VAPORIZATION AND THERMOCHEMICAL PROPERTIES OF LI8ZRO6 AND COMPARISON WITH OTHER LITHIUM-CONTAINING COMPLEX OXIDES

A mass-spectrometric Knudsen effusion method is used for the determina tion of partial pressures of Li (g), LiO (g), Li2O (g), Li2O2 (g), Li3 O (g) and O-2 (g) over Li8ZrO6 (s/l) in the temperature range 1181-142 9 K. From the gas-solid equilibria, enthalpies of formation for Li8ZrO 6 (s) are calculated to be Delta(f)H(298)degrees (Li8ZrO6, s) = -(3558 .5 +/- 16.5) kJ mol(-1) from the elements and Delta(298)degrees (Li8Zr O6, s)= -(66.1 +/- 18.6) kJ mol(-1) from the constituent oxides, Li2O (s) and ZrO2 (s). Over various lithium-containing complex oxides, the partial pressures of Li2O (g) decrease in the following order: Li2O (s ) > Li5AlO4 (1) approximate to Li8PbO6 (s) approximate to Li8ZrO6 (s/l ) approximate to Li4TiO4 (s/l) > Li6Zr2O7 (s) > Li2SnO3 (s) > Li4SiO4 (s/l) > Li2TiO3 (s) approximate to Li2ZrO3 (s) > LiAlO2 (s) approximat e to Li2SiO3 (1) > LiNbO3 (1). Thermodynamic activities and activity c oefficients of the pseudo Li2O component in the complex oxides are eva luated from the partial pressures of Li2O (g). The results show that t he complex oxides with less Li2O molar content have more ability to st abilize the pseudo Li2O component in binary Li2O-MO(x) system (M = Al, Si, Ti and Zr).