Hi!
I have collected the data of a complex of ruthenium and I found the structure with an R=~9% but at room temperature. When I do at 100 K I can't find the structure. I made another measurements at different temperatures and I found that the disorder in increase as i reduce the temperature. Since 155 K I can't find the structure at all. My opinion is some structural change may occur but I want to know other opinions for more experienced people.
If the temperature was 100K and is increased to 300K, do you still have a single crystal showing the same structure as at the beginning?
A phase transition may me either topotactical (you still habe a very similar structure) or reconstructive. If you have a reconstructive phase transition probably you will have no longer a single crystal but a polycrystal. Then you should observe the scattering cones or spots of cones at 100K (X-ray powder pattern of fine or coarse grains). If a topotactical phase transition occures you may hold at low temperatures until the phase transition is complete. Perhaps the single crystal "survives" and you still have a single crystal. Topotatical processes should be reversible with low hysteresis.
The ill defined transition temperature makes a reconstructive phase transition more leliable. But again: what do you observe after coming back to room temperature?
Thanks Robert! Sounds interesting what you said. Yes, If I cool to 100 K and them increased up to room temperature I still can find the structure. Using the same crystal I found that below 160K I can't find the structure. what I recently found is that at 160 K with isotropic refinement, I can see low intensity Q peak beside the structure that resemble the structure which are not present at RT. Could them be some sort of twining or disorder?
If the peaks belonging to the "high temperature" (ht) structure completely vanish at 100K (lt) but reappear as single crystal peaks at 300K you have a topotactical phase transition.
ht-phases show often a higher symmetry than lt-phases (if this is a topotactical phase transition). Then this probably is a phase transition of second order., too This may cause peak splitting, superstructure peaks or other effects representing the lower symmetry at lower temperatures. Does the intensity distribution in reciprocal space of the lt-structure look similar or completely different to the ht-intensity?
As Nita Dragoe suggested a powder pattern (1D reciprocal space), i.e. calculated from the intensity of the single crystal scans, might provide a more simple impression than intensities of the 3D reciprocal space. Are you able to provide this information?
Thanks Robert. sorry for the late reply. I may try to get the powder information.
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