**2. Bismuth titanate and other properties**

Considerable attention has recently been paid to bismuth layer-structured ferroelectric (BLSF) as ferroelectric materials instead of unfriendly lead (Pb)-based ferroelectrics because of its excellent fatigue resistance and Pb-free chemical composition (Algueró et al., 2006, Subbarao, 1961, Xue et al., 2009, Yang et al., 2003). The general formula is given by (Bi2O2)2+ (Am-1BmO3m-1)2- where A = Bi3+, Pb2+ Sr2+, Ba2+, etc. and B = Nb5+, Ta5+, Ti4+, etc. m = 1, 2, 3, 4, 5, etc. (Bi2O2)2+ is the bismuth oxide layer and (Am-1BmO3m+1)2- is the pseudo perovskite layer (Armstrong ,Newnham, 1972, Newnham et al., 1971, Yan et al., 2006). BLSF is expected to have various numbers of pseudo perovskite blocks in unit cells. BLSF, bismuth titanate, Bi4Ti3O12 (m = 3) or BTO has three pseudo perovskite blocks in half-unit cells. In simple words, its structure can be described as formed by three unit cells of (Bi2Ti3O10)2- with perovskite like structure interleaved with (Bi2O2)2+ layers (Ng et al., 2002). BTO is an attractive material that has low processing temperature (700-750oC) than other BLSF (e.g. SrBi2Ta2O9) and strong anisotropy of the spontaneous polarization (Ps) along the *a*-axis ( ~ 50 µC/cm2) and *c*-axis ( ~ 4 µC/cm2) (Wang et al., 1999, Zhi-hui et al., 2010). However, the low remanent polarization (Pr = 5 µC/cm2), low fatigue resistance and high dielectric loss of BTO would limits its application in FRAM applications. The reduction in remanent polarization and fatigue with high dielectric losses become more serious issues due to defects in perovskite structure whereby the Bi ions volatile during sintering process and create the Bi vacancies accompanied by oxygen vacancies. Nevertheless, there are advantages on BTO whereby it has high Curie temperature at 675oC and high dielectric permittivity ( ~ 200), making this material for other possible applications such as capacitors, antennas, sensors and piezoelectric (Golda et al., 2011).
