In this work, a modified sol–gel process using a crown ether, 18-crown-6 (18C6) as complexing agent to synthesize 0.77(0.6Pb(Zn1/3,Nb2/3)O3–0.4Pb(Mg1/3,Nb2/3)O3))–0.23PbTiO3(PZMN–PT) thin films is reported. With the addition of 18C6, perovskite phase directly crystallized from the amorphous films at a temperature as low as 460°C and the crystallinity was significantly enhanced. The promotion of 18C6 on perovskite formation can be attributed to the immobilization of Pb2+ ions, which facilitates the columbite-like crystallization route. The pure-perovskite films obtained by annealing at 460°C exhibit the optical and electrical properties comparable to literature data. Our studies therefore indicate a general approach by using crown ethers as complexing agent to synthesize the thermodynamically unstable ferroelectric materials, such as PMN- and PZN-based systems.