Nimai Chand Pramanik

Effects of tin on IR reflectivity, thermal emissivity, Hall mobility and plasma wavelength of sol-gel indium tin oxide films on glass

Sol–gel indium tin oxide films (ITO) of various composition (In:Sn atomic ratio=90:10 to 30:70) prepared from salt-based precursors were deposited on bare and SiO2 coated (∼200 nm thickness) sheet glass substrates. The films were cured in air and then annealed under N2/H2O at ∼500 °C to obtain ITO films of thickness 250–320 nm. Directional hemispherical reflectance (Rh) and trasmittance (Th) of the films were measured in the wavelength range 0.25–18 μm. The reflectance of the films at 10 μm (near the peak wavelength of black body radiation) was in the range 0.18–0.55. The thermal emissivity (ed) was evaluated from the relation: ed=1−Rh−Th (Th≈0, for sheet glass in the wavelength range 5–18 μm) and it was in the range 0.47–0.90. Reflectance (Rh) was also evaluated from measured sheet resistance values (R□), from the relation Rh=(1+2e0c0R□)−2, where e0 and c0 are the permittivity of electron in vacuum and velocity of light, respectively. Specific resistivity of the films, measured by van-der Pauw method at ambient temperature was in the range 1.7±0.3×10−3 to 6.6±1.2×10−3 Ω cm. The sheet resistance (R□) of the films was in the range 68–212 Ω/□. Free electron carrier concentration (N) and Hall mobility (μ) of the films were in the ranges (0.66±0.18)×1020 to (3.7±1.0)×1020 cm−3 and (4.4±1.5) to (20±5) cm2/V s, respectively. These values were utilized to evaluate plasma wavelength (λP) of the conducting films which were in the range 1.72±0.24–4.07±0.58 μm. Considerable variations of the above properties were observed with increasing Sn content but minimum thermal emissivity and maximum IR reflectivity were observed in the case of In:Sn=70:30.

The effect of Sn(IV) on transformation of co-precipitated hydrated In(III) and Sn(IV) hydroxides to indium tin oxide (ITO) powder

Multicomponent metal oxide (indium tin oxide, ITO) powders were prepared by the hydrolysis of their corresponding metal salts following co-precipitation technique. Indium tin oxide powders with relatively high content of tin were prepared by the treatment of aqueous NH4OH with the mixture of aqueous In(NO3)3 and SnCl4 solution (pH=8.4–8.7) at an ambient temperature. The composition of the powders were 90:10, 70:30 and 50:50 (In/Sn atomic ratio). The air-dried powders were cured at different temperatures and also at different atmospheric conditions [air and H2(5%)–Ar(95%)]. They were characterized by FTIR spectroscopy, thermal analysis and X-ray powder diffraction studies. FTIR spectroscopy and thermal analysis of powders revealed that the air-dried powders existed as hydroxides of In3+ and Sn4+ in the solid state which transformed to ITO via some metastable intermediates after 300 °C. In addition, the formation of InOIn and SnOSn type of bonding was also predicted by FTIR. Below 200 °C, the powders predominantly existed as corresponding hydrated oxide phases which corresponded to possible formulations, In(OH)3 and SnO3H2 and transformed to ITO phases after 300 °C. The powders containing below 30% Sn showed pure cubic In2O3 phase whereas the casseterite structure of SnO2 phase was observed in the case of relatively high Sn content (Sn>30%). The crystallite size of the powders increased with temperature as well as with increase in Sn content.

Optical and electrochromic properties of sol-gel WO3 films on conducting glass

Abstract The precursor containing peroxotungstic acid (PTA) was prepared by the reaction of tungstic acid with H 2 O 2 (30%) solution in water–ethanol mixture. This was utilized for the deposition of WO 3 · n H 2 O film on conducting (F-doped SnO 2 coated) flat glass substrate by the dipping technique. The films were cured in the temperature range of 200–300 °C in air. The optimum thickness of the film (300–500 nm) was obtained by successive operations (3–5 numbers). Films of around 500 nm thickness exhibited 60–70% transmission in the visible region. Electrochromic properties (colouration↔bleaching) of the films were studied by cyclic voltammetry (CV) using a classical three-electrode potentiostatic cell system. The cell system consists of a WO 3 -coated sample as working electrode, a platinum rod as counter electrode, Ag/AgCl as reference electrode and 0.5 M LiClO 4 in propylene carbonate as an electrolyte. Several voltammograms were recorded within the voltage range of +1.5 to −1.8 V with a scan rate of 50 mV/s. A continuous curve was observed for the films at a certain voltage sweep where a random insertion of Li + occurred reversibly in a definite crystallographic site [WO 3 (colourless)+ n Li + + n e − ↔ Li n WO 3 (blue)]. A dark blue colouration (% T =20–30% in the visible region) was observed under a constant voltage of −1.8 V whereas bleaching occurred at +1.0 V (% T =60–70%), which was studied simultaneously along with the voltage sweep of CV. The colouration time ( T col ) and the bleaching time ( T bl ) were almost equal as revealed by the simultaneous study of the second signal (photomultiplier output coupled with the electrochemistry system) during colouration↔bleaching. Coatings of about 500 nm thickness exhibited more that 500 cycles (colouration↔bleaching). The reversibility of the cycle remained good but the intensity of the colouration decreased with the number of cycles. This was possibly due to the structural deformation of WO 3 films for its long time exposure to the electrolytic solution. The cathodic current ( I c ) and anodic current ( I a ) increased with increasing thickness.

Development of nano indium tin oxide (ITO) grains by alkaline hydrolysis of In(III) and Sn(IV) salts

Indium tin oxide (ITO) nano powders of different compositions (In: Sn = 90: 10, 70: 30 and 50: 50) were prepared by heat treatment (300-450°C) of mixed hydroxides of In(III) and Sn(IV). The hydroxides were obtained by the reaction of aq. NH3 with mixed aq. solutions of In(NO3)3 and SnCl4. FTIR and TG/DTA studies revealed that powders existed as In(OH)3H2O—SnO3H2H2O in the solid state and then they transformed to In2O3—SnO2 via some metastable intermediates after 300°C. Cubic phase of In2O3 was identified by XRD for the oxides up to 30% of Sn. Particle size measurements of the solid dispersed in acetone and SEM study for microstructure showed that the oxides were in the nano range (55-75 nm) whereas the size range determined from Debye-Scherrer equation were 11–24 nm.