Microstructural and Dielectric Properties of Zr Doped Microwave SinteredCaCu3Ti4

Abstract

Polycrystalline samples with the chemical formula CaCu 3 Ti 4−x Zr x O 12 ( = 0, 0.02, 0.1, 0.2, 0.5, and 0.1) CCTZO were synthesized from metal nitrate solutions by the sol-gel method, followed by conventional and microwave heat treatments. The X-ray diffraction pattern of powder calcined at 800 ∘ C in conventional furnace for 3 h showed formation of a single phase. The crystal structure did not change on doping with zirconium and it remained cubic in the five studied compositions. The surface morphology of samples sintered at 1000 ∘ C in microwave furnace for 10 min was observed using a high resolution scanning electron microscope (HR-SEM). The grain sizes were in the range of 250 nm-5 m for these samples. HRSEM results show that doping with Zr enhanced grain growth or densification. Energy dispersive X-ray spectroscopy (EDX) confirmed the presence of Zr. The dielectric characteristics of Zr doped CCTO were studied with an LCR meter in the frequency range of 50 Hz-1 MHz. A very high dielectric constant 21,500 was observed for the sample doped with Zr (0.02 mol%) at 50 Hz.

Influence of Zirconium doping on microstructure and dielectric properties of CaCu 3 Ti 4 O 12 synthesized by the sol–gel method

“…Until now, the greatest challenge for CCTO ceramics is to lower the dielectric loss and keep a relative high dielectric constant [39,40] . As mentioned above, the tanδ of the CaCu 3 Ti 3.95 Zr 0.05 O 12 ceramic in this work can be as low as 0.026 at 10 kHz, which is also lower than most results of CCTZO ceramics [22][23][24][25][26][27][28][29][30] . According to previous works [40,41] , the tanδ can be estimated to follow this equation: , where R g and R gb are grain resistances and grain boundary resistances respectively and C 0 is the empty cell capacitance [41] .…”

“…One can find that, compared with Fig.3 (b) In comparison with previous works on Zr doping CCTO [22][23][24][25][26][27][28][29][30] , the CaCu 3 Ti 3.95 Zr 0.05 O 12 ceramic sintered at 1100 o C for 16 h exhibit improved dielectric properties. The ε′ is above 20k with a good frequency stability while the measured frequency is lower than 30 kHz at room temperature, larger than most of the similar works [22,23,[25][26][27][28][29][30] . Until now, the greatest challenge for CCTO ceramics is to lower the dielectric loss and keep a relative high dielectric constant [39,40] .…”

“…Jesurani et al reported that the ε′ did not exhibit a constant variation with frequency for various doping concentrations, and the tanδ of CCTZO were higher than pure CCTO. The minimum tanδ is 0.08 for CaCu 3 Ti 3.9 Zr 0.1 O 12 ceramics with ε′ as low as 1090 [27,30] . Thongbai et al also investigated the microstructural evolution and electric properties of CCTZO, and found the CaCu 3 Ti 3.7 Zr 0.3 O 12 ceramics exhibited improved dielectric properties with ε′ ~4.600 and a reduced tanδ ~0.038 at 1 kHz [29] .…”

Microwave Dielectric Properties of CCTO/PVA Composites

“…On the contrary, CaCu 3 Ti 4 O 12 (CCTO) is a known oxide of the ACu 3 M 4 O 12 family. Subramanian et al have been the first to report the exceptional dielectric properties of CCTO [11], and since then, a significant effort has been devoted to understand the polarization mechanisms that justify the colossal dielectric constant (ε′ > 10 5 ) observed for poly- [12,13] and single-crystalline ceramics [14]. e CCTO is a perovskite-like compound that, depending on the synthesis and sintering process, can present a dielectric constant (at 1 kHz and room temperature) as high as 10 5 and such dielectric properties are almost temperature-and frequencyindependent for large ranges [15][16][17].…”