Thermal expansion in BaRuO3 perovskites – an unusual case of bond strengthening at high temperatures

Abstract

The temperature dependences of the structures of three polytypes of BaRuO₃ have been investigated between room temperature and 1000 °C using high resolution synchrotron X-ray diffraction. The structural studies reveal a systematic decrease of the Ru–Ru distance as the pressure required to prepare the polytype increases. The O–O distance across the shared face increases as the Ru–Ru separation decreases. The 9R and 4H polytypes undergo unexceptional changes with increasing temperature. In 6H-BaRuO₃ there is an apparent increase in the Ru–Ru interaction at around 650 °C and a concurrent reduction in the O–O distance, indicating an anomalous strengthening of the Ru–Ru interactions upon heating.