Medium-range structural ordering and macroscopic interactions in 1 to 2 mm thin two-dimensional platelets of borate glasses

Abstract

A locally ordered microstructure of interconnected planar boroxol rings (basis structural units) in 1 to 2 mm thin 2D (two-dimensional) platelets of a ternary borate glass, with cation ratio B3+/Ba3+(Fe3+) approximate to 0.94, exhibits an up to 57 cm(-1) increase in the infrared characteristic B-O stretching vibration frequencies (BOSF) with respect to those in a powder (or bulk) of confined particle (or domain) size of mu m scale. At 500 to 850 degrees C, the planar network (alpha) forms a planar alpha-beta interface with thermally induced phase separation (beta) of Ba2+ and Fe3+ cations in the network. These cations are interconnected by the network structure in alpha-beta thermodynamic equilibrium. As a result, they are easily mobile to grow up to several mu m long acicular BaFe12O19 crystals, over the network in the basis morphology (elongated hexagonal crystal unit cell of c/a ratio approximate to 3.94) of the BaFe12O19 nuclei driven by the heat flow released in the nucleation and growth processes along the alpha-beta interface coplanar with the network. The BaFe12O19 crystallites, which are precipitated over the network, firmly adhere to the network by strong electromagnetic macroscopic interactions. The crystallized glass, which no longer has such a regularly interconnected network configuration, therefore measures similarly high (or even higher) values of the BOSF as in a highly ordered network