Electrocaloric effect in ultrathin SrRuO3/BaTiO3/SrRuO3 capacitors is calculated using a multiscale thermodynamic model. It is found that the electrocaloric coefficient vs working temperature is shifted to higher temperatures with increasing the BaTiO3 layer thickness (above the critical thickness). The electrocaloric effect above the critical thickness is much stronger than that below it. Furthermore, it is demonstrated that a giant electrocaloric effect (3.5 K under 0.24 V) in such capacitors (six BaTiO3 unit cells) at 300 K can be achieved, which suggests that ultrathin ferroelectric capacitors may be promising candidates for room temperature solid-state refrigeration.

A novel inorganic and organic composite flame retardant (9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide [DOPO]–layered double hydroxide [LDH]) was synthesized via grafting DOPO with organic‐modified Mg/Al‐LDH, which was introduced into poly (methyl methacrylate) (PMMA) resin to prepare the flame‐retardant PMMA composites. Thermogravimetric analyzer (TGA) showed that the T‐50% of DOPO‐LDH/PMMA composites enhanced by about 20°C, and with the 20% flame retardant, the residual char content can be increased by 39.8% in the air atmosphere compared with LDH/PMMA composites. In the UL‐94 and the limiting oxygen index (LOI) tests, it can be found that compared with LDH/PMMA composites, the LOI value of DOPO‐LDH/PMMA composites were raised evidently with the increased flame retardants, and the droplet combustion was greatly improved. These results could be ascribed to the action of DOPO free‐radical, catalytic charring of polymer and the effect of LDH physical barrier. Moreover, the novel DOPO‐LDH not only given PMMA a good flame‐retardant property and thermal stability, but also have higher visible light transmittance, ultraviolet‐shielding effect, and low loss of mechanical properties, which could further facilitate the wide application of inorganic environment‐friendly flame retardants in general resins and engineering resins and broaden the application of polymers.

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