The advantage of neutron powder diffraction is that the scattering power
of light atoms like oxygen is as great as for heavy atoms; for X-rays, the
heavy atoms dominate, so errors for the light atoms will be greater. A
second advantage is that with neutrons you have a larger sample, so a
better powder average is obtained and systematic errors will be generally
smaller. You can also see magnetic structure, and low/high temperature
measurements may be easier. The advantage of X-rays is that X-ray
diffractometers are more common, you can use smaller samples, high
pressures etc. Generally, if you can actually do the experiment using
first class diffractometers with either X-rays and neutrons, the neutron
structure will be better with few exceptions. Rietveld himself considered
that his method was not so reliable for X-rays because of potential
systematic error, though of course some progress has been made since then.
Alan.
Davide Levy said:
> Dear All,
>
> I have a philosophic question for you: the structure obtained by NPD are
> better than the ones found by XRPD?
>
> I explain a little bit more my question, I studied a MgAlFeO4 spinel both
> by
> NDP and XRPD from RT to 1000°C. The O coordinate it is different for two
> data set (0.2581 vs.0.25953). The found error on the oxygen coordinate is
> about 10-5 and 10-4 for NPD and XRPD data respectively. The coordinate
> calculated from cation partitioning and cation radii is similar to the
> XRPD result.
>
> At the moment I did not found a justification of this and I do not know
> which result is the right one.
>
> Do you have any suggestion?
>
> Thank you
>
> Davide
______________________________________________
Dr Alan Hewat, NeutronOptics, Grenoble, FRANCE
<[EMAIL PROTECTED]> +33.476.98.41.68
http://www.NeutronOptics.com/
______________________________________________
