A NEW SERIES OF BISMUTH LAYER-STRUCTURED FERROELECTRICS

The general formula of a phase relation between well-known bismuth laver-structured ferroelectrics (BLSF) such as Bi3TiNbO9, Na0.5Bi2.5Nb2O9, Bi4Ti3O12, and Na0.5Bi4.5Ti4O15 including perovskite compounds (Bi0.5Na0.5) TiO3 and NaNbO3, that is, Na-(m-3+x/2)Bi-(m+5-x/2)Tim-xNbxO3m+3 (2 less than or equal to m less than or equal to 5), was discussed to form the layer structure with the numbers m = 3, 4 and 5 of layer, where x is the number of Nb ions in the layer structure and 1 less than or equal to x less than or equal to 2 for m = 2 and 0 less than or equal to x less than or equal to m for 3 less than or equal to m less than or equal to 5. A new BLSF series is found for m = 3 and x = 1, 2 and 3. The ferroelectricity for m = 4 (x = 3 and 4) was very weak and no single phase with m = 5 was obtained.