ON THE THICKNESS OF FERROELASTIC TWIN WALLS IN LEAD PHOSPHATE PB-3(PO4)(2) - AN X-RAY-DIFFRACTION STUDY

The effective thickness of ferroelastic twin-walls (W-walls) in Pb-3(PO4)(2) at room temperature (approximate to 0.7 T-c) was determined by X-ray diffraction. The diffraction profiles were analysed using a wall profile e=e(0) tanh x/W where W is the effective wall thickness including the effects of wall bending and surface relaxations. The experimental value W is around 10 unit cells which is larger than expected from standard renormalization arguments. The limitations of such experimental studies are discussed.