Hydrogen-Stabilized ScYNdGd Medium-Entropy Alloy for Hydrogen Storage.

The research on the functional properties of medium- and high-entropy alloys (MEAs and HEAs) has been in the spotlight recently. Many significant discoveries have been made lately in hydrogen-based economy-related research where these alloys may be utilized in all of its key sectors: water electrolysis, hydrogen storage, and fuel cell applications. Despite the rapid development of MEAs and HEAs with the ability to reversibly absorb hydrogen, the research is limited to transition-metal-based alloys that crystallize in body-centered cubic solid solution or Laves phase structures. To date, no study has been devoted to the hydrogenation of rare-earth-element (REE)-based MEAs or HEAs, as well as to the alloys crystallizing in face-centered-cubic (FCC) or hexagonal-close-packed structures. Here, we elucidate the formation and hydrogen storage properties of REE-based ScYNdGd MEA. More specifically, we present the astounding stabilization of the single-phase FCC structure induced by the hydrogen absorption process. Moreover, the measured unprecedented high storage capacity of 2.5 H/M has been observed after hydrogenation conducted under mild conditions that proceeded without any phase transformation in the material. The studied MEA can be facilely activated, even after a long passivation time. The results of complementary measurements showed that the hydrogen desorption process proceeds in two steps. In the first, hydrogen is released from octahedral interstitial sites at relatively low temperatures. In the second, high-temperature process, it is associated with the desorption of hydrogen atoms stored in tetrahedral sites. The presented results may impact future research of a novel group of REE-based MEAs and HEAs with adaptable hydrogen storage properties and a broad scope of possible applications.

Colossal room-temperature electrocaloric strength aided by hydrostatic pressure in lead-free multiferroic solid solutions.

Solid-state cooling applications based on electrocaloric (EC) effects are particularly promising from a technological point of view due to their downsize scalability and natural implementation in circuitry. However, EC effects typically involve materials that contain toxic substances and require relatively large electric fields (∼100-1000 kV cm-1) that cause fateful leakage current and dielectric loss problems. Here, we propose a possible solution to these practical issues that consists of concertedly applying hydrostatic pressure and electric fields on lead-free multiferroic materials. We theoretically demonstrate this strategy by performing first-principles simulations on supertetragonal BiFe1-xCoxO3 solid solutions (BFCO). It is shown that hydrostatic pressure, besides adjusting the occurrence of EC effects to near room temperature, can reduce enormously the intensity of driving electric fields. For pressurized BFCO, we estimate a colossal room-temperature EC strength, defined as the ratio of the adiabatic EC temperature change by an applied electric field, of ∼1 K cm kV-1, a value that is several orders of magnitude larger than those routinely measured in uncompressed ferroelectrics.

Giant Thermal Enhancement of the Electric Polarization in Ferrimagnetic BiFe_{1-x}Co_{x}O_{3} Solid Solutions near Room Temperature.

Thermal excitations typically reduce the electric polarization in ferroelectric materials. Here, we show by means of first-principles calculations that multiferroic BiFe_{1-x}Co_{x}O_{3} solid solutions with 0.25≤x≤0.50 (BFCO) represent a noteworthy exception to this behavior. In particular, we find that, at room temperature and for moderate pressures of 0.1-1.0 GPa, depending on the composition, the electric polarization of bulk BFCO increases by ∼150%. The origin of such an exceptional behavior is a phase transformation involving a low-T rhombohedral (R) phase and a high-T supertetragonal (T) phase. Both R and T phases are ferrimagnetic near room temperature with an approximate net magnetization of 0.13 µ_{B} per formula unit. Contrary to what occurs in either bulk BiFeO_{3} or BiCoO_{3}, the T phase is stabilized over the R by increasing temperature due to its higher vibrational entropy. This extraordinary T-induced R→T phase transition is originated by polar phonon modes that involve concerted displacements of transition-metal and oxygen ions.

Minimum protein intake for the preterm neonate determined by protein and amino acid kinetics.

Lower limits of protein needs in prematurely born neonates have not been adequately studied, yet providing protein in amounts maximizing accretion without excess is a goal in these infants' nutritional care. We hypothesized that with the use of amino acid oxidation methodology, it would be possible to define minimum protein requirement. Our objective was to investigate protein kinetics during short-term changes in protein intake by measurement of nitrogen balance and amino acid flux and oxidation using [(15)N]glycine, [(13)C]phenylalanine, and [(13)C]leucine tracers. Protein kinetics were examined in 21 preterm infants (gestational age: 29 +/- 3 wk; birth weight: 1091 +/- 324 g) at five protein intakes (1.0, 1.5, 2.0, 2.5, and 3.0 g x kg(-1) x d(-1)) with 1 d of adaptation to the test intakes. From nitrogen balance data, a protein need of 0.74 g x kg(-1 x -1) was estimated to achieve zero balance. For all three amino acids, flux and oxidation estimates were not different across protein intakes. Whole-body protein synthesis and breakdown estimates from [(15)N]ammonia data were 14.6 +/- 3.4 and 14.4 +/- 4.1 g x kg(-1) x d(-1), respectively. Glycine flux (680 +/- 168 micromol x kg(-1) x h(-1)) was greater than leucine flux (323 +/- 115 micromol x kg(-1) x h(-1)), which was greater than phenylalanine flux (84.3 +/- 35.2 micromol x kg(-1) x h(-1)). Leucine oxidation (36.7 +/- 15.6 micromol x kg(-1) x h(-1)) was also greater than phenylalanine oxidation (6.64 +/- 4.41 micromol x kg(-1) x h(-1)). Infants in our study were able to adapt to short-term changes in protein intake with little consequence to the overall whole-body protein economy, as measured by the three test amino acids.