CexZr1-xO2(1 > x > 0，CZ)因具特殊的儲氧性質(oxygen storage capacity，OSC)，可添加於汽車觸媒轉換器(three way catalyst，TWC)中提高廢氣轉化率(conversion rate)，但其在高溫環境下容易發生相分離(phase separation or decomposition)而導致儲氧性質的劣化，許多研究探討影響CZ儲氧性質的因素包括: 結晶構造(crystal phase)、微結構(texture)及均勻度(homogeniety)等，但對於許多現象的解釋及其形成機制仍未完全瞭解，且結論尚存在不一致性。本研究觀察以化學共沉法合成之Ce0.6Zr0.4O2(C60Z)粉末的相分離行為及探討其相分離機制，並藉由交互通入氧化及還原氣氛以觀察其氧化還原特性，也嘗試添加異價陽離子到C60Z粉末中觀察其抑制相分離的效果。
以化學共沉法合成之C60Z粉末，是透過製程手法提高了Ce/Zr的混合均勻度，但由於所合成之固溶體為熱力學的介穩相，當加入能量或熱量時便會發生相分離以降低系統的自由能，使系統達到最穩態。本研究發現，C60Z粉末的相分離是發生在升溫過程而非降溫過程，應是屬於熱活化過程(thermal activated process)。觀察C60Z粉末在1000°C持溫不同時間的相分離變化，隨著持溫時間的延長C60Z由原本的c'相逐漸分離成c+t兩相，顯示其組成是隨持溫時間延長而逐漸變化。且在相分離發生的初始階段，C60Z粉末的凝聚指數急遽上升，表示C60Z粉末較容易產生凝聚，在相分離過程中其微結構表現是由晶界所主導(grain boundary dominated)。由C60Z粉末的相分離動力學推論其相分離機制為界面控制(interface controlled)，且其相分離的活化能約為398(±20) kJ/mol。由TEM觀察已出現相分離的C60Z粉末，發現Zr會富集在粉末晶粒間的界面上，此現象與粉末的初期燒結(initial sintering)行為相近，並顯示Zr+4在C60Z粉末的相分離過程中扮演著相當重要的角色。且由於Zr+4的離子半徑比Ce+4小，Zr+4的移動(擴散)速率會比Ce+4來得快，其相分離的驅動力來自於粉末間的相互聚集所造成粉末表面與粉末界面間之表面能差異，使得Zr經由擴散傳輸到粉末晶粒間的界面上以降低整體系統的能量，而導致其組成逐漸改變而發生相分離。所以C60Z粉末必須先藉由相互接觸聚集所造成之晶粒表面與晶粒間界面的表面能差異(符合相分離動力學為界面控制機制)，才能進一步地促使Zr擴散到晶粒間的界面上而導致相分離。而比較不同Ce/Zr莫耳比的CZ粉末在等溫1000 °C持溫不同時間的相分離過程，發現C77Z發生相分離所需的持溫時間要比C60Z及C26Z來得長許多。從組成成份的觀點來看，C77Z中Ce所占的比例較多，可能使得Zr較不容易移動而導致其相分離速率變慢。
在還原氣氛下，原來為單一相的C60Z粉末經1200°C煆燒處理後，C60Z不會發生相分離，而是相變為陽離子有序排列的pyrochlore結構。若將已經相分離的C60Z粉末，置於還原氣氛下加熱至1490°C後則會轉變為pyrochlore結構，而後再將其置於空氣環境中經高溫1200°C煆燒處理後，又會由pyrochlore再轉變回原來的相分離狀態，C60Z粉末在還原/氧化反應過程中的有序-無序相變現象應是由於Zr的移動所造成。而當C60Z粉末出現相分離時，其還原溫度及還原比例均往高溫偏移，使得儲氧量明顯地降低。顯示因相分離所導致的成份分佈不均勻(inhomogeneity)會抑制C60Z中氧的釋放能力，造成C60Z的還原特性及儲氧量劣化。
分別添加Al+3及Ba+2到C60Z粉末中觀察其對C60Z相分離的影響。以化學共沉法添加Al+3至C60Z所合成的ACZ-C粉末，可有效阻止C60Z粉末間的相互接觸所造成的凝聚而抑制其晶粒成長及相分離，且符合C60Z相分離為界面控制機制之推論，並可大幅提升C60Z的儲氧性。而以含浸法添加適量的Ba+2到C60Z粉末中，除了可抑制C60Z的相分離及提高其比表面積之外，Ba+2會先與C60Z中擴散速率較快的Zr+4反應形成BaZrO3的二次相，導致C60Z與BaZrO3的界面間存在著大量的活性氧而提升其儲氧性。

CexZr1-xO2 (1>x>0, CZ) has unique oxygen storage capacity (OSC) which can be applied in three way catalysts to promote emission conversion efficiency. But, CZ appeared phase separation after high temperature treatment which deteriorated the OSC. The redox properties of CZ are strongly dependent on the crystal phase, texture and homogeneity. However, the explanation and mechanism for the improved redox properties were not fully resolved yet, and the conclusions still existed controversies. The aims of this study were to observe the phase separation behavior and investigate the phase separation mechanism of Ce0.6Zr0.4O2 (C60Z) prepared by chemical coprecipitation method. The redox properties of C60Z were observed under alternate reduction/oxidation atmosphere. Furthermore, the effects for the addition of aliovalent cations to the influence of C60Z phase separation were also investigated.
The phase separation of C60Z appeared during heating stage which might belong to thermal activated process. We observed the phase separation phenomenon of C60Z calcined at 1000 °C for various durations. The original c'-C60Z gradually separated into c+t phases and the compositions of the two separated phases were gradually changed with the duration time. The A. N. ratios of C60Z increased rapidly in the beginning of phase separation, indicating that C60Z tended to aggregate together. And it also exhibited that the texture behavior of C60Z was grain boundary dominated during phase separation. The phase separation mechanism of C60Z was interface controlled and the activation energy for phase separation was 398(±20) kJ/mol from the kinetic results. We found that Zr enriched at the interface between particles after the appearance of C60Z phase separation from the TEM observation,, which was very similar to the initial stage of sintering and exhibited that Zr+4 played an important role in C60Z phase separation. The diffusion rate of Zr+4 is faster than that of Ce+4 due to the smaller ionic radius of Zr+4 than that of Ce+4. The driving force for phase separation was from the surface energy difference between crystallite surface and interface. Hence, Zr+4 diffused to the interface between particles to lower the surface energy of the system, which resulted in the composition gradually change and led to phase separation. The C60Z powders tended to aggregate in advance to create the surface energy difference between crystallite surface and interface, which induced Zr+4 diffused to the interface between crystallites and appeared C60Z phase separation.
We observed other different Ce/Zr ratios of CZ (C77Z and C26Z) samples calcined at 1000 °C for various durations. It took longer duration time for the appearance of C77Z phase separation than that for the C60Z and C26Z. There are more Ce contents in C77Z than that in C60Z and C26Z, which resulted in Zr movement difficult and retarded phase separation.
The single cubic C60Z powders transformed into cation-ordering pyrochlore structure after calcinations at 1200°C for 2h under a reducing atmosphere, and no phase separation appeared. The two separated phases (Ce-rich and Zr-rich phases) obtained after calcinations at 1100°C for 2 h transformed into a pyrochlore structure after heat treatment at 1490°C under a reducing atmosphere , and then this structure transformed into separated phases after further calcination at 1200°C for 2h in air, suggesting that the order-disorder phase transformation under reduction/re-oxidation treatment might be attributed to Zr diffusion. The reduction peak and the reduction fraction were shifted to higher temperatures and the OSC was also deteriorated after the appearance of phase separation for C60Z. The inhomogeneity originating from the phase separation may inhibit the oxygen release in the CZ system.
The influences of Al+3 or Ba+2 additions to C60Z phase separation were also investigated. The ACZ-C powders synthesized by chemical coprecipitation method could prevent crystallite aggregation and growth, which inhibited C60Z phase separation. The results of ACZ-C were consistent with the interface controlled mechanism of C60Z phase separation. Besides, The OSC properties of ACZ-C were also improved. The addition of an appropriate amount of Ba+2 ions into C60Z by impregnation method was effective in retarding phase separation, and increasing the specific surface area of C60Z. Ba+2 would react with Zr of C60Z to form BaZrO3 which provided active oxygen species between the interfaces of C60Z and BaZrO3, and also promoted OSC.

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