Paramagnetic glasses containing tetrahedral borate species with non-bridging oxygen

Crystalline orthoborates (OB), form either (BO3)3- or BO4-groups with 2-4 non-bridging oxygens. Tetrahedral OB, like [BO4]3- to [BO4]5-, contain higher modifier levels than trigonal (BO3)3-, allowing for interesting applications. Since tetrahedral OB is the high-temperature form, it is not commonly found in glasses. Raman or NMR studies indicated the presence of tetrahedral OB in glasses, but were ambiguous as assignments overlap, species with different number of non-bridging oxygen cannot be distinguished, and NMR cannot be readily conducted on paramagnetic samples.
Diffraction studies on paramagnetic glasses, xMnO–(1-x)[50SrO-50B2O3] with x = 0 to 60 in mol%, with confirmed high tetrahedral borate content (as semi-quantitatively indicated by infrared Spectroscopy) will be measured with SANDALS, as this is well suited to the study of amorphous materials. The diffraction patterns from selected diamagnetic reference materials, e.g. binary metaborates, known crystalline trigonal (LaBO3) and tetrahedral (YBO4) orthoborates, will aid in unambiguous confirmation of tetrahedral OB and help in the future assignment of Raman and IR bands, as well as the strongly overlapping 11B NMR resonances. All samples will be resynthesized using 11B only to avoid neutron absorbing 10B. Flat-plate V foil cells will be used for the non-air-sensitive samples, and sealed TiZr cells for the hygroscopic ones. Small aliquots of each sample will be reserved for x-ray diffraction at Diamond XPDF I15-1.