JOURNAL OF COMPOSITE MATERIALS Article Synthesis and microwave absorption enhancement of BaTiO 3 nanoparticle/ polyvinylbutyral composites Yu ¨ ksel Akinay and Fatih Hayat Abstract Barium titanate (BaTiO 3 )-polyvinyl butyral (PVB) composites at various weight concentrations were prepared via ultra- sonic probe sonicator. The sonication was carried out at 20 kHz and 70% amplitude for about 2 h and BaTiO 3 nano- particles were dispersed well in the mixture of PVB/ethanol under probe sonication. As a microwave absorbent, the microwave absorbing properties of the BaTiO 3 nanoparticle-PVB composites with different mixture ratios of 5 wt.% (RAM1), 10 wt.% (RAM2) and 15 wt.% (RAM3) BaTiO 3 were investigated based on transmission line theory in the frequency range from 1 GHz to 14 GHz. The minimum reflection loss (R L ) of the RAM1 reaches 3.47 dB at 5.57 GHz with a matching thickness of only 7.0 mm. For RAM2 with 4 mm and 4.2 mm thickness (t m ), the R L values are less than 10 dB obtained in the frequency 10.3–13.4 GHz. The RAM3 composite with 15 wt.% BaTiO 3 mixture ratio shows a minimum reflection loss of 43.8 dB at 11.01 GHz with a 15 dB bandwidth over the extended frequency range of 10.2–13.2 GHz for a thickness of 2.8 mm and 44.2 dB at 4.77 GHz for a thickness of 6.5 mm. Keywords Barium titanate, polyvinylbutyral, permittivity, reflection loss Introduction Recently, microwave absorbing materials have received a great deal of interest because of increasing telecom- munication, military and commercial application in the radar cross-section reduction in the gigahertz fre- quency band range for stealth technology purpose. Especially these types of materials have been commonly considered for the stealth technology of aircraft due to light weight, thin thickness and wide microwave absorbing properties. 1,2 The increasing usage of micro- wave absorbing materials results in electromagnetic interface (EMI) issues in the military application. To get over this problem, extensive studies have been made to develop ideal electromagnetic wave absorbing materials that exhibit good microwave absorbing properties. 3–7 The microwave absorbing materials attenuate micro- wave energy through its electric, magnetic and dielectric loss medium. The microwave absorbing performance is mainly determined by the dielectric (permittivity) and magnetic (permeability) properties according to the type of filler used. 8,9 High dielectric constants such as ceramic, metal and ionic fillers can increase the dielectric constant of microwave absorbing materials. Among dielectric filler candidates for microwave absorbing materials, barium titanate (BaTiO 3 ) particles with per- ovskite structure are particularly interesting. 10–12 Optimally, the crystal structure of perovskites can be explained as ABX 3 . The structure of BaTiO 3 consisting of a Ba 2þ (A ion) and O 2– (X ion) forms a face center cubic with Ba 2þ occupies the corner sites, and O 2– anions on the face centers. The titanium (Ti 4þ ) (B ion) and O 2– fitting octahedral structure with titanate ions are located in the center and O 2– on the face center. 10 It is well known that BaTiO 3 nanoparticles are usually applied to multi-layer capacitor (MTCs), optoelectronic devices and dielectric absorber due to their high relative permit- tivity, good ferroelectric properties and propagation constant. Thus, BaTiO 3 is applicable to achieve good microwave absorbing properties. 13–17 Faculty of Engineering, Metallurgical and Materials Engineering, Karabuk University, Turkey Corresponding author: Yu ¨ksel Akinay, Karabuk University, Karabuk 78080, Turkey. Email: yukselakinay@gmail.com Journal of Composite Materials 0(0) 1–9 ! The Author(s) 2018 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0021998318788144 journals.sagepub.com/home/jcm