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• Domain switching and lattice strain in polycrystalline K 0.5 Bi 0.5 TiO 3 -BiFeO 3 -PbTiO 3 is evaluated by in-situ high energy synchrotron XRD. • The tetragonal {200} grain family exhibited the highest effective lattice strain up to 8.2 × 10−3 at an electric field of 5 kV/mm. • A partial phase transformation from tetragonal to rhombohedral occurred at high electric field levels, with an average strain of −1.54 × 10−3. • Relaxation of intergranular stress gives rise to enhanced domain switching in KBT-BF-PT ceramics. • The observed self-adapting mechanism could also be exploited in other high performance, high temperature piezoelectric ceramics. We report an in-situ synchrotron X-ray diffraction study of K 0.5 Bi 0.5 TiO 3 -BiFeO 3 -PbTiO 3 ceramics, which exhibit a T c of around 450 °C. The electromechanical actuation mechanisms comprise contributions from coexisting tetragonal and rhombohedral phases. The tetragonal {200} grain family exhibited the highest effective lattice strain, up to 8.2 × 10−3 at 5 kV/mm. Strong strain anisotropy in the tetragonal phase and field-induced intergranular stresses facilitate a partial transformation from tetragonal (high strain anisotropy) to rhombohedral (low strain anisotropy) at high electric field levels, with an average linear transformation strain of -1.54 × 10-3. The domain switching behavior was effectively enhanced in both tetragonal and rhombohedral phases after the phase transformation, due to the release of intergranular stress. This observed self-adapting mechanism in tuning intergranular stress through partial phase switching in the morphotropic KBT-BF-PT composition with large lattice distortion could also be exploited in other perovskite systems in order to achieve high performance high temperature piezoelectric ceramics. [ABSTRACT FROM AUTHOR]