Abstract
Compositions of (ZrO2)0.92(Y2O3)0.08 (zirconia: 8 mol % yttria—8YSZ) and (CeO2)0.8(Sm2O3)0.2 (ceria: 20 mol % samaria—SDC20) ceramic powders were prepared by attrition milling to form an equimolar powder mixture, followed by uniaxial and isostatic pressing. The pellets were quenched to room temperature from 1200 °C, 1300 °C, 1400 °C and 1500 °C to freeze the defects configuration attained at those temperatures. X-ray diffraction analyses, performed in all quenched pellets, show the evolution of the two (8YSZ and SDC20) cubic fluorite structural phases to a single phase at 1500 °C, identified by Rietveld analysis as a tetragonal phase. Impedance spectroscopy analyses were carried out in pellets either quenched or slowly cooled from 1500 °C. Heating the quenched pellets to 1000 °C decreases the electrical resistivity while it increases in the slowly cooled pellets; the decrease is ascribed to annealing of defects created by lattice micro-tensions during quenching while the increase to partial destabilization of the tetragonal phase.
Highlights
Similar to what happens to high-entropy alloys [1,2,3,4], high-entropy oxides or entropy-stabilized oxides are compounds that result from the combination of an equimolar content of several oxides prepared in such a way that the cations are randomly distributed in the cationic sublattice [5].The preparation involves heat treatment at temperatures that allow for the migration of the cations to thermodynamically minimum energy sites, followed by quenching to room temperature to retain the thermodynamic configuration achieved at high temperatures
It has been suggested that entropy-stabilisation is a “ effective compound with ionic character”, we investigated this suggestion using equimolar combinations of paradigmatic ionic conductors ZrO2 : 8 mol % Y2 O3 (8YSZ) and CeO2 : 20 mol % Sm2 O3 (SDC20). 8YSZ is already commercially available, as a component of electrochemical devices allowing for the environmentally compatible production of electrical energy, heat, and high-temperature solid oxide fuel cells
8 mol % yttria and ceria: 20 mol % samaria shows the evolution of the two original cubic fluorite structuresto toaanew newstructure
Summary
Similar to what happens to high-entropy alloys [1,2,3,4], high-entropy oxides or entropy-stabilized oxides are compounds that result from the combination of an equimolar content of several oxides prepared in such a way that the cations are randomly distributed in the cationic sublattice [5].The preparation involves heat treatment at temperatures that allow for the migration of the cations to thermodynamically minimum energy sites, followed by quenching to room temperature to retain the thermodynamic configuration achieved at high temperatures. X-ray diffraction is the main technique to monitor the phase constitution of the primary components and the evolution of the crystalline structure to that of the final compound. If that transition is reversible, i.e., if the compound can be decomposed back to the primary components, the transition is recognized as entropy-driven [5]. The thermodynamically metastable new compound may have new structural phases and/or lattice parameters with new, eventually enhanced, physical properties. A series of experiments was reported on a new compound based on an equimolar mixture of MgO, CoO, NiO, CuO and ZnO, a five-component oxide with high configurational entropy [5]
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