The Earth’s core consists of iron as the major component. The melting point of iron at the inner core boundary constrains the thermal structure and solidification of the Earth’s core. However, the current estimation of the melting temperature of iron under the core conditions has significant variations. Here, we measured the temperatures of iron shocked up to ~256 GPa using precise pyrometer and velocimeter diagnostics via a two‐stage light‐gas gun. Our results indicated that the melting temperatures of iron at the core‐mantle and inner‐core boundaries are 4300(250) K and 5950(400) K, respectively. These temperatures are significantly lower than some previous shock experiments but are overall consistent with the recent results determined by fast X‐ray diffraction techniques, X‐ray absorption experiments in laser‐heated diamond anvil cells, and by ab initio computations. Our iron melting curve indicates a relatively small Clapeyron slope and supports thermal models for a young inner core.

Piezoceramics with both high piezoelectric properties and broad temperature usage range are highly in demand for sensor and actuator applications. Unfortunately, the trade-off relationship between two properties poses a significant challenge that remains unresolved. Herein, through combined phase boundary engineering and process engineering, we report the simultaneous achievements of substantially enhanced piezoelectric coefficient d₃₃ (from 784 pC/N to 855 pC/N) and piezoelectric strain d₃₃* (from 620 pm/V to 860 pm/V), and ultrahigh temperature stability (i.e., d₃₃ and d₃₃* change less than 7.3% and 4.6% over 25-175 °C, respectively) in Pb_0.92Ba_0.08[Zr_0.50+xTi_0.48-x(Nb_0.5Sb_0.5)_0.02]O₃ (x = 0.4) ceramics, superior to those of other typical piezoceramics. The enhanced piezoelectricity and excellent temperature stability are attributed to three synergistic effects, namely, morphotropic phase boundary concomitant with nano-domains, reduced pores, and inhibited oxygen vacancies. Therefore, our proposed strategy provides a new paradigm to boost both piezoelectricity and its temperature stability and is beneficial to both academia and industry.

The force-electric effect in ferroelectrics is characterized by the release of bound charge during pressure/shock-induced depolarization. In contrast to other electrical energy storage systems, the charge-storage/release by the force-electric effect of ferroelectrics is determined by polarization switching or polar-nonpolar phase transition. This offers a further set of options for materials design in the realm of energy conversion, especially for the high power density applications. Here, we report that a ferroelectric ceramic, $\mathrm{N}{\mathrm{a}}_{0.5}\mathrm{B}{\mathrm{i}}_{0.5}\mathrm{Ti}{\mathrm{O}}_3$ (NBT), can generate a high power output $(3.04\times {10}^8\mathrm{W}/\mathrm{kg})$ under shock compression, which is one of the highest values achieved by the force-electric effect. The in situ synchrotron x-ray diffraction studies reveal that this power output mainly arises from a polar-nonpolar phase transition (rhombohedral-orthorhombic). First-principles calculations show that this is a first-order phase transition that undergoes two-step structure changes. These results extend the application of the force-electric effect and are a key step in understanding the phase transition behaviors of NBT under high pressure.