B-Site Substituted Perovskite High Entropy Oxide Ferroelectric Thin Films

Ferroelectrics are a subset of dielectrics that lack inversion symmetry, allowing for spontaneous polarization which can be reoriented by an external electric field. Their field-induced polar entropy change incites a temperature change, the electrocaloric effect, which can enable a greener, solid-state alternative for cooling systems. High entropy B-site substituted oxide films based on Pb(Zr_xTi_1-x)O₃ were grown in hopes of enhancing the polar entropy change via compositional disorder. Pb(Hf_0.167Zr_0.167Ti_0.167Nb_0.25Al_0.25)O₃, Pb(Hf_0.13Zr_0.13Ti_0.13Nb_0.3Al_0.3)O₃, and Pb(Hf_0.2Zr_0.2Ti_0.2Nb_0.2Ga_0.2)O₃ films were grown on SrTiO₃/SrRuO₃ substrates by pulsed laser deposition. XRD was used to analyze crystal structure. The Al-doped films did not show phase purity, requiring further optimization. Using 15 Hz laser frequency, 100 mTorr O₂ chamber pressure, 600˚C substrate temperature, and 6.2 cm working distance, Ga-substituted films grew single-phase perovskite. It showed a maximum polarization of 41.5 μC/cm² and remanent polarization of 28.65 μC/cm², confirming ferroelectricity. On-going work will further optimize growth conditions and explore the film’s temperature dependence.