Preparation And Conduction Behaviors Of M_1-xD_xP₂O₇(M=Sn⁴⁺, Ti⁴⁺; D=Zn²⁺, Ga³⁺)

As we all know, inorganic proton conductor is a kind of important functionalmaterials for many potential electrochemical applications such as fuel cell, hydrogensensor, ammonia synthesis at atmospheric pressure, etc.Recently, a novel intermediate temperature inorganic proton conductor–pyrophosphate （MP₂O₇） has aroused a great interest. MP₂O₇based ionic conductionmaterials have high proton conductivity in the temperature range of100―600°C, andinsoluble in water, good thermal stability. Until now, the effect of Zn²⁺doping level onphase purity and electrochemical properties of Zn²⁺-doped SnP2O7and Ga³⁺-dopedTiP₂O₇ionic conduction ceramic material have yet not been reported.Therefore, in the thesis，we focused on the conduction behaviors at intermediatetemperature of MP₂O₇based conduction materials. Main works and results in this paperare as follows:（1） Chapter1—Introduction. We introduced briefly some typical solid electrolytematerials, inorganic proton conductor, concerned defect chemistry, proton transferencemechanism, and their applications. In addition, we summarized the internal and externalresearch background on MP₂O₇-based intermediate temperature electrolyte materials,proposed the present theme and the research meaning.（2） Chapter2—Preparation and intermediate temperature conducting performancesof Sn1-xZnxP2O7. A series of Sn1-xZnxP2O7（x=0,0.03,0.06,0.09,0.12） ceramic samplewere prepared. The doping limit of Zn²⁺in SnP2O7is9mol%. The dopant content x inthe samples remarkably influenced the conduction properties. Conductivities increasedin the order: σ （x=0.12）<σ （x=0.00）<σ （x=0.03）<σ （x=0.06）<σ （x=0.09）.Thehighest conductivities were observed for the sample of x=0.09to be1.69×10^-4S·cm^-1in wet air and1.91×10^-4S·cm^-1in wet hydrogen at600°C. The results of the gasconcentration cells suggested that in wet hydrogen atmosphere Sn_0.91Zn_0.09P₂O₇wasalmost a pure ionic conductor; the ionic conduction was contributed mainly to proton and partially to oxide-ion, whereas in wet air atmosphere, the sample was a mixedconductor, and the conduction was contributed mainly to electron hole partially to ion.（2） Chapter3—Preparation and intermediate temperature conducting performancesof TiP₂O₇based ceramic. A series of Ti_1-xGa_xP₂O₇（x=0,0.03,0.06,0.09） sample andTi_0.97Ga_0.03P₂O₇+y wt%ZnO （y=1,2,3） ceramic sample were prepared. The dopinglimit of Ga³⁺in TiP₂O₇is3mol%.Ti_0.97Ga_0.03P₂O₇+2wt%ZnO is of single phasestructure through sintering at1000°C. The highest conductivity was observed forTi_0.97Ga_0.03P₂O₇+2wt%ZnO to be8.02×10^-5S·cm^-1in air at600°C. In high oxygenpartial pressure range （pO2=10-5¹atm）, the conductivity was independent of oxygenpartial pressure, indiating that the sample was almost pure ionic conductor. Whereas inlow oxygen partial pressure (pO₂=10-5¹0^-20atm), the conductivity increased with thedecreasing oxygen partial pressure, indicating that it was a mixed conductor of ion andelectron. The results of the gas concentration cells suggested that in wet hydrogenatmosphere Ti_0.97Ga_0.03P₂O₇+2wt%ZnO was a mixed conductor of ion and electron.Whereas in wet air atmosphere Ti_0.97Ga_0.03P₂O₇+2wt%ZnO was almost a pure ionicconductor, the ionic conduction was contributed mainly to proton and partially tooxide-ion.