Thickness of 90° ferroelectric domain walls in (Ba,Pb)TiO3 single crystals

90° ferroelectric domain boundaries were observed by direct transmission electron microscopy in single crystals of pure BaTiO3 and (Ba,Pb)TiO3 solid solutions. Domain-wall thickness measurements were made from electron image plates by a densitometer-trace-curve-fitting technique. Boundary widths varied from 50 to 150 Å. These results are compared with theoretical estimates of 90° domain-wall thicknesses and correlated with the relative purity levels of the crystals. The temperature variation of the 90° wall thickness is reported for the (Ba,Pb)TiO3 solid solutions.