Quantification of boron coordination changes between lithium borate glasses and melts by neutron diffraction

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The structure of lithium borate glasses and liquids (xLi(2)O center dot(1-x)B2O3 with x=0.1, 0.20, 0.25 and 0.33) has been investigated by neutron diffraction coupled with Li isotopic substitution at temperatures up to 1173-1273 K. Both the short range order around B and Li is changed, with the conversion of BO4 to BO3 and a subsequent increase of NBOs (nonbridging oxygens) around Li as temperature increases. The quantitative boron coordination change has been assessed by a Gaussian fitting of the B-O pair contribution. ne increasing presence of NBOs results in the opening of the borate network and the disappearance of superstructural borate rings. The reorganisation of the structure above the glass transition temperature provides a structural mechanism for the modifications of the thermodynamic and configurational properties of borate liquids.