Not  my area, but it is my daughter's area.  These recent papers might help.  http://rspa.royalsocietypublishing.org/content/470/2168/20140108

http://www.maneyonline.com/doi/abs/10.1179/1743284713Y.0000000403

http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.398.5767

hope you find something useful.

thanks very much for you and your daughter

It is impossible to determine this experimentally as C will occupy only lower energy positions in phase. I would suggest electronic structure simulations with C atoms first in tetrahedral and later in octahedral positions. From total energy difference you can then calculate strain.

I really don't know~

信春哥得永生。