matthew.row...@csiro.au said:
From what I've read of Cagliotti's paper, the V term should always be
negative; or am I reading it wrong?
That's right. If
FWHM^2 = U.tan^2(T) + V.tan(T) + W
then the W term is just the Full Width at Half-Maximum (FWHM) squared at
zero scattering angle (2T). FWHM^2
I didn´t find the crystalline phase
K_6 H_2 Nb_6 O_19 .8H_2 O
in ICSD database
There are very many phases containing niobium oxide blocks, with various
other cations and hydration states, so you may not find an exact match.
You can still use ICSD to help understand the structure if you relax
I didn´t find the crystalline phase
K_6 H_2 Nb_6 O_19 .8H_2 O
in ICSD database
K7(H Nb6O19).(H2O)10 which is already pretty close,
I should have given the reference for this and other similar Nb6O19
cluster compounds as:
Solid-state structures and solution behavior of alkali salts of the
Back to basics and First Principles
As Alan says, the [use of the Cagliotti function is appropriate for the neutron
case], but not really for X-ray and other geometries.
My recollection is the Cagliotti function was adapted to the x-ray case when we
had low resolution x-ray instruments
As I have said before countless time, one should not lose sight of the
objective of Rietveld refinement, that it is to refine a sensible
crystallographic structure. One can reduce R factors in all sorts of
ways by playing with the peak shape functions (even by using lower
symmetry and increasing
Hi to all!,
in fact, the Cagliti's expression is just a way to show the angular
variation of fwhm, as was mentioned was usef for neutron diffraction and
adopted in XRD, we can also build another dependence such as FWMH vs
2theta directly and it is useful to evaluate size and strain, the problem
LANSCE will host its 6th annual Neutron School at the Lujan Neutron Scattering
Center, this year focused on Application of Neutron Scattering to Study Phase
Transformations, on July 7-17, 2009.
The school will include lectures from some of the preeminent scientists in the
field and hands on
