Effect of A-site ionic size variation on TCR and electrical transport properties of (Nd0.7-xLax)0.7Sr0.3MnO3 with x = 0, 0.1 and 0.2

In this work, the structural and transport properties of (Nd0.7-xLax)0.7Sr0.3MnO3 manganites with x 0, 0.1 and 0.2 prepared by solid state reaction route are studied. These compounds are found to be crystallized in orthorhombic structural form. Experimental results showing a shift in the metal to semiconductor/insulator transition temperature (TMI) towards room temperature (289 K) with the substitution of Nd by La, as the value of x is varied in the sequence (0,0.1,0.2), have been provided. The shift in the TMI, from 239 K (for x=0) to near the room temperature 289 K (for x=0.2), is attributed to the fact that the average radius <rA> of site-A increases with the percentage of La. The maximum temperature coefficients of resistance (TCR) of (Nd0.7-xLax)0.7Sr0.3MnO3 (x= 0.1 and 0.2) are found to be higher compared to its parent compound Nd0.7Sr0.3MnO3. The electrical transport mechanisms for (Nd0.7-xLax)0.7Sr0.3MnO3 (x= 0 to 0.2) are explored by using different theoretical models, for temperatures below and above TMI. An appropriate enlightenment for the observed behavior is discussed in detail.