In-situ neutron diffraction study of the rhombohedral to orthorhombic phase transformation in lead zirconate titanate ceramics produced by uniaxial compression

The martensitic transformation from the rhombohedral to the orthorhombic phase in a lead zirconate titanate (Zr/Ti=95/5) ceramic has been studied under uniaxial compressive stress using neutron diffraction. Ferroelastic domain switching in the rhombohedral phase was observed by monitoring the pseudo-cubic {111}p diffraction peaks, whereas the development of the orthorhombic phase texture was revealed most clearly by examining the changes in the {200}p reflections under stress. Rhombohedral grains having the 〈100〉p direction along the compression axis transformed most efficiently, by the development of the c-axis of the orthorhombic phase along this direction. The transformation strain along this direction was most dominant and determined as -1.1×10-2, whereas the lateral strains were measured as 1.0×10-3. In contrast to the case of hydrostatic compression, under uniaxial stress the transformation proceeded progressively as the applied compressive stress increased beyond a level of 200MPa, up to a maximum orthorhombic phase fraction of 70% at a stress of 400MPa. Pronounced hysteresis was observed upon unloading, indicating that the frictional stress required to move a rhombohedral/ orthorhombic interface is approximately 150MPa. By monitoring the lattice strain, it was found that the total stress along 〈100〉p remained approximately constant during the progress of the transformation. This is caused by an increase in the residual tensile stress within {100}p-oriented grains owing to the difference between their transformation strain and that of the surroundings. The above tensile stress is balanced by compressive residual stresses in the surrounding grains.