Crystalline phases and second-order optical nonlinearities in crystallized glasses of (Na,K)NbGeO5 (i.e., xNa2O·(25-x)K 2O·25Nb2O5·50GeO2) are examined. The molar volume of the glasses decreases with increasing Na 2O content, indicating that the glass structure of NaNbGeO 5 glass is more compact compared with KNbGeO5 glass. The optical basicity of the glasses is 0.94-0.95, implying that chemical bonds among constituents ions are basically very ionic. (Na,K)NbGeO5 glasses exhibit a unique crystallization depending on the Na2O/K2O ratio. The main crystalline phase in crystallized NaNbGeO5 glass is the NaNbGeO5 phase. KNbGeO5 glass shows a prominent bulk nanocrystallization giving nanocrystals of the K3.8Nb 5Ge3O20.4 phase. A glass with the composition of K3.8Nb5Ge3O20.4 also shows a bulk nanocrystallization. The crystallized glasses with K3.8Nb 5Ge3O20.4 and NaNbGeO5 crystalline phases do not show a second harmonic generation (SHG) at room temperature. The nonlinear optical (Na,K)NbO3 phases showing a SHG are formed at the surface (∼5 μm) of crystallized glasses with x=15 and 20, giving an orientation of the (110) plane. The present study suggests the presence of mixed-alkali effect in the crystallization behavior of (Na,K)NbGeO5 glasses.
- Optical basicity
- Second harmonic generation
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials