Bismuth titanate nanoparticles dispersed polyacrylates
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Ming-Yao Chen Department of Physics, National Taiwan University, Taipei, Taiwan
Ron-Ming Ho Department of Chemical Engineering, National Tsing Hua Univeristy, Hsinchu, Taiwan (Received 25 February 2004; accepted 26 April 2004)
We successfully dispersed amorphous bismuth titanate nanoparticles (1.6) and good optical transparency (>90% transmittance from 530 to 800 nm). Furthermore, this highly cross-linked material has an improved thermal stability and a lower coefficient of thermal expansion than that of neat polymers. The material also displays a high dielectric constant (>10) without ferroelectricity. Thus the material has potential applications in optical lenses, optical waveguides, and capacitors.
I. INTRODUCTION
Dielectric materials are useful in optical applications and device components such as filters, transmitters, reflectors, lenses, and optical waveguides. They are also utilized widely in electronic devices such as capacitors, actuators, etc. These materials are usually characterized by their refractive indices and dielectric constants. Dielectric materials with high values of refractive indices and dielectric constants can markedly reduce the size of devices, which is highly desirable in integrated circuits, optical systems, electronic systems, and electro-optical systems. Although polymeric organic materials with good tensile strength and impact resistance can be processed easily at low cost, such materials tend to have low refractive indices and dielectric constants. Correspondingly, though many inorganic materials exhibit both high refractive indices and dielectric constants, they remain difficult to process and are heavy, brittle, and expensive.1 Thus, organic/inorganic hybrids have recently emerged as a new class of materials by taking advantage of each species’ merits.2–5 Currently though, the study of high refractive index and high dielectric constant hybrid materials is limited in the literature. Bismuth titanate ceramics have been studied widely due to their electro-optical properties, piezoelectricity, ferroelectricity, ionic conductivity, and low sintering
a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2004.0312 J. Mater. Res., Vol. 19, No. 8, Aug 2004
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temperature. Such ceramics are useful in applications such as actuators, capacitors,6 nonvolatile memory devices,7 microwave filters,8 etc. Polyacrylates exhibit high degrees of optical transparency and are good polar dielectrics. Therefore, we expected bismuth titanate nanoparticle dispersed polyacrylate hybrids to have high refractive indices and high dielectric constants. Here, we used a sol-gel process to synthesize the hybrids at molecular levels and studied their optical and electrical properties.
II. EXPERIMENTAL A. Synthesis of polymerizable bismuth titanium 2-methacryl ethoxide
The synthetic procedures of bismuth titanium 2methacryl ethoxide are modified from our previous reported procedures9 and described as follows. 1. Sodium meth
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