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1. Integration of highly anisotropic multiferroic BaTiO ₃ –Fe nanocomposite thin films on Si towards device applications

   https://doi.org/10.1039/d0na00405g  

   Kalaswad, Matias; Zhang, Bruce; Wang, Xuejing; Wang, Han; Gao, Xingyao; Wang, Haiyan (September 2020, Nanoscale Advances)

   null (Ed.)

   Integration of highly anisotropic multiferroic thin films on silicon substrates is a critical step towards low-cost devices, especially high-speed and low-power consumption memories. In this work, an oxide–metal vertically aligned nanocomposite (VAN) platform has been used to successfully demonstrate self-assembled multiferroic BaTiO 3 –Fe (BTO–Fe) nanocomposite films with high structural anisotropy on Si substrates. The effects of various buffer layers on the crystallinity, microstructure, and physical properties of the BTO–Fe films have been explored. With an appropriate buffer layer design, e.g. SrTiO 3 /TiN bilayer buffer, the epitaxial quality of the BTO matrix and the anisotropy of the Fe nanopillars can be improved greatly, which in turn enhances the physical properties, including the ferromagnetic, ferroelectric, and optical response of the BTO–Fe thin films. This unique combination of properties integrated on Si offers a promising approach in the design of multifunctional nanocomposites for Si-based memories and optical devices. 

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2. Recent Advances in the Synthesis of Polymer-Grafted Low-K and High-K Nanoparticles for Dielectric and Electronic Applications

   https://doi.org/10.3390/molecules26102942  

   Tawade, Bhausaheb V.; Apata, Ikeoluwa E.; Pradhan, Nihar; Karim, Alamgir; Raghavan, Dharmaraj (May 2021, Molecules)

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   The synthesis of polymer-grafted nanoparticles (PGNPs) or hairy nanoparticles (HNPs) by tethering of polymer chains to the surface of nanoparticles is an important technique to obtain nanostructured hybrid materials that have been widely used in the formulation of advanced polymer nanocomposites. Ceramic-based polymer nanocomposites integrate key attributes of polymer and ceramic nanomaterial to improve the dielectric properties such as breakdown strength, energy density and dielectric loss. This review describes the ”grafting from” and ”grafting to” approaches commonly adopted to graft polymer chains on NPs pertaining to nano-dielectrics. The article also covers various surface initiated controlled radical polymerization techniques, along with templated approaches for grafting of polymer chains onto SiO2, TiO2, BaTiO3, and Al2O3 nanomaterials. As a look towards applications, an outlook on high-performance polymer nanocomposite capacitors for the design of high energy density pulsed power thin-film capacitors is also presented. 

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3. Mechanically controllable nonlinear dielectrics

   https://doi.org/10.1126/sciadv.aaz3180  

   Ko, D. L.; Tsai, M. F.; Chen, J. W.; Shao, P. W.; Tan, Y. Z.; Wang, J. J.; Ho, S. Z.; Lai, Y. H.; Chueh, Y. L.; Chen, Y. C.; et al (March 2020, Science Advances)

   Strain-sensitive Ba x Sr 1− x TiO 3 perovskite systems are widely used because of their superior nonlinear dielectric behaviors. In this research, new heterostructures including paraelectric Ba 0.5 Sr 0.5 TiO 3 (BSTO) and ferroelectric BaTiO 3 (BTO) materials were epitaxially fabricated on flexible muscovite substrate. Through simple bending, the application of mechanical force can regulate the dielectric constant of BSTO from −77 to 36% and the channel current of BTO-based ferroelectric field effect transistor by two orders. The detailed mechanism was studied through the exploration of phase transition and determination of band structure. In addition, the phase-field simulations were implemented to provide theoretical support. This research opens a new avenue for mechanically controllable components based on high-quality oxide heteroepitaxy. 

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4. Impact of PTFE particle size in designing BaTiO ₃ dielectric composites under the cold sintering process

   https://doi.org/10.35848/1347-4065/ace145  

   Nunokawa, Takashi; Takashima, Kenji; Mizuno, Kotaro; Randall, Clive A. (July 2023, Japanese Journal of Applied Physics)

   Abstract The Cold Sintering Process (CSP) can provide opportunities to fabricate high-performance BaTiO₃dielectric composites with polymer materials that are typically difficult to impossible to co-process under a conventional sintering process. Therefore, we investigated the preparation process of BaTiO₃sintered body by CSP and integrated a well-dispersed intergranular polymer phase. In this study, we focused on preparing BaTiO₃and Polytetrafluoroethylene (PTFE) composites. We considered the importance of the particle size of the PTFE phase, and correlated the impact on the composite dielectric properties. Through fitting a general-mixing-law to the dielectric properties as a function of volume fraction, we could deduce more homogeneous composites obtained in using the 200 nm PTFE powders. In addition, the temperature dependent dielectric properties and field dependent conductivity of the composites was investigated. It was found that with the good dispersion of the PTFE can suppress the leakage current density in the dielectric composites. 

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5. Negative-pressure enhanced ferroelectricity and piezoelectricity in lead-free BaTiO ₃ ferroelectric nanocomposite films

   https://doi.org/10.1039/d0tc01556c  

   Zhang, Xiyuan; Xu, Ruixing; Gao, Xingyao; Ji, Yanda; Qian, Fengjiao; Fan, Jiyu; Wang, Haiyan; Li, Weiwei; Yang, Hao (June 2020, Journal of Materials Chemistry C)

   null (Ed.)

   Due to environmental concerns and the increasing drive towards miniaturization of electronic circuits and devices, lead-free ferroelectric films with low leakage current and robust ferroelectric and piezoelectric properties are highly desired. The preferred alternative, BaTiO 3 , is non-toxic and has ferroelectric properties, but its high leakage current, poor ferroelectricity and piezoelectricity and low Curie temperature of ∼130 °C in thin film form are obstacles for high-temperature practical applications. Here, we report that a negative-pressure-driven enhancement of ferroelectric Curie temperature and effective piezoelectric coefficient are achieved in (111)-oriented BaTiO 3 nanocomposite films. The enhanced ferroelectric and piezoelectric properties in the emergent monoclinic BaTiO 3 are attributed to the sharp vertical interface and 3D tensile strain that develops upon interspersing stiff and self-assembled vertical Sm 2 O 3 nanopillars through the film thickness. Our work also demonstrates that fabricating oxide films through (111)-oriented epitaxy opens up new avenues for the creation of new phase components and exploration of novel functionalities for developing oxide quantum electronic devices. 

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