Recently, ferroelectric properties and metastable polar phases have been observed in thin layers of doped hafnia and in the solid solution of zirconia with hafnia with composition Zr0.5Hf0.5O2 [1]. Great technological interest has been raised due to their silicon compatibility, chemical simplicity and low toxicity [2]. Although ferroelectricity has been shown to be robust [3], its origin remains elusive and only recently the exact space group of the polar phase has been reported in Gd-doped hafnia [4]. The complexity arises from the fact that only ultra-thin films are ferroelectric and single-phase films are difficult to synthesize. Here, single-phase orthorhombic Zr0.5Hf0.5O2 ferroelectric films have been obtained by Pulsed Laser Deposition on perovskite substrates. The samples grow epitaxially despite the large differences in structure between film and substrate. These differences are accommodated by means of (111)-oriented films, which are organized in four domains (although the (001) orientation also appears in lesser amounts). The single-phase character allows obtaining meaningful TEM images that bring new insight on the origin of the ferroelectric phase.
References
[1] J. Müller et al., NanoLett. 12, 4318 (2012).
[2] M. H. Park et al., Adv.Mater. 27, 1811 (2015).
[3] T. Shimizu et al., Appl.Phys. Lett. 106, 112904 (2015).
[4] X. Sang et al., Appl.Phys. Lett. 106, 162905 (2015).