11B{23Na} Rotational echo double resonance NMR: a new approach for studying the spatial cation distribution in sodium borate glasses

11B{23Na} Rotational echo double resonance (REDOR) NMR has been used to probe the spatial relationship between the network former (boron) and the network modifier (sodium) species in sodium borate glasses. Under conditions of fast magic angle spinning (MAS), site resolved REDOR data have been obtained, revealing that the trigonal (BO3/2) and tetrahedral (BO4/2) units interact more or less equally strongly with the sodium ions. These results are consistent with a homogeneous distribution of sodium within the voids of the borate network and argue strongly against the presence of clustered ionic arrangements.