PNb 9 O 25 , a Wadsley-Roth compound whose structure is obtained by appropriate crystallographic shear of the ReO 3 structure, is a high-power electrode material that can reach 85 % of the equilibrium capacity in 30 minutes and 67% in 6 minutes. Here we show that multielectron redox, as observed through X-ray absorption spectroscopy and X-ray photoelectron spectroscopy, and an insulator-to-metal transition upon lithium insertion, as suggested by a number of complementary techniques, contribute to the impressive performance. Chemically tuning the tetrahedral site between phosphorus and vanadium leads to significant changes in the electrochemistry and kinetics of lithium insertion in the structure, pointing to larger implications for the use of crystallographic shear phases as fast-charging electrode materials.

Alternating cycles of isothermal magnetization and adiabatic demagnetization applied to a magnetocaloric material can drive refrigeration in very much the same manner as cycles of gas compression and expansion. The material property of interest in finding candidate magnetocaloric materials is their gravimetric entropy change upon application of a magnetic field under isothermal conditions. There is, however, no general method of screening materials for such an entropy change without actually carrying out the relevant, time-and effort-intensive magnetic measurements. Here we propose a simple computational proxy based on carrying out non-magnetic and magnetic density functional theory calculations on magnetic materials. This proxy, which we refer to as the magnetic deformation Σ M , is a measure of how much the unit cell deforms when comparing the relaxed structures with and without the inclusion of spin polarization. Σ M appears to correlate very well with experimentally measured magnetic entropy change values. The proxy has been tested against 33 known ferromagnetic materials, including nine materials newly measured for this study. It has then been used to screen 134 ferromagnetic materials for which the magnetic entropyhas not yet been reported, identifying 30 compounds as being promising for further study. As a demonstration of the effectiveness of our approach, we have prepared one of these compounds and measured its isothermal entropy change. MnCoP, with T C = 575 K, shows a maximum ∆S M = −6.0 J kg −1 K −1 for an applied field of H = 5 T.2

We demonstrate that magnetocaloric measurements can rapidly reveal details of the phase diagrams of high temperature skyrmion hosts, concurrently yielding quantitative latent heats of the field-driven magnetic phase transitions. Our approach addresses an outstanding issue in the phase diagram of the skyrmion host FeGe by showing that DC magnetic anomalies can be explained in terms of entropic signatures consistent with a phase diagram containing a single pocket of skyrmionic order and a Brazovskii transition.

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