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Your search keyword '"Parasuraman, Rajasekar"' showing total 21 results
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21 results on '"Parasuraman, Rajasekar"'

1. Predicting the Realizable Maximum Power Factor using the Jonker and Ioffe formulation: Al-doped ZnO Triangular Microcrystals with Graphite Inclusion Case Study

Author

Biswas, Soumya, Dabral, Keshav, Majumder, Saptak, Parasuraman, Rajasekar, Dutt, Aditya S., and Kamble, Vinayak B.

Subjects
Condensed Matter - Materials Science
Abstract

Among the popular TE materials, selenides and tellurides are the benchmarks of high-efficiency systems. However, for the high-temperature application (>700 K), it is required to rely on the silicides and the oxides due to their exceptional thermal stability. ZnO is among the first few oxides in the field of thermoelectricity. Al-doped ZnO is a proven material for its high-temperature thermoelectric applications. However, the high grain boundary resistance limits further improvement of the efficiency of this oxide. Band-engineering, band-modification is a successful approach in lowering the grain boundary resistance. The addition of graphite and graphite-based materials at the grain boundaries is shown to serve this purpose. In this work, graphite powder is added in varying proportions to Al-doped ZnO triangular microcrystals. Thus, prepared materials are characterized to confirm the formation and investigate the nature of interface, morphology, etc. TE parameters such as electrical conductivity, Seebeck coefficient, and thermal conductivity of those materials also have been measured. The theoretical calculation of TE efficiency zT often differs from the actual experimental results due to the wide range of preparation methods, leading to changes in porosity, the nature and density defects, and several other factors. In this paper, an effort has been made to estimate the maximum achievable power factor (PFmax) from the measured TE parameters of this set of samples by the Jonker and Ioffe analysis. Based on the predicted PFmax, an appropriate material composition has been identified to achieve that same. Subsequently, including the measured parameters the TE efficiency (zT) is calculated. Further, a sudden dip observed in the thermal conductivity at the high-temperature range (625 K - 1000 K) of the prepared undoped ZnO graphite composite is investigated in this paper.

Published
2024

8. High thermoelectric performance in p-type ZnSb upon increasing Zn vacancies: an experimental and theoretical study.

Author

Palraj, Jothilal, Sajjad, Muhammad, Moorthy, Manojkumar, Saminathan, Madhuvathani, Srinivasan, Bhuvanesh, Singh, Nirpendra, Parasuraman, Rajasekar, Patole, Shashikant P., Mangalampalli, Kiran, and Perumal, Suresh

Abstract

The high thermoelectric performance of dopant-free, low-cost and eco-friendly p-type Zn1−xSb (x = 0, 0.01, 0.03, and 0.06) is demonstrated by synergistically optimizing its electrical and thermal properties via Zn-vacancy engineering. Upon increasing Zn-vacancies in ZnSb, the bandgap is observed to reduce due to the formation of the impurity states above the valence band, which is theoretically validated using density functional theory (DFT). Remarkably, Zn vacancy-driven point defects significantly influence the hole concentration within the Zn1−xSb samples. At 300 K, the hole concentration (nH) is boosted from 3.6 × 1018 cm−3 (in ZnSb) to 3.4 × 1019 cm−3 for the Zn0.94Sb sample, culminating in a marked enhancement in electrical conductivity (σ) from 1.80 × 104 S m−1 to 7.57 × 104 S m−1 for Zn0.94Sb. Equally noteworthy is the substantial decrease in thermal conductivity (κ) observed in the Zn0.94Sb sample at 673 K, plunging from 2.29 W m−1 K−1 (in ZnSb) to 1.41 W m−1 K−1. This decline in thermal conductivity is attributed to the effective phonon scattering arising from Zn-vacancy-assisted point defects, combined with the efficient coupling of optical and acoustic phonons and the characteristic low group velocity, evidenced by the theoretically calculated phonon dispersion curve. Overall, the high thermoelectric figure of merit, zT of ∼0.8 at 673 K, is achieved for the sample with a 6 mol% Zn deficiency. Furthermore, a maximum theoretical conversion efficiency of ∼7% is predicted at a temperature gradient of 625 K, showing high potential for use in practical devices for mid-temperature applications, and the present work features the effect of a reliable dopant-free approach in improving the overall zT of eco-friendly and low-cost ZnSb. [ABSTRACT FROM AUTHOR]

Published
2024
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19. Room temperature synthesis of transition metal silicide-conducting polymer micro-composites for thermoelectric applications

Author

Ail, Ujwala, Ullah Khan, Zia, Granberg, Hjalmar, Berthold, Fredrik, Parasuraman, Rajasekar, Urnarji, Arun M., Slettengren, Kerstin, Pettersson, Henrik, Crispin, Xavier, Ail, Ujwala, Ullah Khan, Zia, Granberg, Hjalmar, Berthold, Fredrik, Parasuraman, Rajasekar, Urnarji, Arun M., Slettengren, Kerstin, Pettersson, Henrik, and Crispin, Xavier

Abstract

Organic polymer thermoelectrics (TE) as well as transition metal (TM) silicides are two thermoelectric class of materials of interest because they are composed of atomic elements of high abundatice; which is a prerequisite for mass implementation of thermoelectric (TE) solutions for solar and waste heat recovery. But both materials have drawbacks when it comes to finding low-cost manufacturing. The metal silicide needs high temperature (amp;gt;1000 degrees C) for creating TE legs in a device from solid powder, but it is easy to achieve long TE legs in this case. On the contrary, organic TEs are synthesized at low temperature from solution. However, it is difficult to form long legs or thick films because of their low solubility. In this work, we propose a novel method for the room temperature synthesis of TE composite containing the microparticles of chromium disilicide; CrSi2 (inorganic filler) in an organic matrix of nanofibrillated cellulose-poly(3,4-ethyelenedioxythiophene)-polystyrene sulfonate (NFC-PEDOT:PSS). With this method, it is easy to create long TE legs in a room temperature process. The originality of the approach is the use of conducting polymer aerogel microparticles mixed with CrSi2 microparticles to obtain a composite solid at room temperature under pressure. We foresee that the method can be scaled up to fabricate and pattern TE modules. The composite has an electrical conductivity (sigma) of 5.4 +/- 0.5 S/cm and the Seebeck coefficient (a) of 88 +/- 9 mu V/K, power factor (alpha(2)sigma) of 4 +/- 1 mu Wm(-1) K-2 at room temperature. At a temperature difference of 32 degrees C, the output power/unit area drawn across the load, with the resistance same as the internal resistance of the device is 0.6 +/- 0.1 mu W/cm(2). (C) 2017 Elsevier B.V. All rights reserved., Funding Agencies|European Research Council [307596]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009 00971]; "the Power Papers project" - Knut and Alice Wallenberg foundation; RISE - the Research Institutes of Sweden; University Grants Commission, India

Published
2017
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21. Stabilization of Brownmillerite-Type SrCoO2.5by a Cost-Effective Quenching Method for Oxygen-Scavenging Applications

Author

Narayanan, Aswathy M., Parasuraman, Rajasekar, and Umarji, Arun M.

Abstract

Brownmillerite (BM)-type oxide sorbents have gained attention recently for producing oxygen-enriched streams. Herein, a cost-effective method of quenching with the use of an Al foil pad is adapted for the synthesis of brownmillerite SrCoO2.5. The oxygen storage capacity of this oxide has been investigated using a simple home-built volumetric setup. The oxygen-rich phase was formed by a pressurized heat-treatment of a BM sample. The oxygen storage capacity of the sample has been calculated from the pressure change during desorption. The effect of oxygen pressure on the amount of oxygen stored inside the sample has also been evaluated. Furthermore, selective absorption of oxygen is confirmed by performing the absorption in compressed air. The results indicate that 15.28 cm3O2g–1can be stored in the sample at STP. The change in oxygen content in SrCoO2.5+δvaried reversibly up to a δ value of 0.26, which is confirmed by iodometric titration. It is shown that the new method of quenching proposed does not deteriorate the oxygen storage property of the material.

Published
2018
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