@MASTERSTHESIS{ 2021:611880331,
 	title = {Alkaline tantalum germanate glasses and Glass-ceramics for second Harmonic Generation},
 	year = {2021},
 	url = "https://bdtd.unifal-mg.edu.br:8443/handle/tede/1798",
 	abstract = "Transparent and homogeneous alkaline tantalum germanate glasses of molar
 composition (90-x)GeO2-10M2O-xTa2O5 with x=15 and 20 and M=Na, K or Rb were
 prepared by the melt-quenching technique. Final color of the samples were related
 with contaminations from the crucible but the use of pure platinum crucible allowed to
 prepare colorless glasses. The crystallization behavior of these glasses was
 investigated in details in the sodium tantalum germanates glasses and a complex
 multi-step crystallization behavior was identified: fast heat treatments (1h) at the
 onset of crystallization induce precipitation of a perovskite bronze-like crystalline
 phase Na2Ta8O21 from a volume crystallization mechanism. On the other hand,
 longer heat treatments (at least 18h) at the same temperature promote a progressive
 formation and growth of surface spherulites of about 50 m in diameter. In addition,
 these spherulitic glass ceramics exhibit a strong Second Harmonic Generation
 (SHG). Elemental analyzes pointed out a comparative higher tantalum and lower
 germanium content inside these spherulites whereas correlated Raman and SHG
 microscopies were helpful to determine that the spherulites are the source of the
 SHG signals and contain quartz-like -GeO2. Macroscopic SHG investigations also
 suggest a strong dependency of the incident polarization on the SHG intensity,
 related with the crystal structure of -GeO2 and crystallite orientation inside the
 spherulites.",
 	publisher = {Universidade Federal de Alfenas},
 	scholl = {Programa de Pós-Graduação em Química},
 	note = {Instituto de Química}
}