Dear Pragna Dubbaku ,
Thanks for your questions.
Question 1
There are four reported crystal structures of BaIrO3: (1) C 1 2/m 1, (2) I 4/m c m, (3) C 1 2/c 1, and (4) P m -3 m. I found these crystal structures using https://materialsproject.org/, http://aflow.org/, and ICSD.
In addition to crystal structures, Materials Project also reports the relative stability of phases (1), (3), and (4). (1) is the most stable, (3) is 0.03 eV less stable than (1), and (4) is 0.093 eV less stable than (3). Since (1) is the most stable, it is the most relevant for calculating the coordination number (CN).
There are two different coordination environments of Ba in (1): approximately 8-fold coordinated sites and approximately 10-fold coordinated sites. These CN's were calculating using the bond valence model in the VESTA software. The coordination environments of Ba in (3) are similar to that of (1).
The CN of Ba in (2) and (4) is 12, that which is reported in your reference.
Question 2
Here are the Shannon ionic radii for Ba (http://abulafia.mt.ic.ac.uk/shannon/radius.php?Element=Ba). For 8-fold coordination, the ionic radius is 1.56 Å. For 10-fold coordination, it is 1.66 Å and, for 12-fold coordination, it is 1.75 Å. I think that 1.35 Å is an underestimation and would recommend one of these values.
Question 3
If you are interested in the C 2/m, i.e. phase (1) above, then the appropriate CN is 8 at some sites and 10 at the others.
I hope this was helpful. Please let me know if you have any further questions.
RefCode:161961:BaIrO3
Author(s): Zhao J.-G.,Yang L.-X.,Mydeen K.,Li F.Y.,Yu R.C.,Jin C.-Q.
Solid State Communications Year: 2008 Volume: 148 Pages: 361-364
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Ba1, Ba2, Ba3 : for all CN=9
Dear Robert Wexler ,
Thank you for your response.
Question 1 The phases that BaIrO3 exhibits are 9R, 5H,6H and 3C, where 9R is an ambient pressure phase and the others are high pressure phases.I am indeed talking about the 9R phase, which crystallizes into monoclinic with space group C 2/m. If I understood it correct, I think the reference that I mentioned in Q1 is talking about 9R phase with CN 12. Could you confirm this once again?
Question 2 Just to point out, in the name of ionic radii, you are referring to crystal radii.I am assuming it is by mistake.
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