Effect Of Ce Substitution Research Articles

Effect of Ce substitution on magnetic and dielectric properties of BiMn2O5

Polycrystalline BiMn2O5 and Bi0.9Ce0.1Mn2O5 have been prepared by a solid-state reaction. A crystalline structure study shows that all x-ray diffraction patterns can be indexed successfully in an orthorhombic phase. Substitution of Ce for Bi ions induced in the unit cell a slight distortion and enlargement. Magnetic and dielectric measurements all reveal that Ce substitution induces great effects: BiMn2O5 is in the antiferromagnetic (AFM) phase with a Néel transition temperature at about 42K, whereas Bi0.9Ce0.1Mn2O5 is in the ferromagnetic (FM) phase with a Curie temperature at about 46K. The permittivity of Bi0.9Ce0.1Mn2O5 is much higher than that of BiMn2O5, and two dielectric relaxation peaks have been observed in the former, instead of one dielectric loss peak as observed in BiMn2O5. The valent state of Ce ions has been analyzed mainly as tetravalent by the core-level spectrum of Ce 3d from x-ray photoemission spectroscopy. The possible mechanisms of the magnetic transition from AFM to FM and the peculiar dielectric relaxation peaks induced by Ce substitution have been discussed in detail.

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.

NMR of 165Ho in Ho:(Gd 1− xCe x)Rh 2

The effect of Ce substitution on the resonance properties of 165Ho in Ho:(Gd 1− x Ce x )Rh 2 has been investigated and the available data are used to explain the variation of the Ho hf parameters with Ce concentration.

Magnetic and electrical properties of UCu2Ge2

Abstract Of the many interesting U and Ce compounds in the ThCr2,Si2, structure UCu2,Ge2, is unusual in showing the onset of ferromagnetism at a fairly high temperature (105 K) but its apparent replacement by antiferrornagnetism at low temperatures. We have made detailed studies of the magnetic behaviour and electrical resistance in this compound and of the effects of Ce substitution for U and some examination of the effects of Si substitution for Ge. Ce lowers the Curie temperature and fairly rapidly raises the temperature at which antiferromagnetic components appear, and by 50% Ce substitution only antiferromagnetic order is found. Si substitutions for Ge have much less effect on UCu2,Ge2.

Effects of Ce substitution and and reduction on the electronic states of Nd2-xCexCuO4-y studied by x-ray photoelectron.

The effects of Ce substitution and reduction on the core levels and valence electronic states of ${\mathrm{Nd}}_{2\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ce}}_{\mathit{x}}$${\mathrm{CuO}}_{4\mathrm{\ensuremath{-}}\mathit{y}}$ have been investigated using x-ray photoelectron spectroscopy (XPS). It is found that the surfaces could be tremendously degraded by scraping, leading to changes in the electronic structures of Cu, O, and the Fermi edge. The changes in the Cu 2p spectra imply that the Ce substitution and the reduction donate electrons to Cu sites to show the appearance of monovalent Cu. The fraction of monovalent Cu derived from the Cu 2p spectra is less than the amount of Ce, which suggests that Ce is in the mixed-valence state. The XPS valence spectra show the Fermi edge formed by the electrons injected into the electronic state with the Cu 3${\mathit{d}}^{10}$ configuration. The nature of the Fermi edge is discussed in terms of photoionization cross section.