Pivotal role of Ti[sbnd]O bond lengths on crystalline structure transition of sodium titanates during electrochemical deoxidation in CaCl2[sbnd]NaCl melt

Abstract

The crystalline structures transition of TiO2, Na8Ti5O14, Na2TiO3 and Na2Ti3O7 during electrochemical deoxidation in CaCl2NaCl melt were investigated via cyclic voltammetry (CV), constant voltage electrolysis, theoretical analysis and calculation. Both of the reduction potential of Na8Ti5O14, TiO2, Na2TiO3 and Na2Ti3O7 shown in cyclic voltammogram and the valence of titanium (Ti) of main electrolytic products shown in parallel constant voltage electrolysis (3.1 V) indicate that the electro-deoxidation sequences orderly are Na8Ti5O14, TiO2, Na2TiO3 and Na2Ti3O7 from easy to difficult. In addition, the corresponding Raman spectrums show that the TiO bond lengths are expected to decrease as follows: Na8Ti5O14 ＞ TiO2 ＞ Na2TiO3 ＞ Na2Ti3O7. The average TiO bond lengths of Na8Ti5O14, TiO2, Na2TiO3 and Na2Ti3O7 shown in crystal structural are 1.95, 1.92, 1.70 and 1.67 Å, respectively. The TiO lengths information explain above electro-deoxidation sequences. Furthermore, the dissociation energies of Na8Ti5O14 and TiO2 are 6.824 and 8.638 eV, respectively, which indicates that Na8Ti5O14 is easier to be reduced than TiO2. The theoretical analysis and calculation based on TiO bond lengths are consistent with experiment findings, which reveals that pivotal role of TiO bond lengths on crystalline structure transition during electrochemical deoxidation in CaCl2NaCl melt.