Influence of epitaxial strain on structural relaxation in crystalline membranes of fluorite oxides

Using synchrotron X-ray diffraction, we investigated how epitaxial strain influences structural relaxation in freestanding crystalline membranes of fluorite oxides. When epitaxial films of yttrium-doped hafnium oxide Hf0.93Y0.07O2(HYO) with the metastable orthorhombic phase under compressive strain were exfoliated from La0.7Sr0.3MnO3(LSMO)-buffered (110) SrTiO3 substrates, the strain was partially relaxed, while the metastable phase was preserved in the membrane form. In contrast, the metastable orthorhombic phase of zirconium dioxide (ZrO2) films grown on (110) LSMO/STO substrates and under negligibly small strain underwent structural relaxation into the thermodynamically stable monoclinic phase upon exfoliation from the substrate. These results indicate that the energy barrier between the metastable orthorhombic phase and the monoclinic one is less for ZO than for HYO, highlighting that the stability of the metastable phase, which is modulated by the strain, influences the structural relaxation in fluorite oxide membranes.