Investigation of the structural, microstructural, and dielectric properties of Ho-doped PbTiO3 for piezoelectric applications

In this work, sol-gel-processed Ho-doped PbTiO3 powder samples with the compositions Pb1-XHoxTiO3 (x = 0; 1; 3; 6; 9; 12 and 15%) were obtained and calcined at a relatively low temperature (700 degrees C/4H) and their structural, microstructural, dielectric, and piezoelectric properties are investigated. The X-ray diffraction (XRD) patterns of the as-prepared samples heat treated at 700 degrees C during 4H are exempt of any secondary phases and showed the gradual transformation of the crystalline structure of the pure sample (PbTiO3) from tetragonal to pseudo-cubic under doping with Ho. Moreover, analysis of the XRD results showed also that Ho may enter both Pb and Ti sites and revealed a drastic reduction effect on the grain size of the sintered pellets (1100 degrees C/4H) and an improvement of the permittivity at the ferro-paraelectric transition for low and high concentrations in Ho. The phenomenon of resonance was observed from the curves of variation of the permittivity as a function of frequency with x > 1% and allowed the extraction of piezoelectric parameters such as the electromechanical coupling factor, kp, this factor increased with the increase of the holmium content.