Applied Science and Convergence Technology 2020; 29(2): 31-35
Published online March 30, 2020
Copyright © The Korean Vacuum Society.
Sagar M. Mane, Sachin A. Pawar, Dipali S. Patil, Seong Hun Lee, and Jae Cheol Shin*
Department of Physics, Yeungnam University, Gyeongsan 38541, Republic of Korea
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-CommercialLicense (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution,and reproduction in any medium, provided the original work is properly cited.
Composites constructed by combining ferroelectric and ferromagnetic materials are of significant interest owing to their multifunctional features and potential applications in multifunctional devices. Herein, the magnetodielectric effect of a composite containing ferroelectric 0.8Sr0.2TiO3 (BST) and ferrite Co0.9Ni0.1Fe2O4 (CNFO) phases is investigated. This ferroelectric and ferrite composite is synthesized using the co-precipitation method followed by microwave sintering. The tetragonal crystal structure of BST and cubic structure of CNFO are confirmed using X-ray diffraction. All composite samples are characterized using nanoparticle tracking analysis. The measurements of dielectric constant (room temperature) and loss tangent as a function of frequency show an increase in the dielectric constant with an increase in the CNFO phase. The highest value of magnetodielectric coefficient, –40.13 %, is observed for the 60BST–40CNFO composite at 100 Hz, which decreases with an increase in the applied frequency.
Keywords: Ba0.8Sr0.2TiO3–Co0.9Ni0.1Fe2O4 composite, Dielectric properties, Magnetodielectric effect, Co-precipitation, Microwave sintering
Multiferroic materials have attracted significant interest in recent years because of the simultaneous coexistence of two or more phases in a single material. This type of material allows the modification of electrical properties or magnetization upon the application of magnetic or electric field . There are a few single-phase materials that are known to exhibit both spontaneous magnetization and electric polarization, but a low magnetoelectric (ME) coefficient at room temperature restricts the use of single-phase ME materials in many applications . In contrast, composites constructed by combining ferroelectric and ferromagnetic materials exhibit high ME coefficients, and have been rapidly developed because of their multifunctional features and potential applications in multifunctional devices [2,3]. In these composites, the resulting ME coefficients are a product of coupling between the piezoelectric and magnetostrictive effects. A combination of two materials in a single material can result in new properties such as magnetodielectric and magneto-optic properties . Of these, the composite materials possessing magnetodielectric properties are important owing to their useful applications in the miniaturization of devices for advanced technologies [5,6]. In ME composites, the electric polarization can be adjusted by the application of a magnetic field, whereas in magnetodielectric composites, the dielectric properties are modified upon the application of a magnetic field. Magnetodielectric coupling between ferroelectric and ferromagnetic materials is expressed in terms of magnetocapacitance (
Based on the aforementioned discussion, (1-x)Ba0.8Sr0.2TiO3– xCo0.9Ni0.1Fe2O4 ((1-x)BST–xCNFO) composite is prepared via hydroxide co-precipitation in this study. The effect of the application of magnetic field on dielectric properties is investigated for each composite with different x values (x = 10, 20, 30, and 40).
The syntheses of BST and CNFO were performed using a hydroxide co-precipitation method described in a prior literature report . For the synthesis of highly pure BST (99.9 %), analytical reagent (AR)-grade Ba(NO3)2, Sr(NO3)2, and K2TiO(C2O4)2·2H2O were used, and to synthesize CNFO, AR-grade (Fe(NO3)3·9H2O), (Co(NO3)2·6H2O), and (Ni(NO3)2·6H2O) were used as starting materials without any further purification. KOH was used as a precipitating agent in a 1:1.6 ratio of the metal ions and KOH for the complete precipitation of ions. Both phases, i.e. ferroelectric BST and ferromagnetic CNFO, were synthesized individually. The alkaline medium was maintained using the mixture of dilute ammonia solution and distilled to prevent fractional solubility of ions; a pH value of >10 was maintained during the precipitation process. The precipitates of both phases obtained after filtration were dried overnight at 150 °C. The dried powder samples were pulverized for 3 h and calcined at 1000 °C for an additional 3 h. The calcined powders of BST and CNFO were mixed to form magnetodielectric composites with varying CNFO quantities, and these were rigorously grinded for 5–6 h for appropriate mixing. Polyvinyl alcohol (3 %) was used as a binder and mixed with the ground mixture of BST–CNFO. This was further grinded for 30 min and pressed using a hydraulic press. A uniaxial pressure of approximately 5 tons/cm2 was applied to obtain disk-type pellets that were approximately 1 cm in diameter and 2 mm in thickness. These pellets and the remaining powder of the BST–CNFO composite were sintered at 1100 °C for 30 min. A unique, fast microwave sintering technique was used for this purpose, where the heating rate was maintained at 40 °C/min. A microwave furnace with a thermally insulated chamber and 1.3 kW and 2.45 GHz multimode cavity was used.
The structures of the phases in BST–CNFO composites were confirmed using an X-ray diffractometer (Rigaku Miniflex-II, Rigaku Corporation, Tokyo, Japan). Particle size analysis of each composite was performed using a nanoparticle tracking analyzer (Version 2.3) after sonication. The pellets were used for the measurement of dielectric properties; both sides of the pellet were coated using silver paste and dried at 200 °C. To determine the frequency dependence of the dielectric constant and the loss tangent, a high-frequency LCR-Q meter (Wayne-Kerr 6300B, Wayne Kerr Electronics, Bognor Regis, UK) was used. To determine the magnetodielectric constant, the samples were placed between two magnets, and the magnetic field (up to 10 kOe) was measured using a gauss meter and adjusted using a high DC power supply.
Figure 1 shows the X-ray diffraction (XRD) data for magnetodielectric composites with increasing CNFO concentrations, obtained with 2
The crystallite sizes of BST and CNFO increase with an increase in CNFO concentration. The observed lattice parameters, unit cell volumes, and crystallite sizes corresponding to the BST and CNFO phases are listed in Table I.
Figures 2(a)–(d) show the nanoparticle tracking analysis (NTA) results for the BST–CNFO composites with an increase in the CNFO content. Before the NTA, each composite was suspended in highly pure water and sonicated for 30 min. NTA is a useful technique that affords the size distribution profile of small particles in materials with diameters between 10 and 1000 nm. The observed mean particle size (D) for 90BST–10CNFO and 80BST–20CNFO is 42 nm, which increases to 46 nm for 70BST–30CNFO and 132 nm for 60BST–40CNFO. This increase in particle size with increasing CNFO content is in good agreement with the size measurements obtained by XRD.
Dielectric constants and loss tangents for the four magnetodielectric composites (90BST–10CNFO, 80BST–20CNFO, 70BST–30CNFO, and 60BST–40CNFO) were determined by the application of frequencies ranging from 100 Hz to 3 MHz at room temperature. Figure 3 shows the variation of the dielectric constant (
Figures 4(a)–(d) show the variation in the dielectric constant with the change in frequency at different magnetic fields strengths of 0, 0.2, 0.6, and 1 T for the magnetodielectric composites, 90BST–10CNFO, 80BST–20CNFO, 70BST–30CNFO, and 60BST–40CNFO. The variation in the loss tangent upon the application of a magnetic field is shown in the inset of each figure. A combination of two distinct phases (ferroelectric and magnetostrictive) affords the magnetodielectric effect, and this phenomenon can be measured in terms of the change in the dielectric constant. Magnetodielectric coupling can be measured in terms of
A ferroelectric–ferrite composite of BST–CNFO is synthesized via hydroxide coprecipitation followed by microwave sintering. An increase in the crystallite size is observed with an increase in the CNFO content, which is confirmed by NTA. The contribution of different types of polarizations on the dielectric dispersion in each composite can be observed by the variation in the dielectric constant with a change in frequency. The effect of stress on each magnetodielectric composite is observed, leading to a change in its dielectric constant upon the application of a magnetic field. The magnetodielectric coefficient decreases with an increase in frequency, but no change is observed at high frequencies. The dielectric loss tangent also shows a similar trend as that for the dielectric constant.
This work was supported by the National Research Foundation of Korea (NRF-2019M3F5A1A01077146 and NRF-2017M1A2A2048904).