The Study On Preparation, Properties Of Doped ZrO₂ Electrolytes And The DFT For The Conductivity

Yb₂O₃, Sc₂O₃ (Dy₂O₃), Al₂O₃ and/or CaO doped-YSZ electrolyte materials wereprepared by high-temperature solid-state method and combustion synthesis withglycin, respectively. The material properties, including the conductivity, sintering,bending strength and microstructure, were analyzed experimentally. The mechanismof improving material properties by means of doping multi-elements in ZrO₂ wasstudied by the density functional theory (DFT). In addition, the molecular dynamic(MD) simulation was applied to study the interaction of AFM Ni tip and Au (001)substrate.Introducing Y2O3, Yb₂O₃ and Sc₂O₃ (Dy₂O₃) in ZrO₂ could build a stable ZrO₂ cubicstructure in room temperature, induce the increase of crystal constants and oxygenvacancy transfer passage radii (R), and improve the grain boundary condition. Itenhanced the high-temperature conductivity and the aging property of samplesremarkably. The conductivity reached 0.19S/cm at 1000℃with the total additives inthe range of 8⁸.6mol%. The conductivity (1000℃) remained about 0.15S/cm afterworking for 900h. Adding a little amount of Al₂O₃ into the multi-elements doped ZrO₂materials reduced the conductivity slightly, and less CaO could reduce theconductivity to 50%.The results of DFT calculations indicated that the replacement of Zr by Y, Yb andSc in ZrO₂ altered the bond length between the anion and the cation in some extentand the cubic structure of ZrO₂ kept stable, but such replacement led to crystaldistortion and made ionic charge redistributed. Consequently, the position of CB andVB was modulated effectively and the bond gap becomes narrow, the ionicconductivity was improved. The calculation of deformation charge densitydemonstrated that there existed different bonding among the atoms in case of multielementsdoping and there were few electrons in particular areas around doped cation.The MD simulation of AFM Ni tip/Au substrate showed that at certain tip-substratedistances (about 0.23nm), the tip jumped to contact the Au (001) by the van der waalsforce and the potential energy of the system decreased obviously, and then thenanoindentation formed after Ni tip contacting Au (001), some Au atoms adhered tothe Ni tip. The atoms layer distortion and slippage were observed on Au (001) substrate surface, and the system potential energy increased gradually. When the Nitip left the substrate, some Ni and Au atoms were exchanged, at the same time, aconnective neck mainly composed of Au formed between the tip and the substrate.The neck continued to increase until fracture occurred, which accorded to the metalgood ductibility.