Positive effective Q12 electrostrictive coefficient in perovskites
  It is demonstrated that for classical perovskites such as BaTiO3, SrTiO3 and PbTiO3 electrostrictive strain induced by an electric field may not obey traditionally considered "extension along the field, contraction perpendicular to it" behavior if a sample is cut obliquely to the cubic crystallographic directions. 
Alexander Kvasov and Alexander K. Tagantsev
cond-mat.mtrl-sci