Structural and compositional modification of a barium boroaluminosilicate glass surface by thermal poling

In addition to inducing second-order nonlinear properties, significant structural and compositional alteration can be imparted to glass surfaces during the process of thermal poling. In this work, we focus on how thermal poling affects a structurally complex, nominally alkali-free boroaluminosilicate display glass composition. We provide evidence for electrolysis of the glass network, characterized by the migration of both cations (Ba²⁺, Na⁺) and anions (O^-, F^-) towards opposing electrode interfaces. This process results in oxidation of the positively biased electrode and forms a network-former rich, modifier-depleted glass surface layer adjacent to the anodic interface. The modified glass layer thickness is qualitatively correlated to the oxidation resistance of the electrode material, while extrinsic ions such as H⁺/H₃O⁺ at not found in the depletion layer to compensate for the migration of modifier cations out of the region. Rather, FTIR spectroscopy suggests a local restructuring of the B₂O₃-Al₂O₃-SiO₂ network species to accommodate the charge imbalance created by the exodus of network-modifying cations, specifically the conversion of tetrahedral B(4) to trigonal B(3) as Ba or Na ions are removed from B-related sites in the parent network. The resultant poling-induced depletion layer exhibits enhanced hydrolytic resistance under acidic conditions, and the IR spectra are substantially unlike those produced by acid leaching the same glass.