Synthesis & Characterization of Sr0.53Ba0.47Nb2O6 based Ferroelectric Composites for Pyroelectric Applications

Abstract

Currently much research is focused on functional materials due to their wide range of applications. Especially developing materials with good pyroelectric figure of merits is essential for usage in military vigilance, medical diagnostic and industrial quality control applications. Among ferroelectrics, lead based materials are most researched and exploited materials due to their excellent pyroelectric properties in comparison with the lead free materials. Pb0.76Ca0.24TiO3 (PCT) and Pb0.85La0.15TiO3 (PLT) systems having perovskite structure exhibit good ferroelectric and pyroelectric properties with transition temperatures ~300 and ~283 ˚C, respectively. However, due to toxicity of lead, presently research is focussed on developing lead free/low lead content materials. Sr0.53Ba0.47Nb2O6 (SBN) having tetragonal tungsten bronze structure (TTB) exhibits good pyroelectric properties among lead free materials. However, SBN system has disadvantage of low transition temperature (~115oC). Also, the pyroelectric detectors with SBN system can only be operated from -25 to 30˚C temperature range.
It is well known that composites combine the properties of the constituent phases resulting in a material with different properties. In order to tailor the properties of the materials, composites of ferroelectric materials with different structures have been synthesized and reported to show better electrical properties compared to both the constituent materials. In this work, composites (less amounts of lead, weight % < 15%) of SBN and PCT/ PLT ferroelectric materials are prepared by solid state reaction route. These composites are sintered at three different temperatures i.e. 1200, 1250 and 1300˚C. XRD studies revealed the existence of both the phases in the ceramic composites. Ceramic-composites with theoretical density (ρTh) > 90% were obtained. Surface morphology studies revealed inhomogeneity in grain size distribution in the ceramic-composites. The values of dielectric constant (εr) of SBN+xPCTand SBN+xPLT ceramic-composites were found to be lower and higher than that of pure SBN ceramics, respectively. The P-E loops of SBN+xPLT ceramic composites were found to be slimmer in comparison with the P-E loops of SBN+xPCT ceramic composites. The ceramic composites were found to show better pyroelectric properties compared to pure SBN ceramics at RT and at higher temperatures (up to 70 ˚C). SBN+0.1PLT ceramic composite sintered at 1250 ˚C is found to exhibit better pyroelectric properties compared to pure SBN ceramic system.
It is well known that due to fragile nature of ceramics, ceramic-composites cannot be used in applications where large area/flexible detector materials are required. Polymers have the advantage of flexibility and can be drawn as thin wafers. Polyvinylidene fluoride (PVDF) is a ferroelectric polymer with good pyroelectric properties. However, the pyroelectric properties are low in comparison with SBN ceramics. In order to enhance the pyroelectric properties of PVDF by preserving its flexural property, composites of PVDF and SBN[ (1-φ)PVDF+φSBN, φ=10, 20, 30 vol%] were prepared by hot uniaxial press. Structural, dielectric and pyroelectric properties of these (1-φ)PVDF+φSBN composites have been investigated. Enhanced pyroelectric properties compared to pure PVDF were obtained in 0.7PVDF+0.3SBN composites.