Effect of hydrogenation on the microwave absorption properties of BaTiO 3 nanoparticles† Lihong Tian, ab Xiaodong Yan, a JiLian Xu, c Petra Wallenmeyer, a James Murowchick, d Lei Liu * c and Xiaobo Chen * a Microwave absorbing materials (MAMs) have numerous important applications in electronic communications, signal protection, radar dodging, etc. Although it has been proposed as a promising MAM, BaTiO 3 has a high reflection coefficient at the interface with air, causing a large reflection. Thus, its efficiency of microwave absorption is not satisfactory. Here, we report that hydrogenation has largely improved the microwave absorption of BaTiO 3 nanoparticles. Hydrogenation is performed on BaTiO 3 nanoparticles by treating pristine BaTiO 3 nanoparticles at 700  C for 4 hours in a pure H 2 environment. The enhanced microwave absorption efficiency with a reflection loss value (36.9 dB) is attributed to the increased resonance of polar rotations with the incident electromagnetic field which is amplified by the increased interfacial polarization caused by the built-in electrical field along the boundaries between different grains created within these nanoparticles. Introduction Microwave absorbing materials (MAMs) play important roles in electronic communications, signal protection, radar dodging, etc. 1–4 Traditional mechanisms for microwave absorption include dipole rotation and ferromagnetic resonance due to the alignment of the polar groups or the strongly interacting elec- tron spins to the electromagnetic eld in the microwave eld. 1–4 The main-stream MAMs investigated so far are carboneous materials 5–9 and ceramic ferroelectrics such as barium tita- nate, 4,10–13 lead zirconate titanate, 4 ferrites and ferromagnetic materials. 4,10,14 For example, with carbon nanotubes, a permit- tivity value of 10–16 can be obtained in the microwave range of 2–18 GHz, 8 and it can be tuned with the chirality, diameter, length, and doping of carbon nanotubes. 9 The permeability of ferromagnetic llers such as ferrites and carbonyl iron decreases dramatically in the GHz range. 4 However, for ceramic ferroelectrics such as BaTiO 3 , a large microwave reection and low microwave absorption are observed, i.e. in the high frequency range, due to their large reection coefficients at the interface with air, 4 although they have been considered as promising MAMs. 15 The interactions between matter and electromagnetic irradi- ation depend not only on the frequency of the alternating elec- tromagnetic eld, but also on the structure, phase, surface and composition of the materials. In order to be a strong absorber, the material has to be able to allow the electromagnetic wave to enter (impedance matching characteristic) and get entirely absorbed (attenuation characteristic) in the microwave region. Recently, we have demonstrated that by altering the lattice structures of TiO 2 nanoparticles using hydrogenation processes, the interactions of TiO 2 nanoparticles with electromagnetic irradiation changed dramatically not only in the high frequency (visible-light & infrared) region, 16,17 but also in the low frequency (microwave) region. 18,19 The hydrogenated TiO 2 nanoparticles featured with a layer of an amorphous lattice on the outside of the crystalline core. 16,20 The electronic structures of the crystal- line core and the amorphous shell were different, 16,21 which was suggested to cause a built-in electric eld and to facilitate the charge transfer processes. 22 The hydrogenated TiO 2 nano- particles also displayed dramatic changes in their dielectric constants and showed excellent absorption in the microwave regions when compared to normal TiO 2 nanoparticles, which traditionally were not a good MAM. 18,19 A collective-movement-of- interfacial-dipole (CMID) mechanism was proposed to explain the enhanced microwave absorption with a collective interfacial polarization amplied microwave absorption (CIPAMA). 18,19 The CMID was based on the increased interfacial polarization and charge accumulations caused by the built-in electrical eld along the boundaries between different grains within these nano- particles from the hydrogenation process. 18,19 a Department of Chemistry, University of Missouri – Kansas City, Kansas City, MO 64110, USA. E-mail: chenxiaobo@umkc.edu b Hubei Collaborative Innovation Center for Advanced Organochemical Materials, Hubei University, Wuhan, 430062, China c State Key Laboratory of Luminescence and Applications, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun, 130033, China d Department of Geosciences, University of Missouri – Kansas City, Kansas City, MO 64110, USA † Electronic supplementary information (ESI) available. See DOI: 10.1039/c5ta02109j Cite this: DOI: 10.1039/c5ta02109j Received 23rd March 2015 Accepted 6th May 2015 DOI: 10.1039/c5ta02109j www.rsc.org/MaterialsA This journal is © The Royal Society of Chemistry 2015 J. Mater. Chem. A Journal of Materials Chemistry A PAPER Published on 08 May 2015. Downloaded by University of New England on 01/06/2015 04:51:15. View Article Online View Journal