Corresponding author: Kevin Abraham ( kevin_abraham86@yahoo.com ) © 2019 Kevin Abraham, A. K. Thomas, Jini Thomas, K. V. Saban.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Abraham K, Thomas AK, Thomas J, Saban KV (2019) Steady nature of dielectric behaviour in Sm1.5Sr0.5NiO4 – CCTO composites. Modern Electronic Materials 5(4): 145-150. https://doi.org/10.3897/j.moem.5.4.46694
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The composite materials of 0.5 Sm1.5Sr0.5NiO4, 0.5 CCTO and 0.75 Sm1.5Sr0.5NiO4, 0.25 CCTO mixtures were prepared through the conventional solid state reaction in an attempt to obtain good dielectric properties for practical applications. The structural properties were determined by powder X-ray diffraction and single phases were obtained for Sm1.5Sr0.5NiO4 and CaCu3Ti4O12 compounds. The dielectric studies analysed over a range of frequencies (100 KHz–10 MHz) and temperatures (30 to 200 °C) revealed a desired dielectric constant values with a low steady nature of dielectric loss factor. Through impedance spectroscopy, the attained dielectric behaviour was due to the highly insulating grain boundaries at lower frequencies and semiconducting grains at higher frequencies.
composite, dielectric constant, impedance spectroscopy, powder XRD
Colossal dielectric constant materials have been in the peak of its research due to various applications such as capacitors and memory devices [
Sm1.5Sr0.5NiO4 is a K2NiF4 type of material [
Recently many works were done in customizing the dielectric properties of these types of materials by mixing them together to form a composite material [
Ceramic samples of Sm1.5Sr0.5NiO4 and CaCu3Ti4O12 (CCTO) were prepared by solid state reaction method separately from stoichiometric amounts of pure Sm2O3 (99.9%), SrCO3 (99%), Cr2O3 (99.9%) and NiO (99%), CaCO3 (99.9%), CuO (99.9%), TiO2 (99.6%) respectively, all in powder form. The two mixtures were thoroughly mixed separately in an agate mortar. Next the Sm1.5Sr0.5NiO4 and CCTO mixtures were calcined at 1200 and 1000 °C respectively for 12 h to yield the desired material.
Composites of Sm1.5Sr0.5NiO4 and CCTO were prepared by mixing the pre weighed powders of Sm1.5Sr0.5NiO4 and CCTO in an agate mortar. The first composite mixture had 25% of CCTO mixed with 75% of Sm1.5Sr0.5NiO4 while the second mixture had equal measures of both Sm1.5Sr0.5NiO4 and CCTO. Hereby the two composite mixtures will be labelled as SmCTO25 and SmCTO50 respectively throughout this manuscript. The mixed samples were pressed into pellets of 13 mm diameter under a pressure of 2 tonnes. These pellets were sintered for 10 h in air at 1080 °C for the densification of the pellets. The sintering temperature was chosen so as to obtain the desired dielectric properties of the composite without exceeding the melting point of the mixtures.
The powder XRD data was collected using CuKα radiation (λ = 1.5418 Å) on a Bruker D8 Advance X-ray diffractometer. Diffraction data was recorded for 2θ values ranging from 10° to 120°, with a step size of 0.02°. The electrical and the dielectric properties were studied using a Hioki 3535 LCR HiTester on the silver coated pellets in the frequency range 100 KHz to 10 MHz and temperature range 30 to 200 °C.
The powder XRD patterns of Sm1.5Sr0.5NiO4 and CCTO as shown in Fig.
Similarly the powder XRD patterns of Sm1.5Sr0.5NiO4–CCTO composites are shown in Fig.
The SEM images of SmCTO25 and SmCTO50 composites are shown in Fig.
Fig.
Frequency dependence of dielectric constant εr and dielectric loss tan δ for (a) and (b) SmCTO25 and (c) and (d) SmCTO50.
From this it can be seen that the dielectric constant of SmCTO25 (Fig.
Similarly the variation of the dielectric properties of the SmCTO25 and SmCTO50 composites with temperature are shown in Fig.
Temperature variation of dielectric constant εr and dielectric loss tan δ for (a) and (b) SmCTO25 and (c) and (d) SmCTO50.
From the Fig.
The complex impedance plot of the composites (Fig.
Complex impedance spectrum of Sm1.5Sr0.5NiO4–CCTO composites. The inset shows the high frequency range of the spectrum.
Hence the total impedance from the equivalent circuit can be written as
(1)
The data are fitted by the equivalent circuit consisting of two parallel RC connected in series with one RC element in which RgbCgb corresponds to the grain boundaries and RgCg represents the grains. The fitted parameters at room temperature are shown in Table
Sm1.5Sr0.5NiO4–CCTO composites parameters from impedance spectrum.
Composite | Rg | Cg | Rgb | Cgb |
---|---|---|---|---|
Sample | (Ω) | (F) | (Ω) | (F) |
SmCTO 25 | 1250 | 1.53 * 10-10 | 20015 | 3.6 * 10-10 |
SmCTO 50 | 416 | 1.40 * 10-10 | 17354 | 2.15 * 10-10 |
It is observed from the table that the resistance values of the grain boundaries are much higher than those of grain resistances. Thus from Fig.
The effect of Sm1.5Sr0.5NiO4–CaCu3Ti4O12 (CCTO) composite on dielectric properties was studied by combining Sm1.5Sr0.5NiO4and CCTO mixtures taken by the ratio of 0.5 Sm1.5Sr0.5NiO4: 0.5 CCTO (SmCTO50) and 0.75 Sm1.5Sr0.5NiO4: 0.25 CCTO (SmCTO25) were yielded through solid state reaction method. Initially the individual compounds were prepared separately and by powder XRD analysis, a single phase crystal structure was obtained with I4/mmm for Sm1.5Sr0.5NiO4 and Im 3- for CCTO space groups respectively. Slightly higher dielectric values were observed for SmCTO25 than SmCTO50 due to the highly insulating grain boundaries. The main observation from this experiment was the steady behaviour of dielectric loss for both the samples for a particular range of frequency and temperature. Thus these composites make it attractive for industrial purposes with high frequency applications.