Crack growth resistance behavior of lanthanum doped bismuth ferrite–lead titanate: Effect of tetragonality and mixed phase crystal structures

The room temperature crack growth resistance behavior of polycrystalline lanthanum-doped bismuth ferrite-lead titanate was characterized with disc compact-tension specimens. Through lanthanum doping the tetragonality can be adjusted from 1.01 to 1.10, while retaining a mixed phase system. Experimental measurements show changes in toughening behavior with increasing c/a ratio. Fracture results are discussed in conjunction with macroscopic ferroelastic constitutive behavior and stress-dependent neutron diffraction measurements to elucidate the role of a mixed phase system with heterogeneous mechanical properties. Additional X-ray diffraction measurements were performed to determine the effect of possible crack-tip stress-induced phase transformations on R-curve behavior.

► Fracture behavior of La-doped BF-PT is nonlinearly dependent on tetragonality.
► XRD revealed an expansion of the c-axis on the fracture surface.
► The effects of a mixed phase system must be considered in future ferroelastic fracture models.