Structural Transitions and Localization in La_{<b>2</b>-<i><i>x</i>-<i>y</i></i>}Nd_{<i><i>y</i></i>}Sr_{<i><i>x</i></i>}CuO_<b>4</b>with<i><i>p</i>∼<b>1/8</b></i>

In order to clarify the influence of lattice deformation on the electronic states, we have measured ultrasound velocity and X-ray diffraction of La 2- x - y Nd y Sr x CuO 4 (LNSCO) with a particular carrier number of p ∼1/8. As temperature is reduced, LNSCO exhibits a first-order transition to the low-temperature tetragonal phase P 4 2 / n c m , after a second-order transition from the well-known orthorhombic phase B m a b to another orthorhombic phase P c c n . A semiconductor-like upturn is observed in resistivity, indicating tendency of localization in the normal state in these low-temperature phases of P c c n and P 4 2 / n c m . These structural changes are also reflected on the magnetic properties, which are well understood only with taking into consideration the antiferromagnetic coupling between Nd and Cu spins.

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