>Hi there,
>
>a lokal distortion in the structure produces strain, which gives delta
d /
>d and is fitted with Y and Ye in the Thompson-Cox-Hastings.
>
>My question: What produces a symmetric distribution of unit cell edge
>lenghts? Will I get a broadening, which follows tan(theta) as above,
or
>something different?
>
>This problem is of interest for us, because we deal with substituted
iron
>oxides, where individual crystals may have a slightly different
chemistry
>and, hence, different unit cell edge lengths.
>
>Thanks in advance,
>Helge Stanjek
>
Hi Helge,
there was a speech at EPDIC 5, held in Parma/Italy, about this theme.
I have not found my abstract book, so I can't told you the author.
Contents of the speech:
-The covariance marix of the 6 lattice constants contains in
triclinic 21 independent coefficients, in higher symmetries
smaller numbers.
-This give a broadening simga**2(d**2), which is proportional
to a spherical harmonic of all even orders until 4 in hkl,
which means 15 independent coefficients in triclinic.
As a condition, sigma**2 must be positive.
Square root of this item gives the broadening in d**2,
further computation the broadening in d.
I hope, this will help you.
J"org Bergmann
bergmann@rcs.urz.tu-dresden.de