本研究以高濃度，高pH值快速逆滴定之共沉技術製備Co2Z(Ba3Co2Fe24O41)鐵氧磁體前導粉末。結果發現能在低溫600℃持溫2小時直接生成BaM (BaFe12O19)相，避免了α-Fe2O3、BaFe2O4等中間相生成，並在850℃持溫2小時，得到均勻混合之BaM + Co2Y (Ba2Co2Fe12O22)鐵氧磁體粉末。此粉末在1200℃持溫2小時可合成單一之Co2Z結晶相。本研究製備之Co2Z鐵氧磁體在外加磁場6000Oe下，其飽和磁化量Ms=44.66 emu/g，矯頑磁力Hc=15 Oe擁有軟磁、高飽和磁化之優良磁特性。

　　文中透過XRD/SEM/TEM等分析，發現BaM與Co2Y，並非在界面直接固態反應合成Co2Z鐵氧磁體，而是隨溫度升高(＞900℃)，BaM逐漸分解進入Co2Y結構中，形成具有Co2Z組成，但仍維持Co2Y結構之Co2Y*結晶相。隨後Co2Z相才在此Co2Y*基質中成核成長。Co2Y*結晶相由於體積膨脹受周圍之Co2Y束縛，晶格內部受到扭曲，造成其晶格充滿內應力，產生許多雙晶結構。此雙晶結構與殘留應力提高了Co2Z成核能障，而延緩Co2Z相成核，使得其難以在低溫生成單一Co2Z結晶相。

　　使用溼式行星球磨方式，可有效解除Co2Y*之殘留應力，降低Co2Z成核能障。將球磨後之Co2Y*粉末，直接進行造粒、壓胚，可減短原子擴散距離，有利於Co2Z晶核成長，可在1175℃持溫8小時得到一接近單一Co2Z相之燒結體。

　　Co2Z (Ba3Co2Fe24O41) ferrite powder was prepared by co-precipitation technique in this study. It is suggested that a better precursor which could produce a single Co2Z phase at a lower calcination temperature can be produced using reverse titration method under high cation concentration and pH. Intermediate phases, such as α-Fe2O3 and BaFe2O4 were not observed during the reaction process. BaM (BaFe12O19) was directly formed from precursor calcined at 600℃/2h, and subsequently Co2Y(Ba2Co2Fe12O22) was formed at 850℃/2h. Then, single phase Co2Z ferrite which had excellent magnetic properties (Hc=15 Oe, Ms = 44.66emu/g at 6000 Oe).

　　In this study the formation mechanism of Co2Z ferrite was also investigated using XRD, SEM and TEM. It is found that the development of Co2Z was not via the direct reaction of BaM and Co2Y at the interface but via the nucleation and growth process from Co2Y* matrix. As the calcination temperature increased above 900℃, BaM started to decompose and the Ba2+、Fe3+ ions inserted into Co2Y structure, which distorted the structure of Co2Y. The above distorted Co2Y structure which had the stoichiometric composition of Co2Z was called Co2Y*. The twin structure were observed in Co2Y* grains, which was due to the lattice strain induced by the clamping force from the surrounding Co2Y crystallites. Twin structures and residual stress existed in Co2Y* would raise the nucleation barrier of Co2Z. Therefore, it is difficult to obtain a single Co2Z phase at a lower calcination temperature.

　　The lattice strain existed in Co2Y* could be released after a short period of wet planetary milling, which lower the nucleation barrier of Co2Z. The development of Co2Z phase in milled Co2Y* powder could be further enhanced using unidirection pressing method to decrease the atomic diffusion distance. The single Co2Z phase could be obtained after sintering the green body made by milled Co2Y* powder.

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