SPECKLE DIFFRACTION OF LIGHT BY TWINNED ORTHORHOMBIC DOMAINS - A SENSITIVE PROBE OF INTERFACE TOPOLOGY

Many compounds have twinned domains with plane walls sufficiently regu lar to allow Bragg diffraction of light. For a coherent light source w e have shown that diffraction peaks in the twinned orthorhombic phase of DyVO4 and related compounds have speckle features arising from rand omness in domain topology. They evolve with changes in temperature and ordering field, and show qualitative differences between pure DyVO4, where the interfaces are expected to be relatively smooth, and Dy(As0. 154V0.846)O4, where random strains are expected to roughen and pin the interfaces.