Functional Strontium Tantalum Oxynitride Ceramics: Efficient Synthesis, Densification and Dielectric Performance

doi:10.15541/jim20230026

Abstract

Abstract:

The perovskite-type oxynitride with AB(O,N)₃ formula is a new type of functional ceramic materials, which have unique dielectric/magnetic/photocatalytic properties and prospective applications in the field of energy storage and conversion. However, the traditional preparation process takes a long time and the product purity is low. In this study, SrTa(O,N)₃ ceramic powder was synthesized and densified by a pressureless spark plasma sintering equipment with urea as nitrogen source and metal oxides as precursors. Effects of heating rate and synthesis temperature on the composition and microstructure of the powder were deeply investigated, and the dielectric properties of the optimized ceramic bulks were characterized. The results show that higher heating rate and moderate synthesis temperature are beneficial to sufficient nitridation, while the SrTa(O,N)₃ powder prepared at 100 ℃/min and 1000 ℃ possesses the highest purity (~97% oxynitride phase content) with a particle size distribution of 100-300 nm. Elements of Sr, Ta, O and N are evenly distributed. The optimized densification process is firstly sintering at 1300 ℃, with heating rate of 300 ℃/min, and dwelled for 1 min. After sintering, the density of SrTa(O,N)₃ ceramic pellet can reach >94% with a high purity. Dielectric constant and loss tangent of the material are 8349 and 10^-4 level at 300 Hz, respectively, which are superior to that reported in the literature. The high dielectric constant prepared in this study is closely related to standard density and purity, because the existence of pores and impurities can reduce the dielectric constant of materials. Therefore, high density and purity are the key factors to obtain excellent dielectric properties of SrTa(O,N)₃ oxynitride ceramics.

Key words: perovskite, oxynitride, urea, spark plasma sintering, dielectric constant

CLC Number:

TQ174

LI Junsheng, ZENG Liang, LIU Rongjun, WANG Yanfei, WAN Fan, LI Duan. Functional Strontium Tantalum Oxynitride Ceramics: Efficient Synthesis, Densification and Dielectric Performance[J]. Journal of Inorganic Materials, 2023, 38(8): 885-892.

Figures/Tables 13

Fig. 1 Preparation flow chart of the SrTa(O,N)3 ceramic bulk

Table 1 Synthesis conditions (heating strategy) and element content

Sample	Synthesis temperature /℃	Heating rate /(℃·min^-1)	Composition/% (in atomic)				O/N
Sample	Synthesis temperature /℃	Heating rate /(℃·min^-1)	Sr	Ta	O	N	O/N
STON-1000-10	1000	10	9.19	11.05	61.51	18.25	3.37
STON-800-100	800	100	14.59	7.74	57.10	20.57	2.78
STON-900-100	900	100	12.60	10.98	50.24	26.18	1.92
STON-1000-100	1000	100	11.74	11.92	47.83	28.51	1.68
STON-1100-100	1100	100	10.63	13.02	44.86	31.49	1.42
STON-1200-100	1200	100	10.11	13.50	44.17	32.22	1.37

Fig. 2 XRD patterns (a) and Raman spectra (b) of the products obtained at different heating rates

Fig. 3 Optical and SEM images of the products obtained at different heating rates (a) 10 ℃/min; (b) 100 ℃/min

Fig. 4 XRD patterns (a) and Raman spectra (b) of the products obtained at different synthesis temperatures

Fig. 5 Optical and SEM images of the products obtained at different synthesis temperatures (a) 800 ℃; (b) 900 ℃; (c) 1000 ℃; (d) 1100 ℃; (e) 1200 ℃

Fig. 6 Rietveld refinement of XRD pattern for SrTa(O,N)3 Vertical marks indicate the standard Bragg position for SrTaNO2 (upper) and Sr2Ta2O7 (lower)

Fig. 7 SEM image and EDS mappings of SrTa(O,N)3 powder prepared under optimized conditions (a) SEM image; (b) Sr; (c) Ta; (d) O; (e) N

Table 2 Density and porosity of oxynitride ceramics prepared by different SPS processes (100 MPa)

Sample	Heating rate/ (℃·min^-1)	Sintering temperature/℃	Dwell time/min	Density/ (g·cm^-3)	Relative density/%	Open porosity/%	(Open porosity/ Total porosity)/%
STON-SPS-1	300	1100	1	5.69	70.94	3.12	10.77
STON-SPS-2	300	1200	1	6.30	78.54	7.54	35.28
STON-SPS-3	300	1250	0	6.93	86.40	4.37	21.90
STON-SPS-4	300	1250	1	7.13	88.89	0.43	3.89
STON-SPS-5	300	1250	3	7.24	90.26	0.57	5.88
STON-SPS-6	200	1300	1	7.37	91.88	0.69	8.53
STON-SPS-7	300	1300	1	7.55	94.13	0.55	9.52
STON-SPS-8	300	1400	1	7.67	95.62	0.49	11.53

Fig. 8 XRD patterns of SrTa(O,N)3 bulk obtained by SPS

Fig. 9 SEM and optical images of SrTa(O,N)3 bulk obtained by SPS process (a) STON-SPS-1; (b) STON-SPS-4; (c) STON-SPS-7

Fig. 10 Dielectric performance curves of SrTa(O,N)3 ceramic bulk (300 Hz-1 MHz)

Fig. 11 Dielectric constants at low frequency ranges of SrTa(O,N)3 ceramic bulk in this work and literatures[11-12,14,24]

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