磷灰石結構矽酸鑭La10-x(SiO4)6O2+δ具有高氧離子導電率及低活化能，被認為具有作為中低溫固態氧化物燃料電池電解質的潛力，不同於高對稱性的螢石結構電解質YSZ、CeO2和Bi2O3系統或是鈣鈦礦結構的LaGaO3系統，低對稱性的磷灰石結構材料屬六方晶系，存在著可讓氧離子輕易擴散遷移的路徑。但磷灰石結構矽酸鑭固態電解質之製備仍存在許多挑戰，若以固態反應法混合製備，由於其不易燒結之特性，因此需要在高於1600 ℃以上的高溫燒結才具有高緻密度；且由La2O3/SiO2之相圖可知，La9.33(SiO4)6O2為一中間相，合成時易形成第二相La2SiO5及La2Si2O7；此外起始粉末La2O3的不穩定性，故難以控制矽酸鑭的劑量比。
本研究以La(OH)3和SiO2作為起始粉末，利用固態反應法在1200 ℃鍛燒後成功合成矽酸鑭La10(SiO4)6O3，但XRD結果指出在1550和1600 ℃燒結後有La2Si2O7的繞射峰存在。此外以通入還原氣氛H2之TGA測試其熱化學穩定性，顯示矽酸鑭為一抗具有良好抗還原性質的固態電解質材料。在燒結體微結構對導電性質的影響方面，晶粒尺寸約在490-530 nm之不同燒結體，在低溫下導電率隨著晶粒尺寸的增大而增高。而時效測試可知雖然燒結後之矽酸鑭有第二相La2Si2O7的產生，但仍維持穩定的導電率，不隨時效時間的增長而下降。

Lanthanum silicate structural with formula La10-x(SiO4)6O2+δ (LSO) are potential candidates for IT-SOFC and LT-SOFC because of its high ionic conductivity and low activation energy. Rather than fluorite and perovskite structure with high symmetric structure, lanthanum silicate with apatite-type structure is belong to hexagonal structure and believed to migrate via an interstitial conduction mechanism. Studies have indicated that LSO synthesized via solid state reactions have to be sintered at high temperature (＞1600 ℃) to achieve the desired densities. According to phase equilibrium diagram of La2O3/SiO2, the composition of La9.33(SiO4)6O2 is a intermediate phase , and La2SiO5 or La2Si2O7 are easily formed as secondary phases. In addition, it’s difficult to control the stoichiometry of LSO due to the hygroscopicity of its staring materials La2O3.
In this study, apatite-type lanthanum silicates La10(SiO4)6O3 were prepared by solid state reaction using powders of La(OH)3 and SiO2 as starting materials. The calcined samples are characterized by XRD and the results indicate that LSO have been obtained after calcination at 1200 ℃, but the La2Si2O7 impurity is formed after sintered at 1550 and 1600 ℃. TGA of the LSO powders were performed under hydrogen atmosphere, and the results indicates that LSO is a stable SOFC electrolyte materials. The effect of microstructure on the conductivity was also investigated, and the results show that the sintered ceramic with coarse grain size exhibits higher conductivity than fine one at low temperature. In addition, the aging test of LSO indicates that the sintered ceramic with La2Si2O7 impurity maintains a conductive stability.

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