• SATISH VITTA

Articles written in Bulletin of Materials Science

• Foreword

• 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.

• Thermo-transport properties of Zn-substituted layered Li-nickel oxide, LiNiO$_2$

The layered Li-TM-O$_2$ materials have been investigated extensively due to their application as cathodes in Li batteries. The electrical properties of these oxides can be tuned or controlled either by non-stoichiometry or substitution.Hence the thermo-transport properties of Zn-substituted LiNi$_{1−x}$Zn$_x$O$_2$ for $0 \leq x \leq 0.16$ have been investigated in thetemperature range of 300–900 K for potential application as a high-temperature thermoelectric material. For $x$ < 0.08, the compounds were of single phase belonging to the space group R-3mH while for $x$ > 0.08 an additional minority phase, ZnO forms together with the main layered phase.All the compounds exhibit a semiconducting behaviour with electrical resistivity,varying in the range of $\sim$10$^{−4}$ to 10$^{−2}$ $\Omega$m between 300 and 900 K. The electrical resistivity is found to increase with increasing Zn-substitution predominantly due to a decrease in the charge carrier hole mobility. The activation energy remains constant, $\sim$10 meV, with Zn-substitution. The Seebeck coefficient of the compounds is found to decrease with increasingtemperature and increase with increasing Zn-substitution. The Seebeck coefficient decreases from $\sim$95 to 35 $\mu$μV K$^{−1}$ and the corresponding power factor is $\sim$12 $\mu$Wm$^{−1}$ K$^{−2}$ for the $x = 0.16$ compound.

• # 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