Prémio Ordem dos Engenheiros

Vidros Cerâmicos Nanocristalinos Transparentes

Rodrigo Santos, João Bastos, Luís F. Santos*, Rui M. Almeida

Departamento de Engenharia de Materiais/ICEMS, Instituto Superior Técnico/TULisbon,

Av. Rovisco Pais, 1049-001 Lisboa, Portugal

* luis.santos@ist.utl.pt

RESUMO:

Os vidros cerâmicos que contêm no seu interior nanocristais com propriedades ópticas não lineares, nomeadamente a geração de segundos harmónicos (SHG), têm um enorme potencial de aplicação na área da fotónica, podendo integrar sistemas ópticos e optoelectrónicos. Com este trabalho, pretendeu-se preparar e caracterizar amostras vítreas no sistema GeO₂∙SiO₂∙Nb₂O₅∙K₂O e produzir vidros cerâmicos transparentes nanocristalinos a partir daquelas, privilegiando a cristalização em volume.

Prepararam-se amostras vítreas no sistema estudado, tendo-se verificado um aumento da densidade e uma diminuição da temperatura de transição vítrea com o aumento do teor em GeO₂. Tratamentos térmicos efectuados às amostras preparadas permitiram identificar as fases cristalinas K_3.8Nb₅Ge₃O_20.4 e K₃Nb₃Si₂O₁₃ como sendo as fases correspondentes aos primeiros picos de cristalização obtidos por DTA. Um germanosilicato com 50 mol% de formador de vidro revelou capacidade para promover cristalização em volume. De facto, obteve-se um vidro cerâmico transparente com tamanho de cristais de ~20-25 nm.

Palavras chave: Vidros Cerâmicos Transparentes, Germanosilicatos de Nióbio, Cristalização em Volume.

ABSTRACT:

Glass ceramics containing nanocrystalline phases that present non-linear optical properties, namely second harmonic generation (SHG), have potential application in photonics, namely in all-optical and electro-optical systems. The goal of this work was the preparation and characterization of glass samples in the system GeO₂∙SiO₂∙Nb₂O₅∙K₂O, as well as the production of transparent, nanocrystalline glass ceramics. The glass samples were prepared and characterized by density, DTA and Raman spectroscopy measurements. An increase in density and a decrease in T_g and T_x-T_g were observed with increasing amount of GeO₂. Heat treatments were performed and the crystalline phases K_3.8Nb₅Ge₃O_20.4 and K₃Nb₃Si₂O₁₃ were identified and related with the first exothermic peak of the DTA analysis. A germanosilicate composition with 50 mol% of glass former showed good ability to undergo bulk crystallization. In fact, a transparent glass ceramic containing crystal sizes of ~20-25 nm, was obtained.

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