" Are ATZ values calculated automatically by Fullprof program correct? "

Yes  it calculated automatically.

U can try to change it to 0, then refine.

!Nat Dis Ang Pr1 Pr2 Pr3 Jbt Irf Isy Str Furth ATZ Nvk Npr More

1 0 0 0.0 0.0 1.0 0 0 0 0 0 0 0 5 0

Make sure the atom´s occupancies proportional to:

Occ =  site multiplicity of the Wyckoff position / multiplicity of a general position.

dear Maykel you are right, it calculate automatically. my doubt is with defining chemical occupancy , f & t  which is as following

Occ = chemical occupancy (A) × site multiplicity (m) / multiplicity of a general position (M). = Am/M

then calculating f=Occ.M/m = (Am/M)*(M/m) = A = chemical occupancy??

What should be value of t?

How to calculate ATZ manually with for P m -3 m with Z =1, MW = 325. Assuming A at 1a, B at 1b and O at 3c? calculating Occ & f for oxygen (3c) is not clear to me. Kindly elaborate. General multiplicity (M) =48.

What is chemical occupancy of O (at 3c) = 3 or 1 or 1/3?

Not like GSAS or other, Fullprof requires you to correct for overgeneration.

Ex. Pb (Mg,Nb) O3, Pm-3m has 48 equivalent positions, International Table for Crystallography - A (page 673), so;

O occ =  3 / 48 = 0.06250

Pb occ = 1 / 48 = 0.02083 (0.00694+0.01389)

(Mg,Nb) occ = 1 / 48 = 0.02083

I think it follow this proportional rule; 3 : 1 : 1 = 1 :1/3 : 1/3.

For t which is the Brindley coefficient for microabsorption effects is not easy to account. This correction needs the mean particle diameter for every phase as input, which is not accurately known in most cases.

"G.W. BRINDLEY, The effects of grain and particle size on X-ray reflections from mixed powders and alloys, considered in relation to the quantitative determination of crystalline substances by X-ray methods, Phil. Mag. (1945), 36, 347 - 369."

My practice with cement is I use the mixture of known material with the same preparation to get the value.

Thanks for help. This way I have calculated and highlighted by bold letter in question.  Main doubt was regarding chemical occupancy of an atom/ion having multiplicity >1. And I follow your line "it follow this proportional rule; 3 : 1 : 1 = 1 :1/3 : 1/3".

I did SrTiO3 (Pm-3m) simulation with Fullprof ;

- Sr : T i: O = 0.02803 : 0.02803 : 0.06250

- Sr : T i: O = 1 : 1 : 3

I think u'll got the idea of the overgeneration.

What means negative or postive Biso ? 

Yes I agree with what Maykel Manawan said, he gave you the exact answer, great !

anyhow just to make sure that fullprof will calculate the ATZ number correctly the fitting should be good, that means a total chi-squared value < 1.5 . and one important thing the Occ occupational number should be correct and normalized for all phases according to the site multiplicity.

Just to make sure it is clear:

when you are fitting multi-phase pattern, the site OCC number should be normalized to the same value for all phases, as example if you have an Oxygen atom in phase one located at 4F site, choose a normalized OCC number corresponding to it, lets say 0.4, then the Oxygen atom located in the 4F site in the second phase should have the Occ number 0.4 and the Oxygen number which located in the 12K site has the Occ number 1.2, and so on, got it !!

Now for your material you can use the Bilbao Crystallographic - Wyckoff Positions http://www.cryst.ehu.es/cryst/get_wp.html

to check out your sites, "the FullProf generate it automatically form the space group also"

Wyckoff Positions of Group 221 (Pm-3m)

http://www.cryst.ehu.es/cgi-bin/cryst/programs/nph-wp-list?gnum=221

Wyckoff Positions of Group 160 (R3m) [h axes]

http://www.cryst.ehu.es/cgi-bin/cryst/programs/nph-wp-list?gnum=160&grha=hexagonal

the Pm-3m it would be like:

Atom   Wyck.   Site            x/a             y/b              z/c              Occ

Pb+2    1a       m-3m       0.00000    0.00000    0.00000    0.10000

Mg+2   1b       m-3m       0.50000    0.50000    0.50000    0.03333

Nb+5   1b       m-3m       0.50000    0.50000    0.50000    0.06666

O-2      3c       4/mm.m    0.50000    0.50000    0.00000    0.30000

Note that we divide the site occupancy to third and two third according to the chemical occupancy for each element on that site.

note that you may need to refine the (z/c) position for Nb in the first sample (Pm-3m), to fit the atomic position shift that may appear from the larger atomic dopancy, so the Wyckoff position would change to the 6f site (see the table) and the occupation would be one-sixth (1b / 6f) of the remaining occupancy --> (0.1) x (2/3) x (1/6) = 0.01111111

Atom   Wyck.   Site             x/a             y/b              z/c              Occ

Pb+2    1a        m-3m        0.00000    0.00000    0.00000    0.10000

Mg+2   1b        m-3m        0.50000    0.50000    0.50000    0.03333

Nb+5    6f         4m.m        0.50000    0.50000    (0.5 ± z)    0.01111

O-2       3c        4/mm.m    0.50000    0.50000    0.00000    0.30000

the R3m would be like:

Atom   Wyck.   Site      x/a             y/b              z/c              Occ

Pb+2   3a         3m      0.00000    0.00000    -0.02811   0.30000

Mg+2  3a         3m      0.00000    0.00000    0.50000    0.10000

Nb+5   3a        3m      0.00000    0.00000    0.50000    0.20000

O-2      9b         .m       0.16667    0.16667    0.66667    0.90000

in this way you would restrict the normalized occupation number, to set the frame of reference for the software which will use accordingly  to change the phase scale factor value to fit with the accumulative diffracted intensity in your data. As result, the ATZ would be calculated correctly. The Brindly coefficient is not easy to calculate but I guess it would be the same for your material as it depends on the absorption and reflection factor for the material, however, the material preparation may play a rule on this, where the grain size, surface structure on the X-ray testing plate and the ratio of the precursor exactly would change the value of Brindly, anyway it is worth to try this without changing it then you may judge on the result regarding to the XRD pattern for each phase.  

hope this would be helpful for you 

Good luck

Dear Maykel Manawan and Yazan Maswadeh, thanks for your support.

Dear Sir,

Could you please help? I want to refine the following compound Li1.2Ni1/3Co1/3Mn1/3O2  by using full prof software. This compound is isostructural with LiNiO2 layered structure , hexagonal (space group R3m). Li in the 3a site (0,0,0.5), while Ni, Mn and Co in the 3b site (0,0,0), O in the 6c site (0,0,0.25). In addition, Li/Ni  partially replacement is possible. Furthermore, Ni can be present in two oxidation state Ni3+ as well as Ni2+. So, I want to know the exact position of every atom in the structure. I am confused about B and Occ values, what are they mean? how to calculate them. I am beginner to Full Prof.

Looking forward for your kind reply.

Regards,

Mezaal