Page 42 - ILL Annual Report 2019

CHEMISTRY AND CRYSTALLOGRAPHY
Laura Cañadillas-Delgado. Spanish
The ILL
‘ I work on the synthesis and characterisation of multifunctional metal–organic materials, trying to ascertain structure–properties relationships in order to find clues on how to design new materials with desired assets.
The determination of complete structural models including H atoms is necessary to identify relationships among the different properties. Neutron diffraction provides us with crucial information in this context.’
Incommensurate structures
AUTHORS
L. Cañadillas-Delgado, L. Mazzuca, O. Fabelo, J.A. Rodriguez- Velamazán and J. Rodriguez-Carvajal (ILL)
ARTICLE FROM
IUCrJ. (2019)—doi: 10.1107/S2052252518015026
Electric permittivity measurements on compound 1 showed a smooth change in its electric behaviour. However, measurement of the specific heat yielded no evidence about the phase transition temperatures. Single-crystal Laue diffraction is a good tool to survey structural changes,
and in order to be sensitive to changes in the position
of the hydrogen atoms we decided to use neutron diffraction. We used the ILL’s CYCLOPS, a single-crystal, Laue neutron diffractometer with high flux and covering wavelengths from 0.8 to 3.2 Å, permitting a huge part of reciprocal space to be explored in only one image. We identified three phase transitions involving incommensurate structures. The model of each incommensurate structure needs the refinement of not only the positions and thermal ellipsoids of the main structure but also the amplitudes
of the modulation of each atom. The refinement of these amplitudes is dependent on the intensity of the satellites; thus, a large number of observations, including high-Q satellite reflections, are needed. The capture of full scans at several temperatures above and below each phase transition on the monochromatic single-crystal neutron diffractometer D19 allowed us to obtain enough data even at high-Q, thanks to neutron scattering.
Figure 1
View along the wave-vector direction of the model. The graphical representations have been depicted considering a super-cell (10 times the average structure along the c-axis), in order to include at least one complete period.
of the [CH NH ][Co(COOH) ] 333
compound
Single-crystal diffractometers D19 and
Laue single-crystal diffractometer CYCLOPS
The development and characterisation of new materials are key challenges in condensed matter, chemistry and physics. The ability
of metal–organic frameworks to combine different physical properties within the same framework has attracted huge interest in recent years. We have focused our efforts
on finding new multiferroic materials in
which electric and magnetic order coexist.
The [CH3NH3][Co(COOH)3] (1) compound
is a multiferroic of type I material that presents several structural phase transitions that affect
its electrical behaviour. Neutron measurements have been crucial in studying the crystal
structure of this compound in the different phases.
ANNUAL REPORT 2019