Deciphering the structure and potassium-ion transport mechanism of potassium borate glass.

Potassium borate glass has great potential as an ion transport material. The ion transport rate is closely related to the microstructure of the glass. However, the disorder and variations in boron and oxygen atom types in the glass structure pose challenges in the analysis of this complex glass structure. In this work, the structure of potassium borate glass was unveiled through the neutron diffraction method and ab initio molecular dynamics (AIMD) simulations. The B-O, K-O, and O-O atomic interactions, bond lengths, coordination numbers, cavity distribution, ring structure distributions and other detailed information in the microstructure of potassium borate glass were obtained. By comparing the structure and properties of potassium borate glass with those of crystals of similar components, it is found that the bond lengths of 3B-BO (BO, bridging oxygen), 4B-BO and 3B-NBO (NBO, non-bridging oxygen) are longer than those of corresponding crystals, so the structure of the boron-oxygen network is looser and the density is smaller than that of similar crystals. Moreover, we found a rule that in both borate glass and crystal, the increase of NBO shortened the length of the B-O bond, and the increase of 4B increased the length of the B-O bond. The key structures affecting the transport rate of K+ were NBO, chain structure units and cavities. This work will provide reference data for designing and developing electrically conductive amorphous materials with faster potassium-ion transport rates.

Elastic properties and short-range structural order in mixed network former glasses.

Elastic properties of alkali containing glasses are of great interest not only because they provide information about overall structural integrity but also they are related to other properties such as thermal conductivity and ion mobility. In this study, we investigate two mixed-network former glass systems, sodium borosilicate 0.2Na2O + 0.8[xBO1.5 + (1 - x)SiO2] and sodium borogermanate 0.2Na2O + 0.8[xBO1.5 + (1 - x)GeO2] glasses. By mixing network formers, the network topology can be changed while keeping the network modifier concentration constant, which allows for the effect of network structure on elastic properties to be analyzed over a wide parametric range. In addition to non-linear, non-additive mixed-glass former effects, maxima are observed in longitudinal, shear and Young's moduli with increasing atomic number density. By combining results from NMR spectroscopy and Brillouin light scattering with a newly developed statistical thermodynamic reaction equilibrium model, it is possible to determine the relative proportions of all network structural units. This new analysis reveals that the structural characteristic predominantly responsible for effective mechanical load transmission in these glasses is a high density of network cations coordinated by four or more bridging oxygens, as it provides for establishing a network of covalent bonds among these cations with connectivity in three dimensions.

Lone-pair distribution and plumbite network formation in high lead silicate glass, 80PbO·20SiO2.

For the first time a detailed structural model has been determined which shows how the lone-pairs of electrons are arranged relative to each other in a glass network containing lone-pair cations. High energy X-ray and neutron diffraction patterns of a very high lead content silicate glass (80PbO·20SiO2) have been used to build three-dimensional models using empirical potential structure refinement. Coordination number and bond angle distributions reveal structural similarity to crystalline Pb11Si3O17 and α- and ß-PbO, and therefore strong evidence for a plumbite glass network built from pyramidal [PbO(m)] polyhedra (m ~ 3-4), with stereochemically active lone-pairs, although with greater disorder in the first coordination shell of lead compared to the first coordination shell of silicon. The oxygen atoms are coordinated predominantly to four cations. Explicit introduction of lone-pair entities into some models leads to modification of the local Pb environment, whilst still allowing for reproduction of the measured diffraction patterns, thus demonstrating the non-uniqueness of the solutions. Nonetheless, the models share many features with crystalline Pb11Si3O17, including the O-Pb-O bond angle distribution, which is more highly structured than reported for lower Pb content glasses using reverse Monte Carlo techniques. The lone-pair separation of 2.85 Å in the model glasses compares favourably with that estimated in α-PbO as 2.88 Å, and these lone-pairs organise to create voids in the glass, just as they create channels in Pb11Si3O17 and interlayer spaces in the PbO polymorphs.