Structural study and electrical properties of Zr-doped Nd₂Sn₂O₇ pyrochlore compounds

Y D KOLEKAR¹, S B KULKARNI², KEKA CHAKRABORTY³, A DAS³, S K PARANJPE^3,* and P B JOSHI²

¹Physics Department, Shivaji University, Kolhapur 416 004, India

²Physics Department, Shivaji University PG Centre, Solapur 413 255, India

³Condensed Matter Physics Division, Bhabha Atomic Research Centre, Mumbai 400 085, India

^*Present address: International Atomic Energy Agency, Vienna, Austria

E-mail: ydkolekar@yahoo.co.in

Astract. Nd$_{2}$Sn$_{2}$O$_{7}$ pyrochlores with the substitution of Zr$^{4+}$ were prepared by conventional ceramic double sintering technique. The single-phase formation was confirmed by X-ray diffraction and neutron diffraction techniques. Relative intensity calculations for X-ray diffraction analysis were performed for oxygen positional parameters $x = 0.331$ and 0.375, while Rietveld refinements were employed for neutron diffraction data. The neutron diffraction study revealed that there are only two anion sites with 48f and 8b positions. This indicates that the 8a site, i.e. O(3) sublattice, is completely vacant and the structure is a perfect cubic pyrochlore with space group Fd3m (O$^{7}_{h}$).

From the conductivity measurements, it is observed that the electronic conductivity dominates from room temperature up to about 525 K and for $T > 525$ K, the oxygen ion conduction dominates the charge transport in these compositions. Complex impedance spectroscopy indicates the existence of grain and grain boundary as two separate elements.

Keywords. Pyrochlores; neutron diffraction; complex impedance spectroscopy.

PACS Nos 61.12.-q; 61.10.-i; 77.84.-s