Coherence effects of twin domains in diffraction from high Tc YBCOx

Twin domains form during the second order structural phase transition between “high symmetric tetragonal phase” and “low symmetric orthorhombic phase” in YBCOx (YBa2Cu3O6+x, 0 < x < 1).A new analytical approach for coherence effects in diffraction from a twinned model of YBCOx sample has been presented and it is shown that, for small “mean width of the twin domains” (T), and small “strains” (S), coherence effects give rise to extra peaks between {h 0 0} reflections (central peak (c.p)) that their intensity die away as the strain and the mean width of the twin domain are increased. Therefore in diffraction studies of phase characterization or lattice constants, the coherence effects must be taken into account.Researchers who are interested in “structural phase transitions” involving reduction in crystal symmetry may find it necessary to consider the “width of twin domains” as a new kind of order parameter.