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The piezoelectric and ferroelectric applications of heterovalent ternary materials are not well explored. Epitaxial MgSiN₂ films are grown at 600 °C on (111)Pt//(001)Al₂O₃ substrates by the reactive sputtering method using metallic Mg and Si under the N₂ atmosphere. Detailed X-ray diffraction measurements and transmission electron microscopy observations revealed that the epitaxially grown films on the substrates have a hexagonal wurtzite structure with c-axis out-of-plane orientation. The random occupation of this structure by Mg and Si differs from that of the previously reported structure in which these two cations periodically occupy the cationic sites. However, the lattice spacings closely approximate thosemore » that are previously reported, irrespective of the ordering, and they are almost comparable with those of (Al_0.8Sc_0.2)N. The wide bandgap of >5.0 eV in deposited MgSiN₂ is compatible with that of AlN and suggests durability against the application of strong external electric fields, possibly to induce polarization switching. In addition, MgSiN₂ is shown to have piezoelectric properties with an effective d₃₃ value of 2.3 pm V⁻¹ for the first time. This work demonstrates the compositional expansion of hexagonal wurtzite to heterovalent ternary nitrides for novel piezoelectric materials, whose ferroelectricity is expected.« less

Iron-based 1111-type superconductors display high critical temperatures and relatively high critical current densities J_c. The typical approach to increasing J_c is to introduce defects to control dissipative vortex motion. However, when optimized, this approach is theoretically predicted to be limited to achieving a maximum J_c of only ~30% of the depairing current density J_d, which depends on the coherence length and the penetration depth. Here we dramatically boost J_c in SmFeAsO_1–xH_x films using a thermodynamic approach aimed at increasing J_d and incorporating vortex pinning centres. Specifically, we reduce the penetration depth, coherence length and critical field anisotropy by increasing themore » carrier density through high electron doping using H substitution. Remarkably, the quadrupled J_d reaches 415 MA cm^–2, a value comparable to cuprates. Finally, by introducing defects using proton irradiation, we obtain high J_c values in fields up to 25 T. We apply this method to other iron-based superconductors and achieve a similar enhancement of current densities.« less