Electrical and thermal conductivities of rare-earth A2Zr2O7 (A = Pr, Nd, Sm, Gd, and Er)

Structural and thermoelectric properties of rare-earth zirconates A 2 Zr 2 O 7 , with A = Pr, Nd, Sm, Gd, and Er, were studied. Samples were prepared by solid-state reaction at ambient pressure with temperatures between 1000 and 1400 °C. The resulting compounds were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM/EDS). The XRD analyses showed the formation of polycrystalline Pr 2 Zr 2 O 7 , Nd 2 Zr 2 O 7 , Sm 2 Zr 2 O 7 , Gd 2 Zr 2 O 7 and Er 2 Zr 2 O 7 phases, with a cubic cell (space group Fm3m) and traces of the raw used materials. The micrographs obtained by SEM show the formation of heterogeneous grains with a size that ranges from 0.7 to 4.7 μm. All A 2 Zr 2 O 7 samples present porous surfaces. Thermal conductivities were measured at different temperatures, from 300 to 900 K. In most of the samples, the thermal conductivity monotonically decreases with temperature, from 0.40 – 1.17 W/mK at 300 K to 0.27 – 0.77 W/mK at 773.15 K. At a fixed temperature, the thermal conductivity decreases almost monotonically with the ionic radius ( IR ) of the rare-earth elements (where IR (Er 3+ ) = 0.890 A < IR (Gd 3+ ) = 0.938 A < IR (Sm 3+ ) = 0.958 A < IR (Nd 3+ ) = 0.983 A < IR (Pr 3+ ) = 0.99 A).