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Abstract The hafnate perovskites PbHfO3(antiferroelectric) and SrHfO3(“potential” ferroelectric) are studied as epitaxial thin films on SrTiO3(001) substrates with the added opportunity of observing a morphotropic phase boundary (MPB) in the Pb1−
x Srx HfO3system. The resulting (240)‐oriented PbHfO3(Pba 2) films exhibited antiferroelectric switching with a saturation polarization ≈53 µC cm−2at 1.6 MV cm−1, weak‐field dielectric constant ≈186 at 298 K, and an antiferroelectric‐to‐paraelectric phase transition at ≈518 K. (002)‐oriented SrHfO3films exhibited neither ferroelectric behavior nor evidence of a polarP 4mm phase . Instead, the SrHfO3films exhibited a weak‐field dielectric constant ≈25 at 298 K and no signs of a structural transition to a polar phase as a function of temperature (77–623 K) and electric field (–3 to 3 MV cm−1). While the lack of ferroelectric order in SrHfO3removes the potential for MPB, structural and property evolution of the Pb1−x Srx HfO3(0 ≤x < 1) system is explored. Strontium alloying increased the electric‐breakdown strength (E B) and decreased hysteresis loss, thus enhancing the capacitive energy storage density (U r) and efficiency (η). The composition, Pb0.5Sr0.5HfO3produced the best combination ofE B = 5.12 ± 0.5 MV cm−1,U r = 77 ± 5 J cm−3, and η = 97 ± 2%, well out‐performing PbHfO3and other antiferroelectric oxides. -
Abstract Abundant transition metal borides are emerging as substitute electrochemical hydrogen evolution reaction (HER) catalysts for noble metals. Herein, an unusual canonic‐like behavior of the
c lattice parameter in the AlB2‐type solid solution Cr1–x Mox B2(x = 0, 0.25, 0.4, 0.5, 0.6, 0.75, 1) and its direct correlation to the HER activity in 0.5 M H2SO4solution are reported. The activity increases with increasingx , reaching its maximum atx = 0.6 before decreasing again. At high current densities, Cr0.4Mo0.6B2outperforms Pt/C, as it needs 180 mV less overpotential to drive an 800 mA cm−2current density. Cr0.4Mo0.6B2has excellent long‐term stability and durability showing no significant activity loss after 5000 cycles and 25 h of operation in acid. First‐principles calculations have correctly reproduced the nonlinear dependence of thec lattice parameter and have shown that the mixed metal/B layers, such as (110), promote hydrogen evolution more efficiently forx = 0.6, supporting the experimental results.