Ionic conductivity enhancement in Gd_2Zr_2O_7 pyrochlore by Nd doping

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 (dc) varies upon Nd substitution at the Gd site, and a peaking effect in 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 dcT 0 exp(�E/kBT). The activation energy E and the preexponential factor 0, which is a measure of the concentration of the mobile species, increase while going from the ordered Nd2Zr2O7 to the least ordered Gd2Zr2O7. These two processes presumably lead to the peaking of dc at an intermediate Nd content. Our results also suggest that the cooperative motion of mobile ions does not contribute muc ht o the increase in activation energy in this compound.

[1]  A. K. Tyagi,et al.  Preparation and high temperature-XRD studies on a pyrochlore series with the general composition Gd2−xNdxZr2O7 , 2007 .

[2]  A. K. Tyagi,et al.  Phase relations and high temperature-XRD studies of Gd2−xNdxTi2O7 solid solutions , 2007 .

[3]  K. Moreno,et al.  Room-temperature synthesis and conductivity of the pyrochlore type Dy2(Ti1−yZry)2O7 (0⩽y⩽1) solid solution , 2006 .

[4]  K. Moreno,et al.  Mechanochemical synthesis and ionic conductivity in the Gd2(Sn1–yZry)2O7 (0⩽y⩽1) solid solution , 2006 .

[5]  K. Moreno,et al.  Cooperative oxygen ion dynamics in Gd_(2)Ti_(2-y)Zr_(y)O_(7) , 2005 .

[6]  M. Weller,et al.  The pyrochlore family -- a potential panacea for the frustrated perovskite chemist. , 2004, Dalton transactions.

[7]  Jie Lian,et al.  Ion-irradiation-induced amorphization of La 2 Zr 2 O 7 pyrochlore , 2002 .

[8]  J. Maguire,et al.  Oxygen migration in A2B2O7 pyrochlores , 2001 .

[9]  C. Catlow,et al.  Defects and diffusion in pyrochlore structured oxides , 1998 .

[10]  A. N. Yusoff,et al.  Frequency dependence of the complex impedances and dielectric behaviour of some Mg-Zn ferrites , 1997 .

[11]  U. Varadaraju,et al.  Oxide ion conductivity in some substituted rare earth pyrozirconates , 1995 .

[12]  E. Prince,et al.  Fast-ion conducting Y2(ZryTi1−y)2O7 pyrochlores: neutron Rietveld analysis of disorder induced by Zr substitution , 1995 .

[13]  H. Tuller,et al.  Conduction in titanate pyrochlores: role of dopants , 1994 .

[14]  H. Tuller,et al.  Ionic conduction in the Gd2Ti2O7−Gd2Zr2O7 system , 1988 .

[15]  A. Burggraaf,et al.  Oxygen ion and mixed conductivity in compounds with the fluorite and pyrochlore structure , 1983 .

[16]  G. V. Subba Rao,et al.  Oxide pyrochlores — A review , 1983 .

[17]  M. Verkerk,et al.  STRUCTURE AND CONDUCTIVITY OF PYROCHLORE AND FLUORITE TYPE SOLID SOLUTIONS , 1981 .

[18]  R. D. Shannon.  Revised effective ionic radii and systematic studies of interatomic distances in halides and chalcogenides , 1976 .