The proposed experiment involves measurement of the structural changes during the ferroelectric rhombohedral to antiferroelectric orthorhombic phase transformation in PZT ceramics modified with bismuth ferrite. The transformation will be induced by the application of a hydrostatic pressure up to 350 MPa, using a fluorinated oil as the pressurising medium. Dielectric properties will also be determined simultaneously during the experiment so that the changes in the electrical and structural parameters can be correlated directly. The aim of the proposed experiment is to determine the influence of bismuth ferrite on the transformation pressures. The change of lattice parameters under hydrostatic pressure will be used to evaluate the criteria for the phase transformation in terms of the work done by the applied pressure.