@article{jia_chowdhury_xu_2020, title={Complex impedance spectra of polymer-derived SiC annealed at ultrahigh temperature}, volume={103}, ISSN={["1551-2916"]}, DOI={10.1111/jace.17395}, abstractNote={This study reports the complex impedance and alternative current conductivity of polymer-derived ceramic SiC (PDC-SiC) annealed at ultrahigh temperatures. The PDC-SiC shows an inductive response when annealed at temperatures of 1700°C-1900°C due to the percolation of turbostratic carbon. The material returns to a capacitive response at an annealing temperature of 2000°C due to the dissolution of carbon into the SiC lattice. The electrical resistance of the carbon phase decreases with the increase in annealing temperature. These results provide new insights into the effects of processing temperature on microstructure evolution and electrical and dielectric property development of the PDC-SiC ceramic system.}, number={12}, journal={JOURNAL OF THE AMERICAN CERAMIC SOCIETY}, author={Jia, Yujun and Chowdhury, Md Atiqur Rahman and Xu, Chengying}, year={2020}, month={Dec}, pages={6860–6868} }
 @article{chowdhury_wang_jia_xu_2020, title={Electrical Conductivity and Structural Evolution of Polymer Derived SiC Ceramics Pyrolyzed From 1200°C to 1800°C}, volume={8}, ISSN={2166-0468 2166-0476}, url={http://dx.doi.org/10.1115/1.4046191}, DOI={10.1115/1.4046191}, abstractNote={Abstract Room temperature (RT) electrical conductivity and microstructure of polymer-derived SiC pyrolyzed at temperatures ranging from 1200 °C to 1800 °C were studied. We have shown that both free carbon content and pyrolysis temperature have significant effects on the DC conductivity of polymer derived ceramic (PDC) SiC. The RT DC conductivity of the PDC SiC increased gradually with increasing pyrolysis temperature, and it drastically increases 3 orders of magnitude after 1500 °C. This high electrical conductivity occurs due to the formation of a network of turbostratic carbon (percolative network). Below the percolation regime, hopping enables the electron movement from one carbon cluster site to another. Microstructural investigation with X-ray diffraction (XRD), Raman, and transmission electron microscopy (TEM) analysis showed that the crystal size of SiC increases with increasing pyrolysis temperature, and carbon clusters act as an inhibitor for grain growth at lower pyrolysis temperature. Upon dissociation of clusters, accelerated grain growth occurs and graphitization of carbon occurs along the grains.}, number={2}, journal={Journal of Micro and Nano-Manufacturing}, publisher={ASME International}, author={Chowdhury, Md Atiqur and Wang, Kewei and Jia, Yujun and Xu, Chengying}, year={2020}, month={Feb} }
 @article{chowdhury_wang_jia_xu_2020, title={Semiconductor-conductor transition of pristine polymer-derived ceramics SiC pyrolyzed at temperature range from 1200 degrees C to 1800 degrees C}, volume={103}, ISSN={["1551-2916"]}, DOI={10.1111/jace.16961}, abstractNote={This paper studies the effect of pyrolysis temperature on the semiconductor-conductor transition of pristine polymer-derived ceramic silicon carbide (PDC SiC). A comprehensive study of microstructural evolution and conduction mechanism of PDC SiC pyrolyzed at the temperature range of 1200°C-1800°C is presented. At relatively lower pyrolysis temperatures (1200°C-1600°C), the carbon phase goes through a microstructural evolution from amorphous carbon to nanocrystalline carbon. The PDC SiC samples behave as a semiconductor and the electron transport is governed by the band tail hopping (BTH) mechanism in low pyrolysis temperature (1300°C); by a mixed mechanism driven by band tail hopping and tunneling at intermediate temperature (1500°C). At higher pyrolysis temperatures (1700°C-1800°C), a percolative network of continuous turbostratic carbon is formed up along the grain boundary of the crystallized SiC. The samples demonstrate metal-like conductive response and their resistivity increases monotonically with the increasing measuring temperature.}, number={4}, journal={JOURNAL OF THE AMERICAN CERAMIC SOCIETY}, author={Chowdhury, Md Atiqur Rahman and Wang, Kewei and Jia, Yujun and Xu, Chengying}, year={2020}, month={Apr}, pages={2630–2642} }
 @article{jia_chowdhury_zhang_xu_2019, title={Wide-Band Tunable Microwave-Absorbing Ceramic Composites Made of Polymer-Derived SiOC Ceramic and in Situ Partially Surface-Oxidized Ultra-High-Temperature Ceramics}, volume={11}, ISSN={["1944-8252"]}, DOI={10.1021/acsami.9b16475}, abstractNote={Microwave-absorbing materials in a high-temperature harsh environment are highly desired for electronics and aerospace applications. This study reports a novel high-temperature microwave-absorbing ceramic composites made of polymer-derived SiOC ceramic and in situ partially surface-oxidized ultra-high-temperature ceramic (UHTC) ZrB2 nanoparticles. The fabricated composites with a normalized weight fraction of ZrB2 nanoparticles at 40% has a significantly wide microwave absorption bandwidth of 13.5 GHz (26.5-40 GHz) covering the entire Ka-band. This is attributed to the extensive nanointerfaces introduced in the composites, attenuation induced by the interference of electromagnetic wave, attenuation from the formed current loops, and the electronic conduction loss provided by the partially surface-oxidized ZrB2 nanoparticles. The minimum reflection coefficient (RC) was -29.30 dB at 29.47 GHz for a thickness of 1.26 mm for the composites with a normalized weight fraction of ZrB2 nanoparticles at 32.5%. The direct current (dc) conductivity of the nanocomposites showed a clear percolation phenomenon as the normalized weight fraction of ZrB2 nanoparticles increases to 30.49%. The results provide new insights in designing microwave-absorbing materials with a wide absorption frequency range and strong absorption loss for high-temperature harsh environment applications.}, number={49}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Jia, Yujun and Chowdhury, Md Atiqur Rahman and Zhang, Dajie and Xu, Chengying}, year={2019}, month={Dec}, pages={45862–45874} }