Network Connectivity and Crystallization in the Transparent Ferroelectric Nanocomposite LaBGeO5

The LaBGeO5 glass-ceramic composite is a transparent ferroelectric nanocomposite material that has come under attention for its ferroelectric properties and for its straightforward synthesis. The LaBGeO5 crystals-in-glass can be formed through controlled devitrification of glass, as well as through laser irradiation. Recent works have established that both the borate and germanate environments have significant differences in short-range order between the crystalline and glass forms of LaBGeO5. However, there are little available data on the connectivity of the different structural units. We present here a comprehensive nuclear magnetic resonance (NMR) spectroscopy study of the connectivity of crystalline LaBGeO5 and LaBGeO5 glass. Through a combination of 11B, 11B­{10B}, 17O, and 139La NMR spectroscopies, we identify specific structural motifs in the glass. In particular, several structures are positively identified in the glass that are not present in the crystal, including BØ2O–, BØ2O––BØ4–, and GeO6. We present evidence in support of the presence of both 5/6Ge–O–4Ge and 5/6Ge–O–B connectivities. The differences in short-range order and connectivity between the LaBGeO5 glass and crystal suggest a heterogeneous nucleation mechanism.