High Entropy Oxide Ceramics (MgCoNiCuZn)O: Flash Sintering Synthesis and Properties

doi:10.15541/jim20220320

Abstract

Abstract:

Flash sintering is a sintering technology coupled with temperature field and electric field, with characteristics of rapid mass transfer at low temperature, showing significant advantages in the synthesis of high entropy ceramics. In this study, relatively dense high entropy oxide ceramic (MgCoNiCuZn)O was synthesized by flash sintering, which properties were compared with those of conventional sintered samples. Under flash sintering condition of room temperature, the electric field intensity of 50 V/cm and the current density of 300 mA/mm², the time of phase transformation is only 10 s. The maximum relative density of flash sintered sample is 94%, which is 22.8% higher than that of conventional sintered sample. The maximum hardness of flash sintered sample is 5.05 GPa, which is 3.95 GPa higher than that of conventional sintered sample. When the frequency is lower than 2 Hz, the dielectric constant of flash sintering sample is one order of magnitude higher than that of conventional sintered sample. The property improvement of flash sintered samples is attributed to the acceleration of mass transfer by the critical electric field to increase the material density, and the extra defects introduced by the critical electric field.

Key words: high entropy oxide ceramics, flash sintering, phase transformation, dielectric constant

CLC Number:

TQ174

LI Wangguo, LIU Dianguang, WANG Kewei, MA Baisheng, LIU Jinling. High Entropy Oxide Ceramics (MgCoNiCuZn)O: Flash Sintering Synthesis and Properties[J]. Journal of Inorganic Materials, 2022, 37(12): 1289-1294.

Figures/Tables 6

Table 1 Experimental parameters of flash sintering and conventional sintering

Label	E/(V·cm^-1)	J/(mA·mm^-2)	T_f/℃	t	T_e/℃
F1	50	150	300	60 s	990
F2	50	200	300	60 s	1060
F3	50	250	300	60 s	1100
F4	50	300	300	60 s	1130
C1	-	-	990	2 h	-
C2	-	-	1060	2 h	-
C3	-	-	1100	2 h	-
C4	-	-	1130	2 h	-

Fig. 1 Flash sintering curves, XRD patterns of samples and pictures of flash sintered sample in the stable stage Flash sintering curves (a) and XRD patterns at room temperature (b) of samples flash sintered at electric field strength of 50 V/cm, holding time of 60 s, and current densities of 100, 200 and 300 mA/mm2, respectively; Flash sintering curves (c) and XRD patterns at room temperature (d) of samples flash sintered at electric field strength of 50 V/cm, current density of 300 mA/mm2, holding time of 0, 10, 30, 60 s; (e) XRD patterns of conventional sintered samples C1-C4; (f) Photos of flash sintered samples in the stable stage; The holding time referrs to the time during the stable stage of flash sintering; Colorful figures are available on website

Fig. 2 Densities of samples flash sintered at different current densities at 300 ℃ with holding time of 60 s, and of samples conventionally sintered at the corresponding temperatures

Fig. 3 Comparison of microstructures of flash sintered samples with different current densities and conventional sintered samples at corresponding temperatures (a-e) Microstructures of flash sintered samples; (f-j) Microstructures of conventional sintered samples

Fig. 4 Hardness (a) and plot of hardness as a function of porosity(b) of flash sintered and conventional sintered samples

Fig. 5 Real (a) and imaginary (b) parts of the dielectric constants, and tangent loss of flash sintered samples at different current densities and conventional sintered samples at the corresponding temperatures (c)

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