A. Dehelean

Dinuclear manganese centers in the manganese-lead-tellurate glasses

FTIR, UV-VIS and EPR spectra of manganese doped lead-tellurate glasses with composition xMnO·(100-x)[4TeO2·PbO2] where x=0, 1, 5, 10, 20, 30, 40mol% have been studied. The FTIR spectra show the formation of the Mn-O-Pb and Mn-O-Te bridging bonds by increasing of MnO concentration. The UV-VIS spectra show the Mn(+3) species exhibit pronounced absorption, which masks the Mn(+2) spin-forbidden absorption bands when Mn(+2) ions are in high concentrations in these glasses. The EPR spectra exhibit resonance signals characteristic of Mn(+2) ions. The resonance signal located at g≈2 is due to Mn(+2) ions in an environment close to octahedral symmetry, whereas the resonance at g≈4.3 and 3.3 are attributed to the rhombic surroundings of the Mn(+2) ions. The increase in the MnO content gives rise to absorption at g≈2.4 and the paramagnetic ions are involved in dinuclear manganese centers.

Magnetic behaviour of europium ions in some tellurite glasses obtained by the sol – gel method

In the paper, tellurite glasses doped with europium ions have been prepared by the sol-gel method and were studied by magnetic susceptibility measurements. The authors found that xEu2O3(1-x)TeO2 system shows a Curie-Weiss type magnetic behaviour. The magnetic europium ions are present in the host glass matrix in both their 2+ and 3+ valence states. The magnetic interactions between the europium ions are antiferomagnetic.

Magnetic studies of TeO2 – Fe2O3 glass systems obtained by the sol – gel method

Glass of the xFe2O3(1-x)TeO2 systems with x = 0.03–0.40 were obtained by sol-gel method and studied by magnetic susceptibility measurements. The temperature dependence of the reciprocal magnetic susceptibility follows a Curie law till 10 mol% Fe2O3 and over this concentration follows a Curie- Weiss law with the negative paramagnetic Curie temperature. The main result coming out from this behaviour is: at concentrations lower than x = 10 mol% Fe2O3 iron ions are isolated or participates at dipolar interactions and at concentrations larger than 10 mol% Fe2O3 a higher part of iron ions participates at superexchange magnetic interactions.