Effect of Modification with Lanthanum Oxide La₂O₃ on the Structure of the Suprastructural Units in Alkaline Borates

Abstract—The structure-sensitive properties of the B₂O₃–Na₂O melt (or glass) are shown to change substantially with the destruction of suprastructural units when this melt is modified by the La₂O₃ lanthanum oxide, since small rare earth metal oxide additives cause a significant change in the properties of the alkali borate melts. The structure and properties of the molecular models of some suprastructural units were calculated using empirical quantum-chemical methods with the MNDO and PM7 parameters: as a result of optimization, both methods lead to qualitatively similar models, which differ in bond lengths, and to almost the same heat of formation. The suprastructural unit of the considered type is retained and its characteristics change: the occupied volume increases, the newly formed bond has a lower strength, and its ionicity increases.