A simple synthesis of long nanostructured arrays of crystalline strontium titanates at low-temperatures
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Long aligned arrays of crystalline strontium titanate (SrTiO3) nanostructures were synthesized by using simple low-temperature processes that incorporate strontium into titanium oxides. Tubular nanostructures are often confine energy carriers that result in extraordinary transport behaviors in various semiconductors including strontium titanates, which are promising for developing efficient thermoelectric energy conversion materials. However, synthesizing a micron-to-milimeter scale array of one-dimensional ternary nanostructures has been difficult. Moreover, ternary compounds are often obtained as disordered cubic-shape particles at the end of complicated and/or long reactions. In this study, a two-step process—anodization for preparing amorphous titanium oxides and a subsequent thermal annealing process in a mixture of strontium hydroxide, ammonia, and water—was employed. Typical diameter and length of the tubes are ~150 nm and ~160 μm, respectively. It has been found that the amorphous structure of titanium oxides plays an important role in obtaining high-purity long strontium titanate nanotubes at low temperatures (90 and 180 °C) with short reaction times. Comparative and systematic studies with different sample pre-treatments, etching times, temperatures, reaction times, and strontium concentrations revealed reaction mechanisms and key synthesis parameters, which may be utilized to obtain other ternary or quaternary nanostructured compounds such as barium or lead titanates.
KeywordsStrontium Barrier Layer Seebeck Coefficient Strontium Titanate SrF2
This study was supported by the Thermal Transport Processes and the Solid State and Materials Chemistry Programs in the US National Science Foundation (Award No. 0854467), and the Pioneer Research Center Program through the National Research Foundation of Korea (Grant No. 2010-0002231) funded by the Ministry of Education, Science and Technology (MEST). The authors thank Yang for his assistance in acquiring XRD data.
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