Resumen de Electrical and thermal conductivities of rare-earth A_(2)Zr_(2)O_(7) (A = Pr, Nd, Sm, Gd, and Er)
A. Quiroz, V. García Vázquez, C. Guarneros Aguilar, R. Agustín-Serrano, E. Chavira, M. Abatal
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 Å < IR (Gd^(3+)) = 0.938 Å < IR (Sm^(3+)) = 0.958 Å < IR (Nd^(3+)) = 0.983 Å < IR (Pr^(3+)) = 0.99 Å).
