Crystallographic features of the transitional state in La_1-xSr_xTiO₃

Crystallographic features of the transitional state in La_1-xSr_xTiO₃ around x=0.05 have been examined by transmission electron microscopy. In the transitional state, the insulating O' regions with the size of about 3nm are distributed in the metallic O' matrix. Note that the O' and O* phases have the Pbnm structures with the Jahn-Teller distortion and without it, respectively. Because the hole concentration of the O* phase is higher than that of the O' phase, the transitional state is therefore characterized by the static electronic phase separation. In addition, it was also found that the crystal structure of the O' phase should involve not only the (3z²-r²)-type Jahn-Teller displacement with q=0 but also the (x²-y²)-type one with q=<1/2 1/2 0>_c in the cubic Brillouin zone.