Diffusion behaviour of Nb in yttria-stabilized zirconia single crystals: A SIMS, AFM and X-ray reflectometry investigations

Using secondary ion mass spectrometry (SIMS) we have investigated the concentration vs. depth profile of Nb, thermally diffused into (1 0 0)-oriented yttria-stabilized zirconia (YSZ) single crystal substrates. The surface morphology of Nb films and YSZ substrates was analyzed using atomic force microscopy (AFM). The structural disorder and the interface configuration of the samples were investigated by X-ray reflectometry (XRR). Two kinds of substrates were used: as-received (AR) and reduced (R) ones. The R-substrates were obtained by thermal annealing of AR-substrates in air for 2 h at 1250 °C. The bulk diffusion coefficients D_T in the temperature range of 780-1000 °C, activation energy Q, and the pre-exponential factor, D₀, have been obtained for Nb in YSZ. For the AR single crystals, the results can be well represented by the expression: