Can any body know, how we can find the angle of tilt of the octahedra from the atomic co-ordinates?
How we can know about the short and long range cation/vacancy ordering from XRD spectrum? How we can know that these short and long range cation/vacancy ordering indicate tetragonal or orthorhombic distribution?
Thanks Respected Artur Braun , for your valuable suggestion. Can you send me some related documents(papers) related to to the above mention topic.
---------------Thanks once again....................
You are touching a quite complex problem for which A. Braun gives a certainly correct advice, but as you already see in his answer, for the experiments you need very specific equipment like neutron reactor or synchrotron in order to be able to discover ordering effects. Also the vacancy problem is practically solvable only if you make very strong assumptions since the used intensities depend much more on other effects like preferred orientations. This means you have to develop specific procedures to prepare your samples that they are able to generate exactly the signal you are looking for.
However, there is still another thing which puzzles me. The "tilt" of your octahedron. Do you really mean tilt (rigid body rotation), or more a distortion of your "octahedron", or even both? As A. Brauns claimed, both you can extract from an X-ray diffractogram (better than spectrum which is commonly used for an energetic scale and not for an angular scale). Or do you have the crystal structure as model already? In both cases you will get a structure description which you need to transfer into cartesian coordinates in order to calculate the respective angles. Here the question arises, which angle you are intersted in? Within the octahedron it is simple since you only need a software which enables the determinations of angles between planes formed by atoms. If you are interested in the tilt of the octahedron it is a bit more complicated if there are no atoms along edges or planes of the unit cell. It is comparatively easy to calculate these angles but it is not that convinient as in the first case. Personally, I don't know any book which exactly describes this topic in a way that you can use it directly. It is too fundamental, i.e. if you understand geometrical crystallography it should be easy for you to derive the required values from atomic coordinates...and practically every crystallographic software uses these values internally, even if it doesn't visualize them. However, a good start would be to make yourself familiar with the so-called metric tensor. Sounds more horrible than it finally is, but it saves a lot of complicated calculations.
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