A study on the twin domain of Pb3(PO4)2 ferroelastic crystal

Ferroelastic Pb3(PO)4)2 crystal exhibits two types of domain walls. We constructed the geometrical lattice structure in the vicinity of the domain walls and observed the tilted angle of the W'-walls geometrically. Using the polarization microscope we investigated the temperature dependence of the domain wall and the change of the conoscope image at the phase transition temperature. Near Tc. the narrow domains between two W'-walls were widened and new needle shape W-walls appeared. Above Tc we observed the separation of the Isogyre in the conoscope image by the rotation of the crystal plate, which was inferred due to the infinitesimal lattice mismatch between the cleavage planes above Tc.