Evidence for a monoclinic distortion in the ferroelectric Aurivillius phase Bi3LaTi3O12

An alternative chemical approach was used to prepare the ferroelectric Aurivillius phase Bi3LaTi3O12 (BLT1.00) at low temperature (450 degreesC) leading to well-crystallized compounds at 750 degreesC. The existence of 90degrees-oriented twin domains, characteristic of a ferroelectric state, was revealed in selected area electron diffraction and microdiffraction studies. Though the 3D reconstruction of the reciprocal lattice enables to propose the non-centrosymmetrical orthorhombic space group (SG) B2cm, a further convergent-beam electron diffraction study was undertaken in order to ascertain the symmetry. The monoclinic symmetry was clearly identified. BLT1.00 crystallizes in the polar SG B1c1 (no. 7, non-standard setting of P1c1) instead of I4/mmm, as previously reported. 2003 Elsevier Science (USA). All rights reserved.