No abstract

Glass-ceramics (GC) consisting of nano-sized Nb-dielectrics were fabricated in BaO–Na2O–P2O5–Nb2O5 system, and their crystallization and physical features were studied. Precursor of 0.67(2BaO–0.5Na2O)–1P2O5–2.5Nb2O5 glass co-crystallized Ba2NaNb5O15 (BNN) and NaNbO3 phases, which are about 10 nm in size, and resulting GC possessed an optical transparency comparable to the precursor glass, and optical band-gap of the GC was close to that of BNN. It is suggested that the fabricated GC is not merely a GC with transparency but Nb-dielectric GC, in which light scattering due to the crystallized phases evolution is minimized, i.e., practically transparent GC material.

In situ observations of phonon Raman and Boson scattering were performed in high-Nb2O5-content barium–sodium aluminophosphate glass, which crystallizes tungstenbronze-type Ba2NaNb5O15 (BNN), during heating and subsequent cooling processes in order to examine the BNN crystallization dynamics and phase transitions. It is suggested that NbO6 clusters/cohesive regions are present and are subjected to stress by the surrounding aluminophosphate network prior to crystallization of the BNN phase. Furthermore, in the cooling period, a successive phase transition (4/mmm→4mm→mm2) of the BNN phase was observed in the glass-ceramics, implying the possibility of producing functional glass-ceramics with ferroelastic properties.

We prepared a niobiophosphate-glass-crystallizing tungstenbronze-type Ba2NaNb5O15and measured elastic light scattering spectrain situin the glass-ceramics fabrication regime. We found that the studied glass possesses a strong tendency for phase separation into Al2O3P2O5and Nb-rich regions prior to crystallization. It is suggested that the tungstenbronze phase crystallizes in the Nb-rich region separated from the supercooled liquid phase. This study demonstrated thatin situRaman spectroscopy is also useful for observing the phase separation dynamics in glass.