Relationship between the Structural Transitions and the Low Temperature Electronic State of (La, Nd)_2-<i>x</i>M_xCuO₄(M=Ba, Sr;<i>x</i>∼1/8)

Abstract

Relationship between successive structural transitions and transport anomalies of La 2- x - y Nd y Ba x CuO 4 has been studied, where electrical resistivities ρ, Hall coefficients R H , thermoelectric powers S and ultrasonic sound velocities V s were measured. The transport properties exhibit no anomalous behavior at T d2 , the critical temperature of the transition from the low temperature orthorhombic (LTO1) to the low temperature tetragonal (LTT(Ba)) phase, indicating that the conduction electrons are not affected by this transition. Instead, a sudden decrease in S is observed with decreasing temperature for samples with x ∼ 0.125 at T ′ d3 ∼ 70 K. Although T ′ d3 seemed to coincide with the temperature T d3 of the tetragonal → orthorhombic transition reported by Hara et al. , results of the present X-ray diffraction study do not indicate any evidence for the existence of such a transition.