Preparation and Sintering Behavior of High Entropy Ceramic (Zr1/7Hf1/7Ce1/7Y2/7La2/7)O2-δ

doi:10.15541/jim20200374

Abstract

Abstract:

High entropy ceramics (HECs) typically refer to a kind of solid solution consisting of five or more principal elements. In recent years, different kinds of HECs have developed rapidly whereas high entropy oxides with fluorite structure are still in their nascent state. In this study, a new type of high entropy fluorite oxide was successfully synthesized using mechanical ball-milling followed by conventional sintering. Phase transformation, surface morphology and sintering behavior of ceramic were characterized. The results demonstrate that (Zr_1/7Hf_1/7Ce_1/7Y_2/7La_2/7)O_2-_δ is a non-equimolar high entropy ceramic in which all elements distribute homogenously. The powders derived from wet-milling or dry-milling possess different crystal structure and particle size. Raw materials transform into single-phase structure at 1600 ℃ and 1300 ℃, respectively. After dwelling at 1600 ℃ for 1 h, the shrinkage of two discs are 8.5% and 17.8%, approximately, at the same time, the relative densities are 82.25% and 93.23%. These miscellaneous distinctions indicate that ball-milling process is a crucial factor affecting sinterability of HECs. In order to avoid cracks caused by rapid shrinkage and improve density of ceramic, it is vital to decrease heating rate and prolong dwell time in the range of 1300-1600 ℃ as preparing (Zr_1/7Hf_1/7Ce_1/7Y_2/7La_2/7)O_2-_δ by conventional sintering.

Key words: high entropy oxide, non-equimolar, fluorite structure, ball-milling process

CLC Number:

TB332

ZHANG Fengnian, GUO Meng, MIAO Yang, GAO Feng, CHENG Chufei, CHENG Fuhao, LIU Yufeng. Preparation and Sintering Behavior of High Entropy Ceramic (Zr_1/7Hf_1/7Ce_1/7Y_2/7La_2/7)O_2-_δ[J]. Journal of Inorganic Materials, 2021, 36(4): 372-378.

Figures/Tables 10

Table 1 Crystal structures, space groups (number), cation coordination numbers (CN) and corresponding cationic radii (rc) of selected oxides[42]

Oxides	Crystal structure	Space group (number)	CN	r_c/nm
ZrO₂	Cubic	Fm-3m (225)	8	0.084
HfO₂	Monoclinic	P21/c (14)	8	0.083
CeO₂	Fluorite	Fm-3m (225)	8	0.097
Y₂O₃	Bixbyite	Ia-3 (206)	6	0.090
La₂O₃	Trigonal	P-3m (164)	6	0.1032

Table 2 Process, ball-to-powder-ratio (BPR), speed, time and others for raw material preparation

Sample	Process	BPR	Speed /(r·min^-1)	Time /h	Disperser	Desiccation	Energy
A	Wet milling	6 : 1	250	6	Ethanol	60 ℃ /24 h	Low
B	Dry milling	10 : 1	400	40	-	-	High

Fig. 1 (a) Calcining process of raw materials and (b) XRD patterns of raw material A calcined at different temperatures

Fig. 2 XRD pattern together with Rietveld fits of the ZHCYLO sintered at 1600 ℃

Fig. 3 XRD patterns of ZHCYLO annealed at different temperatures

Fig.4 SEM-EDS images of ZHCYLO sintered at 1600 ℃ for 1 h

Fig. 5 TG-DSC curves of raw material A

Fig. 6 Particle size distribution of (a) raw material A and (b) B

Fig. 7 (a) Comparation of XRD patterns from raw material A and B; (b) XRD patterns of raw material B sintered at different temperatures

Fig. 8 Digital camera photographs of different pellets sintered at different temperatures and temper ature/linear shrinkage of different pellets as a function of time (a,c) Pellet A; (b,d) Pellet B

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