Doping means replacing A or B instead of new materials, normally doping new materials occupy A site or B site on its preference, which influences the materials to have some change in characteristic properties like electrical, magnetic etc. which are related to charge ( presence of amount charge in the A- site and B- site) but not in the physical characteristic. which means no physical pressure as your question says chemical pressure. I suggest to find cation distribution from which you try to find chemical pressure using molar equations. It is completely due to cation distribution find the cation distribution by Mössbauer spectroscopy or by cation distribution from X-ray diffraction? Rietveld refinement method or comparison intensity ratios. 

If you substitute any atom by another of smaller size then you generate a positive chemical pressure whereas if you do with larger atom then you generate negative chemical pressure in general. This is just what you expect in the first approximation. But different atoms are electronically different and substitution may cause considerable modification in the electric structure of the material and also the magnetic states. These may introduce additional effects that are normally smaller but need not be always. There are plenty of examples in the literature. You can for example look at a (P-T) and (x,T) phase diagram of EuAs3 in Fig. 3 of (PRB 41, 4358 (1990). You will see there that substitution of As by smaller P produces positive chemical pressure and the two phase diagrams look very similar with similar magnetic phases. A more recent example is the generation of the super conducting phase either by physical pressure or by chemical pressure generated by substituting As atoms by P in BaFe2As2. See Nat. Materials 8, 471 (2009).

I can give you many more examples of such chemical pressure effects in many other solid compounds. In fact when calculations or your experience suggest some interesting effects on a material at negative pressure then you have no other choice than substitution by appropriate atoms without disturbing much the electric structure of the system.