ROLE OF TE VALENCE ON PHASES CRYSTALLIZED IN K2O-NB2O5-TEO2 GLASSES

Differences in crystalline phases between glass-ceramics and sintered ceramics in the K2O-Nb2O5-TeO2 system have been examined, particularly to obtain information on the role of Te valence on crystallization be haviors of TeO2-based glasses. In glasses or glass-ceramics, the valen ce of Te4+ is retained even during heat-treatment up to around 600 deg rees C, leading to the formation of crystalline phases containing Te4, e.g., the face-centered cubic crystalline phase. In a powder sinteri ng method, Te4+ is easily oxidized to Te6+ during sintering at around 600 degrees C in air and compounds such as KNbTeO6 in which Te6+ is pr esent are formed.