Answer to Question #120331 in Inorganic Chemistry for Yuki

Question #120331
The two cubic oxides ReO3and BaRuO3both adopt a cubic perovskite type structure; however whilst ReO3displays Negative Thermal Expansion (NTE) between 10 and 250 K BaRuO3displays Positive Thermal Expansion (PTE) over the same temperature range. The occurrence of NTE in ReO3 has been explained using the concept of Rigid Unit Modes.

Given both ReO3and BaRuO3contain the same structural frameworks what is the likely cause of the absence of NTE in BaRuO3?
Expert's answer


Thermal Expansion in BaRuO3 Perovskites – an unusual case of bond strengthening at 

high temperatures

Paula Kayser, Sean Injac, Brendan J. Kennedy*

and Andre L. Menezes de Oliveira

School of Chemistry, The University of Sydney, Sydney, NSW 2006, Australia

Yuichi Shirako and Masashi Hasegawa

Department of Crystalline Materials Science, Nagoya University, Furo-cho, Chikusa-ku, 

Nagoya 464-8603 Japan


The temperature dependence 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 in 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 around 650 °C and concurrent reduction in the O-O 

distance indicating an anomalous strengthening of the Ru-Ru interactions upon heating. 

Keywords: Thermal Expansion; Perovskite; face sharing perovskites; BaRuO3

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