O. Cozar

EPR and magnetic susceptibility studies of Cu2+ ions in Bi2O3·GeO2 glasses

Abstract Results of EPR and magnetic susceptibility measurements performed on x CuO·(1− x ) [Bi 2 O 3 ·GeO 2 ] glasses with 0 x ≤50 mol % are reported. EPR data suggest a hexacoordinated geometry of the tetragonal-distored octahedral symmetry for Cu 2+ ions. The modification of EPR spectra with the increasing of CuO content are explained supposing that these are the results of a superposition of two EPR absorptions: one is asymmetrical, typical for isolated Cu 2+ ions ( g ‖ ≅2.34 and g ⊥ ≅2.07) and the another a symmetrical line at g ≅2.10, characteristic for clustered ions. The dependence of the g ≅2.10 linewidth vs CuO content shows that between clustered copper ions the dipole-dipole interactions prevail. These data consist with those obtained from magnetic measurements, which indicate that the Cu 2+ ions are magnetically isolated. From the Curie constants it was established that in this glass system the copper ions are in both Cu + and Cu 2+ valence states, the latter being ≈45% of CuO content in all studied glasses.

Structural and magnetic properties of CuOTeO2B2O3SrO glasses

Glasses of the system 70TeO 2 .25B 2 O 3 . 5SrO doped with CuO up to 20 mol% were investigated. Mixed valence states (Cu 2 + and Cu + ) of copper ions were revealed. Depending on CuO concentration, Cu 2 + are distributed as isolated ions in axially distorted octahedral symmetric sites, or associated in clusters. The magnetic behaviour of the studied glasses was interpreted in terms of dipole-dipole interactions.

ESR studies of Mo5+ ions in potassium-borate and soda-phosphate glasses

Abstract The local symmetry and the interaction between metallic ions in potassium-borate and soda-phosphate glasses with molybdenum were investigated by the ESR method. The coordination polyhedra geometry is distorted from the almost Oh symmetry to C4v with the increase of molybdenum content in B2O3ue5f8K2O glasses. Also, the MoO2 oxide becomes a former of the network at high content (x > 40 mol%) together with B2O3 oxide, molybdenum ions occupyi the network-former sites. Mo[5+ ions are essentially coordinated in P2O5ue5f8Na2O glasses by five oxygen ligands in a C4v symmetry with a Moue5fbO double bond. The values of bonding coefficients (β2,β1, ϵ) were estimated using an appropriate LCAO-MO scheme.

Magnetic properties of xCr2O3 · (1 − x)[Bi2O3 · PbO] glasses

Abstract EPR and magnetic susceptibility measurements have been performed on x Cr 2 O 3 · (1 − x )[Bi 2 O 3 · PbO] glasses with 0 x ≤ 30 mol%. These data show that the chromium ions are in the Cr 3+ valence state. For x ≤ 5 mol% most of these ions are isolated or experience dipole-dipole interactions, but for higher Cr 2 O 3 concentrations the dominant part of them are magnetically coupled by negative superexchange interactions.

EPR study of phosphate glasses containing two types of transitional metal ions

Abstract The following glass systems x(CuO·V2O5)(100 − x)[2P2O5 · PbO] and x·(MnO·V2O5)(100 − x)[2P2O5 · Na2O] with 0 ⩽ x ⩽ 40 mol% were prepared and investigated by EPR spectroscopy. The obtained data suggest an octahedral-tetrahedral (Td) distorted local symmetry for Cu2+ and Mn2+ ions, and a square—pyramidal (C4v) coordination for V4+ ions. The mixed exchange pairs (Cu2+−V4+, Mn4+) appear at high transition metal oxides content (x > 10 mol%).

Magnetic properties of YBaCuO ceramics undoped and doped with Ni and Dy

Abstract Different polycrystalline samples of high-T c superconducting compounds Y Ba 3-x Cu 3 O 7-δ ; Y 1-x Dy x Ba 2 Cu 3 O 7-δ and Y 1 Ba 2 Cu 3-x Ni x O 7-δ have been prepared and characterized. They have been investigated by dc magnetic susceptibility and X-ray powder-diffraction pattern. Magnetic susceptibility data show Neel temperature about 200 K and critical temperature between 77–93 K. High-T c superconductivity is not destroyed by the localized magnetic moments of the rare-earth Dy ions, but the copper substitution by nickel determined a gradual diminution of the superconducting phase.