Insights into the atomic structure of the interface of ferroelectric <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>Hf</mml:mi><mml:mrow><mml:mn>0.5</mml:mn></mml:mrow></mml:msub><mml:msub><mml:mi>Zr</mml:mi><mml:mrow><mml:mn>0.5</mml:mn></mml:mrow></mml:msub><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math> grown epitaxially on <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>La</mml:mi><mml:mrow><mml:mn>2</mml:mn><mml:mo>/</mml:mo><mml:mn>3</mml:mn></mml:mrow></mml:msub><mml:msub><mml:mi>Sr</mml:mi><mml:mrow><mml:mn>1</mml:mn><mml:mo>/</mml:mo><mml:mn>3</mml:mn></mml:mrow></mml:msub><mml:mi>Mn</mml:mi><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:mrow></mml:math>
Saúl Estandía, Tengfei Cao, Rohan Mishra, Ignasi Fina, F. Sánchez, Jaume Gàzquez
Abstract
Epitaxial growth of ${\mathrm{Hf}}_{0.5}{\mathrm{Zr}}_{0.5}{\mathrm{O}}_{2}$ (HZO) thin films allows for the stabilization of the metastable orthorhombic phase with robust ferroelectric properties. So far, the ferroelectric phase is most commonly stabilized on perovskite substrates upon insertion of a buffer layer of ${\mathrm{La}}_{2/3}{\mathrm{Sr}}_{1/3}\mathrm{Mn}{\mathrm{O}}_{3}$ (LSMO); however, little is known about the role played by the LSMO buffer layer and the interface between HZO and LSMO. Inspection of a $\mathrm{HZO}/\mathrm{LSMO}/\mathrm{SrTi}{\mathrm{O}}_{3}$ heterostructure by scanning transmission electron microscope imaging and electron energy loss spectroscopy shows that, despite the substantial structural mismatch between HZO and LSMO, the interface between them is relatively sharp spanning \ensuremath{\sim}2 atomic layers. The LSMO surface, expected to be mostly $\mathrm{Mn}{\mathrm{O}}_{2}$ terminated, undergoes a chemical reconstruction consisting of the substitution of the Mn cations by a mixture of Hf/Zr cations. Density functional theory calculations show that the substitution of Mn by Hf on the $\mathrm{Mn}{\mathrm{O}}_{2}$-terminated surface of LSMO is energetically favorable, as the higher electronegativity and valence of Hf with respect to Mn balances the surface charge of the $\mathrm{Mn}{\mathrm{O}}_{2}$ layer.