Effect Of La Substitution Research Articles

Effects of La substitution on the superconducting state ofCeCoIn5

We report effects of La substitution on superconducting state of heavy fermion superconductor CeCoIn5, as seen in transport and magnetization measurements. As opposed to the case of conventional superconductors, pair breaking by nonmagnetic La results in depression of Tc and indicates strong gap anisotropy. Upper critical field Hc2 values decrease with increased La concentration, but the critical field anisotropy, gamma=Hc2(a)/Hc2(c), does not change in the Ce_{1-x}La_xCoIn5 (x=0-0.15). The electronic system is in the clean limit for all values of x.

Effects of La substitution for Nd in (Nd 2− xLa x)BaZnO 5 solid solutions on microwave dielectric properties and crystal structure

The synthesis and microwave dielectric characterization of (Nd 2− x La x )BaZnO 5 solid solutions were studied. The samples obtained were single phase over the whole composition range and the lattice parameters of solid solutions were linearly increased with increasing the composition. Moreover, the expansion of the volume in the RO 8 ( R=Nd and La) and BaO 10 polyhedra and ZnO 4 tetrahedron were recognized when Nd ions were substituted by La. These variations in the lattice parameters and volumes of the polyhedra are basically attributed to the differences in ionic radii between Nd 3+ and La 3+ ions. From the evaluation of microwave dielectric properties, it was shown that the appropriate τ f values ranging from 4.6 to −5.0 ppm/°C are obtained by La substitution for Nd ion, and the highest Q · f value was 17,832 GHz at x=2.

Systematic X-ray absorption study of hole doping in BSCCO-phases

X-ray absorption spectroscopy (XAS) on the O 1s threshold was applied to Bi-based, single crystalline high temperature superconductors (HTcs), whose hole densities in the CuO2 planes were varied by different methods. XAS gives the intensity of the so-called pre-peak of the O 1s line due to the unoccupied part of the Zhang–Rice (ZR) singlet state. The effects of variation of the number n of CuO2-planes per unit cell (n=1,2,3) and the effect of La-substitution for Sr for the n=1 and 2 phases were studied systematically. Furthermore, the symmetry of the states could be probed by the polarization of the impinging radiation.

The effect of La substitution andmagnetic field on non-Fermi-liquid behaviour in CeRu4Sb12

CeRu4Sb12 with the filled skutterudite structure exhibitsa novel non-Fermi-liquid (NFL) behaviour in the low-temperaturespecific heat and electrical resistivity at ambient pressure. Weinvestigated the effect of La substitution and magnetic field onthe NFL state and found that it can be easily destroyed either bythe application of a magnetic field or by a small degree of Lasubstitution. In magnetic fields, C/T becomes strongly depressedand nearly constant below 1 K and ρ(T) turns to following aT2-law, implying that the Fermi-liquid state recovers in highmagnetic fields. The type of critical fluctuation is discussed onthe basis of the results of magnetic susceptibility, electricalresistivity and specific heat measurements.

Effect of La substitution on the microstructure and superconducting properties of Bi-2212/Ag tapes

La-substituted Bi-2212 (Bi 2Sr 2− x La x CaCu 2O y )/Ag tapes with x=0.05, 0.1 and 0.2 were fabricated by a partial melting and subsequent slow cooling technique in oxygen partial pressures ( P O 2 s) of 0.21 and 1 atm. La substitution raised maximum temperature ( T max) of the heat treatment schedule. For x=0.05, grain oriented structure was obtained when processed at both P O 2 s and T max around 920°C, whereas for x=0.1, it was obtained at P O 2 =0.21 atm and T max around 940°C. No grain oriented structure was obtained for x=0.2 at both P O 2 s. The amount of La substituting for Sr in Bi-2212 was scattered and varied from grain to grain. This was independent of P O 2 . Bi-free (Sr,Ca) 2CuO 3 grains were inhomogeneously distributed as colonies in tapes with x=0.05 at P O 2 =0.21 atm, while a large number of Cu-free Bi(Sr,Ca) 2O y grains were present homogeneously in tapes at P O 2 =1 atm. These aligned tapes showed T cs about 80 K and transport J c values of about 20 kA/cm 2 at 4.2 K and 10 T.

Structural and normal state properties of thePrBa2-xLaxCu3O7-δ compound with (0.00⩽x⩽1.00)

The present work investigates the effect of La substitution at the Ba siteon the structural and normal state properties of thePrBa2-xLaxCu3O7-δ compound, with various x values(0.00⩽x⩽1.00). X-ray diffraction results indicate that the clattice parameter decreases with increasing x for all samples. Thesamples with x = 0.00 and 0.25 are clearly quasi-tetragonal single phase,while the samples with x = 0.50, 0.75 and 1.00 are clearly orthorhombicsingle phase with a few small unreacted lines observed in the spectrum ofthe x = 1.0 sample. The effective Cu valence decreases linearly withincreasing La content along with a small increase in the oxygen content.The EDX analysis reveals that the total amount of La and Ba remainsconstant with increasing La content. It is also found that the substitutionof La at the Ba site leads to an unusual drop in the normal stateresistivity as compared to the Pr:123 compound. We suggest that both thehole filling and oxygen disorder effects might be key parameterscontrolling superconductivity as well as the normal state properties of thePr:123 compound. Our results are supported by a host of otherconsiderations and experimental observations.

Magnetic properties of Pr 1− xLa xPtAl

Orthorhombic PrPtAl with a nonmagnetic singlet ground state of Pr 3+ is an induced-moment ferromagnet with T c=5.8 K. We have investigated the effect of La substitution of Pr by measurements of specific heat and magnetization of polycrystalline samples of Pr 1− x La x PtAl (0⩽ x⩽0.3). We have found that with increasing La concentration the reduction of the ordered Pr moment is much weaker in the orthorhombic singlet–singlet system Pr 1− x La x PtAl than in the cubic singlet–triplet system (Pr 1− x La x ) 3Tl.

Magnetic field effect on non-Fermi liquid behaviors in CeRu 4Sb 12

CeRu 4Sb 12 with the filled skutterudite structure exhibits non-Fermi liquid (NFL) behavior in the low-temperature specific heat and electrical resistivity. We investigated the effect of La-substitution and the magnetic field on the NFL state and found that a little La-substitution destroys the NFL behavior of C/ T, probably by impairing the coherency of the Ce sublattice. In applied magnetic fields, C/ T becomes strongly depressed and nearly constant below 1 K and ρ( T) turns to a T 2-law, implying that the Fermi liquid state recovers itself in high magnetic fields.

La-substitution effects on transport properties of APbO 3−δ (a = Ba, Sr and Ca)

Partial substitutions of La for alkaline-earth elements of perovskite-type APbO 3−δ (A = Ba, Sr, and Ca) were studied in order to examine carrier doping effects on the APbO 3−δ system. The solubility limit of La was found to be about 10% for every alkaline-earth element. The temperature dependencies of electrical resistivity and the Seebeck coefficient for A 0.9La 0.1PbO 3−δ samples indicated that they were metallic conductors, irrespective of the ionic size of the alkaline-earth elements. This is in good contrast with the resistivity of APbO 3−δ, which is strongly influenced by the ionic size of A, via the distortion of PbO 6 octahedra. The Seebeck coefficients for the A 1−xLa xPbO 3−δ (x = 0 and 0.1) samples were negative, and absolute values were reduced by the La substitution, which implies that electron carriers were introduced into the conduction band. Superconductivity was not observed in these compounds down to 1.8 K, although the carrier density expected, based on the Seebeck coefficient, was comparable to the value for the superconducting BaPb 1−xBi xO 3.

Effect of La substitution on the CuO2 chain spin gap in Sr14Cu24O41

The compound Sr14Cu24O41 has a unique structure. It consists of an alternating stack of the plane containing edge-sharing CuO2 chains, and the plane containing two-leg Cu2O3 ladders sandwiched by Sr layers. The CuO2 chain also has a singlet ground state originating from a dimerization. The dimerized state in the chain depends critically on the number of holes. The effect of La substitution for Sr on the CuO2 chain spin gap is investigated by measuring the magnetic susceptibility of Sr14−xLaxCu24O41 with x⩽1. Due to the large spin gap, the Cu2O3 plane is magnetically inert below room temperature. For x=0, the susceptibility shows a characteristic decrease below 80 K, followed by an upturn below 20 K due to a Curie contribution. After subtracting the Curie term, the susceptibility is fitted by a dimer description. The dimer number ND=1.45 and the dimer coupling constant JD=139 K are obtained. With increasing La content, both ND and JD decrease gradually, indicating the weakening of the antiferromagnetic interaction between Cu2+ spins in the CuO2 chain. The Curie contribution enhances at the same time, and the gap feature becomes gradually smeared. It is difficult to fit the data when x=1.0.

Influence of the Kondo-hole impurities on the electronic structure of CeNiSn and CeRhSb

The electronic structure of ${\mathrm{Ce}}_{1\ensuremath{-}x}{\mathrm{La}}_{x}\mathrm{NiSn}$ and ${\mathrm{Ce}}_{1\ensuremath{-}x}{\mathrm{La}}_{x}\mathrm{RhSb}$ has been studied by photoelectron spectroscopy. The x-ray excited valence-band spectra are compared with ab initio electronic-structure calculations using the linearized muffin-tin orbital method. The results have been used to compare and contrast the effect of La substitution on the ground state properties of the Kondo insulators CeNiSn and CeRhSb. The $\mathrm{Ce} 3d$ x-ray photoemission spectroscopy spectra show evidence for the mixed valence state of Ce in CeRhSb alloys, as also seen for CeNiSn, whereas the spectra for the La substituted (Ce,La)NiSn compounds show only evidence for a pure ${\mathrm{Ce}}^{3+}$ ground state. We suggest the presence of Kondo-hole states in ${\mathrm{Ce}}_{1\ensuremath{-}x}{\mathrm{La}}_{x}\mathrm{RhSb}.$

Raman spectroscopic study of the La0.5R0.5Ba2Cu3OyRY, rare earth) superconductors

Two series of materials La0.5R0.5Ba2Cu3O(fully oxygenated and deoxygenated,R=Pr, Nd, Sm, Eu, Gd, Dy, Y, Ho, Er, Tm, Yb, Lu) have been prepared with a variation of the solid state reaction technique. X-ray diffraction and Raman measurements have been carried out to study the effect of La substitution for another rare earth. The cell parameters show the usual lanthanide contraction behavior. In the micro-Raman spectra a slight increase of the Agmode frequency of the apex oxygen with increasing average La-R ionic radius is observed, while the mode frequencies corresponding to the Ba, Cu(2) (cuprate plane Cu), and the in-phase vibrations of the O(2,3) (cuprate-plane oxygens) atoms remain practically unaffected. Nevertheless the last show a deviation compared to previous measurements on theR123 samples. On the other hand, the changes induced in the B1gRaman active mode of O(2,3) (out-of-phase vibrations), can be attributed to chemically separated phases rich in either La, R or an intermediate phase. The results are discussed in connection with a previously studied Pr0.5R0.5Ba2Cu3Oyseries.

The effects of La-substitution on the microstructure and magnetic properties of nanocomposite NdFeB melt spun ribbons

The magnetic properties and microstructural evolution of (Nd1−xLax)9.5Fe85.5B5 (x = 0, 0.05, 0.10and0.15) melt spun ribbons have been investigated. It was found that La is effective in refining the grain size of these ribbons. La-substitution is also effective in yielding excellent magnetic properties even when the alloy is melt spun at a lower wheel speed. The magnetic properties of the ribbons are determined by two major factors: (1) the magnetic dilution and (2) the enhancement of exchange coupling between Nd2Fe14B and α-Fe phases of fine grains. Br of 9.9 kG, iHc of 6.2 kOe and (BH)max = 15.5MGOe have been obtained in the alloy ribbons with x = 0.10 when directly quenched at a wheel speed of 18 m/s.

A comparative study of suppression of the energy gap with La substitution in the Kondo insulators: CeNiSn and CeRhSb

We report structural, transport and magnetic measurements on the solid solutions of Ce 1− x La x NiSn and Ce 1− x La x RhSb ( x = 0 to 1). The results have been used to compare and contrast the effect of La substitution on the ground state properties of the Kondo insulators CeNiSn and CeRhSb. The resistivity measurements reveal that the energy gap in CeNiSn and CeRhSb decreases with increasing La concentration; no gap type behaviour was observed for La concentration ≥ 0.2. At low temperature, Ce 1− x La x NiSn alloys show a cross-over from a Kondo insulator ( x = 0) to a single ion Kondo ground state ( x ≥ 0.2) with increasing La concentration, while Ce 1− x La x RhSb alloys show a cross-over from a Kondo insulator ( x = 0) to a coherent Kondo lattice ( x = 0.2) and eventually to a single ion Kondo ground state at x = 0.5. Magnetic susceptibility measurements of Ce 1− x La x NiSn alloys exhibit a dramatic change in behaviour with La concentration; Curie-Weiss behaviour for x = 0, valence fluctuation behaviour for x = 0.2 and again CW behaviour for x ≥ 0.4. On the other hand, susceptibility of Ce 1− x La x RhSb alloys continue to show a valence fluctuation behaviour up to x = 0.7, and CW behaviour for higher La concentrations. CeNiSn and CeRhSb exhibit a large negative magnetoresistance at 20 T field and at 1.5 K.

An investigation of Ca-based hydride electrode materials

The effects of La-substitution for Ca in Ca 1 − xLa xNi 4.7Al 0.3 on metallography, structure and electrochemical properties have been investigated. It was found that Ca and Al segregated over the grain boundaries of the alloys. Based on La substituted CaNi 5 -type alloys, we studied the Zr and Ti addition effects as well. It was found that ZrNi phases or TiNi phases deposited on the boundaries of AB 5 phase improved the anti-corrosion property of the alloys. Annealing improves the electrochemical durability of the Ca 1 − xLa xNi 4.7Al 0.3 alloys by reducing A 2B 7 phase and Ca segregation on the grain boundary.

F-treatment effect on the hydriding properties of the La-substituted AB2 compound (Ti, Zr)(Mn, Cr, Ni)2

The La-substitution effects of AB2 hydriding compounds (Laves phase) Ti0.5−x/2Zr0.5−x/2LaxMn0.8Cr0.8Ni0.4 (x = 0.1-0.1) on the hydriding properties including initial activation characteristics, pressure-composition-temperature property and long storability in air and water have been investigated and compared with those of F-treated alloys. It was found that a small La substitution could dramatically improve the initial activation and surface protection against air or water exposure, especially after F-treatment. La could not be substituted into the AB2 phase but formed La-rich particles which served as catalytic sites for hydrogen uptake and protected against the normally damaging of F-treatment on the AB2 alloy surface. No significant deterioration of the surface reactivity was observed for F-treated 0.05La alloy even after 6 months exposure to air and water. The optimum La content should be in the range of 0.03–0.05.

Cerium Content and Cycle Life of Multicomponent AB 5 Hydride Electrodes

Multicomponent hydrides are attractive replacements for the cadmium electrode in nickel‐cadmium batteries. The archetype compound of the alloy class is , but in a typical battery electrode mischmetal is substituted for La and Ni is substituted in part by various metals. While the effects of Ni substitution have been widely studied, relatively little effort has been focused on the effect of La substitution. Cerium is the predominant rare earth in normal mischmetal, and this paper deals with the effect on cycle life and storage capacity due to the increasing presence of Ce in the alloy series. Alloys were characterized by the determination of pressure‐composition relationships, molar volume of H in the hydride phase and electrode cycle life. The effects due to lattice expansion are taken into account. It was concluded that the rate of loss of electrochemical capacity per charge‐discharge cycle due to electrode corrosion was significantly decreased by the presence of Ce.

Kondo coherence gap and superconductivity in the Ce1-xLaxRhSb system.

CeRhSb is a mixed valent Ce-based compound which shows a rapid rise in resistivity at low temperatures. This resistivity rise has been attributed to the opening of a gap in the electronic density of states. On the other hand, isostructural LaRhSb is a superconductor with ${\mathit{T}}_{\mathit{c}}$ of about 2.5 K. We have investigated the system ${\mathrm{Ce}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{La}}_{\mathit{x}}$RhSb to study the effect of La substitution for Ce on the gap formation in CeRhSb, and the effect of Ce substitution for La on the superconductivity in LaRhSb. It is observed that the rapid rise in resistivity, and hence the gap formation, is suppressed even when a small amount of La is substituted for Ce in CeRhSb, though susceptibility continues to show mixed valent behavior. This suggests that a coherent Kondo lattice state is essential for the gap formation in CeRhSb. On the La rich side, superconductivity is suppressed even by 0.5% replacement of La by Ce. In the intermediate region of substitution, a gradual transformation from a mixed valent to a Curie-Weiss behavior in the susceptibility is observed.

Effect of La substitution on T c and electronic structure of Bi 2201 phase

The critical temperature T c of Bi 2(Sr 1- x La x ) 2CuO y increased with increasing x, reached a maximum of K at x=0.19 and decreased. Determination of the excess oxygen content Δ y by chemical analysis revealed that Δ y decreased with increasing x. The oxygen content and conductivity σ of Bi 1.96(Sr 0.81La 0.19) 2Cu 1.02O y were measured as a function of T and P(O 2 ) at high temperatures and σ at constant y was determined as a function of T. It was found that σ increases with the increase in excess oxygen Δ y. Assuming that one excess oxygen atom creates two holes, the carrier density n and the mobility were calculated. The extension of high-temperature conductivity linked smoothly with the low-temperature one with the same oxygen content when y is high. From the results, an electronic-structure model whereby the conduction behavior can be interpreted was proposed.

Effect of lanthanum substitution at the barium site on the mechanical behaviour in YBCO superconductor

The lanthanum substituted superconducting oxide system YBa 2−xLa xCu 3O 7−δ is prepared by ceramic method. The compacted and sintered pellets containing different percentages of La (x = 0.0→0.5) are indented by a 120° diamond cone. The effect of La substitution on superconducting and bulk mechanical properties as well as the deformation behavior of the material are investigated.