The applications of ferroelectrics are numerous and go far beyond their ability of their spontaneous polarization to switch between a few equivalent states. Many ferroelectric materials are piezoelectric and used in sensors, actuators, frequency generators and microelectromechanical devices. The piezoelectric effect in ferroelectrics (as e.g. PbZr_1-xTi_xO₃) may exceed such in non-ferroelectrics (as e.g. in a-quartz SiO₂) by three orders of magnitude. The connection between piezoelectricity and ferroelectricity remains to be long-standing puzzle and the subject of debates and research for many groups worldwide.

In this talk, I will overview advanced X-ray crystallographic tools for characterization of structural and microstructural mechanisms of polarization switching in ferroelectrics. We question which of these mechanisms enhance piezoelectricity. The experimental tool to get the answer is in-situ and high-resolution time-resolved X-ray diffraction: this is to measure in-situ X-ray diffraction signal (as e.g. single crystal rocking curves, reciprocal space maps and powder diffraction profiles) simultaneously with the macroscopic hysteresis loops. The angular positions of Bragg peaks are used to calculate the field dependence of lattice parameters, the profile shapes; the exchange of intensities between Bragg peaks components are used to follow the change of the domain microstructure. 

I will discuss the origin of piezoelectricity in some archetypical and novel single crystals, including Sr_0.5Ba_0.5Nb₂O₆ and / or Na_0.5Bi_0.5TiO₃ and / or PbZr_1-xTi_xO₃ especially focusing at the separation of intrinsic (crystal structure related) and extrinsic (domain wall motion related) contributions to the piezoelectricity.