Unexpected plasticity of potassium niobate during compression between room temperature and 900 °C

Single crystals of potassium niobate were compressed over a range of temperatures (21 °C to 900 °C) and examined using electron microscopy. The material did not behave in a brittle manner; samples sustained up to 3.7% strain. There was a trend of decreasing strength with increasing temperature, with a (superimposed) increase between 300 °C and 500 °C. Characterization revealed slip lines consistent with slip on {110} planes, domain activity and cracking. Dislocations consistent with the {110}<1−10> slip system were observed in all specimens, while dislocations most likely on the {100}<100> system were also observed in specimens compressed at 900 °C. Domain walls were observed in large numbers only in specimens tested between 300 °C and 500 °C. It is proposed that the shape of the strength-temperature curve results from the combination of contributions from dislocation slip systems and mobility and a strong effect of domain walls only acting in the intermediate temperature range.