dear colleague

your measurement are optical and not electrical.

In general TiO2 is insulator unless you introduce impurities.

what you should conclude from your curves is the transparency, reflectance...etc

any other question ?

regards

There is a general relationship between real and imaginary part of the dielectric function and the conductivity. However, this relation is unique only in one way -- namely, when coming from the conductivity, showing up in the imaginary part. Since here we are dealing with frequency-dependent measurements, any material resonance or relaxation mechanism can also lead to an imaginary part. Have a look e.g. at https://www.tf.uni-kiel.de/matwis/amat/admat_en/kap_3/backbone/r3_4_1.html (as well as https://www.tf.uni-kiel.de/matwis/amat/admat_en/kap_3/backbone/r3_3_1.html and the related subsections) for the details.

Dear Dr. Biswas:

Let’s suppose that measurement were carried out to room temperature, also that temperature marked meaning the temperature of preparation of material. This suggest that as function of increasing of temperature of processing, the average grain size increases with temperature, in the sequence 600, 800 and 1000oC. At 1200oC seems exist an anomaly, its necessary Scanning Electron Microscopy to verify micro crack and or X ray diffraction to verify microstrain level, ...

A priori, if words insulating/conducting are used, the interest concept is focused on the insulator/conductor character of a material. Being this the case, in specific, the concept of electron conduction is directly involved, but is always complex further modeling of the question.

Both concepts, insulator/conductor are connected to the electron mobility or feasibility of move the charge carrier, electron, at long range. This phenomenon has origin from electric field E constant in the time. See, if Electric field is a function of time, at fast oscillating E actuating under the charge carrier (electron) induces a fast electron oscillating, what will reach a moment that is impossible to perform a long range moving, by a kind of inertia.

At this point, it is important represent the data set in a proper physical parameter, in your case, both plots exhibits in abscise axis wavelength, more adequate would be frequency that is reciprocal of wavelength multiplied by light velocity. As expected, optical measurement exhibits a high frequency meaning that long range movement of electron cannot be detected then any type of analysis would be foolhardy. From this point, an analysis of dielectric property is bit more easily to approach. In the classical theory of isolators, the electric field are constants in the time and all charge is a multiple integer of one electron charge, then an isolator is one material that exhibits a great dielectric permittivity, in this sense a material having a great difficulty of allow long range charge movement. Again, “any type of analysis would be foolhardy.”

Also, the phenomena observed in both plots are ascribed to surface, with very slight bulk penetration.

Seems that the observed phenomenon should be approached via concepts that involve charge, electron, oscillation then the concept of charge density emerges. This concept is useful since gives rise a way to work with a “charge” that can oscillate very fast, but that can move only for short range. In a very simple way, these ideas are structured in a polarization theory

For joining the set of ideas above, the material should have well defined Optical dispersion observed in the UV-Vis range. A qualitative analysis can be by further comparison of n and K evolution with other semiconductor oxides. Being your material an oscillator material, with optical dispersion, from Tauc-Lorentz approximation, via adjusting curve, it is possible to derive the Band-gap. From band-gap a decision can be reach at about character insulator or conductor of material. Seems that will be more vantagous use more semiconductor intead conductor or less semiconductor intead insulator.

A band-gap of ZnO is of the order of 3.2 eV, a poor semiconductor, in this sense, are all good semiconductor any semiconductor with band-gap > 3.2 eV.

Qualitative analysis can be carried as fallow. Chemical bond and mass of atoms can be considered as an oscillator. The strong consideration is that the oscillator strength is reciprocal of binding energy.

Analysis is carried out taking into account light/heavy atoms and strong/non-strong bonding giving large band-gap/non so large band-gap. In a broad sense, material having light atom, large band-gap and high bonding energy gives low UV absorption and by consequence high UV transmission.

Another parameters can be noticed as useful in qualitative analysis from concept of polarizability, low bond energy/high bond energy gives high refractive index/low refractive index and therefore is valid the idea of low band-gap/ high band-gap, with direct correlation more semiconductor/more insulator or less semiconductor (very very poor semiconductor).

Finds above are interesting to a qualitative analysis, since real part of dielectric permittivity is proportional to the square of the real part of refraction index; both electronic and lattice vibration participate of dielectric permittivity. Therefore, high refractive index/low refractive and high value real part of dielectric permittivity/ low values of real part of dielectric permittivity gives the idea of low band-gap/ high band-gap, with direct correlation type more semiconductor character/less semiconductor character.

With best regards

Marcos Nobre

Marcos Augusto Lima Nobre

Dear Dr. Marcos Nobre,

Thank you very much for your elaborate discussions. I could gather some knowledge regarding my query. Thanks a lot.

I calculated the band gap from optical absorption spectra. The temperatures indicated are annealing temperatures. Sorry, I forgot to mention that. observed band gaps are 3.63 eV, 3.17 eV, 2.93 eV and 2.52 eV for films anneales at 600 °C,

800 °C, 1000 °C and 1200 °C. we observed as band gap decreases absorption increases. the anomalous behaviour showed by films anneales at 1200 °C is probably de to presence of some TiO phase along with rutile TiO2. NO cracks were observed in the FESEM images. Here I arttach the plots for optical dispersion behaviour.

Thank you once again.

Best regards,

Sayari Biswas.

Dear Dr. Biswas:

Thank you by return good news.

TiO2 exhibits a crystallochemistry complex, starting from crystalline structure that can show some phase transition depending on the particle size during crystallization. Verify together RG another answer at about TiO2, seems that 600 oC is the final temperature of transition Anatase-Rutile, in this sense band gap derived close to this temperature can steam of a particular phenomenon. At higher temperature, band gap can be related to another phenomenon. Also, oxygen vacancies can be present. Atmosphere, and further enveromental characteristics can affect the physic-chemical behavior. There are a giant number of papers but if you can see J. Phys. Chem. C, 2013, 117 (15), pp 7850–7857

Some kind of insight can be reach. with best regards

Marcos Nobre

Marcos Augusto Lima Nobre

Dear Dr. Marcos Nobre,

thank you very much for your response. I'll study deeper on this topic.

Best regards,

Sayari Biswas.