Journal Article

Ionic conductivity enhancement in Gd 2 Zr 2 O 7 pyrochlore by Nd doping

Mandal, B.P., Deshpande, S.K., Tyagi, A.K.

2008

Overview

The pyrochlore compositions Gd 2– y Nd y Zr 2 O 7 ( y = 0.0, 0.1, 0.4, 0.6, 1.0, 1.4, 1.6, and 2.0) were synthesized, and their ionic conductivity was determined (100 Hz–15 MHz, 622–696 K). The direct-current (dc) conductivity ( σ dc ) varies upon Nd substitution at the Gd site, and a peaking effect in σ dc was observed around y = 1.0. This indicates that a significant increase in conductivity can be obtained at moderately high temperatures by suitable doping at the Gd site with isovalent rare-earth ions like Nd. The extent of oxygen ion disorder determined from x-ray diffraction was found to decrease with increasing Nd content. The dc conductivity obeys the Arrhenius relation σ dc T = σ 0 exp(− E / k B T ). The activation energy E and the preexponential factor σ 0 , which is a measure of the concentration of the mobile species, increase while going from the ordered Nd 2 Zr 2 O 7 to the least ordered Gd 2 Zr 2 O 7 . These two processes presumably lead to the peaking of σ dc at an intermediate Nd content. Our results also suggest that the cooperative motion of mobile ions does not contribute much to the increase in activation energy in this compound.