A device for determining an effective piezoelectric coefficient of a thin film of a material of a sample, includes a source of x-rays incident on the sample; a detector of x-rays diffracted by the sample; a device for positioning the x-ray source and the x-ray detector with respect to the sample; a voltage source making contact with the sample; a device for controlling the voltage source so as to apply an electric field to the sample during an electrical cycle, the electric field generating a strain of the sample and a stress on the sample; a device for measuring a diffraction peak of the x-rays as a function of the electric field applied to the sample during the electrical cycle; a processing device configured to determine the piezoelectric coefficient.