Crystal structure of the aurivillius phases in the system Bi4Ti3O12-PbTiO3

The crystal structure of four Aurivillius phases within the pseudo-binary system Bi 4 Ti 3 O 12 -PbTiO 3 is examined using a 3 + ID approach where these phases are treated as commensurately modulated layered structures. The structure of PbBi 4 Ti 4 O 15 , Pb 2 Bi 4 Ti 5 O 18 , Pb 3 Bi 4 Ti 6 O 21 and PbBi 8 Ti 7 O 27 are refined by the Rietveld method using XRPD data from single phased powders. The structure of Pb 3 Bi 4 Ti 6 O 21 and PbBi 8 Ti 7 O 27 is reported for the first time. When the lead content increases, the structure gets less distorted and approaches the prototype paraelectric phase in an apparent close relation with the onset of a "relaxor-like" ferroelectric behaviour. For these relaxor compounds, SAED investigation evidences the existence of a disorder in the form of micro-twinning.