It is impossible to reduce the crystallization temperature of any substance below a certain minimum, since this temperature is determined by the gibbs energy of the substance and is a constant for this substance. The minimum crystallization temperature corresponds to the minimum particle size (you have just such particles), and therefore it will not work to crystallize titanium dioxide below 400°C.

However, your problem can be easily solved if you use a glass substrate made of more heat-resistant glass that can work at 450°C. Such glasses include quartz glass (application temperature up to 1100°C) and even laboratory borosilicate glass, which is operable up to 500°C.

Dear Mahsa,

this is a very interesting technical question. Unfortunately I cannot provide you with a qualified expert answer, as we work in organometallic chemistry. However, I just came across the following potentially useful review article which might help you in your analysis:

Low-temperature crystallization of solution-derived metal oxide thin films assisted by chemical processes

Article Low-temperature crystallization of solution-derived metal ox...

Luckily this very instructive review article has been posted by the authors as public full text on RG. Thus it can be freely accessed and downloaded as pdf file. I'm sure it will be of interest for you.

Good luck with your research and best wishes, Frank Edelmann

I think typical FTO glasses could have no problem with anneling at 450-600 degrees in air. Considering the works of some of my colleagues (typical works in DSSCs, or photocatalytic H2 evolution), with TiO2 nanotubes on FTO (obtained by electrochemical anodization of sputtered Ti) or nanoflakes on FTO (obtained by hydrothermal treatment) - a thermal treatment of the TiO2 layers to anatase is a must. And annealing is usually done at 450deg for 1h, or even up to 600deg (higher temperatures are leading to better results as you will also have a change in the nanostructure plus some Sn diffusion (this usually seen also in XPS at the top of the layer).

For example, I attach one of more recent works (less time consuming to find) where the various TiO2 layers on FTO were annealed at temperatures of up to 650deg. (Zhou et al. Photoelectrochemical performance of TiO2 photoanodes: Nanotube versus nanoflake electrodes, Electrochemistry Communications,124, 2021, 106937, https://doi.org/10.1016/j.elecom.2021.106937.)

Usually for TiO2, the optimal annealing temperature for photoelectrochemical applications is around 400-500deg. You could also anneal at lower temperature (300-400 deg) and optimize the annealing time to fully crystallize the layer.

TiO2 (as rutile) can be deposited at 170-180 ° C using titanium butoxide or TiCl4 using autoclaving and autogenous pressure. In principle, the growth is carried out on the substrate that you incorporate into the reaction mixture. This growth occurs in the form of crystalline nanowires whose properties vary depending on the experimental conditions of synthesis.

dear Frank T. Edelmann ,

Thank you very much for your reply and shared information, the article is very informative and interesting.

Kind regards

Dear Anca Mazare

Thank you very much for the very interesting information.

All the best

Dear Francisco Manuel Marquez

Thank you very much for the reply and very useful information.

Best regards

Dear Vadim Verlotski

Thank you very much for your recommendation.

Best regards