• ARUN M UMARJI

Articles written in Bulletin of Materials Science

• Synthesis, structure and thermoelectric properties of La$_{1−x}$Na$_x$CoO$_3$ perovskite oxides

Monovalent ion doped lanthanum cobaltate La$_{1−x}$Na$_x$CoO$_3$ ($0 \leq x \leq 0.25$) compositions were synthesized by the nitrate–citrate gel combustion method. All the heat treatments were limited to below 1123 K, in order to retain the Na stoichiometry. Structural parameters for all the compounds were confirmed by the Rietveld refinement method usingpowder X-ray diffraction (XRD) data and exhibit the rhombhohedral crystal structure with space group R-3c (No. 167). Thescanning electron microscopy study reveals that the particles are spherical in shape and sizes, in the range of 0.2–0.5 $\mu$m.High temperature electrical resistivity, Seebeck coefficient and thermal conductivity measurements were performed on thehigh density hot pressed pellets in the temperature range of 300–800 K, which exhibit p-type conductivity of pristine anddoped compositions. The X-ray photoelectron spectroscopy (XPS) studies confirm the monotonous increase in Co$^{4+}$ withdoping concentration up to $x = 0.15$, which is correlated with the electrical resistivity and Seebeck coefficient values of thesamples. The highest power factor of 10 $\mu$WmK$^{−2}$ is achieved for 10 at% Na content at 600 K. Thermoelectric figure ofmerit is estimated to be $\sim$$1 \times 10^{−2}$ at 780 K for 15 at% Na-doped samples.

• Dependence of oxygen desorption kinetics on processing methods of SrCoO$_{2.5}$

The effect of processing methods on oxygen storage and exchange kinetics of brownmillerite (BM) SrCoO$_{2.5}$ is compared in terms of their reversible oxygen incorporation and desorption kinetics. BM SrCoO$_{2.5}$ was synthesized through two different methods; solid-state synthesis and the nitrate–citrate gel method, both followed by Al foil pad quenching. Oxygen storage characteristics of synthesized samples were analysed using a home-built volumetric set-up. The maximum oxygenation achievable for BM SrCoO$_{2.5}$ under prevailing conditions of O$_2$ partial pressure (16 bar O$_2$), temperature (673 K) and time (1 h) was unaltered, regardless of the synthesis method. Oxygen exchange kinetics of desorption was faster in the nitrate–citrate synthesized sample than in the solid-state synthesized sample. The kinetics of desorption correlated with the crystallite and particle sizes of the samples. The mechanism of desorption follows nucleation and growth model for nitrate–citrate synthesized sample, while it follows contracting sphere model for solidstate synthesized sample.

• Bulletin of Materials Science

Volume 45, 2022
All articles
Continuous Article Publishing mode

• Dr Shanti Swarup Bhatnagar for Science and Technology

Posted on October 12, 2020

Prof. Subi Jacob George — Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bengaluru
Chemical Sciences 2020

Prof. Surajit Dhara — School of Physics, University of Hyderabad, Hyderabad
Physical Sciences 2020

• Editorial Note on Continuous Article Publication

Posted on July 25, 2019

Click here for Editorial Note on CAP Mode

© 2021-2022 Indian Academy of Sciences, Bengaluru.