Crystallization of LiNbO3 and NaNbO3 in niobiosilicate glass–ceramics

Abstract

AbstractAlthough glass–ceramics have been widely explored for their thermal stability and mechanical properties, they also offer unique symmetry‐dependent properties such as piezoelectricity and pyroelectricity through controlled crystallization of a polar phase. This work examines crystallization of LiNbO3 in a 35SiO2–30Nb2O5–35Li2O mol% composition and crystallization of LiNbO3 and NaNbO3 in a 35SiO2–30Nb2O5–25Li2O–10Na2O mol% composition. Crystallization kinetics are examined using the Johnson–Mehl–Avrami–Kolmogorov (JMAK) theory where the Avrami exponent, n, is calculated to be 1.0–1.5. Microscopical analysis shows dendritic morphology, which when combined with the JMAK analysis, suggests diffusion‐controlled one‐dimensional growth. Adding Na2O to the glass composition increases the inter‐diffusivity of ions which causes LiNbO3 to crystallize faster and lowers the activation energy of transformation from 1054 ± 217 kJ/mol in the ternary composition to 882 ± 212 kJ/mol. Time‐temperature‐transformation diagrams are presented which show that the temperature for maximum rate of transformation for LiNbO3 is ∼650°C and for NaNbO3 is ∼715°C.