I doped TiO2 with Silver using AgNO3 as the precursor. Then I analysed the XRD pattern of pure TiO2 and Silver doped TiO2. Both I got the Anatase phase from XRD. But the main peaks got intensed after doping.
And the crystal size also got increased after doping.
Kindly ask a solution for these questions.
Hi Vishmi,
The intensity of the peaks is the function of the FWHM of the peak, which can be due to the change in crystallite size of your Ag-doped TiO2.
The change in crystallite size changes the intensity of the peaks as per Debye–Scherrer equation.
Firstly, the crystal size will increase if Ag is incorporated in TiO2 crystal (provided ionic radii of Ag+ is larger than Ti4+), and if Ag replaces any of your cations in the unit cell, you will observe a slight shift in the peak PXRD patterns in the doped samples which can give you an idea about the crystal size and crystal volume.
Dear Vishmi Vithanarachchi ,
as already mentioned by Mohit Kumar , smaller peak widths will increase the intensities (FWHM dependence on the crystallite size; e.g. Scherrer equation).
Smaller peak width is obvious here due to the 'better' peak resolution which can be seen around 55^and 70° via the appearance of the double peaks (211)/(105) and (116)/(220) peak pairs there.
You should compare the peak integrals. Then you can see whether there is a net change. I do not expect any net measurable change of these integrals due to the low dopand concentration (although the elastic scatter strength of Ag (Z=47) is about twice that of Ti (Z=22)).
But the anwer onto 'why' the crystallite size is larger in the doped case is still open. Maybe due to some thermal treatment during the doping procedure.
Was your doped sample exposed to elevated temperature for some time?
Best regards
G.M.
Following up on Gerhard Martens comments:
AgNO3 has a low melting point (212 degC). So if your anatase was heated to above this temperature you may have generated a liquid phase that acted as "mineralizer" for the anatase crystallites and promoted their growth.
You may want to follow the suggestions of Vadim S. Gorshkov
in order to understand better what is happening.One other thing you could do is to use another silver salt that decomposes to form silver nanoparticles directly, without melting. For example, silver acetate (see Article Thermal Decomposition of Silver Acetate: Physico-Geometrical...
). If you do that, it's probably desirable to perform the decomposition in an oxidizing atmosphere, in order to prevent formation of oxygen-deficient titania.
Dear Vishmi Vithanarachchi ,
When crystalline-Powder is investigated,, some time the aligment factors of crystaline would enhance peak's intensity.
Suspecting that Ag dopant plays a role to get stronger alligment of TiO2 crystaline in the a same directional impact.
Thank you so much for your valuable answers Mohit Kumar Desmond Ang Emanuel Cooper Vadim S. Gorshkov
Gerhard Martens
Can it be due to much higher Z number of Ag vs Ti and therefore stronger interaction with xrays?
Dear Nikolay Pavlov ,
Ag is the dopand (~1%).
So so when replacing Ti (Z=22) by Ag (Z=47) would expect an increase of peak intensity by about 1% when no change in the crystallite size is happened. The observed height is much stronger.
If i recall typical xray interaction vs Z number grows as Z^3 or so, but indeed it might still unsufficient for the effect seen.
E.g. looking at Veigele, W. J. (1973). Photon cross sections from 0.1 keV to 1 MeV for elements Z = 1 to Z = 94. Atomic Data and Nuclear Data Tables, 5(1), 51–111. doi:10.1016/s0092-640x(73)80015-4
Dear Nikolay Pavlov ,
you are completely right with respect to x-ray attenuation.
X-ray attenuation of Ag is much higher than that of Ti.
So one would expect a decrease of the peak heights when a bit of Ti is replaced by Ag.
But in XRD the 'signal strengths' are in addition governed by the x-ray elastic scatter strength*) of each atom, which is proportional to Z. So from this perspective one would expect a peak height increase. But it is only a bit (for 1% Ag dopand), but can never reach the peak increase here, which is displayed in the pattern given above.
*) shows up as the 'atomic scattering factor' 'fi(q)' in the XRD formulae
Best regards
G.M.
To get a sustainable solution to your problem, please refer to the preprint article given at link DOI: 10.13140/RG.2.2.27720.65287/3 or at link https://www.researchgate.net/publication/352830671.
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