Phase separation and insulator-metal behavior of doped manganites

Structural and magnetic properties of the phase separated state in ${\mathrm{Nd}}_{0.55}({\mathrm{Sr}}_{0.17}{\mathrm{Ca}}_{0.83}{)}_{0.45}{\mathrm{MnO}}_3$ have been investigated by means of synchrotron radiation x-ray as well as neutron powder diffraction experiments. We have observed a phase transformation into the phase separated (two-phase) state below $T_{\mathrm{CO}}\sim 200$ K, and have observed that the lattice constants change discontinuously at the transformation. On the basis of the structural and magnetic data, origin of the insulator-metal behavior is discussed.