Ta solution was prepared from solid Ta2O5 by dissolving the solid in concentrated HF.
Therefore, Ta could be in the form of either Ta2O5 or TaF5. Melting points of Ta2O5 and TaF5 are 1872 °C and 96.8 °C, respectively.
From these data, it could be estimated that Ta is in the form of Ta2O5 because of the significantly higher melting point of this compound.
In order to support this suggestion, Raman spectrum of Ta coated SQT was taken.
Raman spectra of Reference Raman spectrum of Ta2O5 and obtained Raman spectrum of Ta-coated quartz are shown in Fig. 3. These two spectra have the same features.
Therefore, it can be concluded that Ta was coated on SQT in the form of Ta2O5