Further to the recent discussions on corrections for zero point errors
and/or sample height, i did some comparison between the two refinement
strategies (on data collected on a D5000 Cu-alpha1) and compared the
results with one of the world best neutron diffractometers, HRPD at the
ISIS facilty, UK. For this I used two samples, both high quality oxides
prepared using standard solid state techniques.
so the results:
compound 1
zero point 5.71356(6) 21.45782(30) 606.639(18)
sample shift 5.71199(4) 21.45190(28) 606.138(15)
HRPD 5.71200(1) 21.45223(7) 606.148(2)
compound 2
zero point 3.83386(14) 27.8166(12) 408.86(4)
sample shift 3.83303(13) 27.8105(11) 408.59(4)
HRPD 3.83393(1) 27.81471(13) 408.849(2)
in both cases the zero point error was about 0.05deg 2theta, or 2 to 3
step sizes.
Of course the ESD's resulting from the measurement on HRPD are somewhat
smaller than those collected on the D5000. But what is surprising is that
for compound 1 the agreement between the two machines is *best* if you
refine the sample height, however for sample two, it is vice versa.
So, if we are trusting HRPD for a moment, than there is no *best*
strategie based the results of this small number of compounds.
What are we going to believe, what are the real SD's and how are we going
to measure it? Friends what are your thoughts?
regards
Jaap
Jaap Vente
Inorganic Chemistry Laboratory
Department of Chemistry
University of Oxford
South Parks Road
Oxford, OX1 3QR
United Kingdom
E-mail: jaap.vente@chem.ox.ac.uk
tel: (..44)(0)1865-272602
Fax: (..44)(0)1865-272690