الفهرس 
Theoretical background and literature surveyOnly 14 pages are availabe for public view
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Abstract
Pure (TiO2) titania and chromium (Cr) doped TiO2 nanocrystals were
synthesized using hydrolysis method. The used molar ratios of chromium (III)
acetate hydroxide: titanium tetra isopropoxide are 0, 5, 15, and 25 %.
Synthesized nanopigments were classified to three categories first used assynthsized and others annealed at 500 ℃ and 700 ℃ respectively. X − ray
diffraction analyses, FTIR and high-resolution transmission electron microscope
(HRTEM) were utilized to investigate the microstructure and property of
synthesized nanopigment. Also surface area of synthesized samples was
estimated by BET method. Optical property of synthesized nanopigment was
specified by UV/Vis/NIR spectroscopy. The combined influence of calcination
temperature and chromium addition on the phase transformation, grain growth
and near infrared (NIR) reflectivity of nanopigments has been investigated.
Pure titania, annealed at 700 ℃ has shown the highest NIR solar reflectance
(R
∗
) up to 95% .The presence of Cr ion in annealed titania samples caused huge
reduction in NIR reflectivity. While the NIR reflectivity of pure titania, used assynthesized was slightly reduced with increasing Cr ion content. Doped samples
used as-synthesized have NIR solar reflectance higher than obtained for doped
in other annealed series. S4 − 100 sample presented optimum reflectance
behavior for both of cooling and aesthetic sides. The estimated optical energy
gap (Eg), calculated from diffuse reflectance spectrum in sight of Kubelka–
Munk assumptions, of the examined nanopigments were significant reduced in
annealed nanopigments and slightly reduced in nanopigments the assynthesized. The variation in both dielectric constant (ε′), and ac conductivity
(σac) as a function of applied frequency at different doping concentration of Cr
were investigated. The measurements confirms that both ε′ and σac values of
TiO2 were decreased with Cr doping in first series of samples and increased
with Cr doping in second series of samples.