鈮酸鉀 (Potassium niobate, KNbO3) 為一擁有鈣鈦礦結構之鐵電材料，室溫時為斜方晶系 (Orthorhombic)，純鈮酸鉀之相轉換溫度分別為 -10℃、225℃、425℃由菱方晶系依序相轉換為斜方晶系、正方晶系、立方晶系。當KNbO3由立方晶體結構進入到正方晶體結構時，其介電性由沒有自發性極化 (Spontaneous polarization) 的順電性轉變成具有自發性極化的強電性，此一自發性極化之產生是因為晶體結構產生變化，使離子間形成相對位移所導致。根據結晶化學理論，選擇添加La至KNbO3中，使La取代部分K的位置合成 (K1-xLax/3)NbO3固溶體。本次研究採用固態反應法製備 (K1-xLax/3)NbO3粉末，佐以XRD相鑑定及最小平方法計算晶格常數，來分析 (K1-xLax/3)NbO3的固溶範圍。由此次實驗得知，當x=0.2時，(K1-xLax/3)NbO3的晶格常數仍在改變，可能尚未到達固溶極限。根據此次實驗結果，(K1-xLax/3)NbO3系統中 (K0.95La0.05/3)NbO3獲得較佳的性質，相對密度可到達99%。當頻率為1 kHz時，介電常數為1191、品質因子為44.1。此外，確定了(K1-xLax/3)NbO3的極化機制：KNbO3與 (K0.95La0.05/3)NbO3的極化機制包括方向極化、離子極化與電子極化；(K0.9La0.1/3)NbO3的極化機制包括空間電荷極化、方向極化、離子極化與電子極化。

　　Potassium niobate (KNbO3) crystal is a ferroelectric material with a perovskite-type crystal structure. The system of KNbO3 is orthorhombic in room temperature. The phase transition temperature of pure KNbO3 is -10℃, 225℃, and 425℃ from rhombohedral to tetragonal, and then to cubic. The dielectric properties of KNbO3 have changes from paraelectricity without spontaneous polarization to ferroelectricity with spontaneous polarization, when the system structure of KNbO3 changes from cubic to tetragonal. The opposite displacement between the ions causes the change of crystal structure and produce the situation of this spontaneous polarization. According to the crystal chemistry theory, La3+ was doped into KNbO3 with perovskite structure. (K1-xLax/3)NbO3 solid solution was synthesized by La3+ substituting for part sites of K+. Therefore, (K1-xLax/3)NbO3 powders was synthesized by solid state reaction in this study. It has better piezoelectric properties around the boundary of solid-state region. But, the biggest solid-state region was not clearly determined in this study and it may be more then 0.2 lanthanum addition. The component of (K1-xLax/3)NbO3 with best properties is (K0.95La0.5/3)NbO3. Relative density can get up to 99% at 1100℃ for 0.3 h. The relative dielectric constant is 1191 and quality factor is 44.1, when the frequency is 1 kHz. In addition, poling mechanism of (K1-xLax/3)NbO3 were determined according to the relative dielectric constant and quality factor were measured in 1 kHz and 1 MHz.

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