If you do not know these parameters you should not play with software...

http://pd.chem.ucl.ac.uk/pdnn/refine3/adps.htm

https://www.researchgate.net/post/What_are_isotropic_and_anisotropic_displacement_parameters_in_single_crystal_xray_structure_analysis

https://www.crystallographiccourseware.com/ThermalParameters/ThermalParameters.html

https://www.researchgate.net/post/What_is_the_importance_of_atomic_displacement_parameters_U_in_GSAS

http://pd.chem.ucl.ac.uk/pdnn/refine2/tls.htm

http://www.cmbi.ru.nl/bdb/theory/

and now you should find a lot of other key words to look in internet...

Sometimes also a simple book can help. There are tens or more available in libraries, in case you do not have one. Some of them are possibly also free available.

Good luck!

Biso is a very tricky parameter to play with. I would not refine the parameter unless I have a very high quality pattern up to high angles and know quite a lot about the diffractometer used. It is often the case that you get negative B which does not make any physical sense and it is more like a fit routine compensator.

Thank you for answering me but when I refine B evertimes goes to negative and sometimes goes to - 5. Also I want to know the maximum and minimum value up to I should gain this.

B is the atomic displacement parameter. It can not get negative value. Typically if I donot want to play with it, I fix it to 0.05, some tiny value. When by refining B, everything goes wrong and B get negative values, it means that your model is not stable enough. That counts for different parameters. maybe there are some atoms in other positions that you do not know and so on.

As mentioned before, very tricky parameter. Prior to trying refine it, you must be sure that your apparatus-related FWHM parameters (U V W) are correctly estimated using calibration measurements on eg. LaB6 for XRD (NIST660). If so, you can start to play with the strain/size and Biso parameters. Negative value of Biso means that there are some other factors influencing intensities - preferred orientation/disorder at different sites, which are not taken into account in your current model. Strongly negative values of Biso, less than -0.3 means that something is really wrong. Typical values at room temperature should be around 0.5 to 1 depending of the mass of the atom as well as its coordination. Biso may be increased significantly in the vicinities of phase transitions, but this is another story.