In Ba$\mathrm{<mrow\; data-mjx-texclass="ORD">0.6</mrow>}$Sr$\mathrm{<mrow\; data-mjx-texclass="ORD">0.4</mrow>}$TiO$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$ (BSTO)-based epitaxial nanocomposite films increased P r values are demonstrated by up to a factor of 3 compared to standard BSTO films. A strongly reduced temperature coefficient of polarization retention is also obtained, i.e., 0.07% °C$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$ compared to 0.24% °C$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$ . Piezopoling with only marginal leakage current is also achieved up to 200 °C, the highest temperature studied. The origin of the improved performance is the incorporation of Sm$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$O$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$ nanopillars in the films which acted as stiff vertical nanoscaffolds, inducing a strong tetragonal distortion in the BSTO (up to 1.033(7) in terms of the out-of-plane/in-plane lattice dimensions). The films have comparable performance to industry-standard Pb(Zr,Ti)O$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$ films, at the same time as being Pb-free.