The Development of New Multivalent Cation Conducting Solid Electrolyte and Their Application for Gas Sensors

到目前为止，由于三价阳离子的高价状态，一直被认为是固体中迁移能力较差的离子物种，而对一价或二价离子导电固体的研究却很多。最近，我们成功地研制了具有NASICON型结构的三价阳离子导体(M_&lt；0.2&gt；Zr_&lt；0.8&gt；)__&lt；20/19&gt；Nb(PO_4)_3固体电解质(M=三价阳离子)。(M_&lt；0.2&gt；Zr_&lt；0.8&gt；)_&lt；20/19&gt；(PO_4)_3固体的三价离子电导率与具有代表性的二价O^&lt；2-&gt；离子导电固体一样高。然而，要用于各种电化学设备，如气体传感器，就必须提高离子的导电性。此外，由于(M_&lt；0.2&gt；Zr_&lt；0.8&gt；)_&lt；20/19&gt；(PO_4)_3的机械强度不够，我们试图提高(M_&lt；0.2&gt；Zr_&lt；0.8&gt；)_&lt；20/19&gt；(PO_4)_3固体的离子导电性和机械强度。在这里，我们选择了(Al_&lt；0.2&gt；Zr_&lt；0.8&gt；)__lt；20/19&gt；Nb(PO_4)_3作为靶材，合成了(M_&lt；0.2&gt；Zr_&lt；0.8&gt；)；通过在(Al_&lt；0.2&gt；Zr_&lt；0.8&gt；)_&lt；20/19&gt；Nb(PO_4)_3的烧结阶段加入6-8wt%的B_2O_3，使B_2O_3挥发，样品颗粒之间高度聚集，从而获得高机械强度和高密度的烧结体。此外，与未掺杂的B_2O_3样品相比，三价铝离子的电导率也提高了一倍。我们还制备了添加上述B_2O_3的(Al_&lt；0.2&gt；Zr_&lt；0.8&gt；)_&lt；20/19&gt；Nb(PO_4)_3固体以及O^&lt；2-gt；离子导电Y3稳定的氧化锆(YSZ)和稀土硫酸盐敏感辅助电极。传感器输出电动势与CO_2浓度在550℃处的对数符合理论能斯特关系，能准确检测出CO_2浓度。

UP to now, trivalent cation has been believed as a poor migrating ion species in solids because of the high valence state, whereas monovalent or divalent ion conducting solids were intensively studied. Recently, we have been succeeded in developing the trivalent cation conducting (M_<0.2>Zr_<0.8>)_<20/19> Nb(PO_4)_3 solid electrolytes (M = trivalent cations) with NASICON type structure. The trivalent ion conductivity of the (M_<0.2>Zr_<0.8>)_<20/19>(PO_4)_3 solid is as high as those for representative divalent O^<2-> ion conducting solid. However, it is necessary to enhance the ion conductivity to utilize for various electrochemical devises such as gas sensors. Furthermore, since the mechanical strength of (M_<0.2>Zr_<0.8>)_<20/19>(PO_4)_3 is not enough, we try to improve bath the ion conductivity aril the mechanical strength of the (M_<0.2>Zr_<0.8>)_<20/19>(PO_4)_3 solid. Here, we selected (Al_<0.2>Zr_<0.8>)_<20/19> Nb(PO_4)_3 as a target material due to it highest trivalent ion conductivity among the (M_<0.2>Zr_<0.8>)_<20/19>(PO_4)_3 series, and we synthesized the (M_<0.2>Zr_<0.8>)_<20/19>(PO_4)_3 solid with a sintering aid of B_2O_3.By adding 6-8 Wt% B_2O_3 at the sintering step of the (Al_<0.2>Zr_<0.8>)_<20/19> Nb(PO_4)_3 solid, B_2O_3 vaporized With high aggregation between sample particles resulting in high mechanical strength and high density of the sintered sample. Furthermore, the trivalent Al^<3+> ion conductivity was also enhanced two times compared with that for B_2O_3 non-doped sample.We have also fabricated the CO_2 gas sensor with above mentioned B_2O_3 added (Al_<0.2>Zr_<0.8>)_<20/19> Nb(PO_4)_3 solid together with O^<2-> ion conducting yttria stabilized zirconia (YSZ) and rare earth oxysulfate based sensing auxiliary electrode. Tile present sensor can detect the CO_2 concentration exactly with obeying theoretical Nernstian relationship between sensor output EMF and the logarithm of the CO_2 concentration at 550℃.