Dear Norberto, to correct for preferred orientation, Toraya and Marumo seem to apply a different correction function than the universally used one proposed by Dollase. See Mineralogical Journal, 1980, 10, P 211-221. They succesfully apply it to a monoclinic case study, but you may verify if it is applicable also for cubic space groups. Guessing that your are working with Topas, I amsure you will not find it difficult to introduce a proper macro in your input.
Kind Regards, Simona Save the date: 2014, International Year of Crystallography ******************************************************* Simona Galli, Dr Dipartimento di Scienza e Alta Tecnologia Universit? dell'Insubria Via Valleggio, 11 22100 Como - Italy e-mail: [email protected] tel: +39-031-2386627 fax: +39-031-2386630 url: scienze-como.uninsubria.it/sgalli ******************************************************* Dear Friends, I am facing a problem in quantifying magnetite in a complex natural mixture, using the conventional Rietveld method (in its quantitative analysis approach). Apparently, the octahedral morphology of (difficult to grind) magnetite crystals affects itd diffraction pattern. To my knowledge, as certified in the original paper (JAC 1986, 267-272), the ubiquitous and highly performing March-Dollase equation, holding for "any" crystal symmetry, only applies to inequant crystallites (i.e. crystallites with unequal sides), or, better said, to "effectively rod- or disk-shaped specimens" (provided that the geometry of the experiments keeps cylindrical symmetry). Neither octahedral nor cubic (e.g., NaCl) crystals can be considered "inequant". So, the question is: Is there any way do get around this problem (without resorting to spherical hamonics or to grind the specimen in a WC, SiC or BN mill)? Thank you for your patience. Norberto -- Laurie Aldridge 24 Balmer Cres Woonona 2517 NSW Australia Email [email protected]<mailto:[email protected]> Phone +61 (2) 4284 0132 Mobile 0403 718 522
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