Re: GSAS informations

[Nicolae Popa]

Dear Christophe,   The coefficients Lij in the formula you wrote have no significance. This formula  is a naive representation of strain anisotropy that falls at the first analysis. It is enough to change the indices hkl into equivalent indices and you obtain other Gamma. As a consequence, in cubic classes for example, the microstrain anisotropy doesn't exist, which is a nonsense. The correct formulae are indeed in Peter Stephens paper (at least for a part of Laue classes) but also in a paper by Popa, J. Appl. Cryst. (1998) 31, 176-180, where the physical significance of coefficients is explicitly stated. Hence, if denote by Eij the components of the microstrain tensor in an orthogonal coordinate system  related to crystallite, then the coefficients are some linear combinations (specific to every Laue class) of the averages <Eij*Emn>.   Best wishes,   Nicolae Popa     ----- Original Message ----- From: Christophe Chabanier To: [EMAIL PROTECTED] Sent: Wednesday, April 07, 2004 6:45 PM Subject: GSAS informations Hello everybody, i have a question about the GSAS software. Indeed, i would like to know what are exactly the L11, L22, L33....L23 parameters. I saw that these parameters represent the anisotropic microstrain in material. Moreover, there is an empirical _expression_ which uses these parameters as following :  Gamma(L) = L11*h^2 +  L22*k^2 + L33*l^2 + 2*L12*hk + 2*L13*hl + 2*L23*kl  I would like to know and understand the physical representation of these parameters and this _expression_. Thanks in advance   Christophe Chabanier INRS-Énergie, Matériaux et Télécommunications 1650 Blvd. Lionel Boulet C. P. 1020, Varennes Qc, Canada J3X 1S2 Tél: (450) 929 8220 Fax: (450) 929 8102 Courriel: [EMAIL PROTECTED]