifting the absorption edge to UV region by 30–35 nm and is increasing radiation hardness of the crystals about three-fold. Analytical estimations give the increase of the number of Cherenkov photons by a factor of 1.3, which leads to an improvement of the energy resolution of a calorimeter based on NaBi(WO 4) 2:Sc crystals compared with undoped NaBi(WO 4) 2 of approximately 15%.

Structural, magnetic and transport properties of Sc-doped La0.7Sr0.3MnO3

The Sc-doped La0.7Sr0.3MnO3 polycrystallines were prepared by thermal decomposition of complexes of metal ions with ethylenediamine-tetraacetic acid (EDTA). The dependence of structural, magnetic and transport properties on Sc doping was investigated. Moderate Sc doping level results in a sharp drop in Curie temperature, an increase in resistance and enhancement of magnetoresistance effect. At temperatures aboveTMI,R(T) can be described asR(T) = R0exp(T0/T)1/4, which indicates that conduction takes place by hopping between the localized states. The experimental data reveal that the change in magnetoresistance property is related to the structure.

Electronic structures of hydrogen in perovskite-type oxide, SrTiO 3

The electronic structures of hydrogen in SrTiO 3 are simulated by the DV-X α molecular orbital method. In pure SrTiO 3, there is a band gap of about 3.5 eV between the O-2p valence band and the Ti-3d conduction band, in agreement with experiments. When Sc is doped into SrTiO 3, an acceptor level appears just above the valence band. On the other hand, when hydrogen is introduced into SrTiO 3, a donor level appears below the conduction band. The molecular orbital of the donor level is composed mostly of the Ti-3d and O-2p electrons, but still there is a small occupancy (6%∼12%) of the H-1s electrons in it. When both Sc and hydrogen coexist in SrTiO 3, charge transfer takes place from the donor level to the acceptor level. As a result of this charge compensation, the effective ionicity of hydrogen becomes about +0.17∼+0.24, the value of which is dependent on the hydrogen positions in the crystal lattice. Also, the chemical bond strengths between constituent ions are modified largely by dopants. For example, the Sc doping tends to strengthen the chemical bond between hydrogen and oxygen ions, but instead to weaken the chemical bond between the oxygen ion and the surrounding metal ions. In addition, it is shown that an oxygen ion vacancy makes the defect level below the conduction band in the Sc-doped oxide.

Reduction of degradation of Y 3(Al,Ga) 5O 12:Tb phosphors by Sc doping

It was found that introduction of Sc into Y 3(Al,Ga) 5O 12:Tb is effective for reducing the phosphor degradation by electron bombardment. Thermoluminescence (TL) measurements show that no new TL active traps related to Sc are formed in the phosphor lattice. It was also observed that the TL intensity decreases with an increase in Sc concentration. It is proposed that this effect of the Sc doping is related to the more closed packing of the lattice.

Dopant effects on the grain structure and electrical property of PZT thin films prepared by sol-gel process

PZT ( Zr Ti = 53 47 ), PNZT (4% Nb doped PZT), PSZT (2% Sc doped PZT) and PSNZT (1% Sc and 1% Nb doped PZT) thin films were prepared by a sol-gel process. They were characterized by XRD, SEM, AFM and TEM. It was observed that the crystallographic orientation and the grain size of PZT film can be changed by doping. Pt/PZT/Pt capacitors were fabricated for the measurement of ferroelectric properties. By the doping of Sc and Nb together, the fatigue property of PZT was considerably improved and the coercive field was decreased, while the remanent polarization was not changed.

TiOCl, TiOBr-are these RVB d1, S=1/2 materials? The results of scandium substitution set in the context of other S=1/2 systems of current interest for high-temperature superconductivity and the metal-insulator transition

The title materials display anomalous electrical, magnetic and optical properties. They have the characteristics of Mott insulators showing high electrical resistance and ligand-field optical spectra, but at the same time they adopt a magnetic ground state which is neither of Curie-Weiss type nor indeed of some standard antiferromagnetically ordered condition. The observed state is one of lowish, isotropic, and almost temperature-independent paramagnetism. The authors have studied the magnetic properties of Sc-doped TiOX, seeking possible indications of the existence of the resonant valence bond or RVB state-the state currently suggested by some to be responsible for high-temperature superconductivity in the mixed-valence cuprates. It is necessary to distinguish between RVB and some extreme case of magnetic frustration in these S=1/2, 2D oxyhalide systems. The authors' tentative conclusion is that TiOX presents an RVB ground state which Sc doping renders glassy and static.

Magnetization and Superconductivity of Impurity-Doped Y9Co7

Magnetic and superconducting transition temperatures of pure and impurity-doped Y9Co7 are summarized. Doping of Al, Sc, Zr and Gd extremely enhances the ferromagnetism and suppresses the superconductivity, while doping of La, Lu and 3d transition metals influence moderately. The result suggests that the introduction of randomness into the lattice has crucial influence on the magnetism and the superconductivity. Superconductivity of Y9Co7 is suggested to coexist with a very large spin fluctuation of one dimensional ferromagnetism.

Electrical properties and the metal-insulator transition in(ScxTi1−x)2O3

The resistivity, thermoelectric power, and lattice parameters of ${\mathrm{Ti}}_{2}$${\mathrm{O}}_{3}$ doped with varying amounts of scandium have been measured between 77 and 700 K. A metal-to-insulator transition has been encountered in all specimens between approximately 400 and 600 K. The magnitude of the transition is nearly independent of Sc doping up to 0.33 at.% and grows with further increase in Sc content of the specimens. The activation energy for conduction at first declines and then increases with increasing Sc content. Since Sc doping has no large effect on the transition temperature, it is concluded that the transition is largely lattice dominated.