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Study of Nd2±xHf2±xO7±δ system: the ionic and thermal transport properties
The phase composition, microstructure, electrical and thermal conductivity of Nd2±xHf2±xO7±δ ceramic materials have been studied. (Nd2-xHfx)Hf2O7+x/2 (x = 0.2, 0.32, 0.39) composites, containing 4–16 wt% HfO2, have the highest conductivity and the brightest narrow-band luminescence among materials under study. The (Nd2-xHfx)Hf2O7+x/2 (x = 0.2) composite, containing ~ 4 wt % HfO2, is shown to have the lowest thermal conductivity: 1.52 W m–1 K–1 at 300 K. XRD and Raman spectroscopy results show that (Nd2-xHfx)Hf2O7+x/2 (x = 0.2, 0.32, 0.39, 1.14) are composites consisting of a mixture of pyrochlore solid solutions with Hf on the Nd site and two HfO2 polymorphs (m - HfO2 and γ2 - HfO2 nanodomains). The properties of the (Nd2-xHfx)Hf2O7+x/2 (x = 0.2, 0.32, 0.39, 1.14) composites are compared to that of the Nd2(Hf2-xNdx)O7-x/2 (x = 0, 0.1) pyrochlores, and the best properties were shown by the (Nd2-xHfx)Hf2O7+x/2 (x = 0.2, 0.32) composites.