Lanthanum zirconate ceramic toughened by BaTiO3 secondary phase

La2Zr2O7 (LZ) is a promising thermal barrier coating material for the high-temperature applications, which could be significantly toughened by the BaTiO3 piezoelectric phase incorporated into the matrix. The composites of xBaTiO3/(1 − x)LZ (x = 5, 10, 15, 20 vol%, LZ-x-BaTiO3) were densified by means of high-pressure sintering (HPS) under a pressure of 4.5 GPa at 1450 °C for 10 min, by which a high relative density above 93% could be obtained. The morphologies of the fractured surfaces were investigated by the scanning electron microscope, and the fracture toughness and Vicker's hardness of the composites were evaluated by the microindentation. The grain size of the LZ matrix drops significantly with the addition of BaTiO3 piezoelectric phase and the fracture type changes from the intergranular to a mixture type of the transgranular and intergranular in the composites. The LZ-10-BaTiO3 composite has a fracture toughness of 1.98 MPa m1/2, which is obviously higher than that of the pure LZ (1.60 MPa m1/2), and the toughening mechanism might be attributed to the ferroelastic domain switching of ferroelectric phase BaTiO3.