Evidence for a monoclinic distortion in the ferroelectric Aurivillius phase Bi3LaTi3O12

Crystal structure of the Aurivillius phases in the system Bi4Ti3O12—PbTiO3

The crystal structure of four Aurivillius phases within the pseudo-binary system Bi4Ti3O12—PbTiO3 is examined using a 3 + 1D approach where these phases are treated as commensurately modulated layered structures. The structure of PbBi4Ti4O15, Pb2Bi4Ti5O18, Pb3Bi4Ti6O21 and PbBi8Ti7O27 are refined by the Rietveld method using XRPD data from single phased powders. The structure of Pb3Bi4Ti6O21 and PbBi8Ti7O27 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.