HIGH-TEMPERATURE CREEP OF SINGLE-CRYSTAL STRONTIUM-TITANATE (SRTIO3) - A CONTRIBUTION TO CREEP SYSTEMATICS IN PEROVSKITES

Compression tests were made on single crystals of SrTiO3 perovskite along the [100] and [110] directions at temperatures of 1473-1793 K (0.64-0.78 T(m)). The results show a power-law creep behavior with a stress exponent of 3.5 +/- 0.1 in both orientations. However, a strong plastic anisotropy has been observed: creep along the [110] orientation is much easier than creep along the [100] orientation. The activation energy for the [100] orientation is significantly higher than that for the [110] orientation. The dependence on oxygen fugacity is also different between the two orientations. Transmission electron microscope (TEM) observations indicate that gently curved dislocations with b = [100] are generated in the crystals compressed along the [110] orientation, whereas very straight dislocations with b = [110] are generated in the crystals compressed along the [100] orientation. We interpret the observed plastic anisotropy in terms of structure of dislocations in the perovskite crystal: it is proposed that the [110] dislocations are more difficult to glide than the [100]) dislocations because of a larger amount of shear and a larger number of strong Ti-O bonds cut during the glide of [110] dislocations. Comparison of the present results with data on other perovskites shows that the data for the soft orientation do not converge even after normalization, but the data for the hard orientation do converge into a well-defined trend. Because creep in a polycrystalline aggregate is controlled by the strong slip system(s), we suggest that an analogue materials approach could be useful in the study of creep in perovskite only when the strong slip system(s) is also investigated.