• ROBBI VIVEK VARDHAN

      Articles written in Bulletin of Materials Science

    • Effect of annealing-temperature-assisted phase evolution on conductivity of solution combustion processed calcium vanadium oxide films

      G MANJUNATH ROBBI VIVEK VARDHAN ASHRITHA SALIAN RASHI JAGANNATHA MAYANK KEDIA SAUMEN MANDAL

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      In thiswork, the effect of annealing temperature on the conductivity of solution-combustion-synthesized calcium vanadium oxide (CVO) films was studied. Conductivity was tailored by the appearance of the phases like CaVO$_3$, CaV$_2$O$_5$ and Ca$_2$V$_2$O$_7$ as a function of annealing temperature; CaVO$_3$ and CaV$_2$O$_5$ are responsible for high conductivity, whereas V$^{5+}$ presence in Ca$_2$V$_2$O$_7$ contributes towards dielectric nature. Evolution of phases of CVO was identified through X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. A detailed conductivity measurement as a function of annealing temperature helps us to identify the decreasing trend of conductivity with increasing temperature up to 400$^{\circ}$C; beyond this it behaves like an insulator. There was a stable conductivity while aging the films in ambient for a few days. This study revealed safe application temperature domain of CVO, and a clear correlation of electrical conductivity with the in-depth structural–compositional–morphological study.

    • A facile, low temperature spray pyrolysed tungsten oxide (WO$_3$): an approach to antifouling coating by amalgamating scratch resistant and water repellent properties

      ROBBI VIVEK VARDHAN SUBODH KUMAR SAUMEN MANDAL

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      In this study, a facile spray pyrolysed hydrophobic robust tungsten oxide (WO$_3$) films were deposited at an annealing temperature of 400$^{\circ}$C on inexpensive glass substrates, using clear and homogeneous precursor solution containing tungsten hexachloride and 2-methoxyethanol. The 10 and 15 times sprayed films were polycrystalline with the monoclinic crystal structure, uniform with the submicron-sized grain morphology (size $\sim$320–420 nm), with an average surface roughness ranging from 12 to 17 nm and transparent above 60% in the visible region with a thickness of 380 and 550 nm, respectively. Elemental existence of tungsten and oxygen was recognized on the surface of the films possessing the highest lattice oxygen percentage of 91.1. Increment in the scratch hardness of the films with the number of sprays compared to uncoated glass was identified. The films were hydrophilic in nature (water contact angle <8$^{\circ}$), converted to hydrophobic (>120$^{\circ}$) by treating chemically with octadecyltrichlorosilane to form a self-assembled monolayer on the top and the hydrophobicity remained same ($\sim$120$^{\circ}$) even after a year. These films with unique and combined properties of scratch hardness and hydrophobicity can serve in the potential application as antifouling coatings.

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