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

In this work, the structural, microstructural, dielectric and piezoelectric properties of sol–gel processed rare earth-doped PbTiO3 (PT) samples with the compositions Pb0.86La0.14HoxTi1−xO3 (x = 0, 0.5, 1.5, 0.2 and 2.5%) (PLHTx), calcined at 700 °C for 2 h and sintered at 1100 °C for 4 h, were studied. X-ray diffraction and Raman spectroscopy results showed that the samples exhibited the pseudo-cubic phase (P4mm), without any secondary phase, and that Ho3+ ions can occupy both Pb and Ti sites in the Pb0.86La0.14HoxTi1−xO3 matrix. Scanning electron microscopy (SEM) analysis showed that the average grain size in the samples was 366–416 nm. Dielectric measurements revealed that holmium substitution has no effect on the temperature of the permittivity maximum at the ferroelectric to paraelectric transition (FPT). Moreover, relatively high values of the dielectric permittivity and low values of the dielectric losses were obtained under holmium doping, and the value of the maximum of the dielectric constant (εr max) at the FPT showed a particular behavior. The resonance phenomenon was observed in the permittivity dependence on frequency in the frequency range 100 Hz–2 MHz, allowing the extraction of some piezoelectric parameters such as the electromechanical coupling factor, kp, that increased with the increase in the holmium content.