Lead‐free dielectric ceramics with ultrahigh energy storage performance are the best potential stocks used in next‐generation advanced pulse power capacitors. Here, an ultrahigh recoverable energy storage density Wrec of ≈7.57 J cm−3 and a large efficiency η of ≈81.4% are first realized in (Bi0.5K0.5)TiO3 (BKT)‐based relaxor ferroelectric ceramics with an ultrahigh Vickers hardness Hv ≈ 8.63 Gpa by adding BaTiO3 and NaNbO3 in order to synergistically design the domain and microstructure in multiscale, leading to the existence of ultrasmall polar nanoregions, ultrafine grain size, compact grain boundaries, dense microstructure, and large band gap Eg simultaneously. Encouragingly, an excellent energy storage temperature stability (Wrec ≈ 4.31 ± 0.25 J cm−3, η ≈ 86 ± 5%, 20–200 °C), frequency stability (Wrec ≈ 5.14 ± 0.12 J cm−3, η ≈ 81.3 ± 1.2%, 5–100 Hz), and excellent charge/discharge performance (power density PD ≈ 103.2 MW cm−3, discharge energy density WD ≈ 2.4 J cm−3, discharge rate t0.9 ≈ 130 ns) are also achieved in BKT‐based ceramics. The results demonstrate that BKT‐based ceramics can be very competitive lead‐free relaxors for energy storage capacitors in pulsed power devices.

In this paper, photoinduced intermolecular charge transfer (PICT) and fluorescence resonance energy transfer (FRET) in donor-acceptor systems have been investigated experimentally and theoretically. We attempt to investigate the natural relationship between FRET and PICT, and reveal the advantages of FRET enhanced PICT. The driving force for PICT in the FRET system equals the reorganization energy, which gives barrier-less charge transfer according to Marcus theory. The rates of PICT in the FRET system can be estimated with our simplified Marcus equation. Our results can promote the deeper understanding of the nature of FRET enhanced PICT, and benefit rational design for the use of the FRET system in organic solar cells.

Deformation caused due to the thermal expansion of a material at high temperatures impairs the functioning of the device. Hence, high-temperature zero thermal expansion (ZTE) compounds are widely used in many high-precision devices. However, the domination of magnetic behavior over the thermal expansion of magnetic compounds makes it difficult to display ZTE at high temperatures. Herein, we report a high-temperature ZTE in a Fe-rich HfFe2+δ compound, whose ZTE operating temperature could reach 583 K, the highest temperature reached by ZTE metal-based compounds. Synchrotron X-ray diffractometry (SXRD), neutron powder diffractometry, Mössbauer spectroscopy, first-principle calculations, and macroscopic magnetic measurements revealed that the additional Fe atoms occupy the Hf sites and introduced extra ferromagnetic exchange interaction paths with the neighboring Fe atoms, thereby enhancing the magnetic transition temperature and the ZTE temperature region. Moreover, it was experimentally shown that the generation of ZTE by HfFe2.5 was due to the mutual cancellation of lattice shrinkage caused by the transformation of magnetic moments of Fe from ordered to disordered state and lattice expansion caused by lattice vibration. This study not only reports a high-temperature ZTE material but also provides an unusual method to modulate the magnetic systems to obtain high-temperature ZTE compounds.

Negative thermal expansion (NTE) alloys possess great practical merit as thermal offsets for positive thermal expansion due to its metallic properties. However, achieving a large NTE with a wide temperature range remains a great challenge. Herein, a metallic framework-like material FeZr2 is found to exhibit a giant uniaxial (1D) NTE with a wide temperature range (93-1078 K, $${\bar{\alpha }}_{l}=-34.01\times {10}^{-6}\,{{{{{{\rm{K}}}}}}}^{-1}$$ α ¯ l = − 34.01 × 10 − 6 K − 1 ). Such uniaxial NTE is the strongest in all metal-based NTE materials. The direct experimental evidence and DFT calculations reveal that the origin of giant NTE is the couple with phonons, flexible framework-like structure, and soft bonds. Interestingly, the present metallic FeZr2 excites giant 1D NTE mainly driven by high-frequency optical branches. It is unlike the NTE in traditional framework materials, which are generally dominated by low energy acoustic branches. In the present study, a giant uniaxial NTE alloy is reported, and the complex mechanism has been revealed. It is of great significance for understanding the nature of thermal expansion and guiding the regulation of thermal expansion.