Experimental and theoretical investigations of the copper–lead–germanate glasses

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Glasses in the system xCuO·(100 − x)[7GeO 2·3PbO 2] with 0 ⩽ x ⩽ 60 mol% have been prepared from melt quenching method. In this paper, we investigated changes in coordination number of the germanium in copper–lead–germanate glasses through investigations of FTIR, UV–VIS and EPR spectroscopy and calculations of density functional theory (DFT). The observations presented in these mechanisms show that by increasing of CuO content up to 20 mol%, the [GeO 4] tetrahedral structural units were converted in [GeO 6] octahedral structural units up to the maximum. In this manner the excess oxygen added to the glass upon the addition of the CuO is taken up by forming [GeO 6] octahedrons and the excess negative charge is compensated by nearby copper ions. In addition, non-bridging oxygens do not frame. The conversion of Ge(IV) to Ge(VI) does not continue further to the formation of the isolated octahedrons because begins to reconvert Ge(VI) back to Ge(IV) and Ge(V) with the simultaneous formation of non-bridging oxygens. The excess of oxygen can be accommodated in the host network by the formation of the [CuO n ] structural units.