這論文中主要是研究高品質機械因子之無鉛鈮酸鈉鉀基（NKN-based）壓電陶瓷開發及其在壓電變壓器之應用。本論文開發出燒結促進劑CuTa2O6（CT）化合物並加入鉛鈮酸鈉鉀陶瓷中，因此獲得高密度與高機電偶合係數之陶瓷體，此外，鉛鈮酸鈉鉀陶瓷之機械品質因子Qm也從67增加至1,550。添加燒結促劑CT後之NKN陶瓷可獲得良好的壓電特性：kp:42.5%；kt:49.1%；Qm:1,550；壓電係數d33:96pC/N. 另一方面，補償NKN陶瓷也是一重要因素，因為適當補償將會影響到微結構及壓電特性。在NKN摻雜CT陶瓷中，氧空缺的濃度主導著Qm值的大小。然而，在非當量NKN摻雜CT的陶瓷中，最大的Qm值並非對應到較高濃度的氧空缺，主要因素猜測是因為氧空缺的形成是由A位置的缺陷與銅離子取代鈮離子所組成，最直接影響到Qm值的大小是少價數取代多價數後所產生的氧空缺，而並非是非當量所造成的氧空缺。
氧化銅對於提升壓電特性之NKN陶瓷而言也是一不錯之添加物。使用傳統法（MO method）所製備之NKN摻雜CuO陶瓷（NKNCx）呈現的微結構為不均勻的，相反的，當NKN摻雜CuO陶瓷使用二階段煆燒法（TC method）製備呈現出較均勻之微結構，且電特性也隨之改善。使用二階段煆燒法所製備的NKN摻雜CuO陶瓷其Qm值與介電常數均比使用傳統法所製備出的陶瓷體分別多出21%與25%。在NKN摻雜CuO陶瓷中，藉由量測並計算出內建電場（internal bias field）與活化能（activation energy）來確認氧空缺的存在，使用二階段煆燒法所製備的NKN摻雜CuO陶瓷因為較多氧空缺的形成而使得內建電場也隨之增加，此外低活化能也對應到高的Qm值。使用二階段煆燒法所製備的NKN摻雜CuO陶瓷之最大Qm值可達到2,000以上，其他特性包含密度、介電損失、kp、壓電係數d33和介電常數分別為4.488 g/cm3, 0.15 %, 41.5 %, 95 pC/N和280，這些值都比非當量NKN摻雜CT陶瓷的特性要來的好。比較NKN摻雜ZnO（NKNZx）與CuO陶瓷，有著不同的結果，ZnO摻雜並沒有明顯的提升NKN陶瓷體的壓電特性。NKN摻雜ZnO陶瓷之Qm值並沒有像摻雜CuO那樣子高，藉由內建電場所量測的值接近0，說明了並無氧空缺的形成。在NKN摻雜ZnO陶瓷的壓電特性之所以會有些微的提升主要還是受到密度的影響。
在元件應用上，探討利用兩種不同製備陶瓷方式，製作成壓電變壓器（PTs），並比較其壓電變壓器之性能。由實驗結果得知，使用二階段煆燒法合成的陶瓷所製作出的壓電變壓器均能提升變壓器之輸出功率與溫度穩定性，主要因素是受到陶瓷體本身有較小之共振阻抗。此外還發現到，壓電變壓器之輸出功率受到共振阻抗的影響比Qm值來的大。為使能應用在電子安定器上，製備不同之壓電變壓器的電極面積，考量到壓電變壓器在負載為1kΩ下之效率、升壓比與元件溫升，因此採用內徑為15mm的電極面積，並結合電路設計，成功驅動13-W T5螢光燈燈管。當燈管驅動時，壓電變壓器之溫升與效別為6oC與82.4%（壓電變壓器＋電路）。目前相關研究中，此輸出功率是最大的。

In this thesis, development of lead-free (Na0.5K0.5)NbO3-based (NKN-based) piezoelectric ceramics with high mechanical quality factor (Qm) and their application on piezoelectric transformers, was investigated. Sintering aid CuTa2O6 (CT) compound was developed and then doped into NKN ceramics. A high bulk density (4.595 g/cm3) and electromechanical coupling factors (kp, kt) were obtained. Moreover, the mechanical quality factor (Qm) also increased from 67 to 1,550 as the concentrations of CT doping from 0 to 0.5 mole %. NKN ceramics with sintering aid CT doping showed good piezoelectric properties: kp: 42.5 %; kt: 49.1%; Qm: 1,550; and d33: 96 pC/N. On the other hand, the compensation for NKN ceramics was also an important role to affect the microstructure and piezoelectric properties. In CT-doped NKN ceramics, the concentration of oxygen vacancy dominates the magnitude of Qm value. However, non-stoichiometry NKN with CT doping showed the Qm value did not correspond to a higher concentration of oxygen vacancies. This reason guesses that the oxygen vacancies were induced from the defect of A-site and the replacement of Nb ions by Cu ions. The magnitude of Qm value was directly attributed to the formation of oxygen vacancy which was induced as the high valence ion (Nb5+) be substituted by low valence ion (Cu2+).
Copper oxide was also a good dopant for enhancing the piezoelectric properties of NKN ceramics. The microstructure of CuO-doped NKN (NKNCx) ceramics prepared using the conventional mixed oxide method (MO method) exhibited obviously inhomogeneous microstructure. In contrast, the two-step calcination process (TC method) improved the compositional homogeneity as well as the electrical properties. The Qm value and dielectric constant (ε33T/ε0) of NKNCx ceramics prepared using the TC method were therefore by 21 % and 25 % better, respectively. The internal bias field and activation energy were measured and calculated to confirm the presence of oxygen vacancies. The ceramics prepared using the TC method exhibited the formation of more oxygen vacancies, resulting in an increase in the internal bias field. In addition, low activation energy corresponded to high Qm value. The maximum Qm value of NKNCx ceramics prepared using the TC method was more than 2,000 and other properties, including the bulk density, dielectric loss, kp, d33 and ε33T/ε0, were 4.488 g/cm3, 0.15 %, 41.5 %, 95 pC/N and 280, respectively. Unlike CuO, ZnO-doped NKN (NKNZx) ceramics could not significantly enhance the piezoelectric properties of the samples. The Qm values of the NKNZx ceramics were not as high as those of NKNCx ceramics due to a lack of oxygen vacancies in the former. The internal bias field was used to demonstrate the presence of oxygen vacancies. In ZnO-doped NKN ceramics, the piezoelectric properties only improved slightly because ZnO used as a sintering aid which enhanced the densification of samples. A high Qm value was obtained for CuO-doped NKN ceramics mainly due to the formation of oxygen vacancies.
The performances of piezoelectric transformers (PTs) made with two substrates were compared (the ceramics prepared using the MO and TC methods). Experimental results showed that the output power and temperature stability of PTs were enhanced due to lower resonant impedance of the ceramics prepared using the TC method. In addition, the output power of PTs was more affected by the resonant impedance than by the mechanical quality factor (Qm) of the ceramics. For application on ballasts, PTs with different electrode areas were fabricated using the CuO-doped NKN ceramics prepared using the TC method. Considering the efficiency, voltage gain, and raising temperature of PTs at a load resistance of 1 kΩ, PTs with an electrode with an inner diameter of 15 mm were combined with the circuit design for driving a 13-W T5 fluorescent lamp. A raising temperature of 6 oC and a total efficiency of 82.4 % (PT and circuit) were obtained using the present PTs. This output power in the lead-free disk-type PTs was the best reported so far.

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