Mass Spectrometric Study of the Thermal Emission of Alkali-Metal Ions from Lithium Orthosilicate

Thermal emission from the solid electrolyte Li(4)SiO(4) was studied in the temperature range 760-1185 K. Both intrinsic (Li(+)) and extrinsic (Na(+), K(+), Rb(+), Cs(+)) ions were detected by thermal-ionization mass spectrometry. Ion work functions, determined by an equation of the Richardson-Dushman type, are 3.25 +/- 0.12 (Na(+)), 2.7 +/- 0.3 (K(+)), 4.2 +/- 0.7 (Rb(+)), and 3.1 +/- 0.25 (Cs(+)) below the phase-transition temperature (T < 880 K) and 2.84 +/- 0.13 (Li(+)), 2.24 +/- 0.15 (Na(+)), 2.21 +/- 0.05 (K(+)), 2.3 +/- 0.1 (Rb(+)), and 2.36 +/- 0.15 (Cs(+)) for T > 880 K. Ion intensities grow in time at a constant temperature. The apparent activation energies (eV) of ion diffusion to the surface are 1.76 +/- 0.14 (Li(+)), 2.23 +/- 0.15 (Na(+)), 2.26 +/- 0.16 (K(+)), 2.39 +/- 0.22 (Rb(+)), and 2.56 +/- 0.24 (Cs(+)).