Network Connectivity and Crystallization in the Transparent Ferroelectric Nanocomposite LaBGeO₅
2019
Paterson, Alexander L. | Werner-Zwanziger, Ulrike | Zwanziger, Josef W.
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.
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