Fluorite ferroelectrics have been gaining increasing attention since their first report in 2011 [1]. This unexpected ferroelectricity was proven to originate from the formation of a non-centrosymmetric orthorhombic phase with space group of Pca21 [2]. A temperature dependent phase transition involved with this new polar phase was suggested to be promising for various applications based on pyroelectricity [3,4]. However, phase transitions in hafnia thin films doped with various dopants have not been comprehensively studied to date. Although the valence number, size, spatial distribution of dopants, the grain size distribution, and the distribution oxygen vacancies are expected to influence the phase transition, their effect has not been investigated in depth. In this presentation, therefore, the effects of aforementioned factors on the phase transition are systematically examined. The temperature dependent phase transitions in hafnia thin films were strongly affected by the valence number of dopants. Doping tri-valent ions increases the oxygen vacancy concentration, and it is believed that the spatial inhomogeneity of these oxygen vacancies can potentially broaden the phase transition in hafnia thin films.
References
[1] T. S. Boescke et al. Appl. Phys. Lett. 99, 102903 (2011).
[2] X. Sang et al. Appl. Phys. Lett. 106, 162905 (2015).
[3] M. H. Park et al. Nano Energy 12, 131 (2015).
[4] M. Hoffmann et al. Nano Energy 18, 154 (2015).