Short-range order changes induced by heat treatment in yttrium–aluminosilicate glasses

Short-range order and local atomic configuration in yttrium–aluminosilicate glasses doped with gadolinium were studied by infrared (IR) spectroscopy, 27Al magic-angle-spinning nuclear magnetic resonance (MAS-NMR) and Gd3+ electron spin resonance (EPR) on as-prepared and heat-treated samples.A small amount of yttrium was replaced by gadolinium in the host glass because Y3+ and Gd3+ cations are quite similar and gadolinium ions can be used as structural sensor in electron paramagnetic resonance measurements. The results evidence weak changes in the structure of as-prepared glasses with respect to the coordination of aluminium atoms produced by gadolinium doping (0.2 and 0.5 mol%). New IR bands recorded from heat-treated samples are associated with stretching modes of hexacoordinated aluminium in AlO6 octahedra. The effect of the heat treatment on aluminium environment is estimated by analysing the relative intensity of the component lines of simulated 27Al MAS-NMR spectra. High-coordinated AlOn species were identified in all samples. EPR results evidence the increase of the number of gadolinium sites with weak crystal field as effect of the structural relaxation.