Ce0.5Yb0.5O1.75 was prepared for the first time through high temperature (1600 degrees C for 5 h) solid state reaction, after high energy milling to enhance the mechano-chemical interaction of precursor oxides (CeO2 and Yb2O3). Single phase formation was confirmed by powder X-ray diffraction. Impedance spectroscopy data obtained under wide temperature (300-800 degrees C) and oxygen partial pressure (0.21 to about 10(-25) atm) ranges indicates that this material exhibits predominant oxide-ion conductivity under oxidizing conditions while n-type electronic conductivity prevails at low oxygen partial pressure. The mixed oxide shows modest ionic conductivity (1.1 x 10(-3) S cm(-1) at 800 degrees C) with activation energy of 1.3 eV in the 600-800 degrees C temperature range. When combined with molten carbonates (Li2CO3+Na2CO3, 1:1 molar ratio) to produce composite electrolytes, Ce0.3Yb0.5O1.73 slightly decomposed. However, the composite electrical performance is still acceptable and closely matches the conductivity of similar materials (>0.1 S cm(-1) immediately above 500 degrees C). (C) 2015 Elsevier Ltd. All rights reserved.