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The relaxor-like behavior in CaCu3Ti4O12 was investigated in details. The dielectric anomaly was found to be an extrinsic phenomenon related to oxygen vacancy. Annealing treatments in N2 and O2 atmospheres revealed that the relaxor-like behavior is composed of two types of relaxations with close relaxation parameters. Impedance analysis showed that the relaxations appearing in the low- and high-temperature wings of the anomaly are related to the dipolar and Maxwell-Wagner (MW) relaxation, respectively. Both relaxations are induced by the hopping motions of confined carriers related to single-ionized oxygen vacancies, and they are intimately linked with each other. The relaxor-like anomaly is attributed to the combining effect of these two relaxations, i.e., the dipolar relaxation first creates a steplike increase followed by a rapid decrease in dielectric constant caused by the MW relaxation, thereby, giving rise to the relaxor-like behavior.

Heterostructured TiO2/C/Co nanomaterial has been derived from a carbonized zeolitic imidazolate (ZIF-67) porous framework. The obtained uniform nanospheres wrapped with TiO2 have shown superior microwave absorption properties. Traditionally, the interaction of phonons within a confined system in terms of microwave absorption has not been studied in the literature to date. Here, we demonstrate that the phonon confinement is pivotal in the improvement of impedance matching, besides the multiple interfacial dielectric relaxations at different dielectric media (TiO2/C, C/Co) in the composite. Because of the specially crafted phonon confinement and multiple interface dielectric relaxations, the as-synthesized (TiO2/C/Co) composite manifests a maximum reflection loss of −42 dB with a broad bandwidth of 5 GHz. This work explains the possible mechanism of electromagnetic shielding in a confined system with multiple interfaces and may lead to design of advanced materials for microwave shielding.

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The transport property ( ) and flux motion together with the superconductivity of Fe Se2 single crystals are studied. In the transport measurement, contrasting behavior is observed under two different magnetic field orientations, i.e., and , which is ascribed to different vortex configurations. In the flux motion study, the tail of the well fits the description of the vortex-glass (VG) critical behavior, which is confirmed by VG scaling. The strong pinning nature of Fe Se2 implies great sustainability under high magnetic fields and the potential for practical application of the system. The relation under Tc follows Arrhenius thermally activated flux flow (TAFF) behavior. The existence of a crossover behavior in a magnetic field is discovered via the magnetic dependence of the effective pinning barrier, which is related to the change in pinning strength of the point defects and the entanglements of the flux lines. Finally, a vortex phase diagram is proposed based on the evolution of upper critical field and other dynamic characteristics.