Secondary ion mass spectrom6try has been applied for measuring the tracer diffusivity of oxygen in the c direction of singlecrystal rutile for a temperature range of 1150 to 1450 K at 6000 Pa pressure of oxygen gas. Specimens diffusion-annealed in oxygen gas containing l H 0 were subsequently continuously sputtered and analyzed for ' ' 0 and "0. The tracer diffusivity was determined from the depth profile of lH0, taking into account a surface exchange reaction of oxygen. The tracer diffusivity in CrpOs-doped rutile was 3 to 8 times larger than that in pure rutile. For pure rutile, the diffusivity is expressed by D(m2/ s ) = 3 . 4 x lo-' exp[ -25l(kJ/mol)/RT], and for 0.08 mol% Cr,O,,-doped rutile, by D(m2/s)=2.0x lo-' exp[ -204(kJ/ mol)/RT]. The Cr,O, doping had a catalytic effect on the rate constant of the surface exchange reaction on the c surface. The rate constant is represented, for pure rutile, by k(m/ s ) = 2 . 4~ lo-' exp[ -246(kJ/mol)/RT], and for 0.08 mol% Cr,O,,-doped rutile, k ( d s ) = 3 . 5~ exp[ -13l(kJ/mol)/RT].
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