Ferroelectricity has been one of the most used and studied phenomena in both scientific and industrial communities. Properties of ferroelectrics materials make them particularly suitable for a wide range of applications, ranging from sensors and actuators to optical or memory devices. Numerous applications using such an effect have been developed. Ferroelectric materials have been able to be adapted to more and more systems in our daily life (ultrasound or thermal imaging, accelerometers, gyroscopes, filters etc.), and promising breakthrough applications are still under development (non?volatile memory, optical devices...), which make it one of tomorrow's most important materials. Ferroelectrics with diffuse phase transition (DPT) characterized by a broad peak in the temperature dependence of dielectric permittivity with a frequency independent peak temperature (Tm) called ferroelectric relaxors. In the last few years, the dielectric and optical properties of relaxor ferroelectrics have been widely investigated for applications in wireless communications, metal-oxide-semiconductor field-effect transistors, and optical and microwave dielectrics.