Transparent ferroelectric glass ceramics of the ABO <inf>3</inf> type

Abstract

Ferroelectric glass ceramics based on ABCb crystals, obtained by the direct crystallization of the glasses, were investigated. The glass samples, of composition within the system (Li or Na or K) 2 O - (Nb or Ta) 2 O 5 - SiO 2 - Al 2 O 3 were prepared by the melting process, after which they were subjected to crystallization by heat treatment at appropriate temperatures for appropriate times. It was found that stable glasses could only be obtained over a very narrow composition range. The Layton mole ratio B/N has a significant influence on the nucleation rate of the crystal phase. The Kokubo alumina content is also an important parameter for the transparency of the glass ceramics. It was found that, besides these two parameters, the type and content of the alkali metal oxides are also very important for the crystallization mechanism of the glasses. Lithium ions facilitate the rapidity of nucleation and the crystal growth of the glasses much more than either sodium or potassium ions. The mechanism of crystallization of ABO 3 crystals is based on phase separation of the glasses, followed by nucleation of the crystal phase. The measured values of the dielectric constant and the refractive index show that these change in a very complex way, depending on the development of the microstructure.