Phase transitions of (1 - x)BaZr0.2Ti0.8O3-xBa(0.7)Ca(0.3)TiO(3) (BZT-xBCT) powders under tensile stress were investigated using in-situ X-ray diffraction (XRD). Uniaxial stress was applied to the designed BZT-xBCT/polyimide composite films during XRD. Under stress, the rhombohedral (R) phase was found to transform into a tetragonal (T) phase, while the [001] direction of the T phase tends to be parallel to the tensile direction. T -> R phase transition was not observed in the films upon tensile stress loading, implying that R -> T phase transitions may be the decisive factor for the huge piezoelectric response of the BZT-xBCT system. (C) 2014 Elsevier B.V. All rights reserved.