Excercises on AMPLIMODES and FullProf: Symmetry modes crystallography ===================================================================== The purpose of these exercises if to learn how to build up a PCR file adequate for working with symmetry modes in FullProf and how to visualise modes with FullProf Studio We will use the case of LaMnO3 as an example of using the AMPLIMODES program in the Bilbao Crystallographic Server (http://www.cryst.ehu.es/) in order to create a PCR file for FullProf. The following problems will be treated: - Selection of the high symmetry phase (Pm3m, ideal cubic perovskite) - Generate a PCR file for calculation purposes using the ideal perovskite and just the cell and space group of the distorted phase in AMPLIMODES. - Standard setting Pnma and conversion to Pbnm - Determine the amplitudes of symmetry modes (Simulated annealing and least-squares) - Constraints in amplitudes - Visualisation of distorted structures and symmetry modes with FullProf Studio Excercise 1: LaMnO3 (J. Rodriguez-Carvajal et al. PRB 57(6), R3189, 1998) ============ The neutron data have been recorded in the 3T2 diffractometer at LLB with a wavelenght of Lambda= 1.2272 angstroms. The space group is Pbnm (standard setting Pnma, #62) with cell parameters a=5.53648, b=5.74713 and c=7.692561 angstroms. Approximate values for the gaussian part of the IRF parameters are: u=0.176 v=-0.1978 w=0.09146 (degrees^2). The format of the data file corresponds to INS=6 (angular range: (0, 125) in 2Theta). - Generate a PCR file from AMPLIMODES and adapt it to the above parameters - Use this, removing the structural information, to create a PCR file appropriate for a Le Bail fit to the data. - Perform a Le Bail fit generating integrated and profile intensities for simulated annealing (SAnn) (More=1, Jvi=11, Jtyp=1, Ipr=-1) - Create a file appropriate for SAnn including the symmetry modes information (hint: use the first file generated by AMPLIMODES with EdPCR and transform it to SAnn) - Run FullProf trying to determine ab initio the amplitudes of the modes (SAnn) - Refine the powder data using the Rietveld method and the amplitudes of the modes as free parameters. - Visualise the different modes using FullProf Studio Excercise 2: CaTiO3 (Neutron data provided by Saurabh Tripathi) ============ The exercise is similar to the previous one. Just consider a refinement of the powder diffraction pattern and compare the results obtained with the case of LaMnO3. In this case we have the following parameters: Lambda= 1.249 angstroms. The space group is Pbnm (standard setting Pnma, #62) with cell parameters a=5.3795, b=5.4407 and c=7.6446 angstroms. Approximate values for the gaussian part of the IRF parameters are: u=0.646 v=-0.309 0.14234 (degrees^2). The format of the data file corresponds to INS=0 (angular range: (0, 133) in 2Theta). - Generate a PCR file from AMPLIMODES and adapt it to the above parameters. One can also modify the PCR file of LaMnO3 and adapt it to this case. - Refine the powder data using the Rietveld method and the amplitudes of the modes as free parameters, putting the constrain of a maximum amplitude of 1.5 angstroms. - Compare the results with the case of LaMnO3. Excercise 3: LiMn2O4 (J. Rodriguez-Carvajal et al. PRL 81(21), 4660, 1998) ============ The neutron data have been obtained in 3T2 (LLB). At 350K the structure correspond to a normal spinel SPG: F d -3 m. The wavelength is 1.2253 angstroms. Approximate values for the gaussian part of the IRF parameters are: u=0.2433 v=-0.2863 w=0.1632 (degrees^2). The format of the data file corresponds to INS=6 (angular range: (0, 125) in 2Theta). The complete information is given in file LiMn_350K.pcr. The low temprature phase is orthorhombic F d d d with a tripling of the a and b axes. - Refine the data at 350K to obtain the structural parameters of the HS phase - Generate a PCR file from AMPLIMODES for the LT phase trying to find the origin shift - Refine the powder data directly using the Rietveld method and limiting the amplitudes of the modes to a maximum of 1.0 angstrom.