Microstructure and nanoscale piezoelectric/ferroelectric properties in Ln2Ti2O7 (Ln = La, Pr and Nd) oxide thin films grown by pulsed laser deposition

• Highly c-axis oriented Ln2Ti2O7 thin films were grown by pulsed laser deposition.
• The synthesis temperature and cation size affect the micro-strain of the films.
• Nanoscale ferroelectricity of Ln2Ti2O7 (Ln = La, Pr, Nd) thin films was confirmed.

Ferroelectric lead-free Ln2Ti2O7 thin films (Ln = La, Pr and Nd) have been grown on (110)-oriented SrTiO3 substrates by pulsed laser deposition. The X-ray diffraction study reveals that all films are highly (00l)-oriented. This is in good agreement with the compatibility between the film/substrate crystal lattices. The Williamson–Hall plots evidence the effect of the Ln3 + cation size on the micro-strain in the film while the average size of the crystallites deduced from these plots is shown to correlate the average size of the dense grains, as observed by atomic force microscopy. Finally, through piezoloops recording carried out by piezoresponse force microscopy, nanoscale ferroelectricity is highlighted in these layered-perovskite Ln2Ti2O7 films. These results confirm that these lead-free oxides can be used as functional material in nanoelectronic devices.