Effects of the t/J perturbation in the one- and two-dimensional t-J models

We apply the perturbation theory up to order (t/J)2 to investigating phase diagrams of the 1-dimensional and 2-dimensional t-J models. In the same way as the 1-dimensional case, we find that for the 2-dimensional case there is to be stabilized the phase separation state into a hole-rich and a no-hole phases for small values of t/J. When we take sufficiently large values of t/J, on the other hand, a state of lower energy which has taken sufficient effect of t/J into consideration appears in the region of small hole concentration. (orig.)