Phonon confinement in TiO2 sandwiched MOF particles for high temperature dielectric energy storage

Phonon confinement of TiO 2 core and coating provides ZIF-67 structure stable energy density at elevated temperatures. • Phonon-modulated polarization dynamics. • Dual Debye relaxations and Maxwell-Wagner relaxations at high temperatures. • The crucial role of phonon dynamics in the energy storage capabilities. For promising energy storage applications, high surface area materials containing both ionic and organic components are ideal candidates. While Metal Organic Frameworks (MOFs) exhibit the desired characteristic, they generally lack high-temperature structural stability observed in conventional inorganic metal-based compounds. Here we propose a novel composite material comprising TiO 2 - incorporated and encapsulated carbonized ZIF-67 (TZT), showing stable dielectric and energy storage performance at elevated temperatures than other MOF composites. By integrating TiO 2 within the ZIF-67 framework, the composite achieves significant phonon confinement for enhanced dielectric polarization, with permittivity achieving a value of 50, while the external coating gives the imidazole structure temperature sustainability. The current density shows a prominent increase with the increase of temperature and frequency and hence lowering of activation energy and Schottky barrier potential, that results in a prominent rise of polarization with respect to electric filed. The study elucidates the underlying mechanisms of phonon-modulated polarization dynamics, demonstrating dual Debye relaxations at low temperatures and Maxwell-Wagner relaxations at high temperatures. These findings highlight the crucial role of phonon dynamics in enhancing the energy storage capabilities and dielectric performance of the composite material, making TZT a superior candidate for advanced high-temperature energy storage devices.