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Sahu, Manisha,Hajra, Sugato,Choudhary, Ram Naresh Prasad Materials Research Society of Korea 2019 한국재료학회지 Vol.29 No.8
A lead-free bulk ceramic having a chemical formula $Ba_{0.8}Ca_{0.2}(Ti_{0.8}Zr_{0.1}Ce_{0.1})O_3$ (further termed as BCTZCO) is synthesized using mixed oxide route. The structural, dielectric, impedance, and conductivity properties, as well as the modulus of the synthesized sample are discussed in the present work. Analysis of X-ray diffraction data obtained at room temperature reveals the existence of some impurity phases. The natural surface morphology shows close packing of grains with few voids. Attempts have been made to study the (a) effect of microstructures containing grains, grain boundaries, and electrodes on impedance and capacitive characteristics, (b) relationship between properties and crystal structure, and (c) nature of the relaxation mechanism of the prepared samples. The relationship between the structure and physical properties is established. The frequency and temperature dependence of the dielectric properties reveal that this complex system has a high dielectric constant and low tangent loss. An analysis of impedance and related parameters illuminates the contributions of grains. The activation energy is determined for only the high temperature region in the temperature dependent AC conductivity graph. Deviation from the Debye behavior is seen in the Nyquist plot at different temperatures. The relaxation mechanism and the electrical transport properties in the sample are investigated with the help of various spectroscopic (i.e., dielectric, modulus, and impedance) techniques. This lead free sample will serve as a base for device engineering.
Sahu, Manisha,Panigrahi, Basanta Kumar,Kim, Hoe Joon,Deepti, PL,Hajra, Sugato,Mohanta, Kalyani Materials Research Society of Korea 2020 한국재료학회지 Vol.30 No.10
The various sintered samples comprising of 72 wt% (Al<sub>2</sub>O<sub>3</sub>) : 28 wt% (SiO<sub>2</sub>) based ceramics were fabricated using a colloidal processing route. The phase analysis of the ceramics was performed using an X-ray diffractometer (XRD) at room temperature confirming the presence of Al<sub>2</sub>O<sub>5</sub>Si and Al<sub>5.33</sub>Si<sub>0.67</sub>O<sub>9.33</sub>. The surface morphology of the fracture surface of the different sintered samples having different sizes of grain distribution. The resistive and capacitive properties of the three different sintered samples at frequency sweep (1 kHz to 1 MHz). The contribution of grain and the non-Debye relaxation process is seen for various sintered samples in the Nyquist plot. The ferroelectric loop of the various sintered sample shows a slim shape giving rise to low remnant polarization. The excitation performance of the sample at a constant electric signal has been examined utilizing a designed electrical circuit. The above result suggests that the prepared lead-free ceramic can act as a base for designing of dielectric capacitors or resonators.
Kyungtaek Lee,Sugato Hajra,Manisha Sahu,Yogendra Kumar Mishra,김회준 한국공업화학회 2022 Journal of Industrial and Engineering Chemistry Vol.106 No.-
The development of gas sensors with high sensitivity, stability, and selectivity is vital in detecting hazardousgas leaks and monitoring air pollution. The perovskite comprises a stable chemical structureand offers multifunctional properties to act as a base for several device engineering. Specifically, perovskitespossess a great potential for chemical sensors with their semiconducting nature and ease to dopewith other elements to further improve gas sensing properties. In this present study, a rare-earth gadoliniumorthoferrite, GdFeO3 (GFO), and Co-doped GFO were systematically investigated by evaluating theirstructural, morphological, electrical, and gas sensing properties. A high-temperature solid-state reactionsynthesized the phase-pure compounds. The magnetic properties of Co-doped GFO significantlyimproved than pure GFO. The pellet-type gas sensor was fabricated, which does not need any sophisticatedinstrumentation such as microfabrication. When exposed to 20 ppm of NO2 gas, a GdFe0.7Co0.3O3(GFOC3) device gave 6.86% response at 200C, along with a response time of 104 s and the recovery timeof 97 s. Additionally, Co-doped GFO sensors showed a detectable response even at room temperature,enabling- practical applications in an ambient environment. The gas sensor revealed stable gas responsecharacteristics even after several months. Therefore, this study elucidates that the Co-doped GFO has bettergas sensing performance compared to a bare GFO and that it is highly selective towards the NO2 gas.